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1. Which statement explains why ammonia can act - WordPress.com

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1.
Which statement explains why ammonia can act as a Lewis base?
A.
Ammonia can donate a lone pair of electrons.
B.
Ammonia can accept a lone pair of electrons.
C.
Ammonia can donate a proton.
D.
Ammonia can accept a proton.
(Total 1 mark)
2.
Consider the equilibrium below.
CH3CH2COOH(aq) + H2O(l)
CH3CH2COO–(aq) + H3O+(aq)
Which species represent a conjugate acid-base pair?
A.
CH3CH2COOH and H2O
B.
H2O and CH3CH2COO–
C.
H3O+ and H2O
D.
CH3CH2COO– and H3O+
(Total 1 mark)
3.
Define the terms acid and base according to the BrГёnsted-Lowry theory and state one example
of a weak acid and one example of a strong base.
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(Total 2 marks)
4.
Describe two different methods, one chemical and one physical, other than measuring the pH,
that could be used to distinguish between ethanoic acid and hydrochloric acid solutions of the
same concentration.
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(Total 4 marks)
5.
Black coffee has a pH of 5 and toothpaste has a pH of 8. Identify which is more acidic and
deduce how many times the [H+] is greater in the more acidic product.
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(Total 2 marks)
6.
Which salts will produce an acidic solution when dissolved in water?
I.
CH3COOK
II.
NH4NO3
III.
Al2(SO4)3
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
(Total 1 mark)
7.
The Kb value for a base is 5.0 × 10–2 mol dm–3 at 298 K. What is the Ka value for its conjugate
acid at this temperature?
A.
5.0 × 10–2
B.
2.0 × 10–6
C.
2.0 × 10–12
D.
2.0 × 10–13
(Total 1 mark)
8.
Which compounds can be mixed together as solutions of equal volume and concentration to
form a buffer solution?
A.
Nitric acid and potassium hydroxide
B.
Nitric acid and potassium nitrate
C.
Propanoic acid and potassium hydroxide
D.
Propanoic acid and potassium propanoate
(Total 1 mark)
9.
In an experiment conducted at 25.0 В°C, the initial concentration of propanoic acid and methanol
were 1.6 mol dm–3 and 2.0 mol dm–3 respectively. Once equilibrium was established, a sample
of the mixture was removed and analysed. It was found to contain 0.80 mol dm–3of compound
X.
(i)
Calculate the concentrations of the other three species present at equilibrium.
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(3)
(ii)
State the equilibrium constant expression, Kc, and calculate the equilibrium constant for
this reaction at 25.0 В°C.
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(2)
(Total 5 marks)
10.
(i)
Define the terms acid and base according to the BrГёnsted-Lowry theory. Distinguish
between a weak base and a strong base. State one example of a weak base.
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(3)
(ii)
Weak acids in the environment may cause damage. Identify a weak acid in the
environment and outline one of its effects.
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(2)
(Total 5 marks)
11.
The graph below indicates the pH change during the titration of 20.0 cm3 of 0.100 mol dm–3 of
CH3COOH(aq) with 0.100 mol dm–3 KOH(aq). From the graph, identify the volume of
KOH(aq) and the pH at the equivalence point.
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(Total 2 marks)
12.
(i)
Describe how an indicator works.
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(3)
(ii)
Using Table 16 of the Data Booklet, identify the most appropriate indicator for the
titration of ethanoic acid with potassium hydroxide. Explain your choice.
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(2)
(Total 5 marks)
13.
Explain, using an equation, whether a solution of 0.10 mol dm–3 FeCl3(aq) would be acidic,
alkaline or neutral.
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(Total 2 marks)
14.
Determine the pH of the solution resulting when 100 cm3 of 0.50 mol dm–3 HCl(aq) is mixed
with 200 cm3 of 0.10 mol dm–3 NaOH(aq).
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(Total 5 marks)
15.
Which is not a conjugate acid-base pair?
A.
HNO3 and NO3–
B.
CH3COOH and CH3COO–
C.
H3O+ and OH–
D.
HSO4– and SO42–
(Total 1 mark)
16.
Which 0.10 mol dm–3 solution would have the highest conductivity?
A.
HCl
B.
NH3
C.
CH3COOH
D.
H2CO3
(Total 1 mark)
17.
The pH of a solution changes from pH = 2 to pH = 5. What happens to the concentration of the
hydrogen ions during this pH change?
A.
It decreases by a factor of 1000
B.
It increases by a factor of 1000
C.
It decreases by a factor of 100
D.
It increases by a factor of 100
(Total 1 mark)
18.
Define an acid in terms of the Lewis theory. Deduce, giving a reason, whether NF3 is able to
function as a Lewis acid or as a Lewis base.
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(Total 2 marks)
19.
Describe two different properties that could be used to distinguish between a 1.00 mol dm–3
solution of a strong monoprotic acid and a 1.00 mol dm–3 solution of a weak monoprotic acid.
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(Total 2 marks)
20.
Explain, using the BrГёnsted-Lowry theory, how water can act either as an acid or a base. In
each case identify the conjugate acid or base formed.
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(Total 2 marks)
21.
Based on information in the table below, which acid is the strongest?
Acid
pKa
Ka
A.
HA
2.0
–
B.
HB
–
1 × 10–3
C.
HC
4.0
–
D.
HD
–
1 × 10–5
(Total 1 mark)
22.
Which combination will form a buffer solution?
A.
100 cm3 of 0.10 mol dm–3 hydrochloric acid with 50 cm3 of 0.10 mol dm–3 sodium
hydroxide.
B.
100 cm3 of 0.10 mol dm–3 ethanoic acid with 50 cm3 of 0.10 mol dm–3 sodium
hydroxide.
C.
50 cm3 of 0.10 mol dm–3 hydrochloric acid with 100 cm3 of 0.10 mol dm–3 sodium
hydroxide.
D.
50 cm3 of 0.10 mol dm–3 ethanoic acid with 100 cm3 of 0.10 mol dm–3 sodium
hydroxide.
(Total 1 mark)
23.
The graph below shows the titration curve of 25 cm3 of 0.100 mol dm–3 of hydrochloric acid
with sodium hydroxide, of 0.100 mol dm–3 concentration. The indicator methyl orange was
used to determine the equivalence point. Methyl orange has a pH range of 3.2–4.4.
If the hydrochloric acid was replaced by ethanoic acid of the same volume and concentration,
which property of the titration would remain the same?
A.
The initial pH
B.
The pH at the equivalence point
C.
The volume of strong base, NaOH, needed to reach the equivalence point
D.
The colour of the titration mixture just before the equivalence point is reached
(Total 1 mark)
24.
Ammonia, NH3, is a weak base. It has a pKb value of 4.75.
Calculate the pH of a 1.00 × 10–2 mol dm–3 aqueous solution of ammonia at 298 K.
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(Total 4 marks)
25.
(i)
25.0 cm3 of 1.00 × 10–2 mol dm–3 hydrochloric acid solution is added to 50.0 cm3 of
1.00 × 10–2 mol dm–3 aqueous ammonia solution. Calculate the concentrations of both
ammonia and ammonium ions in the resulting solution and hence determine the pH of the
solution.
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(5)
(ii)
State what is meant by a buffer solution and explain how the solution in (i), which
contains ammonium chloride dissolved in aqueous ammonia, can function as a buffer
solution.
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(3)
(Total 8 marks)
26.
Salts may form neutral, acidic or alkaline solutions when dissolved in water.
(i)
Explain why a solution of sodium chloride is neutral but sodium carbonate forms an
alkaline solution when it dissolves in water.
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(2)
(ii)
Explain why iron(III) chloride, [Fe(H2O)6]Cl3, forms an acidic solution in water.
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(2)
(Total 4 marks)
27.
Which property is characteristic of acids in aqueous solution?
A.
Acids react with ammonia solution to produce hydrogen gas and a salt.
B.
Acids react with metal oxides to produce oxygen gas, a salt and water.
C.
Acids react with reactive metals to produce hydrogen gas and a salt.
D.
Acids react with metal carbonates to produce hydrogen gas, a salt and water.
(Total 1 mark)
28.
A student has equal volumes of 1.0 mol dm–3 sodium hydroxide and ammonia solutions.
Which statement about the solutions is correct?
A.
Sodium hydroxide has a lower electrical conductivity than ammonia.
B.
Sodium hydroxide has a higher hydrogen ion concentration than ammonia.
C.
Sodium hydroxide has a higher pH than ammonia.
D.
Sodium hydroxide has a higher hydroxide ion concentration than ammonia.
(Total 1 mark)
29.
Which statement about acids is correct?
A.
A BrГёnsted-Lowry acid donates an electron pair.
B.
A Lewis acid donates a proton.
C.
A BrГёnsted-Lowry acid accepts a proton.
D.
A Lewis acid accepts an electron pair.
(Total 1 mark)
30.
What is the Kb expression for the reaction of ethylamine with water?
A.
Kb = [CH3CH2NH3+][OH–]
B.
Kb =
C.
[CH 3 CH 2 NH 3 ][H 2 O]
Kb =
[CH 3 CH 2 NH 2 ]
D.
Kb = [CH3CH2NH2][H2O]
пЂ«
[CH 3 CH 2 NH 3 ][OH пЂ­ ]
[CH 3 CH 2 NH 2 ]
пЂ«
(Total 1 mark)
31.
When these 1.0 mol dm–3 acidic solutions are arranged in order of increasing strength (weakest
first), what is the correct order?
A.
X<Z<Y
B.
X<Y<Z
C.
Z<X<Y
D.
Y<X<Z
acid in solution X
Ka = 1.74 × 10–5 mol dm–3 at 298 K
acid in solution Y
Ka = 1.38 × 10–3 mol dm–3 at 298 K
acid in solution Z
Ka
= 1.78 × 10–5 mol dm–3 at 298 K
(Total 1 mark)
32.
Consider an acid-base indicator solution.
HIn(aq)
colour A
H+(aq) + In–(aq)
colour B
What is the effect on this acid-base indicator when sodium hydroxide solution is added to it?
A.
Equilibrium shifts to the right and more of colour B is seen.
B.
Equilibrium shifts to the left and more of colour B is seen.
C.
Equilibrium shifts to the right and more of colour A is seen.
D.
Equilibrium shifts to the left and more of colour A is seen.
(Total 1 mark)
33.
(a)
(i)
State an equation for the reaction of ethanoic acid with water.
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(1)
(ii)
Calculate the pH of 0.200 mol dm–3 ethanoic acid (pKa = 4.76).
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(3)
(b)
Determine the pH of a solution formed from adding 50.0 cm3 of 1.00 mol dm–3 ethanoic
acid, CH3COOH(aq), to 50.0 cm3 of 0.600 mol dm–3 sodium hydroxide, NaOH(aq).
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(4)
(c)
Explain how the solution formed in part (b) can act as a buffer. Use equations to support
your answer.
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(2)
(Total 10 marks)
34.
Which species behave as BrГёnsted-Lowry acids in the following reversible reaction?
H2PO4–(aq) + CN–(aq)
A.
HCN and CN–
B.
HCN and HPO42–
C.
H2PO4– and HPO42–
D.
HCN and H2PO4–
HCN(aq) + HPO42–(aq)
(Total 1 mark)
35.
Which of the following are weak acids in aqueous solution?
I.
CH3COOH
II.
H2CO3
III.
HCl
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
(Total 1 mark)
36.
Water is an important substance that is abundant on the Earth’s surface. Water dissociates
according to the following equation.
H2O(l)
(i)
H+(aq) + OH–(aq)
State the equilibrium constant expression for the dissociation of water.
(1)
(ii)
Explain why even a very acidic aqueous solution still has some OH– ions present in it.
(1)
(iii)
State and explain the effect of increasing temperature on the equilibrium constant above
given that the dissociation of water is an endothermic process.
(3)
(iv)
The pH of a solution is 2. If its pH is increased to 6, deduce how the hydrogen ion
concentration changes.
(2)
(Total 7 marks)
37.
pKw for water at 10 В°C = 14.54. What is the pH of pure water at this temperature?
A.
6.73
B.
7.00
C.
7.27
D.
7.54
(Total 1 mark)
38.
What is Kb for the aqueous fluoride ion given that Kw is 1.0 × 10–14 and Ka for HF is 6.8 × 10–4
at 298 K?
A.
B.
C.
D.
1
6.8 п‚ґ 10 пЂ­ 4
(6.8 × 10–4)(1.0 × 10–14)
1.0 п‚ґ10 пЂ­14
6.8 п‚ґ 10 пЂ­ 4
6.8 × 10–4
(Total 1 mark)
39.
Which of the following could be added to a solution of ethanoic acid to prepare a buffer?
A.
Sodium hydroxide
B.
Hydrochloric acid
C.
Sodium chloride
D.
More ethanoic acid
(Total 1 mark)
40.
Which aqueous solution has a pH less than 7?
A.
KNO3(aq)
B.
Na2CO3(aq)
C.
[Fe(H2O)6]Cl3(aq)
D.
CH3COONa(aq)
(Total 1 mark)
41.
Water is an important substance that is abundant on the Earth’s surface.
(i)
State the expression for the ionic product constant of water, Kw.
(1)
(ii)
Explain why even a very acidic aqueous solution still has some OH– ions present in it.
(1)
(iii)
State and explain the effect of increasing temperature on the value of Kw given that the
ionization of water is an endothermic process.
(3)
(iv)
State and explain the effect of increasing temperature on the pH of water.
(2)
(Total 7 marks)
42.
Buffer solutions resist small changes in pH. A phosphate buffer can be made by dissolving
NaH2PO4 and Na2HPO4 in water, in which NaH2PO4 produces the acidic ion and Na2HPO4
produces the conjugate base ion.
(i)
Deduce the acid and conjugate base ions that make up the phosphate buffer and state the
ionic equation that represents the phosphate buffer.
(3)
(ii)
Describe how the phosphate buffer minimizes the effect of the addition of a strong base,
OH–(aq), to the buffer. Illustrate your answer with an ionic equation.
(2)
(iii)
Describe how the phosphate buffer minimizes the effect of the addition of a strong acid,
H+(aq), to the buffer. Illustrate your answer with an ionic equation.
(2)
(Total 7 marks)
43.
A 0.10 mol dm–3 ammonia solution is placed in a flask and titrated with a 0.10 mol dm–3
hydrochloric acid solution.
(i)
Explain why the pH of the ammonia solution is less than 13.
(2)
(ii)
Estimate the pH at the equivalence point for the titration of hydrochloric acid with
ammonia and explain your reasoning.
(2)
(iii)
State the equation for the reaction of ammonia with water and write the Kb expression for
NH3(aq).
(2)
(iv)
When half the ammonia has been neutralized (the half-equivalence point), the pH of the
solution is 9.25. Deduce the relationship between [NH3] and [NH4+] at the
half-equivalence point.
(1)
(v)
Determine pKb and Kb for ammonia based on the pH at the half-equivalence point.
(3)
(vi)
Describe the significance of the half-equivalence point in terms of its effectiveness as a
buffer.
(1)
(Total 11 marks)
44.
What is the conjugate base of H2CO3 according to the BrГёnsted-Lowry theory?
A.
CO32–
B.
HCO3–
C.
H3CO3+
D.
CO2
(Total 1 mark)
45.
A solution of acid A has a pH of 1 and a solution of acid B has a pH of 2. Which statement
must be correct?
A.
Acid A is stronger than acid B
B.
[A] > [B]
C.
The concentration of H+ ions in A is higher than in B
D.
The concentration of H+ ions in B is twice the concentration of H+ ions in A
(Total 1 mark)
46.
(a)
The nitrite ion is present in nitrous acid, HNO2, which is a weak acid. The nitrate ion is
present in nitric acid, HNO3, which is a strong acid. Distinguish between the terms
strong and weak acid and state the equations used to show the dissociation of each acid
in aqueous solution.
(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.
(2)
(c)
A student decided to investigate the reactions of the two acids with separate samples of
0.20 mol dm–3 sodium hydroxide solution.
(i)
Calculate the volume of the sodium hydroxide solution required to react exactly
with a 15.0 cm3 solution of 0.10 mol dm–3 nitric acid.
(1)
(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)
(d)
The graph below shows how the conductivity of the two acids changes with
concentration.
Identify Acid 1 and explain your choice.
(2)
(Total 9 marks)
47.
Which mixtures act as buffer solutions?
I.
100 cm3 0.1 mol dm–3 ethanoic acid and 100 cm3 0.1 mol dm–3 sodium ethanoate
II.
100 cm3 0.1 mol dm–3 ethanoic acid and 50 cm3 0.1 mol dm–3 sodium hydroxide
III.
100 cm3 0.1 mol dm–3 ethanoic acid and 100 cm3 0.5 mol dm–3 sodium hydroxide
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
(Total 1 mark)
48.
Which solutions have a pH less than 7?
I.
Na2CO3(aq)
II.
[Fe(H2O)6]Cl3(aq)
III.
(NH4)2SO4(aq)
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
(Total 1 mark)
49.
Equal volumes and concentrations of hydrochloric acid and ethanoic acid are titrated with
sodium hydroxide solutions of the same concentration. Which statement is correct?
A.
The initial pH values of both acids are equal.
B.
At the equivalence points, the solutions of both titrations have pH values of 7.
C.
The same volume of sodium hydroxide is needed to reach the equivalence point.
D.
The pH values of both acids increase equally until the equivalence points are reached.
(Total 1 mark)
50.
Bromophenol blue changes from yellow to blue over the pH range of 3.0 to 4.6. Which
statement is correct?
A.
Molecules of bromophenol blue, HIn, are blue.
B.
At pH < 3.0, a solution of bromophenol blue contains more ions, In–, than molecules,
HIn.
C.
The pKa of bromophenol blue is between 3.0 and 4.6.
D.
Bromophenol blue is a suitable indicator to titrate ethanoic acid with potassium
hydroxide solution.
(Total 1 mark)
51.
(a)
Ammonia can be converted into nitric acid, HNO3(aq), and hydrocyanic acid, HCN(aq).
The pKa of hydrocyanic acid is 9.21.
(i)
Distinguish between the terms strong and weak acid and state the equations used
to show the dissociation of each acid in aqueous solution.
(3)
(ii)
Deduce the expression for the ionization constant, Ka, of hydrocyanic acid and
calculate its value from the pKa value given.
(2)
(iii)
Use your answer from part (a) (ii) to calculate the [H+] and the pH of an aqueous
solution of hydrocyanic acid of concentration 0.108 mol dm–3. State one
assumption made in arriving at your answer.
(4)
(b)
A small piece of magnesium ribbon is added to solutions of nitric and hydrocyanic acid
of the same concentration at the same temperature. Describe two observations that would
allow you to distinguish between the two acids.
(2)
(c)
A student decided to investigate the reactions of the two acids with separate samples of
0.20 mol dm–3 sodium hydroxide solution.
(i)
Calculate the volume of the sodium hydroxide solution required to react exactly
with a 15.0 cm3 solution of 0.10 mol dm–3 nitric acid.
(1)
(ii)
The following hypothesis was suggested by the student: “Since hydrocyanic 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)
(iii)
Use Table 16 of the Data Booklet to identify a suitable indicator for the titration of
sodium hydroxide and hydrocyanic acid.
(1)
(d)
The graph below shows how the conductivity of the two acids changes with
concentration.
Identify Acid 1 and explain your choice.
(2)
(Total 16 marks)
52.
For equal volumes of 1.0 mol dm–3 solutions of hydrochloric acid, HCl(aq), and methanoic
acid, HCOOH(aq), which statements are correct?
I.
HCl dissociates more than HCOOH
II.
HCl is a better electrical conductor than HCOOH
III.
HCl will neutralize more NaOH than HCOOH
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
(Total 1 mark)
53.
When equal volumes of four 0.1 mol dm–3 solutions are arranged in order of increasing pH
(lowest pH first), what is the correct order?
A.
CH3COOH < HNO3 < CH3CH2NH2 < KOH
B.
HNO3 < CH3COOH < CH3CH2NH2 < KOH
C.
CH3CH2NH2 < HNO3 < CH3COOH < KOH
D.
KOH < CH3CH2NH2 < CH3COOH < HNO3
(Total 1 mark)
54.
(i)
Define a BrГёnsted-Lowry acid.
(1)
(ii)
Deduce the two acids and their conjugate bases in the following reaction:
H2O(l) + NH3(aq)
OH–(aq) + NH4+(aq)
(2)
(iii)
Explain why the following reaction can also be described as an acid-base reaction.
F–(g) + BF3(g)
BF4–(s)
(2)
(Total 5 marks)
55.
Ethanoic acid, CH3COOH, is a weak acid.
(i)
Define the term weak acid and state the equation for the reaction of ethanoic acid with
water.
(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.
(2)
(Total 4 marks)
56.
What is the correct expression for the ionic product constant of water, Kw?
[H пЂ« ]
A.
KW =
B.
KW =
C.
KW = [H+] + [OH–]
D.
KW = [H+][OH–]
[OH пЂ­ ]
[ H 2 O]
[H пЂ« ][OH пЂ­ ]
(Total 1 mark)
57.
Which mixtures could act as buffers?
I.
NaOH(aq) and HCl(aq)
II.
NaOH(aq) and CH3COOH(aq)
III.
HCl(aq) and CH3COONa(aq)
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
(Total 1 mark)
58.
What is the approximate pH of a 0.01 mol dm–3 ammonia solution?
A.
2
B.
More than 2 but less than 7
C.
More than 7 but less than 12
D.
12
(Total 1 mark)
59.
The pKa value for propanoic acid is given in Table 15 of the Data Booklet.
(a)
(i)
State the equation for the reaction of propanoic acid with water.
...........................................................................................................................
...........................................................................................................................
(1)
(ii)
Calculate the hydrogen ion concentration (in mol dm–3) of an aqueous solution of
0.100 mol dm–3 propanoic acid.
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...........................................................................................................................
...........................................................................................................................
(2)
(b)
The graph below shows a computer simulation of a titration of 25.0 cm3 of
0.100 mol dm–3 hydrochloric acid with 0.100 mol dm–3 sodium hydroxide and the pH
range of phenol red indicator.
Sketch the graph that would be obtained for the titration of 25.0 cm3 of 0.100 mol dm–3
propanoic acid with 0.100 mol dm–3 potassium hydroxide using bromophenol blue as an
indicator. (The pH range of bromophenol blue can be found in Table 16 of the Data
Booklet).
(3)
(Total 6 marks)
60.
Which are definitions of an acid according to the BrГёnsted-Lowry and Lewis theories?
BrГёnsted-Lowry theory
Lewis theory
A.
proton donor
electron pair acceptor
B.
proton acceptor
electron pair acceptor
C.
proton acceptor
electron pair donor
D.
proton donor
electron pair donor
(Total 1 mark)
61.
Which list contains only strong acids?
A.
CH3COOH, H2CO3, H3PO4
B.
HCl, HNO3, H2CO3
C.
CH3COOH, HNO3, H2SO4
D.
HCl, HNO3, H2SO4
(Total 1 mark)
62.
An example of a strong acid solution is perchloric acid, HClO4, in water. Which statement is
correct for this solution?
A.
HClO4 is completely dissociated in the solution.
B.
HClO4 exists mainly as molecules in the solution.
C.
The solution reacts only with strong bases.
D.
The solution has a pH value greater than 7.
(Total 1 mark)
63.
100 cm3 of a NaOH solution of pH 12 is mixed with 900 cm3 of water. What is the pH of the
resulting solution?
A.
1
B.
3
C.
11
D.
13
(Total 1 mark)
64.
Ammonia acts as a weak base when it reacts with water. What is the Kb expression for this
reaction?
пЂ«
A.
B.
C.
[ NH 4 ][OH пЂ­ ]
[NH 3 ][H 2 O]
[ NH 3 ][H 2 O]
пЂ«
[NH 4 ][OH пЂ­ ]
[ NH 3 ]
пЂ«
[NH 4 ][OH пЂ­ ]
пЂ«
D.
[ NH 4 ][OH пЂ­ ]
[NH 3 ]
(Total 1 mark)
65.
The indicator, HIn is used in a titration between an acid and base. Which statement about the
dissociation of the indicator, HIn is correct?
HIn (aq)
colour A
H+ (aq) + In– (aq)
colour B
A.
In a strongly alkaline solution, colour B would be observed.
B.
In a strongly acidic solution, colour B would be observed.
C.
[In–] is greater than [HIn] at the equivalence point.
D.
In a weakly acidic solution colour B would be observed.
(Total 1 mark)
66.
At the same concentration, which acid would have the lowest pH?
A.
HNO2
Ka = 5.6 × 10–4 mol dm–3
B.
HF
Ka = 6.8 × 10–4 mol dm–3
C.
C6H5COOH
Ka = 6.3 × 10–5 mol dm–3
D.
HCN
Ka = 4.9 × 10–10 mol dm–3
(Total 1 mark)
67.
Some of the most important processes in chemistry involve acid-base reactions.
(i)
Calculate the Ka value of benzoic acid, C6H5COOH, using Table 15 in the Data Booklet.
......................................................................................................................................
......................................................................................................................................
(1)
(ii)
Based on its Ka value, state and explain whether benzoic acid is a strong or weak acid.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
(2)
(iii)
Determine the hydrogen ion concentration and the pH of a 0.010 mol dm–3 benzoic acid
solution. State one assumption made in your calculation.
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(4)
(Total 7 marks)
68.
What is the formula of the conjugate base of the hydrogenphosphate ion, HPO42–?
A.
H2PO4–
B.
H3PO4
C.
HPO4–
D.
PO43–
(Total 1 mark)
69.
Which pH value is that of an aqueous solution of carbon dioxide?
A.
2.1
B.
5.6
C.
9.8
D.
12.2
(Total 1 mark)
70.
The equations of two acid-base reactions are given below.
Reaction A
NH3(aq) + H2O(l)
пЂ«
NH 4 (aq) + OH–(aq)
The reaction mixture in A consists mainly of reactants because the equilibrium lies to the left.
Reaction B
NH2–(aq) + H2O(l)
NH 3 (aq) + OH–(aq)
The reaction mixture in B consists mainly of products because the equilibrium lies to the right.
(i)
For each of the reactions A and B, deduce whether water is acting as an acid or a base
and explain your answer.
(2)
(ii)
In reaction B, identify the stronger base, NH2– or OH– and explain your answer.
(2)
(iii)
In reactions A and B, identify the stronger acid, NH4+ or NH3 (underlined) and explain
your answer.
(2)
(Total 6 marks)
71.
(a)
Describe two different experimental methods to distinguish between aqueous solutions
of a strong base and a weak base.
(5)
(b)
Two acidic solutions, X and Y, of equal concentrations have pH values of 2 and 6
respectively.
(i)
Calculate the hydrogen ion concentrations in the two solutions and identify the
stronger acid.
(2)
(ii)
Determine the ratio of the hydrogen ion concentrations in the two solutions X and
Y.
(1)
(Total 8 marks)
72.
(i)
Define a Lewis acid and state an example that is not a BrГёnsted-Lowry acid.
(2)
(ii)
Draw structural formulas to represent the reaction between the Lewis acid named in (i)
and a Lewis base and identify the nature of the bond formed in the product.
(4)
(Total 6 marks)
73.
According to the BrГёnsted-Lowry theory, how does each species act in the equilibrium below?
CH3COOH + H2SO4
CH3COOH2+ + HSO4–
CH3COOH
H2SO4
CH3COOH2+
HSO4–
A.
acid
base
base
acid
B.
acid
base
acid
base
C.
base
acid
base
acid
D.
base
acid
acid
base
(Total 1 mark)
74.
If 20 cm3 samples of 0.1 mol dm–3 solutions of the acids below are taken, which acid would
require a different volume of 0.1 mol dm–3 sodium hydroxide for complete neutralization?
A.
Nitric acid
B.
Sulfuric acid
C.
Ethanoic acid
D.
Hydrochloric acid
(Total 1 mark)
75.
Which mixture of acid and alkali would produce a buffer solution?
Acid
Alkali
A.
40 cm3 0.1 mol dm–3 HCl
60 cm3 0.1 mol dm–3 NaOH
B.
60 cm3 0.1 mol dm–3 HCl
40 cm3 0.1 mol dm–3 NaOH
C.
40 cm3 0.1 mol dm–3 HCl
60 cm3 0.1 mol dm–3 NH3
D.
60 cm3 0.1 mol dm–3 HCl
40 cm3 0.1 mol dm–3 NH3
(Total 1 mark)
76.
Which aqueous solution would have a pH > 7?
A.
Sodium sulfate
B.
Ammonium nitrate
C.
Sodium ethanoate
D.
Aluminium nitrate
(Total 1 mark)
77.
Which indicator would be the most appropriate for titrating aqueous ethylamine, CH3CH2NH2,
with nitric acid, HNO3?
A.
Bromophenol blue (pKa = 4.1)
B.
Bromothymol blue (pKa = 7.3)
C.
Phenol red (pKa = 8.0)
D.
Thymolphthalein (pKa = 10.0)
(Total 1 mark)
78.
A 25.0 cm3 solution of a weak monoprotic acid, HA(aq), is titrated with 0.155 mol dm–3
sodium hydroxide, NaOH(aq), and the following graph is obtained.
(i)
Determine the pH at the equivalence point.
(1)
(ii)
Explain, using an equation, why the equivalence point is not at pH = 7.
(3)
(iii)
Calculate the concentration of the weak acid before the addition of any NaOH(aq).
(2)
(iv)
Estimate, using data from the graph, the dissociation constant, Ka, of the weak acid, HA,
showing your working.
(3)
(v)
Suggest an appropriate indicator for this titration.
(1)
(Total 10 marks)
79.
Describe qualitatively the action of an acid-base indicator.
(Total 3 marks)
80.
(i)
Explain what is meant by the term buffer solution.
(2)
(ii)
Calculate the pH of a solution prepared by mixing 50.0 cm3 of 0.200 mol dm–3
CH3COOH(aq) and 50.0 cm3 of 0.100 mol dm–3 NaOH(aq), showing your working.
(3)
(Total 5 marks)
81.
State whether AlCl3 is acidic, basic or neutral in an aqueous solution. Write an equation to
support your answer.
(Total 2 marks)
82.
0.100 mol of ammonia, NH3, was dissolved in water to make 1.00 dm3 of solution.
This solution has a hydroxide ion concentration of 1.28 × 10–3 mol dm–3.
(i)
Determine the pH of the solution.
(2)
(ii)
Calculate the base dissociation constant, Kb, for ammonia.
(3)
(Total 5 marks)
83.
Which species can act as a Lewis acid?
A.
BF3
B.
OH–
C.
H2O
D.
NH3
(Total 1 mark)
84.
Which substance, when dissolved in water, to give a 0.1 mol dm–3 solution, has the highest pH?
A.
HCl
B.
NaCl
C.
NH3
D.
NaOH
(Total 1 mark)
85.
The pKb values of some amines are shown in Table 15 of the Data Booklet. Write an equation
for the reaction of ethylamine with water. State and explain how the basicity of ethylamine
compares to that of ammonia.
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(Total 4 marks)
86.
Which methods will distinguish between equimolar solutions of a strong base and a strong
acid?
I.
Add magnesium to each solution and look for the formation of gas bubbles.
II.
Add aqueous sodium hydroxide to each solution and measure the temperature
change.
III.
Use each solution in a circuit with a battery and lamp and see how bright the lamp
glows.
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
(Total 1 mark)
87.
Which values are correct for a 0.010 mol dm–3 solution of NaOH(aq) at 298 K?
(Kw = 1.0×10–14 mol2 dm–6 at 298 K)
A.
[H+] = 1.0×10–12 mol dm–3 and pH = 12.00
B.
[OH–] = 1.0×10–12 mol dm–3 and pH = 12.00
C.
[H+] = 1.0×10–12 mol dm–3 and pOH = 12.00
D.
[OH–] = 1.0×10–12 mol dm–3 and pOH = 12.00
(Total 1 mark)
88.
At 25 °C, Ka for an acid is 1.0×10–2. What is the value of Kb for its conjugate base?
A.
1.0Г—102
B.
1.0×10–2
C.
1.0Г—1012
D.
1.0×10–12
(Total 1 mark)
89.
Which statement about indicators is always correct?
A.
The mid-point of the pH range of an indicator is 7.
B.
The pH range is greater for indicators with higher pKa values.
C.
The colour red indicates an acidic solution.
D.
The pKa value of the indicator is within its pH range.
(Total 1 mark)
90.
(a)
Predict and explain, using equations where appropriate, whether the following solutions
are acidic, alkaline or neutral.
(i)
0.1 mol dm–3 FeCl3(aq)
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...........................................................................................................................
...........................................................................................................................
(1)
(ii)
0.1 mol dm–3 NaNO3(aq)
...........................................................................................................................
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...........................................................................................................................
(1)
(iii)
0.1 mol dm–3 Na2CO3(aq)
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(1)
(b)
Acidic gases can be released into the atmosphere that have an environmental impact
when they are deposited as acid rain. State two elements that form the acidic gases and
describe two impacts they have on the natural environment.
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(3)
(Total 6 marks)
91.
An experiment was carried out to determine the concentration of aqueous ammonia by titrating
it with a 0.150 mol dm–3 sulfuric acid solution. It was found that 25.0 cm3 of the aqueous
ammonia required 20.1 cm3 of the sulfuric acid solution for neutralization.
(a)
Write the equation for the reaction and calculate the concentration, in mol dm–3, of the
aqueous ammonia.
(4)
(b)
Several acid-base indicators are listed in Table 16 of the Data Booklet. Identify one
indicator that could be used for this experiment. Explain your answer.
(3)
(c)
(i)
Determine the pOH of 0.121 mol dm–3 aqueous ammonia (pKb = 4.75).
(4)
(ii)
State what is meant by the term buffer solution, and describe the composition of an
acid buffer solution in general terms.
(3)
(iii)
Calculate the pH of a mixture of 50.0 cm3 of 0.100 mol dm–3 aqueous ammonia
and 50.0 cm3 of 0.0500 mol dm–3 hydrochloric acid solution.
(4)
(Total 18 marks)
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