Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2020 Winter Zone 3

The names of nine substances are shown.

aluminium oxide
ammonia
carbon monoxide
anhydrous cobalt(II) chloride
hydrated copper(II) sulfate
iron(III) oxide
nitrogen dioxide
silver
steel

Answer the following questions using these substances. Each substance may be used once, more than once or not at all.

Name the substance that is:

(a) the main constituent of hematite .............................................................. [1]

(b) a gas produced in car engines which causes acid rain ................................ [1]

(c) an alkaline gas ................................................................. [1]

(d) an element ................................................................. [1]

(e) a gas formed by the incomplete combustion of fossil fuels ................................ [1]

(f) used to test for the presence of water. ................................ [1]

The table gives information about five particles, A, B, C, D and E.

[Table_1]

(a) State the atomic number of A.
................................................................................................... [1]

(b) State the nucleon number of B.
................................................................................................... [1]

(c) Write the electronic structure of C.
................................................................................................... [1]

(d) Give the letters of all the particles which are:

(i) atoms .................................................................................... [1]

(ii) positive ions ................................................................................ [1]

(iii) negative ions ............................................................................... [1]

(iv) isotopes of each other. ............................................................... [1]

This question is about nitrogen and some of its compounds.
(a) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of nitrogen, $N_2$.
Show the outer shell electrons only.

[2]
(b) Nitrogen can be converted into ammonia by the Haber process.
(i) Describe how nitrogen is obtained for the Haber process.
....................................................................................................................
....................................................................................................................
[2]
(ii) Give the essential reaction conditions and write a chemical equation for the reaction occurring in the Haber process.
chemical equation: ....................................................................................................
...................................................................................................................
reaction conditions: ..................................................................................................
...................................................................................................................
...................................................................................................................
...................................................................................................................
[5]

(c) Some of the ammonia made by the Haber process is converted into nitric acid.
The first stage of this process is the oxidation of ammonia to make nitrogen monoxide.
$$4NH_3(g) + 5O_2(g) ightleftharpoons 4NO(g) + 6H_2O(g)$$
The process is carried out at 900°C and a pressure of 5 atmospheres using an alloy of platinum and rhodium as a catalyst.
The forward reaction is exothermic.
(i) State the meaning of the term catalyst.
....................................................................................................................
....................................................................................................................
[2]
(ii) State the meaning of the term oxidation.
....................................................................................................................
[1]
(iii) Complete the table using the words increase, decrease, or no change.
[Table_1]
[4]
(d) Nitrogen monoxide, $NO$, is converted into nitrogen dioxide, $NO_2$.
$$2NO(g) + O_2(g) ightarrow 2NO_2(g)$$
The nitrogen dioxide reacts with oxygen and water to produce nitric acid as the only product.
Write a chemical equation for this reaction.
....................................................................................................................
[2]
(e) Ammonium nitrate, $NH_4NO_3$, is a fertiliser.
Calculate the percentage by mass of nitrogen in ammonium nitrate.
....................................................................................................................%
[2]

Zinc is manufactured from zinc blende. Zinc blende is an ore which consists mainly of zinc sulfide, ZnS.

(a) Zinc blende is roasted in air. One of the products is zinc oxide.

Name the other product formed in this reaction.
............................................................................................................................................... [1]

(b) Zinc oxide is then converted into zinc.

Zinc oxide and coke, a source of carbon, are heated in a furnace. Hot air is blown into the furnace.

(i) Give two reasons why coke is needed.

1 ................................................................................................................................................................
2 ................................................................................................................................................................[2]

(ii) Write a chemical equation for the formation of zinc in the furnace.
............................................................................................................................................... [1]

(iii) Zinc has a melting point of 420°C and a boiling point of 907°C. The temperature inside the furnace is 1200°C.

Explain how this information shows that the zinc produced inside the furnace is a gas.
............................................................................................................................................... [1]

(iv) The gaseous zinc is converted to molten zinc.

Name this change of state.
............................................................................................................................................... [1]

(c) Zinc reacts with dilute sulfuric acid to produce aqueous zinc sulfate.

$$ \text{Zn(s) + H}_2\text{SO}_4\text{(aq)} \rightarrow \text{ZnSO}_4\text{(aq)} + \text{H}_2\text{(g)} $$

Hydrated zinc sulfate crystals are made from aqueous zinc sulfate.

Step 1 Solid zinc is added to dilute sulfuric acid until zinc is in excess.
Step 2 Excess zinc is separated from aqueous zinc sulfate by filtration.
Step 3 Aqueous zinc sulfate is heated until the solution is saturated.
Step 4 The saturated solution is allowed to cool and crystallise.
Step 5 The crystals are removed and dried.

(i) Name the residue in step 2.
............................................................................................................................................... [1]

(ii) In step 3, a saturated solution is produced. Describe what a saturated solution is.
................................................................................................................................................................
................................................................................................................................................................[2]

(iii) Name two compounds each of which react with dilute sulfuric acid to produce aqueous zinc sulfate.

1 ................................................................................................................................................................
2 ................................................................................................................................................................ [2]

(d) When hydrated magnesium sulfate crystals, MgSO$_4$·xH$_2$O, are heated they give off water.

$$ \text{MgSO}_4\cdot x\text{H}_2\text{O(s)} \rightarrow \text{MgSO}_4\text{(s)} + x\text{H}_2\text{O(g)} $$

A student carries out an experiment to determine the value of x in MgSO$_4$·xH$_2$O.

Step 1 Hydrated magnesium sulfate crystals were weighed.
Step 2 Hydrated magnesium sulfate crystals were heated.
Step 3 The remaining solid was weighed.

(i) Describe how the student can ensure that all the water is given off.
................................................................................................................................................................
................................................................................................................................................................
................................................................................................................................................................ [2]

(ii) In an experiment, all the water was removed from 1.23 g of MgSO$_4$·xH$_2$O. The mass of MgSO$_4$ remaining was 0.60 g.

$$ M_r: \text{MgSO}_4 = 120; \ M_r: \text{H}_2\text{O} = 18 $$

Determine the value of x using the following steps.

• Calculate the number of moles of MgSO$_4$ remaining.

moles of MgSO$_4$ = ................................

• Calculate the mass of H$_2$O given off.

mass of H$_2$O = ................................ g

• Calculate the moles of H$_2$O given off.

moles of H$_2$O = .................................

• Determine the value of x.

x = ....................................................... [4]

(a) Describe the trend in the reactivity of Group I elements. ............................................................................................................................................................................................. .............................................................................................................................................................................................

(b) When potassium is added to water a chemical reaction occurs.
(i) State two observations that can be made when potassium is added to water. ............................................................................................................................................................................................. ............................................................................................................................................................................................. [2]
(ii) Write a chemical equation for the reaction of potassium with water. .............................................................................................................................................................................................

(c) Excess aqueous potassium iodide is added to chlorine.
(i) Write a chemical equation for the reaction that occurs when aqueous potassium iodide is added to chlorine. .............................................................................................................................................................................................
(ii) State the final colour of the reaction mixture. .............................................................................................................................................................................................

(d) Sodium is extracted from sodium chloride by electrolysis.
(i) State the meaning of the term electrolysis. ............................................................................................................................................................................................. .............................................................................................................................................................................................
(ii) State what must be done to sodium chloride before it can be electrolysed to produce sodium. .............................................................................................................................................................................................
(iii) Write an ionic half-equation for the change that occurs at the cathode during this electrolysis. .............................................................................................................................................................................................

(e) Chromium is a transition element.
• Chromium has a high melting point.
• Chromium is a good conductor of electricity.
• Many chromium compounds are soluble in water.
• Hydrated chromium(III) sulfate is green.
• Chromium forms the chlorides CrCl$_2$ and CrCl$_3$.
• Oxides of chromium act as catalysts in the manufacture of poly(ethene).
(i) Use this information to give two properties of chromium which are different from properties of Group I elements such as sodium.
1 .............................................................................................................................................................................................
2 .............................................................................................................................................................................................
(ii) Use this information to give two properties of chromium which are similar to properties of Group I elements such as sodium.
1 .............................................................................................................................................................................................
2 .............................................................................................................................................................................................

(a) A carboxylic acid and an ester are structural isomers.

(i) State the meaning of the term structural isomers.   [2]

(ii) Draw the structures of the carboxylic acid and the ester which both contain two carbon atoms.

Show all of the atoms and all of the bonds.

Name the carboxylic acid and the ester.   [4]

(b) Part of a polyester chain is shown. This polyester is made from one monomer.

(i) On the diagram draw a ring around one unit of the polymer that is repeated. [1]

(ii) Name the type of polymerisation that produces polyesters.   [1]

(iii) Complete the diagram to show the structure of the monomer used to produce this polyester.

Show all of the atoms and all of the bonds in the functional groups.  [2]

(c) A polyamide is made from the two monomers shown.

Complete the diagram to show a section of the polyamide made from the two monomers.

Show all of the atoms and all of the bonds in the linkages.   [2]

(d) Naturally occurring polyamides are constituents of food.

(i) State the name given to naturally occurring polyamides. [1]

(ii) Name the monomers which form naturally occurring polyamides.   [1]