C8 IDENTIFICATION OF IONS BY CHEMICAL AND SPECTROSCOPIC MEANS Question Practice Name: ________________________ Class: ________________________ Date: ________________________ Time: 164 minutes Marks: 163 marks Comments: GCSE CHEMISTRY ONLY Page 1 of 60 Immanuel+College
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C8 IDENTIFICATION OF IONS BYCHEMICAL AND SPECTROSCOPICMEANSQuestion Practice
Name: ________________________
Class: ________________________
Date: ________________________
Time: 164 minutes
Marks: 163 marks
Comments: GCSE CHEMISTRY ONLY
Page 1 of 60Immanuel+College
This question is about reactions of ethanoic acid and the analysis of salts.
(a) Figure 1 shows the apparatus used to investigate the reaction of ethanoic acid withcalcium carbonate.
(i) Describe a change that would be seen in each test tube.
Give a reason for each change.
Test tube 1 ____________________________________________________
(ii) The student tested the Cheshunt solution and the result of the test indicated thatsulfate ions are in the solution.
Complete the sentence.
The student added a solution of ________________ in the presence of
dilute hydrochloric acid and a ________________ precipitate was produced.
(2)
(Total 7 marks)
Read the information in the box and then answer the questions.
Seidlitz Powder is the name of a medicine.
Seidlitz Powder comes as two powders. One powder is wrapped in white paper andcontains tartaric acid (C4H6O6). The other powder is wrapped in blue paper andcontains potassium sodium tartrate (KNaC4H4O6) and sodium hydrogencarbonate(NaHCO3).
The contents of the blue paper are completely dissolved in water and then thecontents of the white paper are added.
Read the information about protecting the bottoms of ships.
A Copper-bottomed Investment
From the 16th to the 19th century, the bottoms of many wooden ships were protectedfrom marine organisms by being covered with sheets of metal.
At first lead was used on the bottoms of ships, then copper was used until 1832when Muntz Metal replaced it. Muntz Metal is an alloy of two transition metals,copper and zinc.
Table of data
Lead Copper Muntz Metal
Cost (£/kg) £1.20 £3.20 £2.30
Melting point (°C) 327 1083 904
Stops sea worms attacking wood Yes Yes Yes
Stops barnacles and seaweedsticking to the bottom of the ship
No Yes Yes
(a) Use the information to answer the following questions.
(b) Read the following information and then answer the questions.
Salt – friend or foe?
Sodium chloride (salt) is an essential mineral for our health. It is used to flavourand preserve foods. Too much sodium in our diet may increase the risk of highblood pressure and heart disease. Heart disease is the biggest cause of death inthe United Kingdom. Some people claim that excess sodium is a poison that cancause cancer, while others say that more evidence is needed.
Many processed foods contain salt, so it is easy to exceed the recommendeddaily upper limit of about 5 g of salt per person. A ‘healthier’ amount should beabout 3 g. In the United Kingdom many people consume over 10 g of salt eachday.
One way to reduce sodium in our diet is to use Low Sodium Salt. This has twothirds of the sodium chloride replaced by potassium chloride.
A national newspaper asked readers for their views on two options.
Option 1: Ban the use of sodium chloride in foods.
Option 2: Reduce the amount of sodium chloride in all foods to a ‘healthier’ level.
(ii) When a flame test was carried out on My Baby Food, the presence of calcium ionswas not seen. A yellow flame was produced.Name the ion which gives a yellow flame test.
(b) Read the information in the box below and then answer the question.
Calcium carbonate occurs naturally as marble and limestone. They areimportant building materials and are often used for gravestones.
Calcium carbonate is also an essential mineral for good health and ispresent in many baby foods in small amounts.
My Baby Food is recommended as being the closest to a mother’s ownbreast milk. It is given free to mothers in the developing world – without ittheir babies might die of malnutrition.
Responsible Mothers Are Us (RMAU) is a United Kingdom pressure group.They want to ban chemicals in baby foods. The group was founded by MrsI. M. Right who has made a career in ‘goodness’ and is paid from donationsgiven to RMAU by members of the public.
When interviewed, she said: “Calcium carbonate is a chemical and so it is apollutant. My Baby Food must be banned to prevent the mass medication ofbabies. I don’t feed my baby the stuff of gravestones.”
(c) the metal ion in solution C. _____________________________________________
(1)
(Total 5 marks)
9
Page 17 of 60Immanuel+College
A student investigated food dyes using paper chromatography.
This is the method used.
1. Put a spot of food colouring X on the start line.2. Put spots of four separate dyes, A, B, C and D, on the start line.3. Place the bottom of the paper in water and leave it for several minutes.
Figure 1 shows the apparatus the student used.
Figure 1
(a) Write down two mistakes the student made in setting up the experiment and explain whatproblems one of the mistakes would cause.
(ii) Describe the two further tests the student would have to do to show that salt Xcontains magnesium ions, and not the two metal ions you identified in part (c) (i).
(b) Some scientists wanted to investigate the amount of lead found in egg shells.They used a modern instrumental method which was more sensitive than older methods.
(i) Name one modern instrumental method used to identify elements.
(ii) A student made some ammonium sulfate in a school laboratory.
The student carried out a titration, using a suitable indicator, to find the volumes ofsulfuric acid and ammonia solution that should be reacted together.
Name a suitable indicator for strong acid-weak alkali titrations.
(iii) The student found that 25.0 cm3 of ammonia solution reacted completely with32.0 cm3 of sulfuric acid of concentration 0.050 moles per cubic decimetre.
The equation that represents this reaction is:
2H2SO4(aq) + 2NH3(aq) → (NH4)2SO4 (aq)
Calculate the concentration of this ammonia solution in moles per cubic decimetre.
Concentration = _________________ moles per cubic decimetre
(3)
(iv) Use your answer to (b)(iii) to calculate the concentration of ammonia in grams percubic decimetre.
(If you did not answer part (b)(iii), assume that the concentration of the ammoniasolution is 0.15 moles per cubic decimetre. This is not the correct answer to part(b)(iii).)
allow calcium carbonate decreases in size or dissolves1
because carbon dioxide produced / released
allow because gas produced / released1
limewater turns cloudy / milky / white1
because (a precipitate of or solid) calcium carbonate forms
allow because of carbon dioxide if not already credited1
1
(ii)
allow -OH
do not allow lower case ‘h’1
(iii) acid
must be in this order
ignore any name of an acid1
ester(s)1
(b) white (precipitate) no change
no change no change
all four correct 2 marks
any two correct 1 mark2
(c) (i) lilac
allow purple1
red1
must be in this order
(ii) colours are masked / changed by each flame colour1
[12]
Page 40 of 60Immanuel+College
(a) (i) carbon dioxide / CO212
carbonate / CO32-
answers must be in the order shown
marks are independent1
(ii) ammonia / NH31
litmus
answers must be in the order shown
marks are independent1
(b) (i) solution is blue
accept blue precipitate only if sodium hydroxide added
allow blue liquid
allow copper sulfate / copper ions are blue1
(ii) barium chloride / BaCl2
allow barium nitrate / barium ions / Ba2+
1
white
answers must be in the order shown
marks are independent1
[7]
(a) limewater / calcium hydroxide13
(limewater) goes milky / cloudy
do not allow this mark if lime water added to solution or powder
or
gives white precipitate / solid1
(b) eg flame colour of (Na) and flame colour of (K) interfere / mask / mix witheach other
accept difficult to determine the colour
or
hard to distinguish
accept some indication that two distinct colours are not seen1
Page 41 of 60Immanuel+College
(c) (i) barium chloride (solution) / BaCl2ignore mention of acidification but
do not allow sulfuric acid.
wrong reagent = no mark1
white precipitate / white solid
allow white barium sulfate
or
barium sulfate precipitate1
(ii) white precipitate / white solid
ignore goes milky
do not accept any mention of precipitate dissolving1
[6]
(a) (i) it = copper
(copper) stops barnacles / seaweed (sticking)
accept lead doesn’t stop barnacles / seaweed (sticking)
ignore all other properties1
4
(ii) it = Muntz Metal
(Muntz Metal) is less expensive / cheaper / cheapest
must be a comparison
accept copper is more expensive
ignore other properties1
(b) (i) atomic absorption spec(troscopy) / spectrometry or mass spec(trometry) /spectroscopy
accept spectroscopy / spectrometry alone
allow AAS / MS
do not allow NMR spectroscopy
or IR spectrometry or chromatography1
(ii) it = instrumental method
sensitive or detect (very) small amountsor only small sample needed
allow (more) precise
ignore accurate
allow converse for chemical method
ignore metal contains small amount / low concentration of iron1
Page 42 of 60Immanuel+College
(c) any two from:
transition elements (= they)
• unreactive / not very reactive
allow does not corrode
ignore reference to rust
• strong / hard
ignore tough / durable / hard wearing
• malleable / easy to shape
ignore ductile / density / melting point2
[6]
(a) (acidified) barium chloride / nitrate
incorrect reagent or no reagent = 0 marks
do not accept acidified with sulfuric
acid (still allow result mark if correct)
allow solution of barium ions / salt not barium solution
do not accept barium hydroxide1
5
(white) precipitate / solid
do not accept incorrect colour for precipitate
allow barium sulfate (formed)
ignore ‘it goes white / cloudy’1
(b) (white) precipitate / solid
allow aluminium hydroxide (formed)
do not allow incorrect colour for precipitate1
(precipitate) dissolves (in excess)
allow sodium aluminate (formed)
allow goes clear / colourless
if incorrect colour precipitate then allow dissolves (in excess)1
Page 43 of 60Immanuel+College
(c) any two from:
apply list principle
• yellow = sodium (alum)
allow orange or yellow orange
• lilac = potassium (alum)
allow purple
• colourless = ammonium (alum)
if no colours given, allow ‘different coloured flames’ for 1 mark2
[6]
(a) (i) hydrochloric acid / HCl
accept any (named) acid1
carbon dioxide / CO2
accept bubbles / fizz / gas or limewater gets milky
ignore ‘add limewater’
do not accept other named gases
2nd mark dependant on first mark
accept for this answer only heat gives CO2 / limewater milky = 1mark
1
6
(ii) (white) precipitate / solid
ignore names of substances even if incorrect
accept white deposit / substance
do not accept any coloured precipitate1
(iii) eg flame colour of (Na) and flame colour of (K)interfere / mask / mix with each other
accept ‘can’t see the colours’ or ‘difficult to determine the colour’ or‘both produce different colours’ or a correct statement of colours orhard to distinguish
1
(b) (i) eg essential (mineral) or everyoneneeds it / some (salt) or problemswith health if have no salt
accept preservative / flavouring / taste
it = salt
(all) foods contain / use it / sodium chloride / salt1
Page 44 of 60Immanuel+College
(ii)
mark positively ie no list principle
advantages
any two from:
ignore economic arguments throughout or people eat less salt
• more people will be healthier
• (should have) less heart disease
• (should have) less cancer
• (more people with) lower blood pressure2
disadvantages
any one from:
ignore references to too much / too little (salt)
• not everyone affected
• not enough evidence
• does not provide choice
• undemocratic
• less taste / flavour
ignore no flavour / taste
• shorter shelf life / not preserved (as long)
ignore references to sell by dates
• too much potassium chloride might be bad1
[8]
(a) (i) red / brick-red / orange-red / red-orange
allow red-brown or brown-red
do not accept orange alone eg ‘red or orange’ = 01
7
(ii) sodium
allow sodium compounds
ignore incorrect symbol
or Na / Na+
if symbol alone given do not accept Na2+ or Na–
1
Page 45 of 60Immanuel+College
(iii) any one from
• accurate / sensitive
• use small amounts
• fast / quick / rapid
• ease of automation
• reliable / efficient
• operatives do not need chemical skills
ignore cost / safety / human error or ease of use or shows all theelements
1
(iv) (atomic absorption) spectroscopy or (mass) spectrometry
accept AAS / aas or mass specaccept atomic absorptionignore ms / MSdo not allow UV / IR / NMR / chromatography / GLC
1
Page 46 of 60Immanuel+College
(b) any three from:
• (safe because) similar to mothers. milk
allow calcium carbonate is in breast milkallow some mothers unable to breast feedignore ‘recommended’ alone
• babies (in developing world) would die
accept causes malnutrition
• if banned there would be a cost involved
allow it is free
• it is not a pollutant / harmful / dangerous
accept not all chemicals are pollutants / harmful / dangerous
• not mass medication
• not just used for gravestones
allow it has many usesignore only small amounts of it or it occurs naturally
• (calcium carbonate) is needed for bones / teeth / health
allow ‘essential mineral’
• Mrs Right has a personal interest or not impartial or distortsinformation / bias or she is paid by a charity
accept ‘it is (only) her opinion’3
[7]
(a) kills bacteria / sterilises (water)
allow kills microorganisms / microbes / germs
allow ‘makes (water) safe (to drink)’ or disinfectant
ignore cleans water or removes impurities / bacteria1
8
(b) goes colourless / decolourised (from red / red-brown / brown / yellow / orange)
allow colour disappears
ignore ‘goes clear’ or discoloured
do not accept incorrect initial colour
do not accept precipitate1
(c) (i) Br2 and 2Cl–
allow multiples / fractions if whole equation balanced1
Page 47 of 60Immanuel+College
(ii) changes to red / red-brown / brown / yellow / orange
do not accept effervescence / fizzing / precipitate / gas given off
ignore vapour / temperature changes / ignore initial colour1
(d) (i) 7 outer electrons or
same number of outer electrons
allow last / final shell for outerallow energy level / orbit / ring for shellallow ‘need to gain 1 e – to have a full outer shell’ignore ‘similar number of outer electrons’
1
(ii) bromine / it (atom) is bigger or
must be a comparison
outer electrons (level / shell) further from nucleus or more shells
do not accept more outer shellsignore more electrons
forces / attractions are weaker or more shielding or attracts less
do not accept magnetic / gravitational / intermolecular forcesallow ‘electron(s) attracted less easily’
electron(s) gained less easily
“outer / last / final” must be mentioned once, otherwise max 2marks.accept converse for chlorine throughout where clearly stated
3
(e) (i) white precipitate or white solid
ignore names of chemicals1
(ii) cream precipitate or cream solid
allow pale yellow / off-white precipitate / solidignore names of chemicals
(a) water level above the start lineandstart line drawn in ink
allow water level too high1
10
water levelfood colours would dissolve into waterorstart linethe ink would ‘run’ on the paper
1
(b) (distance moved by A) 2.8cm and 8.2 cm (distance moved by solvent)
allow values in range 2.7 − 2.9 cm and 8.1 − 8.3 cm1
1
0.34
allow 0.33 or 0.35
allow ecf from incorrect measurement to final answer for 2 marks ifgiven to 2 significant figures
accept 0.34 without working shown for 3 marks1
(c) 6.6 cm
allow values between 6.48 and 6.64 cm1
(d) solvent moves through paper1
different dyes have different solubilities in solvent1
Page 49 of 60Immanuel+College
and different attractions for the paper1
and so are carried different distances1
(e) calcium ions
allow Ca2+
1
sodium ions
allow Na+
1
(f) two different coloursorCa2+ / one is orange-red and Na+ / the other is yellow
allow brick red for Ca2+ and / or orange for Na+
allow incorrect colours if consistent with answer to 7.51
(so) colours mixor(so) one colour masks the other
1
(g) (Student A was incorrect)because sodium compounds are white not green
orbecause sodium carbonate is soluble
1
so can’t contain sodium ions1
(Student B was incorrect)because adding acid to carbonate produces carbon dioxide
1
so must contain carbonate not chloride ions1
[18]
(a) X:Fe2+ / iron(II), SO4
2- / sulfate
allow iron(II) sulfateor FeSO4
1
11
Y:Na+ / sodium, I- / iodide
allow sodium iodideor NaI
1
Page 50 of 60Immanuel+College
Z:Fe3+ / iron(III), Br- / bromide
allow iron(III) bromideor FeBr3
correct identification of any two ions = one mark
correct identification of any four ions = two marks1
(b) any five from:
allow converse arguments
method 1
• weighing is accurate• not all barium sulfate may be precipitated• precipitate may be lost• precipitate may not be dry• takes longer• requires energy
allow not all the barium hydroxide has reacted
method 2• accurate• works for low concentrations
allow reliable / precise5
[8]
(a) (i) ionic (bonding)112
(ii) ions cannot move in solid or are in fixed positions
do not accept electrons / atoms / molecules
ignore particles
must mention ions1
but can move in solution1
(b) silver chloride formed1
which is insoluble1
(c) (i) aluminium1
calcium
accept other metal ions that also give white precipitates (such aslead and zinc)
1
Page 51 of 60Immanuel+College
(ii) add excess sodium hydroxide solution
the second mark of each pair is dependent on the first mark beingawarded.
1
precipitate remains1
carry out a flame test1
not red / orange
accept any colour that is not orange / red
give full credit for answers that correctly eliminate other cations in(c)(i) that would give white precipitates with a few drops of NaOH
1
[11]
Page 52 of 60Immanuel+College
Marks awarded for this answer will be determined by the Quality of Communication (QC) as wellas the standard of the scientific response. Examiners should also apply a ‘best-fit’ approach tothe marking.
0 marksNo relevant content
Level 1 (1 – 2 marks)Any description of a method used and / or a result given
Level 2 (3 – 4 marks)Description of workable methods used, with results to identify positive or negative ions
Level 3 (5 – 6 marks)Description of methods used to identify both positive and negative ions, with relevantresults
examples of the points made in the response
extra information
Test: add (platinum / nichrome) wire (for the flame test)
accept any method of introducing the solution into the flame, eg asplint soaked in the solution or sprayed from a bottle
Result: the sodium compounds result in a yellow / orange / gold flame or the potassiumcompound results in a lilac / purple / mauve flame
student could state that potassium carbonate gives a differentcolour to the three sodium compounds as long as it is clear that theflame test colour comes from Na+ or K+
Test: add dilute nitric acid to all four solutions
allow any acid
Result: sodium carbonate and potassium carbonate will effervesce or sodium chloride andsodium iodide will not effervesce
Test: add dilute nitric acid followed by silver nitrate
Result: sodium chloride and sodium iodide produce a precipitate or sodium chlorideproduces a white precipitate and sodium iodide produces a yellow precipitate
accept sodium carbonate and potassium carbonate do not producea precipitate
[6]
13
Page 53 of 60Immanuel+College
(a) lithium
allow Li+ / Li1
yellow
allow orange1
(b) silver nitrate (solution)
incorrect test = 0 marks
ignore (nitric) acid
do not allow other named acids1
white precipitate1
(c) blue precipitate (with sodium hydroxide) indicates copper ions
allow Cu2+
1
and white precipitate (with barium chloride) indicates sulfate ions
allow SO42-
accept compound X is copper sulfate / CuSO4 for 1 mark1
but iron(II) ions produce a green precipitate (with sodium hydroxide)1
[7]
14
(a) (i) Na2CO3: HCl → gas / effervescence / bubbles (1) CO2 / carbon dioxide / turns lime water milky (1)