Question 19N.3.sl.TZ0.b(ii)
| Date | November 2019 | Marks available | [Maximum mark: 2] | Reference code | 19N.3.sl.TZ0.b(ii) |
| Level | sl | Paper | 3 | Time zone | TZ0 |
| Command term | Explain | Question number | b(ii) | Adapted from | N/A |
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]
Explain why the rate of reaction of limestone with nitric acid decreases and reaches zero over the period of five days.
[2]
acid used up
OR
acid is the limiting reactant ✔
concentration of acid decreases
OR
less frequent collisions ✔
NOTE: Award [1 max] for "surface area decreases" if the idea that CaCO3 is used up/acts as the limiting reactant” is conveyed for M1.
Do not accept “reaction reaches equilibrium” for M2.
