Cambridge IGCSE Chemistry - 0620 - Core Paper 3 2015 Winter Zone 1

The structures of six compounds are shown below.

Answer the following questions about these substances. Each compound may be used once, more than once or not at all.
(a) Which substance, A, B, C, D, E or F,
(i) gives a white precipitate on addition of an aqueous solution of sodium sulfate, ............................... [1]
(ii) is a component of many fertilisers, ............................... [1]
(iii) contains a Group III element, ............................... [1]
(iv) is an acidic gas at room temperature, ............................... [1]
(v) turns anhydrous cobalt chloride pink, ............................... [1]
(vi) is the main component of natural gas? ............................... [1]


(b) Compound A can be made by direct combination of chlorine and aluminium using the apparatus shown below.

(i) On the diagram above, draw an arrow to show where heat is applied. [1]
(ii) Suggest one safety precaution that should be taken when carrying out this experiment. ........................................................................................................................... [1]
(iii) Complete the symbol equation for this reaction. $$2Al + .......Cl_2 \rightarrow Al_2Cl_6$$ [1]

A student measures the maximum temperature changes when five different solids, P, Q, R, S and T, are dissolved separately in water. She uses the apparatus shown below.



(a) The student stirs the mixture as each solid is added.
Suggest why she does this.
..........................................................................................................................
.......................................................................................................................... [1]

(b) Suggest two factors which should be kept the same to make the experiment a fair test.
1. ........................................................................................................................
2. ........................................................................................................................ [2]

(c) The table of results is shown below.

[Table_1]

(i) Which solid gave the greatest temperature change when dissolved in water?
.......................................................................................................................... [1]

(ii) Which solids gave an endothermic energy change when dissolved in water?
............................................................ and ............................................................ [2]

(d) Radioactive isotopes can be used as a source of energy.

(i) Which one of the following isotopes is a radioactive isotope?
Put a ring around the correct answer.
$$^{12}_{6}C \quad ^{235}_{92}U \quad ^{1}_{1}H \quad ^{65}_{30}Zn$$ [1]

(ii) An isotope of radium, Ra, has 226 nucleons in its nucleus.
How many neutrons does this isotope contain?
Use your Periodic Table.
.......................................................................................................................... [1]

(iii) Give one use of radioactive isotopes in medicine.
.......................................................................................................................... [1]

(e) Fractions obtained from the distillation of petroleum are also sources of energy.

(i) Which one of the following fractions is used as a fuel for jet aircraft?
Put a ring around the correct answer.
bitumen\quad gasoline\quad kerosene\quad naphtha [1]

(ii) Heptadecane, $C_{17}H_{36}$, is present in the fuel oil fraction.
Complete the equation for the cracking of heptadecane to form two hydrocarbons.
$$C_{17}H_{36} \rightarrow C_{12}H_{26} + \text{..................}$$ [1]

(a) Nickel is extracted from nickel(II) oxide, NiO, by heating with carbon.
Complete the symbol equation for this reaction.
.....NiO + C → 2Ni + .............. [2]

(b) Nickel is refined by electrolysis.
(i) Complete the boxes to label the diagram below to show
• the negative electrode (cathode),
• the positive electrode (anode),
• the electrolyte. [2]
(ii) At which electrode is the pure nickel formed?
........................................................................................................ [1]

(c) Molten nickel(II) chloride can be electrolysed using graphite electrodes.
(i) Predict the products of this electrolysis at
the positive electrode (anode), ............................................................
the negative electrode (cathode). .................................................... [2]
(ii) Give two reasons why graphite is used for electrodes.
1. .......................................................................................................
2. ....................................................................................................... [2]

(d) The structures of diamond and graphite are shown below.
(i) Explain how the structure of diamond relates to its use in cutting hard materials.
............................................................................................................
............................................................................................................
............................................................................................................ [2]
(ii) Explain how the structure of graphite relates to its use as a lubricant.
............................................................................................................
............................................................................................................
............................................................................................................ [2]

A teacher demonstrated the reactivity of calcium with water. He used the apparatus shown below.

(a) The teacher measured the volume of gas given off at various times during the reaction. He then repeated the experiment using strontium but keeping all the conditions the same. The graph obtained from the results is shown below.

(i) Explain how the graph shows that strontium is more reactive than calcium.
....................................................................................................................................
.................................................................................................................................... [1]
(ii) For the reaction between calcium and water, deduce the volume of gas produced in the first 50 seconds.
.................. cm³ [1]
(iii) At what time was the reaction between strontium and water complete?
.................. s [1]
(iv) How do you know from the graph that the reaction between calcium and water was not complete 100 seconds after the reaction started?
....................................................................................................................................
.................................................................................................................................... [1]
(v) Suggest how the rate of reaction changes when the same mass of calcium is used but in smaller pieces.
....................................................................................................................................
.................................................................................................................................... [1]
(b) The solution formed at the end of the reaction between strontium and water is alkaline. It is a solution of strontium hydroxide. The teacher titrated this solution with hydrochloric acid using the apparatus shown below.

(i) What piece of apparatus should be used to put exactly 25.0 cm³ of the strontium hydroxide solution into the flask?
.................................................................................................................................... [1]
(ii) A few drops of litmus solution was added to the flask.
Explain why litmus is added to the flask and describe what happens to the litmus as the titration proceeds.
....................................................................................................................................
....................................................................................................................................
.................................................................................................................................... [2]
(c) The graph below shows how the pH of the solution in the flask changes as the acid is added.

(i) Describe how the pH of the solution changes as the titration proceeds.
....................................................................................................................................
....................................................................................................................................
.................................................................................................................................... [3]
(ii) What volume of acid had been added when the solution had a neutral pH?
.................................................................................................................................... [1]
(iii) The symbol equation for the reaction is
Sr(OH)₂ + 2HCl → SrCl₂ + 2H₂O
Give the name of the salt formed in this reaction.
.................................................................................................................................... [1]

A student left a cube of ice on a plate in a warm room. The diagrams below show what happened to the ice.

(a) Describe and explain what happened to the ice. In your answer,
• describe and explain the change of state which occurs,
• explain this change using the kinetic particle theory.
....................................
....................................
....................................
....................................
....................................
[5]
(b) Water is used in industry and in the home.
(i) Give one use of water in industry.
....................................
[1]
(ii) Give one use of water in the home.
....................................
[1]
(c) The symbol equation for the reaction of lithium with water is shown below.
$$2\text{Li}(s) + 2\text{H}_2\text{O}(l) \rightarrow 2\text{LiOH}(aq) + \text{H}_2(g)$$
(i) Write the word equation for this reaction.
....................................
[1]
(ii) Describe two observations which can be made when lithium reacts with water.
....................................
....................................
[2]
(iii) Describe how the reactivity of potassium with water compares with the reactivity of lithium with water.
....................................
[1]
(d) Ethanol can be made by the reaction of steam with ethene.
(i) Draw the structure of ethene showing all atoms and all bonds.

[1]
(ii) Describe the conditions required for this reaction
....................................
[2]
(e) The table below describes the reaction of water or steam with different metals.
[Table_1]
Put these metals in order of their reactivity.
least reactive _______________________ most reactive

[2]

When rubber is distilled, a chemical called isoprene is formed. The structure of isoprene is shown below.

(a) Deduce the molecular formula of isoprene.
................................................................................................................. [1]
(b) Isoprene is an unsaturated compound.
Describe a test for an unsaturated compound.
test ..........................................................................................................................................
result ........................................................................................................................................ [2]
(c) Isoprene forms an addition polymer.
(i) What feature of the isoprene molecule is responsible for it forming an addition polymer?
................................................................................................................. [1]
(ii) Give the name of another addition polymer.
................................................................................................................. [1]
(d) Isoprene does not conduct electricity.
Explain why.
................................................................................................................. [1]
(e) State the names of two substances formed when isoprene undergoes incomplete combustion.
.................................................. and .................................................. [2]
(f) Isoprene can be prepared from 3-methylbutan-1-ol.
To which group of compounds does 3-methylbutan-1-ol belong?
Tick one box.
alcohols []
alkanes []
alkenes []
carboxylic acids [] [1]

(a) Sodium is in Group I of the Periodic Table.

Describe the structure of a sodium atom. In your answer refer to,
• the type and number of each subatomic particle present,
• the charges on each type of subatomic particle,
• the position of each type of subatomic particle in the atom.
............................................................................................................................................
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............................................................................................................................................
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............................................................................................................................................ [5]

(b) Sodium carbide, $\text{Na}_2\text{C}_2$, reacts with water to form ethyne, $\text{C}_2\text{H}_2$.

(i) Complete the symbol equation for this reaction.

$\text{Na}_2\text{C}_2 + ....... \text{H}_2\text{O} \rightarrow ....... \text{NaOH} + \text{C}_2\text{H}_2$ [2]

(ii) Ethyne is a hydrocarbon.

What is the meaning of the term \textit{hydrocarbon}?
............................................................................................................................................ [1]

(iii) Calculate the relative formula mass of sodium carbide.
............................................................................................................................................ [1]