DP Chemistry (last assessment 2024)
Question 18N.3.hl.TZ0.14d
| Date | November 2018 | Marks available | [Maximum mark: 2] | Reference code | 18N.3.hl.TZ0.14d |
| Level | hl | Paper | 3 | Time zone | TZ0 |
| Command term | Explain | Question number | d | Adapted from | N/A |
d.
[Maximum mark: 2]
18N.3.hl.TZ0.14d
Solar energy, which is freely available, is indispensable to life on earth.
(d)
Explain, using an equation, the effect of increased carbon dioxide in the atmosphere on the pH of lake water.
[2]
Markscheme
CO2 (g) + H2O (l) H+ (aq) + HCO3– (aq)
OR
CO2 (g) CO2 (aq) AND CO2 (aq) + H2O (l) H+ (aq) + HCO3– (aq) ✔
«increasing [CO2 (g)]» shifts equilibrium/reaction to right AND pH decreases ✔
Accept “H2CO3 (aq)” for “CO2 (aq) + H2O (l)”.
Equilibrium arrows required for M1.
State symbols required for CO2 (g) CO2 (aq) equation only for M1.
Accept “concentration of H+/[H+] increases AND pH decreases” for M2.
