Cambridge IGCSE Chemistry - 0620 - Core Paper 3 2013 Summer Zone 2

The structures of five substances, A, B, C, D and E, are shown below.
[Images showing substances A, B, C, D, E]
(a) Answer the following questions about these substances. Each substance may be used once, more than once or not at all.
(i) Which two substances are elements? ............. and .............
(ii) Which substance has a giant covalent structure? .............
(iii) Which substance turns damp red litmus blue? .............
(iv) Which substance is a product of fermentation? .............
(v) Which substance is used as a lubricant? ............. [6]
(b) Complete the following sentences about compounds using words from the list below.
atom combined copper covalent ionic metals molecules separated
A compound is a substance containing two or more types of ........................ chemically ........................ .
Compounds such as water and sulfur dioxide exist as simple ........................ .
Others, such as sodium chloride, are giant ........................ structures. [4]

(a) Describe the general trend in density of the transition elements across Period 4. ............................................................................................................................................... [1]

(b) Suggest a value for the density of vanadium, V. ............................................................................................................................................... [1]

(c) Many transition elements and their compounds are catalysts. What is the meaning of the term catalyst? ............................................................................................................................................... [1]

(d) Describe three properties of transition metals, apart from catalytic activity, which make them different from Group I metals.
1. ...............................................................................................................................................
2. ...............................................................................................................................................
3. ............................................................................................................................................... [3]

(e) Iron reacts with steam to form an oxide with the formula $Fe_3O_4$. Complete the symbol equation for this reaction.
.......$Fe(s)$ + .......$H_2O(g)$ → $Fe_3O_4(s)$ + $4H_2(g)$ [2]

(f) Iron reacts with sulfuric acid. Complete the word equation for this reaction.
iron + sulfuric acid → ............................... + ...............................
............................... [2]

The concentration of alkali in a solution can be determined from the results of a titration. The apparatus used is shown below.

(a) State the name of each of these pieces of apparatus.
A ....................................................
B ....................................................
C ....................................................
D ....................................................
[4]

(b) The graph below shows how the pH changes when an alkali is neutralised by an acid.

(i) What is the pH of the alkali at the start of the experiment?
pH = .................... [1]
(ii) What volume of acid has been added when the pH is 12?
.................... cm$^3$ [1]
(iii) What is the value of the pH when the solution is neutral? Put a ring around the correct answer.
pH 0 pH 5 pH 7 pH 9 pH 14 [1]

(c) (i) Which two of the following compounds could a farmer use to control the pH of soils which are too acidic?
Tick two boxes.
aluminium chloride [ ]
calcium carbonate [ ]
calcium oxide [ ]
copper sulfate [ ]
potassium chloride [ ]
[2]
(ii) Explain why farmers need to control the pH of soils which are too acidic.
........................................................
........................................................ [1]

Methane belongs to the alkane homologous series.

(a) (i) Draw the structure of methane showing all atoms and bonds. [1]

(ii) State the name of \text{one} other member of the alkane homologous series.
................................................................................................................... [1]

(iii) Methane is an atmospheric pollutant.
Give \text{one} natural source of methane in the atmosphere.
................................................................................................................... [1]

(iv) Methane burns in excess oxygen to form carbon dioxide and water.
Complete the symbol equation for this reaction.
$$\text{CH}_4 + \text{........O}_2 \rightarrow \text{....... + } 2\text{H}_2\text{O}$$ [2]

(b) (i) In an oil refinery, hydrocarbons are separated into different fractions. On what physical property does this fractionation depend?
................................................................................................................... [1]

(ii) Match the fraction on the left with the use of the fraction on the right. The first one has been done for you.



gasoline - fuel for lorries
diesel - fuel for cars
fuel oil - fuel for ships
kerosene - making chemicals
naphtha - fuel for jet aircraft [4]

Clean air is a mixture of gases.
(a) State the composition of clean air and describe how it gets polluted by gases such as sulfur dioxide, carbon monoxide and oxides of nitrogen.
In your answer, include
• the names and percentages of the two main gases present in clean air,
• the source of each of the pollutant gases named above.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................ [5]

(b) Lead is an atmospheric pollutant. It is extracted by heating ores containing lead sulfide.
(i) The structure of lead sulfide is shown below.

Deduce the simplest formula for lead sulfide.
............................................................................................................................ [1]

(ii) The last stage in extracting lead involves reducing lead(II) oxide with carbon.
$$ ext{PbO + C → Pb + CO}$$
How does this equation show that lead oxide gets reduced?
............................................................................................................................ [1]

(c) Dichloroethane used to be added to petrol to prevent the build-up of lead deposits in car engines.
The structure of dichloroethane is shown below.

(i) Dichloroethane is a liquid.
Describe the arrangement and closeness of the particles in a liquid.
arrangement ...................................................................................................
closeness ...................................................................................................... [2]

(ii) Deduce the molecular formula for dichloroethane.
............................................................................................................................ [1]

(iii) Calculate the relative molecular mass of dichloroethane. You must show all your working.
............................................................................................................................ [2]

(a) The table below describes the reaction of some metals with water.

[Table_1]

Put these metals in order of their reactivity.
least reactive ___________________ most reactive [2]

(b) The list below shows part of the reactivity series.

potassium
sodium
aluminium
carbon
increasing
reactivity
zinc
iron

Give the names of two metals from this list that can be extracted from their oxide ores by heating with carbon.
_______________________________ and _______________________________ [1]

(c) A magnesium atom has 12 electrons.
(i) Complete the diagram below to show the electronic structure of an atom of magnesium. [2]



(ii) An isotope of magnesium has a nucleon number (mass number) of 26. Deduce the number of neutrons in one atom of this isotope of magnesium. [1]
_______________________________________________

The table shows some properties of sulfur, sucrose (sugar) and zinc chloride.

[Table]

The table contents:
property | sulfur | sucrose | zinc chloride
state at room temperature | solid | solid | solid
solubility in water | insoluble | soluble | soluble
electrical conductivity of aqueous solution | does not conduct | conducts
structure | molecular | molecular | ionic

(a) Suggest why an aqueous solution of zinc chloride conducts electricity.
............................................................................................................................. [1]

(b) Suggest why an aqueous solution of sucrose does not conduct electricity.
............................................................................................................................. [1]

(c) Suggest how you could separate a mixture of solid sucrose and solid sulfur.
.............................................................................................................................
.............................................................................................................................
............................................................................................................................. [2]

(d) Molten zinc chloride can be electrolysed using the apparatus shown below.



(i) Which one of the letters, A, B, C or D, represents the cathode?
............................................................................................................................. [1]

(ii) Which one of the following substances is the most suitable for use as an electrode in this electrolysis?
Put a ring around the correct answer.
copper graphite sodium sulfur [1]

(iii) Predict the products of the electrolysis of molten zinc chloride at
the negative electrode, ...........................................................................................
the positive electrode. ........................................................................................... [2]

(iv) Describe a test for chloride ions.
test ........................................................................................................................
result ........................................................................................................................ [3]

A student placed a spoonful of sugar in the bottom of a glass of cold tea and left it undisturbed for several minutes. After 2 minutes, she used a straw to taste some of the tea from the top of the glass. It did not taste sweet. After 10 minutes, the sugar had disappeared and the solution at the top of the glass tasted sweet.



(a) Use the kinetic particle theory to explain these observations.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
........................................................................................................................... [4]

(b) Glucose is a sugar. The structure of a glucose molecule is shown below.



(i) How many different types of atom are there in one molecule of glucose?
........................................................................................................................... [1]

(ii) How many hydrogen atoms are there in one molecule of glucose?
........................................................................................................................... [1]

(iii) On the diagram of the glucose molecule above, put a ring around an alcohol functional group.
......................................................................................................................... [1]

(iv) Glucose is oxidised in the body by a process called respiration. Complete the word equation for respiration.

glucose + oxygen → ............................. + water
.............................
........................................................................................................................... [1]

(v) When glucose solution is fermented, ethanol is produced. Describe how you would carry out fermentation in the laboratory.
.........................................................................................................................
.........................................................................................................................
......................................................................................................................... [2]

(vi) State one use of ethanol other than in alcoholic drinks.
........................................................................................................................... [1]