Question
. This question is about ammonia.
(a) Nitrogen reacts with hydrogen to form ammonia in an industrial process.
\(N_2(g) + 3H_2(g) 2NH_3(g)\)
(i) Name this industrial process.
(ii) State the meaning of the symbol \(\leftrightarrow \).
(iii) State the conditions used in this industrial process. Include units.
temperature ……………………………………………..
pressure …………………………………………………..
(iv) Name the catalyst used in this industrial process.
(v) If the pressure is increased, the yield of ammonia increases.
Explain why, in terms of equilibrium.
(vi) If the temperature is increased, the rate of reaction increases.
Explain why, in terms of particles.
(b) Ammonia reacts with sulfuric acid to make a compound which is used as a fertiliser.
Write the chemical equation for the reaction between ammonia and sulfuric acid.
Answer/Explanation
Answer:
(a) (i) Haber
(ii) reversible/equilibrium
(iii) 450 °C (1)
200 atm (1)
(iv) iron / Fe
(v) equilibrium shifts / moves in forwards direction (1)
fewer molecules / moles (of gas) on RHS (1)
(vi) particles have more energy (1)
more collisions (between particles) occur per second / per unit time (1)
a greater percentage / proportion / fraction of collisions (of particles) are successful / have energy above activation
energy / have energy equal to activation energy (1)
(b) \(2NH_3 + H2SO_4 \Rightarrow (NH_4)_2SO_4\)
\((NH_4)_2SO_4\) (1) correct equation (1)
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:
Question
Period 3 contains the elements sodium to argon. This question asks about the chemistry of each of the Period 3 elements or their compounds.
(a) Sodium nitrate is a white crystalline solid. When heated it melts and the following reaction occurs.
\(2NaNO_3(l) → 2NaNO_2(l) + O_2\)(g)
A 3.40g sample of sodium nitrate is heated. Calculate the
• number of moles of \(NaNO_3\) used, ……………………………. mol
• number of moles of \(O_2\) formed, ……………………………. mol
• volume of \(O_2\) formed, in \(dm^{3}\) (measured at r.t.p.). …………………………….\( dm^{3}\)
[3]
(b) Magnesium reacts slowly with warm water to form a base, magnesium hydroxide.
(i) Explain what is meant by the term base.
……………………………………………………………………………………………………………………… [1]
(ii) Write a chemical equation for the reaction between magnesium and warm water.
……………………………………………………………………………………………………………………… [2]
(c) Aluminium oxide is amphoteric. It is insoluble in water. Describe experiments to show that aluminium oxide is amphoteric.
…………………………………………………………………………………………………………………………………. …………………………………………………………………………………………………………………………………. …………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………. [3]
(d) Silicon(IV) oxide has a giant structure.
(i) Name the type of bonding in silicon(IV) oxide.
……………………………………………………………………………………………………………………… [1]
(ii) Give two physical properties of silicon(IV) oxide.
……………………………………………………………………………………………………………………………
……………………………………………………………………………………………………………………… [2]
(e) Calcium phosphate is used in fertilisers. The bonding in calcium phosphate is ionic. Calcium phosphate contains the phosphate ion, \(PO_4\)\
(i) What is ionic bonding?
…………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………… [2]
(ii) Deduce the formula of calcium phosphate. ……………………………………………………………………………………………………………………… [1]
(f) Sulfur tetrafluoride, \(SF_4\), can be made by combining gaseous sulfur with fluorine.
\(S(g) + 2F_2(g) → SF_4(g)\)
The reaction is exothermic.
(i) Complete the energy level diagram for this reaction. Include an arrow which clearly shows the energy change during the reaction.
(ii) During the reaction the amount of energy given out is 780kJ/mol.
The F–F bond energy is 160kJ/mol.
Use this information to determine the bond energy, in kJ /mol, of one S–F bond in \(SF_4\).
……………………………. kJ/mol [3]
(g) Chlorine and compounds of chlorine are important in water treatment and in laboratory testing for water.
(i) Chlorine is added to water to make the water safe to drink.
Explain why adding chlorine makes water safe to drink.
……………………………………………………………………………………………………………………… [1]
(ii) A compound of chlorine is used in the laboratory to test for the presence of water.
Name the compound of chlorine used in this test and describe the colour change seen in a positive result of this test.
name of compound ……………………………………………………………………………………………….
colour change from …………………………………………… to ……………………………………………
[3]
(h) Argon is an unreactive noble gas.
(i) Explain why argon is unreactive.
……………………………………………………………………………………………………………………… [1]
(ii) Give one use of argon.
……………………………………………………………………………………………………………………… [1] [Total:27]
Answer/Explanation
2(a)
number of moles of \(NaNO_3\) used: 3.40/85 = 0.04(00) (mol)
OR
\(4.(00)× 10^–2 \)(mol);
number of moles of O2 formed: 0.04/2 = 0.02(00) (mol)
OR
\(2.(00)× 10^–2\) (mol);
volume of\( O_2\) formed: 0.02× 24 = 0.48\( (dm^3)\);
2(b)(i) (a substance which is) a proton/H+ /hydrogen ion acceptor; 1
2(b)(ii) \(Mg(s) + 2H_2O(l) → Mg(OH)_2(aq) + H_2(g)\)
\(Mg(OH)_2\); rest of equation;
2(c)
M1 add a named acid, e.g. HCl and a named alkali, e.g. NaOH;
M2 \(Al_2O_3\) will react with/neutralises both reagents;
M3 and so it will dissolve into the reagent/form a solution;
2(d)(i) covalent;
2(d)(ii) any 2 from: high melting point/high boiling point;
poor conductor (of electricity); hard; insoluble;
2(e)(i)
M1 (electrostatic) attraction;
M2 between oppositely charged ions;
2(e)(ii) \(Ca_3(PO_4)_2\);
2(f)(i)
M1 exothermic mark: horizontal product energy line at lower energy than that of reactant energy line;
M2 label of product mark: \(SF_4\);
M3 correct direction of vertical heat of reaction arrow: arrow must start level with reactant energy and finish level with product energy and must have only one (correct) arrow-head;
2(f)(ii)
M1 bond energy of \(2F_2: 2 × F–F = 2 × 160 = 320 (kJ/mol)\);
M2 bond energy of all bonds in SF4: 780 + 320 = 1100 (kJ/mol);
M3 calculated bond energy of \(SF_4\) divided by 4: 1100/4 = 275 (kJ/mol);
2(g)(i) kills bacteria;
2(g)(ii) name of compound: cobalt(II) chloride;
from: blue;
to: pink;
2(h)(i) it has a complete outer shell/a full outer shell/8 electrons in the outer shell; 1
2(h)(ii) (in) lamps;