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Question 19N.3.sl.TZ0.b(iii)

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Date November 2019 Marks available [Maximum mark: 1] Reference code 19N.3.sl.TZ0.b(iii)
Level sl Paper 3 Time zone TZ0
Command term Suggest Question number b(iii) Adapted from N/A
b(iii).
[Maximum mark: 1]
19N.3.sl.TZ0.b(iii)

A student investigated how the type of acid in acid deposition affects limestone, a building material mainly composed of calcium carbonate.

The student monitored the mass of six similarly sized pieces of limestone. Three were placed in beakers containing 200.0 cm3 of 0.100 mol dm−3 nitric acid, HNO3 (aq), and the other three in 200.0 cm3 of 0.100 mol dm−3 sulfuric acid, H2SO4 (aq).

The limestone was removed from the acid, washed, dried with a paper towel and weighed every day at the same time and then replaced in the beakers.

The student plotted the mass of one of the pieces of limestone placed in nitric acid against time.

[Source: © International Baccalaureate Organization 2019]

Suggest a source of error in the procedure, assuming no human errors occurred and the balance was accurate.

[1]

Markscheme

surface area not uniform
NOTE: Accept “acids impure.

OR
limestone pieces do not have same composition/source
NOTE: Accept “«limestone» contains impurities”.

OR
limestone absorbed water «which increased mass»

OR
acid removed from solution when limestone removed
NOTE: Accept “loss of limestone when dried" OR "loss of limestone due to crumbling when removed from beaker”.

OR
«some» calcium sulfate deposited on limestone lost

OR
pieces of paper towel may have stuck to limestone

OR
beakers not covered/evaporation

OR
temperature was not controlled ✔

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