Mol decreased the nitrite ion present nitrous acid
Define the terms acid and base according to the Brønsted-Lowry theory and state one example of a weak acid and one example of a strong base.
acid is a proton/H+ donor and base is a proton/H+
acceptor;
H2CO3/CH3COOH and NaOH/KOH/Ba(OH)2;
black coffee;
103/1000 times;
Define the terms acid and base according to the Brønsted-Lowry theory. Distinguish between a weak base and a strong base. State one example of a weak base.
OR
nitrous acid/HNO2;
corrodes marble/limestone buildings/statues / leaching in soils /
harms/kills plants;
Explain, using the Brønsted-Lowry theory, how water can act either as an acid or a base. In each case identify the conjugate acid or base formed.
water can act as a Brønsted-Lowry acid by donating a proton/H+ to
form OH–;
water can act as a Brønsted-Lowry base by accepting a proton/H+ to form
H3O+
(ii) Explain why even a very acidic aqueous solution still has some OH– ions present in it.
(1)
(i) Kc = 
/ Kw = [H+][OH–]/Kw =
[H3O+][OH–];
Do not award mark if [ ] are omitted or other brackets are
used.
Expression must be consistent with Kc/Kw. 1
(ii) [H+] increases, [OH–] decreases but still some present (Kw / Kc constant) / [OH–]
cannot go to zero as equilibrium present / [OH–] =, thus [OH–]
cannot be zero / OWTTE;
Accept equilibrium present. 1
(3)
(b) A small piece of magnesium ribbon is added to solutions of nitric and nitrous acid of the same concentration at the same temperature. Describe two observations that would allow you to distinguish between the two acids.
(ii) The following hypothesis was suggested by the student: “Since nitrous acid is a weak acid it will react with a smaller volume of the 0.20 mol dm–3 sodium hydroxide solution.” Comment on whether or not this is a valid hypothesis.
(1)
(a) strong acid completely dissociated/ionized and
weak acid partially
dissociated/ionized;
HNO3(aq) → H+(aq) + NO3–(aq);
HNO2(aq) 
H+(aq) + NO2–(aq);
Allow only arrows as shown.
State symbols not needed.
Accept H2O and H3O+. 3
(b) With HNO3:
faster rate of bubble/gas/hydrogen production;
faster rate of magnesium dissolving;
higher temperature change;
Accept opposite argument for HNO2.
Award [1] if 2 observations given but acid is not identified.
Reference to specific observations needed. 2 max
(i) Define a Brønsted-Lowry acid.
(1)
F–(g) + BF3(g)
(i) donates a proton / H+ ion; 1
(2)
(ii) Vinegar, which contains ethanoic acid, can be used to clean deposits of calcium carbonate from the elements of electric kettles. State the equation for the reaction of ethanoic acid with calcium carbonate.
The reaction mixture in A consists mainly of reactants because the equilibrium lies to the left.
Reaction B NH2–(aq) + H2O(l)
+ OH–(aq)
(2)
(iii) In reactions A and B, identify the stronger acid, NH4+ or NH3 (underlined) and explain your answer.
(5)
(b) Two acidic solutions, X and Y, of equal concentrations have pH values of 2 and 6 respectively.
pH meter;
strong base has a higher pH / weak base has lower pH;
indicator paper/U.I solution;
strong base has a higher pH/more purple / weak base has lower pH/blue not
purple / OWTTE;
measuring conductivity (with conductivity meter);
strong base has a higher conductivity / weak base has lower conductivity;
comparing heat of neutralization with acid;
strong base releases more heat / weak base releases less heat;
Award [4 max] for two correct methods with expected results. 5(b) (i) X;
[X] = 10–2 (mol dm–3) and [Y] = 10–6 (mol dm–3); 2
(i) Outline the process responsible for the production of each acid and state an equation to show its formation.
Acid 1:
Acid 2:
(H2SO3/H2SO4) from burning of coal / smelting plants / sulfuric
acid plants / volcanic activity;
Do not accept combustion of fossil fuels.SO2 + H2O → H2SO3 / SO3 + H2O → H2SO4; 4 max