whachemistry.files.wordpress.com  · Web viewGFM = 159.6, n = 0.5 moles, m = 79.8gCalculate the mass of calcium carbonate solution that must be dissolved in 1 litre of distilled

Wallace Hall Academy

Preparing for Higher Chemistry

CalculationsMarking Scheme

Using the Triangles Practice Questions

Answer the following questions showing all of your working.

For some questions, you will have to use both triangles to get to the final answer.

1. Calculate the number of moles present in 4.4 g of CO2. 0.1 moles

2. Calculate the number of moles present in 1.28 g of oxygen. 0.04 moles

3. Calculate the mass of 0.25 moles of aluminium chloride. 33.375 g

4. 0.5 moles of an unknown substance has a mass of 8 g. Suggest a formula for the

substance. GFM = 16 g so formula = CH4

5. Calculate the concentration of a substance prepared by dissolving 0.2 moles of

solute in 100 cm3 of solution. 2 mol l-1

6. Calculate the volume of 0.1 mol l-1 solution which would contain 1 mole of solute

particles. 10 litres

7. Calculate the mass of CuSO4 that must be dissolved in 250 cm3 of distilled water to

make a 2 mol l-1 solution. GFM = 159.6, n = 0.5 moles, m = 79.8g

8. Calculate the mass of calcium carbonate solution that must be dissolved in 1 litre of

distilled water to make a 0.75 mol l-1 solution. GFM = 100.1, n = 0.75, m = 75.075g

9. Calculate the concentration of magnesium nitrate solution if 0.74 g is dissolved in 50

cm3 of distilled water. GFM = 148.3, n = 0.005, c = 0.1 mol l-1

10. Calculate the concentration of copper(II) nitrate solution if 18.7 g is dissolved in 120

cm3 of distilled water. GFM = 187.5, n = 0.1 moles, c = 0.83 mol l-1

Extension Questions (use the internet to help you)

1. What number is represented by ‘1 mole’? 6.02 x 1023

2. How many particles are present in 0.5 moles? 3.01 x 1023

3. How many particles are present in 0.2 moles? 1.204 x 1023

4. What is distilled water? Water that has been evaporated and condensed in a

separate flask to remove any impurities.

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You may have to determine the

formula yourself.

5. Why is distilled water used over tap water when making certain solutions, such as

ammonium phosphate? Ions/impurities in the water can react with some chemicals.

Balanced Equations Practice Questions

Balance each of the following equations and write a sentence similar to the one in the box on the previous page.

1. CH4 + 4Cl2 CCl4 + 4HCl

1 mole of methane reacts with 4 moles of chlorine to give 1 mole of carbon

tetrachloride and 4 moles of hydrogen chloride.

2. C3H8 + 5O2 3CO2 + 4H2O

1 mole of propane reacts with 5 moles of oxygen to give 3 moles of carbon dioxide

and 4 moles of water.

3. 2HgO 2Hg + O2

2 moles of mercury oxide decompose to give 2 moles of mercury and 1 mole of

oxygen.

4. Cu + 2AgNO3 Cu(NO3)2 + 2Ag

1 mole of copper reacts with 2 moles of silver nitrate to give 1 mole of copper nitrate

and 2 moles of silver.

Using Molar Ratio Practice Questions 1

1. Look at the following balanced equation:

2Na + Cl2 2NaCl 2 : 1 : 21 : 0.5 : 1

1. Copy the balanced equation and write the molar ratio underneath. 2. Write the actual molar ratio for if 1 mole of Na was added into the reaction.3. How many moles of sodium chloride would be produced if 0.4 moles of Cl2 reacted

with enough sodium? 0.8 moles4. How many moles of each reactant would be required to produce 0.025 mol of

product? 0.025 moles of Na and 0.0125 moles of chlorine.5. Extension: if 4 moles of Na was added to 3 moles of Cl2, which reactant would there

be too much of, and by how much? Chlorine by 1 mole.

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Using Molar Ratios Practice Questions 2

Start by writing the molar ratio for the two chemicals mentioned then use the method above to get to the answer.

1. 2Al + 3Cl2 2AlCl3

a) How many moles of chlorine will react with 2.47 moles of aluminium? 3.705b) How many moles of aluminium chloride will be produced from 0.032 moles of

chlorine? 0.021

2. 2P + 3Cl2 2PCl3

a) How many moles of phosphorous will react with 0.0045 moles of chlorine? 0.003b) How many moles of phosphorous chloride will be produced from 0.97 moles of

chlorine? 0.647

3. 3Ag2S + 2Al 6Ag + Al2S3

a) How many moles of aluminium are required to react with 55 moles of silver sulphide? 36.67

b) How many moles of aluminium would have to react to produce 0.0014 moles of silver? 0.000467

4. 2C2H2 + 5O2 4CO2 + 2H2O a) How many moles of oxygen are required to burn 0.007 moles of acetylene, C2H2?

0.0175b) How many moles of moles of carbon dioxide are produced when this number of

moles of acetylene is burned? 0.014

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Titration Questions

Use the worked example shown on the previous page to help you carry out the following calculations.

1. In a titration experiment, 25 cm3 of 0.1 mol l-1 hydrochloric acid, HCl, reacted with 50 cm3 of sodium hydroxide solution, NaOH. Calculate the concentration of the sodium hydroxide solution. 0.05 mol l-1

HCl + NaOH NaCl + H2O

2. In a titration experiment, 20 cm3 of 1.0 mol l-1 nitric acid, HNO3, reacted with 25 cm3 of sodium hydroxide solution, NaOH. Calculate the concentration of the sodium hydroxide solution. 0.8 mol l-1

HNO3 + NaOH NaNO3 + H2O

3. In a titration experiment, 25 cm3 of 0.5 mol l-1 sulfuric acid, H2SO4 reacted with 25 cm3 of sodium hydroxide solution, NaOH. Calculate the concentration of the sodium hydroxide solution. 1 mol l-1

H2SO4 + 2NaOH Na2SO4 + 2H2O

4. In a titration experiment, 20.4 cm3 of 0.15 mol l-1 phosphoric acid, H3PO4, reacted with 10 cm3 of sodium hydroxide solution, NaOH. Calculate the concentration of the sodium hydroxide solution. 0.918 mol l-1

H3PO4 + 3NaOH Na3PO4 + 3H2O

Extension Questions

1. In a redox titration, 18.6 cm3 of 0.2 mol l-1 potassium permanganate solution is required to react with 20 cm3 of iron sulfate solution. Determine the concentration of iron(II) ions. 0.93 mol l-1

5Fe2+(aq) + MnO4

−(aq) + 8H+

(aq) 5Fe3+(aq) + Mn2+

(aq) + 4H2O(l)

2. A 50 cm3 sample of contaminated drinking water was titrated and required 27.4 cm3 of 0.02 mol l-1 iron (II) sulfate solution to reach the end point. Calculate the concentration of chromate ions, CrO4

2-, in solution. 0.00365 mol l-1

3Fe2+(aq) + CrO4

2-(aq) + 8H+

(aq) 3Fe3+(aq) + Cr3+

(aq) + 4H2O(l)

Calculations Based on Balanced Equations Practice Questions

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1. Calculate the mass of carbon dioxide produced when 160 g of methane burns completely in air. 440 g

CH4 + 2O2 CO2 + 2H2O

2. Calculate the mass of water produced when 440 g of propane burns completely in air. 720 g

C3H8 + 5O2 3CO2 + 4H2O

3. Calculate the mass of magnesium oxide produced when 100 g of magnesium carbonate decomposes completely on heating. 47.8 g

MgCO3 CO2 + MgO

4. Calculate the mass of silicon carbide produced when 15 g of carbon reacts with excess silicon oxide. 16.67 g

3C + SiO2 2CO + SiC

5. The chemical equation for the photosynthesis reaction is:

6H2O + 6CO2 C6H12O6 + 6O2

How many grams of H2O would react with 20 g of CO2? 8.18 g

6. Decomposition of potassium chlorate, KClO3, serves as a convenient laboratory source of small amounts of oxygen gas. The reaction is:

2KClO3 2KCl + 3O2

Calculate the mass of KClO3 must be heated to produce 8 g of O2? 20.4 g

7. Calculate the mass of copper nitrate which would be produced when 3.17 g of copper reacts with excess silver nitrate solution. 9.36 g

Cu + 2AgNO3 2Ag + Cu(NO3)2

7. Using Proportion for Problem Solving Questions

Identifying Proportion Practice Questions

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For each of the following questions:1. Identify the proportion and write out as above2. Use the proportion calculation to determine the answer.

1. The maximum dosage of paracetamol is 60 mg per kg of body mass. What is the maximum dosage for a 73 kg man?1 kg 60 mg73 kg 4380 mg

2. A gas occupies 24 litres per mole. How many moles of gas would take up 86 litres?24 litres 1 mole86 litres 3.58 moles

3. Diamond costs £44,000 per gram. How many grams could £1m buy?£44,000 1g£1,000,000 22.73 g

4. Driving lessons cost £30 per hour. How many hours of lessons would £495 buy?£30 1 hour£495 16.5 hours

5. Methanol costs £12.80 per 500 cm3. A reaction requires 1.2 litres of methanol – how much will this cost? (Hint: convert to cm3).£12.80 500cm3

£30.72 1200cm3

6. Bromobenzene costs £18.40 per 500 g. A reaction requires 15.7 g of bromobenzene – how much will this cost? £18.40 500 g£0.578 15.7 g

7. Palladium powder to be used as a catalyst costs £373 per 5 g. A reaction requires 1.25 g of catalyst – how much will this cost?£373 5g£93.25 1.25g

Problem Solving Past Paper Style Questions

Use the worked example to help you work through the following past paper style problem solving questions.

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1. It is recommended an adult female takes in 14·8 mg of iron per day. 100 g of a breakfast cereal contains 12·0 mg of iron. Calculate the percentage of the recommended daily amount of iron provided for an adult female by a 30 g serving. (Higher 2017). 24%

2. Alpha-amanitin is a highly toxic cyclic peptide found in death cap mushrooms. The lethal dose for humans is 100 mg per kg of body mass. 1·0 g of death cap mushrooms contains 250 mg of alpha-amanitin. Calculate the minimum mass of death cap mushrooms that would contain the lethal dose for a 75 kg adult. (Higher 2016). 30g

3. The student obtained 3·7g of methyl cinnamate from 6·5g of cinnamic acid. The student wanted to scale up the experiment to make 100 g of methyl cinnamate. Cinnamic acid costs £35·00 per 250 g. Calculate the cost of cinnamic acid needed to produce 100 g of methyl cinnamate. (Higher 2015). £24.59

4. Coumarin is another compound found in the brand name perfume. It is present in the spice cinnamon and can be harmful if eaten in large quantities. The European Food Safety Authority gives a tolerable daily intake of coumarin at 0·10 mg per kilogram of body weight. 1·0kg of cinnamon powder from a particular source contains 4·4g of coumarin. Calculate the mass of cinnamon powder, in g, which would need to be consumed by an adult weighing 75 kg to reach the tolerable daily intake. (Higher 2015). 1.7g

5. The emulsion contains 2·0g of ibuprofen in every 100cm of emulsion. The recommended dose for treating a three month old baby is 0·050 g. Calculate the volume, in cm3, of “infant formula” needed to treat a three month old baby. (Specimen Paper 2014). 2.5 cm3

6. Theobromine, a compound present in chocolate, can cause illness in dogs and cats. To decide if treatment is necessary, vets must calculate the mass of theobromine consumed. 1·0 g of chocolate contains 1·4 mg of theobromine. Calculate the mass, in mg, of theobromine in a 17 g biscuit of which 28% is chocolate. (Revised Higher 2013). 6.7 mg

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