Chemistry (9-1) 0971 | Paper 6 Mock 01 | Alternative to Practical
Question 1 Report
A student is asked to plan an experiment to investigate how the surface area of calcium carbonate affects the rate of its reaction with dilute hydrochloric acid. The rate will be followed by measuring the volume of carbon dioxide gas collected.
(a) Name the gas produced in this reaction and give a chemical test for it, including the result. [2]
(b) Describe the apparatus you would use to collect and measure the volume of gas produced. [2]
(c) Plan a detailed method to investigate how the surface area of the calcium carbonate affects the rate. Include the different forms of calcium carbonate used, the measurements you would take, and how you would make it a fair test. [6]
(d) Complete Table 21.1 by writing suitable column headings, with units, for the measurements you would record. [3]
| …… | …… | …… |
|---|---|---|
| …… | …… | …… |
| …… | …… | …… |
| …… | …… | …… |
(e) State the independent variable and the dependent variable in this experiment. [2]
(f) Suggest how you would display the results to compare the rates of the different forms. [1]
(g) Identify one hazard in this experiment and give a suitable precaution. [2]
This planning question is about how surface area of calcium carbonate affects its rate of reaction with hydrochloric acid, followed by the carbon dioxide given off: \( \text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} + \text{CO}_2 \).
(a) The gas is carbon dioxide [1]; the test is to bubble it through limewater, which turns milky / cloudy [1].
(b) To collect and measure the gas, connect the reaction (conical) flask by a delivery tube to a gas syringe, or to an inverted measuring cylinder or burette filled with water over a trough [2] (one mark for a sound collection method, one for a way of measuring the volume).
(c) A detailed method scores up to six marks [6]: use the same mass of calcium carbonate in different forms, for example large chips, small chips and powder [1]; use the same volume of acid [1]; use the same concentration of acid [1]; add the acid, start the stopclock and connect the gas syringe at once [1]; record the volume of gas collected at fixed time intervals, or the time to collect a fixed volume [1]; keep the temperature constant and repeat each run, then average [1].
(d) Suitable headings, each with a unit where needed [3]:
| form of calcium carbonate | time / s | volume of gas / cm3 |
|---|---|---|
| large chips | ||
| small chips | ||
| powder |
(e) The independent variable is the surface area (form) of the calcium carbonate [1]; the dependent variable is the volume of gas collected in a fixed time, that is the rate [1].
(f) Display the results by plotting the volume of gas against time for each form on the same axes, or by drawing a bar chart of the rates, so the forms can be compared directly [1].
(g) Hazard: dilute hydrochloric acid is irritant or corrosive [1]; precaution: wear eye protection (goggles) [1].
Answer Details
This planning question is about how surface area of calcium carbonate affects its rate of reaction with hydrochloric acid, followed by the carbon dioxide given off: \( \text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} + \text{CO}_2 \).
(a) The gas is carbon dioxide [1]; the test is to bubble it through limewater, which turns milky / cloudy [1].
(b) To collect and measure the gas, connect the reaction (conical) flask by a delivery tube to a gas syringe, or to an inverted measuring cylinder or burette filled with water over a trough [2] (one mark for a sound collection method, one for a way of measuring the volume).
(c) A detailed method scores up to six marks [6]: use the same mass of calcium carbonate in different forms, for example large chips, small chips and powder [1]; use the same volume of acid [1]; use the same concentration of acid [1]; add the acid, start the stopclock and connect the gas syringe at once [1]; record the volume of gas collected at fixed time intervals, or the time to collect a fixed volume [1]; keep the temperature constant and repeat each run, then average [1].
(d) Suitable headings, each with a unit where needed [3]:
| form of calcium carbonate | time / s | volume of gas / cm3 |
|---|---|---|
| large chips | ||
| small chips | ||
| powder |
(e) The independent variable is the surface area (form) of the calcium carbonate [1]; the dependent variable is the volume of gas collected in a fixed time, that is the rate [1].
(f) Display the results by plotting the volume of gas against time for each form on the same axes, or by drawing a bar chart of the rates, so the forms can be compared directly [1].
(g) Hazard: dilute hydrochloric acid is irritant or corrosive [1]; precaution: wear eye protection (goggles) [1].
Question 2 Report
A student reacted black copper(II) oxide with warm dilute sulfuric acid to make copper(II) sulfate. When the reaction was over, some black solid had not dissolved. Fig. 1.1 shows the apparatus the student used to separate this excess black solid from the aqueous copper(II) sulfate. Three parts of the apparatus are labelled A, B and C.
(a) Name the parts of the apparatus labelled A, B and C on Fig. 1.1. [3]
(b) Name the solid that is left behind as the residue. [1]
(c) State the name of the salt that is present in the filtrate. [1]
This question tests naming filtration apparatus and identifying the residue and filtrate when excess insoluble solid is removed after making a soluble salt.
(a) The labelled parts are: A = filter funnel [1]; B = filter paper (the folded cone inside the funnel) [1]; C = conical flask (a beaker is accepted) that collects what passes through [1]. [3]
(b) The excess black solid trapped on the paper as the residue is the unreacted copper(II) oxide [1] (it was added in excess so that all the acid reacted).
(c) The salt in the blue filtrate that passes through is copper(II) sulfate [1], formed by \(CuO + H_2SO_4 \rightarrow CuSO_4 + H_2O\).
Exam tip: in filtration the residue stays on the paper (insoluble) and the filtrate passes through (the dissolved salt).
Answer Details
This question tests naming filtration apparatus and identifying the residue and filtrate when excess insoluble solid is removed after making a soluble salt.
(a) The labelled parts are: A = filter funnel [1]; B = filter paper (the folded cone inside the funnel) [1]; C = conical flask (a beaker is accepted) that collects what passes through [1]. [3]
(b) The excess black solid trapped on the paper as the residue is the unreacted copper(II) oxide [1] (it was added in excess so that all the acid reacted).
(c) The salt in the blue filtrate that passes through is copper(II) sulfate [1], formed by \(CuO + H_2SO_4 \rightarrow CuSO_4 + H_2O\).
Exam tip: in filtration the residue stays on the paper (insoluble) and the filtrate passes through (the dissolved salt).
Question 3 Report
A student used paper chromatography to find out which known food dyes are present in a mixture M. Fig. 13.1 shows the chromatogram. Lane M is the mixture, and lanes 1, 2 and 3 are three pure known dyes. The distance from the start line to the solvent front is 13.0 cm. Table 13.1 shows the distance each spot moved from the start line.
| spot | distance moved by spot / cm | Rf (spot ÷ 13.0) |
|---|---|---|
| dye 1 | 6.5 | |
| dye 2 | 9.75 | 0.75 |
| dye 3 | 13.0 |
(a) State why lane M produces two spots. [1]
(b) Complete Table 13.1 by calculating the Rf values for dye 1 and dye 3. Show your working. [2]
(c) The two spots in mixture M moved the same distances as dye 1 and dye 3. Use the chromatogram to identify which dyes are present in mixture M, and state whether dye 2 is present. [2]
(d) State why all the spots must be placed on the same start line. [1]
(e) Explain why the start line must be above the level of the solvent in the tank. [2]
(f) Describe how you would make the spots visible if the dyes had been colourless. [1]
(g) Give the name used for the solvent that moves up the paper. [1]
(h) State the Rf value of a spot that does not move from the start line. [1]
This question is paper chromatography used to identify dyes, including calculating Rf values. Rf compares how far a spot moves with how far the solvent moves.
(a) Lane M produces two spots because M is a mixture of two different substances (dyes), and each dye travels its own distance up the paper [1].
(b) \( R_f = \dfrac{\text{distance moved by spot}}{\text{distance moved by solvent}} \), with the solvent front at 13.0 cm.
| spot | distance moved / cm | Rf (spot ÷ 13.0) |
|---|---|---|
| dye 1 | 6.5 | 0.5 |
| dye 2 | 9.75 | 0.75 |
| dye 3 | 13.0 | 1.0 |
Dye 1: \( R_f = 6.5 \div 13.0 = 0.5 \) [1]. Dye 3: \( R_f = 13.0 \div 13.0 = 1.0 \) [1]. (Rf has no units and is always between 0 and 1.)
(c) The two spots in M moved the same distances as dye 1 and dye 3, so dye 1 and dye 3 are present in M [1]. Dye 2 is not present, because M has no spot at the height dye 2 reached [1].
(d) All spots must be placed on the same start line so that every spot travels for the same distance and the distances moved can be compared fairly from the same starting point [1].
(e) The start line must be above the level of the solvent because if it were below the solvent [1], the spots would dissolve straight into the solvent and wash away instead of rising up the paper and separating [1].
(f) If the dyes were colourless, make the spots visible by spraying with a locating agent or by viewing under ultraviolet light [1].
(g) The solvent that moves up the paper is called the mobile phase (the solvent) [1].
(h) A spot that does not move from the start line has \( R_f = 0 \) [1], because the distance it moved is zero.
Exam tip: always draw the start line in pencil above the solvent, and remember Rf = spot distance divided by solvent distance, never the other way round.
Answer Details
This question is paper chromatography used to identify dyes, including calculating Rf values. Rf compares how far a spot moves with how far the solvent moves.
(a) Lane M produces two spots because M is a mixture of two different substances (dyes), and each dye travels its own distance up the paper [1].
(b) \( R_f = \dfrac{\text{distance moved by spot}}{\text{distance moved by solvent}} \), with the solvent front at 13.0 cm.
| spot | distance moved / cm | Rf (spot ÷ 13.0) |
|---|---|---|
| dye 1 | 6.5 | 0.5 |
| dye 2 | 9.75 | 0.75 |
| dye 3 | 13.0 | 1.0 |
Dye 1: \( R_f = 6.5 \div 13.0 = 0.5 \) [1]. Dye 3: \( R_f = 13.0 \div 13.0 = 1.0 \) [1]. (Rf has no units and is always between 0 and 1.)
(c) The two spots in M moved the same distances as dye 1 and dye 3, so dye 1 and dye 3 are present in M [1]. Dye 2 is not present, because M has no spot at the height dye 2 reached [1].
(d) All spots must be placed on the same start line so that every spot travels for the same distance and the distances moved can be compared fairly from the same starting point [1].
(e) The start line must be above the level of the solvent because if it were below the solvent [1], the spots would dissolve straight into the solvent and wash away instead of rising up the paper and separating [1].
(f) If the dyes were colourless, make the spots visible by spraying with a locating agent or by viewing under ultraviolet light [1].
(g) The solvent that moves up the paper is called the mobile phase (the solvent) [1].
(h) A spot that does not move from the start line has \( R_f = 0 \) [1], because the distance it moved is zero.
Exam tip: always draw the start line in pencil above the solvent, and remember Rf = spot distance divided by solvent distance, never the other way round.
Question 4 Report
A student has two gas jars. One contains ethane and the other contains ethene, but the labels have come off. Fig. 4.1 shows apparatus that can be used to bubble a gas through a portion of bromine water.
(a) Plan how the student could use bromine water to find out which gas jar contains the alkene. State the apparatus used and the observations expected. [3]
(b) State the colour change seen with the alkene. [1]
(c) Name the alkene used in this experiment. [1]
(d) Suggest why the same volume of bromine water should be used for each gas. [1]
This question tests how to design a fair test to identify an alkene using bromine water, and how to describe the result.
(a) A suitable plan [3]:
- Bubble the gas from each jar separately through its own portion of bromine water using the delivery tube shown [1].
- The jar whose gas turns the bromine water from orange to colourless contains the alkene [1].
- The other jar's gas (the alkane) leaves the bromine water orange, giving no change [1].
(b) With the alkene, the bromine water changes from orange to colourless (decolourised) [1].
(c) The alkene used here is ethene [1] (the alkane in the pair is ethane).
(d) The same volume of bromine water should be used for each gas so that the comparison is fair and any colour change is due only to the gas, not to different amounts of bromine water [1].
Exam tip: "decolourises bromine water" is the single observation that identifies an alkene; describe it as orange to colourless, not "clear".
Answer Details
This question tests how to design a fair test to identify an alkene using bromine water, and how to describe the result.
(a) A suitable plan [3]:
- Bubble the gas from each jar separately through its own portion of bromine water using the delivery tube shown [1].
- The jar whose gas turns the bromine water from orange to colourless contains the alkene [1].
- The other jar's gas (the alkane) leaves the bromine water orange, giving no change [1].
(b) With the alkene, the bromine water changes from orange to colourless (decolourised) [1].
(c) The alkene used here is ethene [1] (the alkane in the pair is ethane).
(d) The same volume of bromine water should be used for each gas so that the comparison is fair and any colour change is due only to the gas, not to different amounts of bromine water [1].
Exam tip: "decolourises bromine water" is the single observation that identifies an alkene; describe it as orange to colourless, not "clear".
