Question 116 marks
Question
You are going to investigate the rate at which hydrogen gas is made when magnesium reacts with dilute sulfuric acid. Read all of the instructions carefully before starting the experiments. Instructions You are going to do five experiments using the apparatus shown. rubber delivery tube clamp bung inverted 100 cm3 measuring cylinder conical flask trough water Experiment 1 ● Use a 25 cm3 measuring cylinder to pour 25 cm3 of dilute sulfuric acid into the conical flask. ● Use a 50 cm3 measuring cylinder to pour 30 cm3 of distilled water into the conical flask. ● Set up the apparatus as shown in the diagram. Ensure the inverted measuring cylinder is full of water. ● Remove the bung from the conical flask. ● Add a coiled length of magnesium ribbon to the conical flask, immediately replace the bung and start the timer. ● Measure the volume of gas collected in the inverted measuring cylinder after 30 seconds. Record the volume of gas collected in the table in (a). Experiment 2 ● Empty the conical flask and rinse it with distilled water. ● Repeat Experiment 1 using 20 cm3 of distilled water instead of 30 cm3. Measure the water using the second 25 cm3 measuring cylinder. Experiment 3 ● Repeat Experiment 2 using 10 cm3 of distilled water instead of 20 cm3. Experiment 4 ● Repeat Experiment 3 using 5 cm3 of distilled water instead of 10 cm3. Experiment 5 ● Repeat Experiment 4 but do not add any distilled water to the dilute sulfuric acid. (a) Complete the table. volume of dilute volume of volume of gas collected experiment sulfuric acid / cm3 distilled water / cm3 in 30 seconds / cm3 1 2 3 4 5 [4] (b) Write a suitable scale on the y-axis and plot your results from Experiments 1 to 5 on the grid. Draw a smooth curve of best fit. volume of gas collected in 30 seconds / cm3 0 0 5 10 15 20 25 30 35 40 volume of distilled water / cm3 [4] (c) Extrapolate (extend) the line on your graph and deduce the volume of gas that would be collected in 30 seconds if 35 cm3 of distilled water was added to the dilute sulfuric acid. …… cm3 [2] (d) The rate of reaction can be calculated using the equation shown. volume of gas collected rate of reaction = time taken to collect the gas (i) Use this equation to calculate the rate of reaction in Experiment 3. Give the units for the rate you have calculated. rate = …… units = …… [2] (ii) State which Experiment, 1, 2, 3, 4 or 5, had the highest rate of reaction. . …… [1] (e) The volume of the dilute sulfuric acid was measured using a measuring cylinder. A 25 cm3 pipette can be used instead of a measuring cylinder. (i) State one advantage of using a 25 cm3 pipette instead of a measuring cylinder. . …… [1] (ii) State one disadvantage of using a 25 cm3 pipette instead of a measuring cylinder. . …… [1] (f) Name another item of apparatus, which can be used instead of an inverted measuring cylinder, to collect and measure the volume of gas made in the reaction. . …… [1] (g) The diagram shows a modified conical flask that can be used in this investigation. glass divider magnesium dilute sulfuric acid Explain the advantage of using this type of conical flask instead of the type you used in the investigation. . …… . …… [2] [Total: 18] 2 You are provided with two solids, solid I and solid J. Do the following tests on the substances, recording all of your observations at each stage. tests on solid I Place solid I in a boiling tube. Add about 10 cm3 of distilled water to the boiling tube. Place a stopper in the boiling tube and shake the tube to dissolve solid I and form solution I. Divide solution I into four approximately equal portions in four test-tubes. (a) To the first portion of solution I, add aqueous sodium hydroxide dropwise and then in excess. Record your observations. . …… . …… . …… [2] (b) To the second portion of solution I, add aqueous ammonia gradually until there is no further change. Record your observations. . …… . …… [2] (c) To the third portion of solution I, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Leave the mixture to stand for about 5 minutes. Record your observations. . …… [1] (d) To the fourth portion of solution I, add about 2 cm depth of aqueous sodium carbonate. Record your observations. . …… [1] (e) Use your observations from (a), (b) and (c) to identify solid I. . …… . …… [2] tests on solid J (f) Carry out a flame test on solid J. Record your observations. . …… [1] (g) (i) Place approximately half of solid J in a boiling tube. Add about 10 cm3 of dilute sulfuric acid to solid J in the boiling tube. Test any gas produced. Record your observations. . …… . …… [2] (ii) Identify the gas produced in (g)(i). . …… [1] (h) Place the remaining solid J in a boiling tube. Add about 10 cm3 of distilled water to the boiling tube. Place a stopper in the boiling tube and shake the tube to dissolve solid J and form solution J. Divide solution J into two approximately equal portions in two test-tubes. (i) To the first portion of solution J, add about 1 cm depth of aqueous sodium hydroxide. Record your observations. . …… . …… [1] (ii) To the second portion of solution J, add about 2 cm depth of aqueous copper(II) sulfate. Record your observations. . …… . …… [1] (i) Use your observations from (f) and (g) to identify solid J. . …… . …… [2] [Total: 16]
Mark scheme
1(a) all experiments have volume of sulfuric acid of 25 cm3 1 all volumes of water correct (30, 20, 10, 5, 0) and all volumes in table given to the same precision 1 volumes of gas increase as table descended. 1 volume of gas for experiment 5 comparable to supervisors 1 1(b) suitable scale for y-axis 1 plotting – all 5 correct scores 2, 4 corrects scores 1 2 suitable best fit line 1 1(c) appropriate extrapolation of line to 35 1 correct reading from extrapolation 1 1(d)(i) correct calculation of volume for experiment 3 ÷ 30 1 cm3 / s 1 1(d)(ii) 5 1 1(e)(i) more accurate 1 1(e)(ii) slower / takes more time 1 1(f) (gas) syringe 1 1(g) any 2 from: 2 • the reaction can be started by tipping the flask • do not have to replace/remove the bung • so no gas escapes (while the bung is being removed / replaced) Tests on solid I