Edexcel A-Level Chemistry AS Paper 1, June 2023: Question 8

Question Answer Additional Guidance Mark

Number

8(a)(i) An answer that makes reference to the following (2)

points:

• decrease the concentration (of the nitric acid) / Allow use a different acid that is less reactive

use ethanoic acid / a weak acid (1)

• decrease in reaction rate would result in slower M2 dependent on M1

formation of carbon dioxide (so less gas lost) (1) Allow just results in a decrease in reaction rate

Allow it will take longer to react

Number

8(a)(ii) An answer that makes reference to the following Credit may be scored in (a)(i) (2)

points:

• use a pot / container / tube / vial to contain the Allow put the test tube of calcium carbonate in the conical flask

calcium carbonate / acid (to keep them (1) Allow a container for the acid

separate) Allow the point / container / ignition tube to be tied to a piece of

string and trapped by the bung

Do not award adding the calcium carbonate and replace the bung

quickly

• replace the bung and then shake / agitate / swirl Allow bung is lifted very slightly to allow a container attached to

the conical flask so the substances mix (1) string to mix with the acid

Move the flask so the reactants mix / reaction happens

Scores 1

Allow for 1 mark

attach large chips / calcium carbonate to string / thread

and

lift the bung very slightly to allow the calcium carbonate to drop /

Number

8(b) An answer that makes reference to two of the (2)

following points: One mark from each pair

• use a gas syringe (instead of collecting over

water)

or

bubble CO2 through the water (before the Allow saturate it with carbon dioxide first

experiment to form a saturated solution) (1) Ignore changing water to a different solvent

• bubble CO2 through the nitric acid (before the

experiment to saturate the solution)

or

add a pinch of (calcium) carbonate to the acid Allow saturate it with carbon dioxide first

before the reaction (to saturate the solution) (1)

Number

8(c)(i) Example of calculation: (3)

Either

• correct reading of the volume for a for 0.25 g of calcium carbonate the volume of gas produced is 56 cm3

selected mass of calcium carbonate

from the line of best fit to within half a

square on the scale (1)

0.25 = 0.0025 / 2.5 x 10‒3

• calculation of the number of moles of

calcium carbonate for a particular mass (1) 100

• calculation of the molar volume giving molar volume = 56 = 22,400 (cm3 mol‒1) = 22.4 (dm3 mol‒1)

the answer in dm3 (1) 0.0025

Allow TE on their mass and volume for M2 and M3

Ignore SF except 1 SF unless 1 SF is correct from their values of mass

and volume, when 1 SF should be ignored

Or

• correct reading of the volume for a

for 0.25 g of calcium carbonate the volume of gas produced is 56 cm3

selected mass of calcium carbonate

from the line of best fit to within half a

square on the scale (1)

for 0.10 g of calcium carbonate the volume of gas produced is 22 cm3

• second correct reading of the volume

for a selected mass (1)

• calculation of the gradient and molar 56 ‒ 22 = 226.67

volume, giving the answer in dm3 (1) 0.25 – 0.10

= 22.7 (dm3 mol‒1)

An answer between 21.6 and 23.2 with no working scores (1)

Correct answer with some working scores (3)

Number

8(c)(ii) Example of calculation: (3)

• rearranges the ideal gas equation (1) V = nRT

P

• converts temperature into Kelvin (1) T = 22 + 273 = 295 (K)

• calculates V and gives unit (1) V = 1 x 8.31 x 295 = 0.024272 m3 / 24.272 dm3 mol‒1

101000

TE on M2

Allow dm3

Correct answer with no working scores (1)

Correct answer with some correct working in M2 scores (3)

Ignore SF except 1 SF

(Total for Question 8 = 12 marks)