Sulfur dioxide and oxygen are mixed to form sulfur trioxide according to
2SO₂(g) + O₂(g) => 2SO₃(g)
Which one of the following best describes the effect of adding the catalyst V₂O₅ to the mixture?

Solution

Deuterium (symbol D) is an isotope of hydrogen. Water made from deuterium has the symbol D₂O and has similar properties to normal water. D₂O ionises according to the equilibrium
D₂O => D⁺ + OD^-–
K_d = [D⁺] [OD^-–] = 1.82 X 10–¹⁶ M² at 25°C.
In a neutral solution of pure D₂O at 25°C the concentration of D⁺, in mole per litre, is
A. 1.00 X 10–⁷
B. 1.35 X 10–⁸
C. 0.91 X 10–¹⁶
D. 1.82 X 10–¹⁶

Solution

Dinitrogen tetroxide (N₂O₄) is a colourless gas. It exists in equilibrium with nitrogen dioxide (NO₂), a brown
gas. The concentration of NO₂ in
for the reaction is
N₂O₄(g) => 2NO₂(g); K = 5.5 X 10–³ M at 25°C ....................................(1)

Write the expression for the equilibrium constant for this reaction.

Solution

Some pure NO₂ is placed in a gas syringe at 25°C and allowed to reach equilibrium.
Keeping the volume constant the temperature is then raised to 35°C. The brown colour then becomes more intense. Is the above reaction (1) exothermic or endothermic? Explain your answer.

Solution

Keeping the temperature at 35°C the plunger of the syringe is then pushed in so as to halve the volume.
Equilibrium is then re-established. Is the brown colour of the mixture more intense or less intense than before the volume was halved?

Solution

Give the numerical value at 25°C of the equilibrium constant of the reaction below.
NO₂(g) =>1/ 2N₂O₂(g)

Solution

To live, the human body needs a regular supply of oxygen, which is distributed throughout the body by the red
pigment, haemoglobin (Hb). Hb is carried around the body by the red blood cells in the blood.
a. Write a simple equation showing oxygen reacting with haemoglobin.
Solution

b. Using this equation explain, in terms of equilibrium principles, how a low oxygen concentration can lead
to the cells in a human body being deprived of oxygen.
Solution

c. At high altitudes, the pressure of atmospheric oxygen is significantly less than it is at sea level. People who
live most of their lives on very high mountains normally have a number of special adaptations to living
at high altitudes. One such adaptation is the possession of a signiÞ cantly higher red blood count (that is,
a larger number of red blood cells in the blood) compared with people living at sea level. Explain how a
high blood count is a useful adaptation to high altitude living.

Solution

Ethanoic acid (CH₃COOH) is a weak acid in water.
Write an equation showing the ionisation of ethanoic acid in water.
Solution

A 0.100 M solution of ethanoic acid in water at 25°C has a pH of 2.88.
i. Calculate the hydrogen ion concentration in a 0.100 M solution of ethanoic acid.

Solution
ii. Calculate the acidity constant of ethanoic acid at 25°C.
Solution

At 25°C, methanoic acid (HCOOH) has an acidity constant that is approximately ten times greater than the acidity constant of ethanoic acid.

i. Comparing two 0.10 M solutions of methanoic and ethanoic acids, which solution would have the
higher pH? Give a simple qualitative explanation for your answer.

Solution
ii. Equal volumes of both solutions were titrated against a 0.10 M solution of NaOH. Which of the
solutions, if either, would require the greater volume of the NaOH solution for complete neutralisation?
Explain your conclusion.

Solution