€¦  · Web view2021. 6. 17. · Paper chromatography is a technique used to separate mixtures of soluble substances. It is particularly important for scientists testing food colourings,

YEAR 11

Separate Chemistry – Booklet 2B

Lesson Recall Knowledge Check

7. Purity, Formulations and Identification of Gases /8 /88. Chromatography /8 /89. Chromatography Practical /8 /810. Identifying Ions Part 1 /8 /811. Identifying Ions Part 2 /8 /8

1

Name: ____________________________________________

Teacher: __________________________________________

Class: _____________________________________________

Chemistry Knowledge Web

2

Overview of the topics and skills taught over Year 11

3

Knowledge

Biology

Inheritance, Variation and Evolution

Ecology

Chemistry

The Rate and Extent of Chemical Change

Organic Chemistry

Chemical Analysis

Physics

Waves

Magnetism and Electromagnetism

Space (Separate Science Only)

Key Skills

Using laboratory equipment safely

Practical skills using scientific equipment

Making and recording observations

Using models to understand concepts

Using key vocabulary

Topic Big Statement

The aim of the topics taught in this booklet is to explain how useful products can be obtained from crude oil and to understand how different techniques can be used to separate mixtures and identify the chemicals that they are made of.

Where the Unit Fits in the Sequence

These are the final topics you will learn in chemistry, as they build on all of the ideas you have learned so far and require you to use the skills that you have acquired.

The target 9 activities in this booklet will extend your knowledge.

4

Threshold Concepts

By the end of the unit you should be able to: R A G

State the general formula of alkanes.

Describe the process of fractional distillation.

Identify alkanes and alkenes using bromine water.

Describe the reactions of alkenes, alcohols and carboxylic acids.

Describe the process of polymerisation.

Explain how mixtures are separated by chromatography.

Calculate Rf values.

Use simple tests to identify common gases.

Describe the tests to identify different ions.

Relevant core questions, linked to this unit: 5

Core Question: Answer:Define the term hydrocarbon.

Hydrocarbons are compounds that contain hydrogen and carbon only.

Name the process used to separate crude oil.

Fractional distillation.

Describe how the flammability of hydrocarbons changes as the length of hydrocarbon increases.

As hydrocarbons get longer, their flammability decreases.

Describe the products of cracking.

During cracking, long alkanes are split into a shorter alkane and alkene.

Explain why pencil is used to draw the start line on a chromatogram.

Pencil does not dissolve in the solvent and therefore it will not affect the results.

Describe the test for hydrogen gas.

There is a squeaky pop sound when you insert a burning splint into a tube of the gas.

Describe the test for carbon dioxide

When carbon dioxide is bubbled through limewater, the limewater changes from clear and colourless to cloudy and milky.

6

Knowledge OrganiserThe keywords for this topic will appear in this order:

Word Meaning

crude oil A fossil fuel, in the liquid state, formed from the remains of microscopic dead plants and animals that lived in the sea.

fractional distillation

A method of separating a mixture of liquids with different boiling points into individual components (fractions).

viscosity How thick or runny a liquid is. Low viscosity is very runny, high viscosity is thick.

alkane A hydrocarbon in which all the bonds between the carbon atoms are single bonds.

general formula A type of formula that represents the composition of any member of an homologous series.

alkene A hydrocarbon in which there are one or more double bonds between carbon atoms.

cracking A chemical reaction in which large alkane molecules are split into two or more smaller alkanes and alkenes.

alcohols An homologous series of compounds that contain the –OH functional group.

carboxylic acids An homologous series of compounds that contain the –COOH functional group.

polymerisation A reaction in which a large number of small molecules (monomers) join together to form a long chain molecule (polymer).

chromatography A technique for separating the components of a mixture – for example different food colouring agents.

7

Tier 3 Vocabulary

Word Meaning In a sentence

crude oil A fossil fuel, in the liquid state, formed from the remains of microscopic dead plants and animals that lived in the sea.

Crude oil is a mixture of hydrocarbons.

hydrocarbon A compound containing hydrogen and carbon only.

Hydrocarbons are found in crude oil.

fraction A component of a mixture that has been separated by fractional distillation.

The different hydrocarbons in crude oil are called fractions.

fractional distillation

A method of separating a mixture of liquids with different boiling points into individual components (fractions).

Fractional distillation is used to separate the different fractions in crude oil.

viscosity How thick or runny a liquid is. Low viscosity is very runny, high viscosity is thick.

Higher viscosity hydrocarbon have higher boiling points.

alkane A hydrocarbon in which all the bonds between the carbon atoms are single bonds.

Alkanes are saturated hydrocarbons.

general formula A type of formula that represents the composition of any member of an homologous series.

The general formula for an alkane is CnH2n+2.

alkene A hydrocarbon in which there are one or more double bonds between carbon atoms.

Alkenes are unsaturated hydrocarbons.

cracking A chemical reaction in which large alkane molecules are split into two or more smaller alkanes and alkenes.

Cracking turns large alkanes into shorter, more useful alkanes and alkenes.

saturated A molecule that contains only single bonds between the carbon atoms in a chain.

Saturated hydrocarbons only contain single bonds.

unsaturated A molecule that contains one or more double bonds between carbon atoms in a chain.

Unsaturated hydrocarbons contain one or more double bonds.

8

Word Meaning In a sentence

homologous series

A family of compounds that have the same general formula and similar properties, but have different numbers of carbon atoms.

Compounds in a homologous series have the same general formula.

alcohols An homologous series of compounds that contain the –OH functional group.

Alcohols burn well in oxygen.

carboxylic acids An homologous series of compounds that contain the –COOH functional group.

Carboxylic acids are weak acids.

monomer A small molecule used to make a polymer.

Monomers are joined together to make polymers.

polymer A long-chain molecule made by joining many smaller molecules (monomers) together.

Polymers are made over several hundred or thousand monomers.

9

10

Lesson 7 – Purity, Formulations and Identification of GasesRecall

1. State the group of the periodic table that contains the alkali metals.2. Describe the arrangement and movement of particles in a liquid.

3-7. Sand and salt are stirred in water and then filtered. Complete the 5 labels in the diagram.

8. Which method would be used to extract a very reactive metal, like sodium?

Pure Substances vs Mixtures

A pure substance is a single element or compound, so we could have pure oxygen (an element) or pure water (a compound).

Mixtures contain more than one substance and could contain elements and/or compounds, for example, orange juice is a mixture of water, citric acid, vitamin C, glucose and other substances.

A scientist would not consider this orange juice to be pure.

11

The melting point of a substance is the temperature where it changes from a solid to a liquid as it is heated. As freezing is just the opposite of melting, a substance would also freeze at this temperature and change from a liquid into a solid as it is cooled. The boiling point of a substance the temperature where it boils and the substance rapidly changes from a liquid into a gas.

Tier 3 Vocab Task

Use the information above, to write a definition for each term.

Tier 3 Vocab DefinitionPure

Mixture

Melting Point

Boiling Point

Pure substances melt and boil at specific temperatures. For example, pure water melts at 0⁰C and boils at 100⁰C. During a state change, the substance stays at this temperature – so boiling water stays at 100⁰C – it will only exceed this temperature when all of the water has turned into steam.

Mixtures, however, change state over a range of temperatures. We use this knowledge a lot in everyday life: for example, salt water (a mixture) freezes between – 5 and – 10⁰C, which is why the salt in grit stops roads from freezing in winter.

12

Look at the freezing point on these graphs and work out which graph shows a pure substance and how you can tell?

_______________________________

_______________________________

_______________________________

A B

Formulation

A formulation is a mixture that has been designed as a useful product. Several substances are mixed together in very carefully measured quantities to make sure that the product has the properties that you want.

Eg. Calpol is a mixture of paracetamol (to relieve pain), malitol (to make it sweeter) and some solvents for these substances to dissolve in, so that it is a liquid medicine and therefore suitable for children.

Imagine you have been asked to design a metal alloy for aeroplane wings. What properties do you think your formulation would need?

_____________________________________________________________________________

_____________________________________________________________________________

What could happen if you chose the wrong metals, in the wrong quantities, for your formulation?

_____________________________________________________________________________

_____________________________________________________________________________

13

Identifying Gases

Over the course of your GCSE so far, you have learned about many experiments that produce a gas during the reaction. Most of these gases are odourless and colourless, it is therefore important to understand the scientific tests that can be used to identify which gas has been produced.

Do the following tests and describe the results.

Gas Test Picture of Experiment Result Oxygen (O2) Insert a glowing

splint into a tube of the gas.

Hydrogen (H2) Insert a lit (burning) splint into a tube of the gas.

Carbon Dioxide (CO2) Bubble the gas through limewater (calcium hydroxide solution).

Chlorine (Cl2) Insert damp blue or red litmus into the gas.

14

Knowledge Check

1. Define the term “pure”.

2. Describe how boiling points are different in pure substances and mixtures.3. Give the melting and boiling point of water.

MP =BP =

4. Explain why alloys are considered to be formulations, not simple mixtures.5. Describe the test for oxygen.

6. Name the gas that produces a squeaky pop when tested using a lit splint.7. Describe the test for chlorine.

8. Name the chemical used in the test for carbon dioxide.

15

Target 9 extension task: [check answers in appendix]

Understanding Melting Points

1. At 20⁰C, would the element be a solid, liquid or gas?

HINT: If the temperature is higher than the melting point, the substance would be a liquid. If the temperature is higher than the boiling point, the substance would be a gas.

Fluorine –

Chlorine –

Bromine –

Iodine –

Astatine –

2. The boiling point of water is 100⁰C.

The boiling point of salt is 801⁰C.

If I had some salt water, what temperature would it boil at? ___________________

____________________________________________________________________

When you have a ___________ of substances, they melt and boil over a _______ of temperatures. _______ substances have a ___________ boiling point.

range / pure / mixture / specific

16

Lesson 8 – ChromatographyRecall

1. Define the term “hydrocarbon”.

2. Explain why graphite can conduct electricity but diamond can’t.

3. Complete the half equation: Al3+ + e– Al

4. Calculate the number of neutrons in an argon atom – its mass number is 40 and its atomic number is 18.5 – 6. Name the products when sodium and water react together.

Sodium + water ________________ + _____________

7. Define the term “pure”.

8. Describe the colour change when carbon dioxide is bubbled through limewater.

Chromatography Required Practical

You have completed this practical in year 7 and year 9, but we are now going to look into the experiment in more detail and interpret the results more thoroughly.

Paper chromatography is a technique used to separate mixtures of soluble substances. It is particularly important for scientists testing food colourings, inks and dyes to see if they are safe.

Watch the video and put the steps of the chromatography practical in order:

https://www.youtube.com/watch?v=pnTGNAfu6GE

17

Allow the solvent (water) to move through the paper, but remove the chromatogram before the solvent reaches the top.Add small spots of ink/dye to the pencil line on the paper.

Measure the distance travelled by the solvent and by the different dyes in each spot.

Place the paper into the container with a very small amount of the solvent in the bottom. Make sure the pencil line and spots are above the level of the solvent.Allow the chromatogram to dry.

Draw a pencil line across the chromatography paper, 1-2cm from the bottom.

Understanding Chromatography

Use the words below to fill-in the gaps.

A ______ substance will always produce one spot in chromatography, no matter which solvent you use. ___________ usually produce more than one _______, one for each ____________ in the mixture. It is possible that two _____________ in a mixture will show up as one spot in some solvents and you may need to ____________ the experiment with a different ___________ to distinguish between the substances.

The paper is known as the _______________ phase of chromatography because it stays still and the solvent is known as the _________________ phase because it moves up the sheet.

It is important to draw the line in _____________: if you drew the line in ink, the ink could ____________ in the solvent and disrupt the experiment. The substances that are most ___________ travel furthest up the paper. Any ____________ substances would not move up the paper at all.

stationary / insoluble / spot / substance / solvent / mobile / pencil / substances / pure / dissolve / mixtures / soluble / repeat

18

Rf Values

In order to identify specific substances by chromatography, we need to calculate the retention factor for the substance.

Solvent front = the distance travelled by the solvent

New position of compound = the distance travelled by a particular dye

Origin/baseline = the pencil line on which you placed the dots of dye/ink

The calculation for the Rf value is:

Rf value = distance travelled by the substance

distance travelled by the solvent

In the example above: Rf = 2.1

2.8

= 0.75

Rf values are ALWAYS a decimal between 0 and 1, as the substance cannot move further than the solvent. If a substance had an Rf value of 0, that would mean that the ink spot did not move from the origin line because it was insoluble in the solvent.

Use the information from the diagram to calculate the Rf value for each substance in the reaction mixture:

A =

B =

C =

19

For each of the following chromatograms calculate the Rf values for all of the spots.

Red = Purple =

Yellow = Light Green =

Light Blue = Orange =

Calculate the Rf value of

A, B and C and work out

which colour they are

likely to be:

Bright Blue = A =

Dark Green = B =

Dark Blue = C =

Which of these felt tip pens contained an ink that was insoluble in water? How can you tell?

____________________________

____________________________

____________________________

____________________________

20

Knowledge Check

1. Name the process used to identify the dyes used in food colourings and inks.2. Explain why the origin line is drawn in pencil, not ink.

3. Describe how to place the paper into the container during chromatography.

4. Name the two phases of chromatography.

5. Suggest where the spot of the most soluble dye would be found on a chromatogram.6. Describe where a spot of an insoluble dye would be found on a chromatogram.7. State the calculation for an Rf value.

8. Calculate the Rf value when a solvent has moved 6cm and the dot of a substance has moved 1.5cm.

Target 9 extension task: [check answers in appendix]

Questions

Q1. Some food colourings are a mixture of soluble, coloured substances. Mixtures of soluble substances can be separated by paper chromatography.

Paper chromatography was used to try to separate the coloured substances in five food colourings, V, W, X, Y and Z.

Figure 3 shows the spots for the five food colourings on the chromatography paper at the start of the experiment. The paper was placed in a beaker with the bottom of the paper in the solvent.

Figure 321

(i)   Identify the stationary phase in this experiment.

(1) .............................................................................................................................................

(ii)  Give a reason why the spots of the food colourings must be above the level of the solvent when the paper is placed in the solvent.

(1) .............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

(iii)  Figure 4 shows the chromatogram at the end of the experiment.

Figure 4Give the reason why the spot of food colouring V has not moved during the chromatography experiment.

(1) .............................................................................................................................................

.............................................................................................................................................

(iv)  Explain, by referring to Figure 4, which food colouring contained the greatest number of soluble, coloured substances.

(2) .............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

(v)  One coloured substance in food colouring X moved 5.8 cm when the solvent front moved 6.6 cm.

Calculate the Rf value for this substance, giving your answer to two significant figures.(2)

Rf value = ...........................................................

(Total for question = 7 marks)

22

 Lesson 9 – Chromatography PracticalRecall

1-2. Name the two changes of state that occur during simple distillation.

3. Beryllium is in group 2, describe how beryllium atoms become ions.4. State the charge will beryllium ions have as a result.5. Describe what happens when alkenes are tested using bromine water.

6. Describe the trend in flammability as you move up the fractionating column in fractional distillation.7. Name the type of substance that melts over a range of temperatures instead of having a distinct melting point.8. Describe how you would test to see if a gas was hydrogen.

Chromatography Recap

Use a pencil to draw a _______ 2cm from the bottom of the _______. We use pencil, not pen, because it is __________ and therefore won’t _________ up the paper. Spots of ______ are then placed on the line. A small amount of __________ (normally water) is then placed in the bottom of a beaker. The paper is then put in the beaker so that the line is __________ the solvent – if it was below, the ink would just go _______ into the solvent and not go up the paper. The chromatogram is left for about 15 __________ so that the solvent moves up the paper. The place where the solvent ___________ is then marked on the paper and then measured along with the ____________ moved by the dot of each ___________ in the ink. These measurements can then be used to calculate the ____________ factor (Rf).

above / insoluble / line / colour / down / distance / paper / travel / retention / minutes / ink solvent / reached

23

Interpreting Results

This is a chromatogram produced from a grey felt tip pen.

1. How many different coloured dyes are found in the grey ink? ________2. Calculate the retention factor (Rf) value for the purple dye.

Rf = ___________3. If you did another chromatogram of a different felt tip, how would you know if it contained the same purple dye?____________________________________________________________________________________________________

Understanding the Process

Look at the chromatography recap on the previous page and write down some important do’s and don’ts when you are doing a chromatography experiment and say why each thing is important.

Do’s Don’ts

24

25

Extended writing challenge: Chromatography

The diagram shows chromatography equipment set up with two mistakes.

Identify the mistakes and explain why they need to be changed.

A, B and C are blue food colouring samples and X is an unknown substance that contains one of the food colourings. Explain how chromatography could be used to identify which food colouring the substance contained.

Knowledge Check

1. Describe how to draw the origin line on the chromatogram.

2. Name the solvent used in most chromatography experiments.3. State the term that is abbreviated to Rf.

4. Describe what would happen if the inks were below the level of the solvent.

5. Describe how you can tell if the same dye is in two different inks.

6. Name the equipment used to measure the distance travelled by the different spots of dye.7. Explain why the origin line should not the drawn in pen. 8. Suggest why a lid would be put on the beaker during chromatography.

Target 9 extension task: [check answers in appendix]

Q1. P, Q, R and S are mixtures of food colourings. They are investigated using paper chromatography.

Figure 4 shows the chromatogram at the end of the experiment.

(i)  Which mixture contains an insoluble food colouring?

(1)

   A    mixture P

   B    mixture Q

   C    mixture R

26

(6 marks)

   D    mixture S

Figure 4 (ii)  Give a change that could be made to the experiment to obtain an Rf value for the insoluble colouring.

(1) .............................................................................................................................................

.............................................................................................................................................

(iii)  Explain, by referring to Figure 4, which mixture is separated into the greatest number of soluble food colourings by this chromatography experiment.

(2) .............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

(Total for question = 4 marks) 

Q2. 

Mixtures of coloured substances can be separated by paper chromatography.

Paper chromatography was used to separate a mixture of blue and red inks. A spot of the mixture was placed on chromatography paper as shown in Figure 1.

Figure 1

27

(i)  Give a reason why the start line is drawn in pencil rather than in ink.

(1) .............................................................................................................................................

.............................................................................................................................................

(ii)  The chromatography paper, with the spot of mixture on it, was placed in a beaker with the bottom of the paper in water.

On Figure 2, complete the diagram showing the position of the chromatography paper with the spot of mixture at the start of the experiment.

(1)

Figure 2(iii)  The chromatography was carried out and the result is shown in Figure 3.

Figure 3The blue spot had moved 14.5 cm and the solvent front had moved 15.3 cm.Calculate the Rf value of the substance in the blue spot, giving your answer to 2 significant figures.

28

(2)

Rf value = ........................................................... (Total for question = 4 marks)

Lesson 10 – Identifying Ions Part 1Recall

1. Name a simple covalent compound.

2. Name a giant covalent compound.

3. Name an ionic compound.

4. Explain why metals can conduct electricity.

5. Explain why metals are malleable.

6. Describe the test for carbon dioxide.

7. Define the term “activation energy”.

8. Explain how you can tell that this reaction is reversible.

Ions Recap

Compounds of metals and non-metals are made of ions. They are called ionic compounds and contain both positive and negative ions. For example, sodium fluoride contains sodium ions (Na+) and fluoride ions (F–). The electrostatic attraction between these ions holds the compound together. Positive ions are called cations and negative ions are called anions.

29

Comprehension Task

1. Which compounds contain ions?

_____________________________________________________________________________

2. Which ions do ionic compounds contain?

_____________________________________________________________________________

3. What holds ionic compounds together?

_____________________________________________________________________________

4. What is a cation?

_____________________________________________________________________________

5. What is an anion?

_____________________________________________________________________________

Cation Tests: Flame Tests Practical

Some positive ions give distinctive colours in flame tests.

1. Clean the nichrome wire loop.2. Dip the loop into the solution of

an ionic compound.3. Hold the loop in the roaring (blue)

flame of a Bunsen burner4. Record the colour seen.5. Identify the compound using the

chart below.6. Repeat with the other compounds, ensuring the wire loop is clean

each time.

30

Cation ColourCopper (Cu2+) GreenLithium (Li+) CrimsonCalcium (Ca2+) Orange-RedSodium (Na+) YellowPotassium (K+) Lilac

If the flame test was done on a mixture containing more than one positive ion, the colours would be mixed and therefore it may not be possible to identify the ions using this method.

Compound A B C D EColourCation

Cover Write Check Task

Learn the colours of the cations using cover write check. The cations have been jumbled each time to test you further.

31

Cation ColourCopper (Cu2+) GreenLithium (Li+) CrimsonCalcium (Ca2+) Orange-RedSodium (Na+) YellowPotassium (K+) Lilac

Cation ColourCopper (Cu2+)Lithium (Li+)Calcium (Ca2+)Sodium (Na+)Potassium (K+)

Cation ColourCalcium (Ca2+)Copper (Cu2+)Potassium (K+)Lithium (Li+)Sodium (Na+)

Cation ColourPotassium (K+)Sodium (Na+)Copper (Cu2+)Lithium (Li+)Calcium (Ca2+)

Cation ColourLithium (Li+)Potassium (K+)Sodium (Na+)Calcium (Ca2+)Copper (Cu2+)

Cation ColourCopper (Cu2+)Calcium (Ca2+)Sodium (Na+)Potassium (K+)Lithium (Li+)

Cation Tests: Sodium Hydroxide Solution Test

Most metal hydroxides, aside from group 1 metal hydroxides, are insoluble. When you react sodium hydroxide with an ionic compound of a metal from a different group, a displacement reaction occurs:

eg. word equation: copper sulfate + sodium hydroxide sodium sulfate + copper hydroxide

symbol equation: CuSO4 (aq) + 2NaOH(aq) Na2SO4(aq) + Cu(OH)2(s)

In this equation, soluble compounds have the (aq) symbol, showing they are aqueous solutions – which means dissolved in water. The copper hydroxide in the equation has an (s) symbol, showing it is a solid, which means that it is insoluble and you would see it as a precipitate that has come out of the solution.

The formation of the precipitate can be shown as an ionic equation:

eg. Cu2+(aq) + 2OH–

(aq) Cu(OH)2(s)

You can identify some of the cations by looking at the colour of the precipitate, but there are multiple cations that form white precipitates, so there needs to be another method to distinguish between those – to distinguish between them, an excess of sodium hydroxide is added and you see if the precipitate then dissolves.

Cation Colour of Precipitate When a Few Drops of Sodium Hydroxide

What Happens When the Sodium Hydroxide is Added to Excess

Copper (Cu2+) ions Blue X

Iron (Fe2+) ions Green X

32

Iron (Fe3+) ions Brown X

Magnesium (Mg2+) ions White The precipitate does not dissolve

Calcium (Ca2+) ions White The precipitate does not dissolve

Aluminium (Al3+) ions White The precipitate dissolves

1. Describe how you could use sodium hydroxide solution to distinguish between Fe2+ and Fe3+ ions. (describe the test and the results)

_____________________________________________________________________________

_____________________________________________________________________________

_____________________________________________________________________________

2. If you had an unknown ionic compound, added a few drops of sodium hydroxide solution and saw a green precipitate form, which cation did the compound contain?

________________________________

3. a) If you had an unknown ionic compound, added a few drops of sodium hydroxide solution and saw a white precipitate form, which three cations could it contain?

_____________________________________________________________________________

3. b) If you then added an excess of sodium hydroxide solution and the precipitate of the unknown ionic compound dissolved, which cation must it have contained?

________________________________

3. c) If the ionic compound did not dissolve when an excess of sodium hydroxide of sodium hydroxide, describe how you could use a flame test to distinguish between the ions that it could contain. (describe the test and the results)

_____________________________________________________________________________

_____________________________________________________________________________

_____________________________________________________________________________

_____________________________________________________________________________

4. If you add sodium hydroxide solution to calcium chloride solution, sodium chloride solution and a calcium hydroxide precipitate are formed:

33

Write a word equation:

__________________ + __________________ _________________ + ________________

Balance the symbol equation:

NaOH + CaCl2 NaCl + Ca (OH)2

Write an ionic equation for the formation of the calcium hydroxide:

___________________ + __________________ _________________

Instrumental Analysis

In addition to chemical tests like the ones in this lesson, scientists also identify elements and compounds through instrumental analysis. These methods are used to analyse blood samples, food contents, water and air quality and the purity of medicines.

Using instruments (machines) instead of chemical analysis is better because they are more:

sensitive informative rapid accurate

An example of an instrumental method of analysis is flame emission spectroscopy: this is a sophisticated way of doing flame tests and can be used to identify the metal ions (even if they are a similar colour) and measure the concentration of the metal ion (which cannot be done in a regular flame test).

The spectroscope in the machine can measure the wavelength of the light given off by the ion. This is used to produce a line spectrum, which can be used to identify the ion with more certainty.

From the image of the flame tests on page 76, you can see that lithium and calcium have similar colours when their compounds are burned, but if you look at the emission spectrum of each ion, you can see that they are very different:

34

Knowledge Check

1. Name the ion that burns with a lilac flame.

2. Name the ion that burns with a crimson flame.3. Name the ion that burns with a green flame.4. Name the ion that burns with a yellow flame.5. Name the ion that burns with an orange-red flame.6. Name the ion that forms a blue precipitate with sodium hydroxide.7. Name the ion that forms a brown precipitate with sodium hydroxide.8. Name the ion that forms a white precipitate with sodium hydroxide, which then dissolves when sodium hydroxide is added in excess.

Target 9 extension task: [check answers in appendix]

Q1.35

Sodium sulfate is tested to show the ions present in it.

(i)  Describe how to carry out a flame test on solid sodium sulfate.

(3) .............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

(ii)  State what colour would be seen in the flame.

(1) ...........................................................

(Total for question = 4 marks) 

Q2. 

Iron(III) ions, Fe3+, react with hydroxide ions in solution to form iron(III) hydroxide.

Complete the ionic equation for this reaction.

(1)

Fe3+ + 3OH– → ......................................................................

(Total for question = 1 mark) 

Q3. 

Qualitative tests are used to identify ions in compounds.

Instrumental methods are often used for analysis.

Give a reason why instrumental analysis may be better than other methods of analysis.

(1) .............................................................................................................................................

.............................................................................................................................................

36

(Total for question = 1 mark) 

Q4. 

A sample of potassium carbonate is contaminated with a small amount of sodium carbonate. When a flame test is carried out on the sample, a bright yellow flame is seen.

Describe how you could show that potassium and sodium ions are present in this sample.

(2) .............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

(Total for question = 2 marks) 

Lesson 11 – Identifying Ions Part 2Recall

1. Name the ion that forms a green precipitate with sodium hydroxide.2. Name the ion that forms a brown precipitate with sodium hydroxide.3. Name two ions that form white precipitates with sodium hydroxide that do not dissolve when sodium hydroxide is added in excess.4. Name the ion that burns with a green flame.5. Name the ion that burns with a lilac flame.

6. Name the ion that burns with a crimson flame.7. Name the ion that burns with a yellow flame.8. Name the ion that burns with an orange-red flame.

Anion Tests: Testing for Carbonate Ions

37

Carbonate (CO32–) ions can be identified using a very simple test:

When dilute acid is added to a metal carbonate, there is fizzing due to the formation of carbon dioxide gas. This gas needs to be collected and then bubbled through limewater. The limewater will change from clear and colourless to cloudy and milky due to the carbon dioxide.

Compound Observations When Bubbled Through LimewaterA Stays clear and colourlessB Turns cloudy and milkyC Turns cloudy and milkyD Stays clear and colourless

Which compounds contained carbonate ions? How can you tell?

_____________________________________________________________________________

_____________________________________________________________________________

Anion Tests: Testing for Sulfate Ions

Sulfate (SO42–) ions can also be identified using a simple test:

Add dilute hydrochloric acid to the metal sulphate, followed by barium chloride solution. If a white precipitate forms, the compound contains sulfate ions – this precipitate is barium sulphate.

Word equation: barium chloride + sodium sulfate barium sulfate + sodium chloride

Balanced equation: BaCl2(aq) + Na2SO4(aq) BaSO4(s) + 2NaCl(aq)

Ionic equation: Ba2+(aq) + SO4

2–(aq) BaSO4(s)

Compound Observations When Tested with Hydrochloric Acid and Barium Chloride

W White precipitateX No precipitateY White precipitateZ No precipitate

Which compounds contained sulfate ions? How can you tell?

_____________________________________________________________________________

_____________________________________________________________________________38

Anion Tests: Testing for Halide Ions

Group 7 elements are called halogens. Ions of the these elements are known as halides. The three that you need to be able to identify are chloride (Cl–), bromide (Br–) and iodide (I–) ions. There is a simple test for this:

Add nitric acid to the metal halide, followed by silver nitrate. A precipitate will then form, the colour of which depends on the halide involved. Chloride (Cl–) ions form a white precipitate, bromide (Br–) ions form a cream precipitate and iodide (I–) ions form a yellow precipitate.

Eg.

Word equation: silver nitrate + potassium iodide silver iodide + potassium nitrate

Balanced equation: AgNO3(aq) + KI(aq) AgI(s) + KNO3(aq)

Ionic equation: Ag+(aq) + I–

(aq) AgI(s)

Compound Observations When Tested with Nitric Acid and Silver Nitrate

K Yellow precipitateL White precipitateM No precipitate

Which compound contained chloride ions? How can you tell?

_____________________________________________________________________________

_____________________________________________________________________________

Identifying Ions Task

Use the tests from this lesson and last lesson to identify the cations and anions when the results of different tests are described.

Worked example: (to go through with your teacher)

Compound X was analysed. It gave a lilac flame in a flame test. When hydrochloric acid followed by barium chloride solution was added to a solution of X, a white precipitate was produced.

39

a. Identify the positive ion in compound X.

___________________________________

b. Identify the negative ion in compound X.

___________________________________

c. Write the name and formula of compound X.

___________________________________

d. Write a balanced equation for the formation of the white precipitate.

_____________________________________________________________________________

e. Write an ionic equation for the formation of the white precipitate.

_____________________________________________________________________________

Question 1

Compound A was analysed. It gave a yellow flame in a flame test. When dilute acid was added to a sample of A, a gas was given off that turned limewater cloudy.

a. Identify the positive ion in compound A.

___________________________________

b. Identify the negative ion in compound A.

___________________________________

c. Write the name and formula of compound A.

___________________________________

d. Name the gas the turned the limewater cloudy.

___________________________________

Question 2

Compound B was analysed. It gave a green flame in a flame test. When nitric acid followed by silver nitrate solution was added to a solution of B, a white precipitate was produced.

a. Identify the positive ion in compound B.

40

___________________________________

b. Identify the negative ion in compound B.

___________________________________

c. Write the name and formula of compound B.

___________________________________

d. Write a balanced equation for the formation of the white precipitate.

_____________________________________________________________________________

e. Write an ionic equation for the formation of the white precipitate.

_____________________________________________________________________________

Question 3

Compound C was analysed. A green precipitate was produced when sodium hydroxide solution was added to a solution of C. A yellow precipitate was produced when nitric acid, followed by silver nitrate, was added to a separate solution of C.

a. Identify the positive ion in compound C.

___________________________________

b. Identify the negative ion in compound C.

___________________________________

c. Write the name and formula of compound C.

___________________________________

d. Write a balanced equation for the formation of the green precipitate.

_____________________________________________________________________________

e. Write a balanced equation for the formation of the yellow precipitate.

_____________________________________________________________________________

f. Write an ionic equation for the formation of the green precipitate.

_____________________________________________________________________________

41

g. Write an ionic equation for the formation of the yellow precipitate.

_____________________________________________________________________________

Question 4

Compound D was analysed. It gave a crimson flame in a flame test. When dilute acid was added to a sample of D, a gas was given off that turned limewater cloudy.

a. Identify the positive ion in compound D.

___________________________________

b. Identify the negative ion in compound D.

___________________________________

c. Write the name and formula of compound D.

___________________________________

Question 5

Compound E was analysed. It gave a red-orange flame in a flame test. A white precipitate was produced when sodium hydroxide solution was added to a solution of E. This precipitate did not dissolve when more sodium hydroxide was added. A cream precipitate was produced when nitric acid, followed by silver nitrate, was added to a separate solution of E.

a. Identify the positive ion in compound E.

___________________________________

b. Identify the negative ion in compound E.

___________________________________

c. Write the name and formula of compound E.

___________________________________

d. Write a balanced equation for the formation of the white precipitate.

_____________________________________________________________________________

e. Write a balanced equation for the formation of the cream precipitate.

_____________________________________________________________________________

f. Write an ionic equation for the formation of the white precipitate.

42

_____________________________________________________________________________

g. Write an ionic equation for the formation of the cream precipitate.

_____________________________________________________________________________

Question 6

Compound F was analysed. A white precipitate was produced when sodium hydroxide solution was added to a solution of F. This precipitate dissolved when more sodium hydroxide was added. When hydrochloric acid, followed by barium chloride solution, was added to a separate solution of F, a white precipitate was produced.

a. Identify the positive ion in compound F.

___________________________________

b. Identify the negative ion in compound F.

___________________________________

c. Write the name and formula of compound F.

___________________________________

d. Write a balanced equation for the formation of the white precipitate when sodium hydroxide was added.

_____________________________________________________________________________

e. Write a balanced equation for the formation of the white precipitate when barium chloride was added.

_____________________________________________________________________________

43

f. Write an ionic equation for the formation of the white precipitate when sodium hydroxide was added.

_____________________________________________________________________________

g. Write an ionic equation for the formation of the white precipitate when barium chloride was added.

_____________________________________________________________________________

Knowledge Check

Compound S was analysed. A brown precipitate was produced when sodium hydroxide was added to a solution of S. When hydrochloric acid followed by barium chloride solution was added to a separate solution of S, a white precipitate was produced.

1. Identify the positive ion in compound S.

2. Identify the negative ion in compound S.

3. Write the name and formula of compound S.4. Write a balanced equation for the formation of the brown precipitate when sodium hydroxide is added.5. Write a balanced equation for the formation of the white precipitate when barium chloride is added.6. Write an ionic equation for the formation of the brown precipitate when sodium hydroxide is added.7. Write an ionic equation for the formation of the white precipitate when barium chloride is added.

44

8. Describe how the iron ion would be different if a green precipitate had been formed with the sodium hydroxide instead.

Target 9 extension task: [check answers in appendix]

Q1. (a) Substance X is an ammonium salt.  Complete the sentence by putting a cross ( ) in the box next to your answer.

A test was carried out to find which anion is present in substance X. Dilute hydrochloric acid was added to a sample of substance X. There was effervescence and the gas given off turned limewater milky. The anion present in substance X is

(1)    A   carbonate ion, CO3

2–

   B   chloride ion, Cl–

   C   nitrate ion, NO3–

   D   sulfate ion, SO42–

 (b) Aluminium ions, Al3+, react with hydroxide ions in solution to give a white precipitate of aluminium hydroxide.       Write the ionic equation for this reaction.

(3)      ..............................................................................................................................................

 *(c) A technician found some colourless crystals of a substance left, unlabelled, in a beaker in a laboratory. She knew the substance was one of potassium sulfate, potassium iodide, sodium sulfate or sodium iodide. Explain how, using chemical tests, the technician could find out if the substance left in the beaker was potassium sulfate, potassium iodide, sodium sulfate or sodium iodide. You may include equations in your answer.

(6)      ..............................................................................................................................................

      ..............................................................................................................................................

      ..............................................................................................................................................

      ..............................................................................................................................................45

      ..............................................................................................................................................

      ..............................................................................................................................................

      ..............................................................................................................................................

      ..............................................................................................................................................

      ..............................................................................................................................................

      ..............................................................................................................................................

      ..............................................................................................................................................

      ..............................................................................................................................................

      ..............................................................................................................................................

      ..............................................................................................................................................

      ..............................................................................................................................................

      ..............................................................................................................................................

Appendix 1 – Answers to target 9 questions

Lesson 7 – Mark Scheme

1. Fluorine – gas

Chlorine – gas

Bromine – liquid

Iodine – solid

Astatine – solid

2. The boiling point of water is 100⁰C.

The boiling point of salt is 801⁰C.

If I had some salt water, what temperature would it boil at? it wouldn’t have a specific boiling point – it would boil from 100⁰C to 801⁰C.

When you have a mixture of substances, they melt and boil over a range of temperatures. Pure substances have a specific boiling point.

46

Lesson 8 - Mark Scheme

Q1. 

47

48

Lesson 9 - Mark Scheme

Q1. 

Q2. 

49

Lesson 10 - Mark Scheme

Q1.(i) Clean the wire (1)Dip the wire into the solution of the compound (1)Put the wire into the roaring flame of the Bunsen burner (1) 

Q2. 

Q3. 

50

Q4. 

Lesson 11 - Mark Scheme

Q1.

  Answer Acceptable answers

Mark

(a) A carbonate ion CO3

2-  

(1)(b) Al3++ 3OH-→ Al(OH)3

OH- (1) Al(OH)3 (1) balancing 3, conditional on correct formulae (1)

allow multiples allow HO- (1) allow Al(HO)3 (1) do not allow Al(HO)3/lower case h ignore state symbols/3Na+ on both sides (3)

  Indicative Content Mark QWC *(c) An explanation including some of the following

points test for cation flame test if the flame is yellow/not lilac, sodium ions are present if the flame is lilac/not yellow, potassium ions are presenttest for iodide ions make a solution of the crystals in water add dilute nitric acid add silver nitrate solution

(6)

51

if there is a yellow precipitate, iodide ions are present if there is no precipitate, sulfate ions are present Ag+ + I¯ → AgIOR make a solution of the crystals in water add chlorine water then cyclohexane if the cyclohexane/top layer turns purple, iodide ions were present if there is no colour change, sulfate ions are present Cl2 + 2I- → 2Cl- + I2test for sulfate ions make a solution of the crystals in water add dilute hydrochloric/nitric acid add barium chloride/nitrate solution if there is a white precipitate, sulfate ions are present if there is no precipitate, iodide ions are present Ba2+ + SO4

2- → BaSO4

Level 0 No rewardable content 1 1 - 2

a limited description of test for any 1 ion e.g. flame test, yellow flame, sodium ions are present. the answer communicates ideas using simple language and uses limited scientific terminology spelling, punctuation and grammar are used with limited accuracy

2 3 - 4 a simple description to identify a cation and an anion e.g. if the substance is sodium sulfate, it will give a yellow flame in a flame test and a white precipitate with barium chloride solution. the answer communicates ideas showing some evidence of clarity and organisation and uses scientific terminology appropriately spelling, punctuation and grammar are used with some accuracy

3 5 - 6 a detailed description to identify at least 3 ions e.g. carry out a flame test, yellow flame, sodium ions present, lilac flame, potassium ions present, add silver nitrate solution to solution of substance, yellow precipitate, iodide ion. the answer communicates ideas clearly and coherently uses a range of scientific terminology accurately spelling, punctuation and grammar are used with few errors

52

53