Question 17N.2.sl.TZ0.5
| Date | November 2017 | Marks available | [Maximum mark: 7] | Reference code | 17N.2.sl.TZ0.5 |
| Level | sl | Paper | 2 | Time zone | TZ0 |
| Command term | Evaluate, Identify, Outline, State | Question number | 5 | Adapted from | N/A |
Many reactions are in a state of equilibrium.
The following reaction was allowed to reach equilibrium at 761 K.
H2 (g) + I2 (g) 2HI (g) ΔHθ < 0
Outline the effect, if any, of each of the following changes on the position of equilibrium, giving a reason in each case.
[2]
Award [1 max] if both effects are correct.
Reason for increasing volume:
Accept “concentration of all reagents reduced by an equal amount so cancels out in Kc expression”.
Accept “affects both forward and backward rates equally”.
The equations for two acid-base reactions are given below.
HCO3– (aq) + H2O (l) H2CO3 (aq) + OH– (aq)
HCO3– (aq) + H2O (l) CO32– (aq) + H3O+ (aq)
Identify two different amphiprotic species in the above reactions.
[1]
HCO3– AND H2O
State what is meant by the term conjugate base.
[1]
species that has one less proton/H+ ion «than its conjugate acid»
OR
species that forms its conjugate acid by accepting a proton
OR
species that is formed when an acid donates a proton
Do not accept “differs by one proton/H+ from conjugate acid”.
State the conjugate base of the hydroxide ion, OH–.
[1]
oxide ion/O2–
A student working in the laboratory classified HNO3, H2SO4, H3PO4 and HClO4 as acids based on their pH. He hypothesized that “all acids contain oxygen and hydrogen”.
Evaluate his hypothesis.
[2]
insufficient data to make generalization
OR
need to consider a «much» larger number of acids
OR
hypothesis will continue to be tested with new acids to see if it can stand the test of time
«hypothesis is false as» other acids/HCl/HBr/HCN/transition metal ion/BF3 do not contain oxygen
OR
other acids/HCl/HBr/HCN/transition metal ion/BF3 falsify hypothesis
correct inductive reasoning «based on limited sample»
«hypothesis not valid as» it contradicts current/accepted theories/Brønsted-Lowry/Lewis theory
[Max 2 Marks]
