Question
(a) Aqueous ammonium sulfate, $\left(\mathrm{NH}_4\right)_2 \mathrm{SO}_4$, is warmed with aqueous sodium hydroxide. The pungent-smelling gas ammonia, $\mathrm{NH}_3$, is produced. Balance the equation for this reaction.
$
\left(\mathrm{NH}_4\right)_2 \mathrm{SO}_4+\ldots . . \mathrm{NaOH} \rightarrow \ldots . . \mathrm{NH}_3+\ldots . . \mathrm{H}_2 \mathrm{O}+\mathrm{Na}_2 \mathrm{SO}_4
$
(b) A $2.8 \mathrm{~g}$ sample of impure ammonium sulfate is found to contain $0.7 \mathrm{~g}$ of impurities.
Calculate the percentage of ammonium sulfate in this sample.
percentage of ammonium sulfate $=$ $\%[1]$
(c) Describe a test for ammonia gas.
test………………………………………
result………………………………………[2]
(d) Ammonia gas is prepared at the front of a laboratory.
The pungent smell of ammonia spreads throughout the laboratory slowly.
(i) Name the process that occurs when ammonia gas spreads throughout the laboratory. [1]
(ii) Explain, using ideas about particles, why ammonia gas spreads throughout the laboratory.
(iii) Explain why carbon dioxide gas, $\mathrm{CO}_2$, will spread throughout the laboratory at a slower rate than ammonia gas, $\mathrm{NH}_3$.
(e) Ammonia is produced in the Haber process.
The equation for the reaction is shown.
$
\mathrm{N}_2(\mathrm{~g})+3 \mathrm{H}_2(\mathrm{~g}) \rightarrow 2 \mathrm{NH}_3(\mathrm{~g})
$
(i) In the Haber process, a temperature of $450^{\circ} \mathrm{C}$ and a pressure of 200 atmospheres are used in the presence of finely-divided iron.
A larger equilibrium yield of ammonia would be produced if a lower temperature and a higher pressure are used.
Explain why a lower temperature and a higher pressure are not used.
lower temperature…………………………………………………………………….
higher pressure………………………………………………………………………………[2]
(ii) State the role of iron in the Haber process.[1]
(f) Ammonia is a weak base.
(i) Explain the meaning of the term base.
(ii) Suggest the pH of aqueous ammonia………………………………………………………………………………………………………………………. [1] [Total: 13]
▶️Answer/Explanation
Ans:
3(a)(i) 2→ 2 + 2 1
3(b) 75(%) 1
3(c) test: (damp red) litmus paper (1)
result: (litmus goes) blue (1)
3(d)(i) diffusion 1
3(d)(ii) particles move from an area of high to low concentration
particles move randomly
3(d)(iii) $\mathrm{CO}_2$ molecules are heavier (than $\mathrm{NH}_3$ )
3(e)(i) lower temperature: (rate of reaction) slower (1)
higher pressure: expensive/specialist equipment
3(e)(ii) catalyst
3(f)(i) proton acceptor
3(f)(ii) any value greater than 7 up to 12
Question
Iron is a typical transition element.
Iron:
● acts as a catalyst
● forms coloured compounds
● has more than one oxidation state.
(a) Name one major industrial process that uses iron as a catalyst and name the product made in
this process.
process ……………………………………………………………………………………………………………………..
product made ……………………………………………………………………………………………………………..
(b) When aqueous sodium hydroxide is added to aqueous iron(II) sulfate, a precipitate forms.
(i) What colour is this precipitate?
(ii) Write the ionic equation for this reaction. Include state symbols.
(c) Iron(II) sulfate can be converted to iron(III) sulfate by potassium manganate(VII) at room
temperature.
(i) What is the role of potassium manganate(VII) in this reaction?
(ii) What condition must be used for this reaction to occur?
(iii) In terms of electron transfer, what happens to the iron(II) ions in this reaction?
(iv) State the colour change seen during this reaction.
from purple to …………………………………………………………………………………………………
(d) Deduce the charge on the iron ion in each of these compounds.
\(FeF_3\) ………………………………………………………………………………………………………………………….
\(Fe(NO_3)_3\) ……………………………………………………………………………………………………………………
Answer/Explanation
Answer:
(a) Haber (process) (1)
ammonia (1)
(b) (i) green
(ii) \(Fe^{2+}(aq) + 2OH^–(aq) \rightarrow Fe(OH)_2(s)\)
\(Fe(OH)_2\) (as only product) (1)
\(Fe^{2+}\) and \(2OH^–\) (as reactants) (1)
state symbols (1)
(c) (i) oxidising agent
(ii) presence of an acid
(iii) lose an electron
(iv) colourless
(d) 3+
3+
Question
This question is about ammonia.
(a) When ammonia gas reacts with hydrogen chloride gas, white fumes of ammonium chloride are formed.
NH3 + HCl → NH4Cl
(i) What type of chemical reaction is this?
Draw a circle around the correct answer.
decomposition neutralization oxidation reduction [1]
(ii) Watch-glasses of aqueous ammonia and concentrated hydrochloric acid were placed near each other on a table.
At first no white fumes were seen.
After a short time, white fumes were seen between the watch-glasses.
Explain these observations using the kinetic particle model.[3]
(b) Ammonia is used in the manufacture of fertilizers.
Name the three elements present in most fertilizers which improve plant growth.[3]
1
2
3
(c) Aqueous ammonia can be used to test for aluminum ions and zinc ions.
Complete the table to show the expected observations.
[3] [Total: 10]
Answer/Explanation
Ans:
(a)(i) neutralization
(a)(ii) 1 mark each for any three of:
-
-
- evaporation / molecules escape from surface of the liquids
- diffusion
- molecules in (constant) movement / molecules collide
- (movement of) molecules is random / in every direction
- molecules spread out / molecules mix
- (molecules spread) from higher concentration to lower
- concentration
- molecules react (when they collide)
-
(b) nitrogen (1)
phosphorus (1)
potassium (1)
(c) 1 mark each for any three of:
