Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2012 Winter Zone 1

A list of techniques used to separate mixtures is given below.

filtration
diffusion
fractional distillation
simple distillation
crystallisation
chromatography

From this list, choose the most suitable technique to separate the following mixtures.
A technique may be used once, more than once or not at all.

(a) butane from a mixture of propane and butane .................................................. [1]
(b) oxygen from liquid air .............................................................................. [1]
(c) water from aqueous magnesium sulfate ............................................... [1]
(d) potassium chloride from aqueous potassium chloride ........................ [1]
(e) silver chloride from a mixture of silver chloride and water ..................... [1]
(f) glucose from a mixture of glucose and maltose ................................... [1]

Three of the halogens in Group VII are listed below.

chlorine
bromine
iodine

(a) (i) How does their colour change down the Group?
................................................................................................................. [1]

(ii) How do their melting points and boiling points change down the Group?
................................................................................................................. [1]

(iii) Predict the colour and physical state (solid, liquid or gas) of astatine, At.
colour ...........................................................................................................
physical state .............................................................................................. [2]

(b) A radioactive isotope of iodine, $^{131}_{53}I$, is used to treat cancer.

(i) Define the term isotope.
........................................................................................................................
........................................................................................................................ [2]

(ii) How many protons, electrons and neutrons are there in one atom of $^{131}_{53}I$?
number of protons .............
number of electrons ............
number of neutrons ............. [2]

(iii) When this isotope, $^{131}_{53}I$, emits radiation, a different element with a proton number of 54 is formed.
What is the name of this element?
........................................................................................................................ [1]

(c) Fluorine, the most reactive halogen, forms compounds with the other halogens. It forms two compounds with bromine.
Deduce their formulae from the following information.

compound 1
The mass of one mole of this compound is 137 g.
Its formula is .................................. [1]

compound 2
0.02 moles of this compound contain 0.02 moles of bromine atoms and 0.1 moles of fluorine atoms.
Its formula is .................................. [1]

(a) Reaction speed increases as the temperature increases.
(i) Explain why reaction speed increases with temperature.
..........................................................
.........................................................
.........................................................

(ii) Reactions involving enzymes do not follow the above pattern. The following graph shows how the speed of such a reaction varies with temperature.

Suggest an explanation why initially the reaction speed increases then above a certain temperature the speed decreases.
..........................................................
.........................................................

(b) An organic compound decomposes to give off nitrogen.
$$C_6H_5N_2Cl(aq) \rightarrow C_6H_5Cl(l) + N_2(g)$$
The speed of this reaction can be determined by measuring the volume of nitrogen formed at regular intervals. Typical results are shown in the graph below.

(i) The reaction is catalysed by copper. Sketch the graph for the catalysed reaction on the diagram above. [2]
(ii) How does the speed of this reaction vary with time?
........................................................... [1]
(iii) Why does the speed of reaction vary with time?
...........................................................
........................................................... [2]

(c) Catalytic converters reduce the pollution from motor vehicles.

(i) Describe how carbon monoxide and the oxides of nitrogen are formed in car engines.
...........................................................
...........................................................
...........................................................
........................................................... [4]
(ii) Describe the reaction(s) inside the catalytic converter which change these pollutants into less harmful gases. Include at least one equation in your description.
...........................................................
...........................................................
........................................................... [3]

Silicon(IV) oxide, SiO₂, and zirconium(IV) oxide, ZrO₂, are both macromolecules.
They have similar physical properties but silicon(IV) oxide is acidic and zirconium(IV) oxide is amphoteric.
(a) Define the term macromolecule.
...........................................................................................................................
........................................................................................................................... [1]
(b) (i) Predict three physical properties of these two oxides.
...........................................................................................................................
...........................................................................................................................
........................................................................................................................... [3]
(ii) Name an element which has the same physical properties as these two oxides.
........................................................................................................................... [1]
(c) (i) Name a reagent that reacts with the oxides of both elements.
........................................................................................................................... [1]
(ii) Name a reagent that reacts with only one of the oxides.
reagent .................................................................................................
oxide which reacts .............................................................................. [2]

Carbonyl chloride, $COCl_2$, is widely used in industry to make polymers, dyes and pharmaceuticals.
(a) Carbonyl chloride was first made in 1812 by exposing a mixture of carbon monoxide and chlorine to bright sunlight. This is a photochemical reaction.
$$CO(g) + Cl_2(g) \rightarrow COCl_2(g)$$
(i) Explain the phrase photochemical reaction.
..........................................................................................................................
................................................................................................................. [2]
(ii) Give another example of a photochemical reaction and explain why it is important either to the environment or in industry.
..........................................................................................................................
..........................................................................................................................
................................................................................................................. [3]
(b) Carbonyl chloride is now made by the reversible reaction given below.
$$CO(g) + Cl_2(g) \rightleftharpoons COCl_2(g)$$
The forward reaction is exothermic. The reaction is catalysed by carbon within a temperature range of 50 to 150 $\degree$C.
(i) Predict the effect on the yield of carbonyl chloride of increasing the pressure.
Explain your answer.
..........................................................................................................................
................................................................................................................. [2]
(ii) If the temperature is allowed to increase to above 200 $\degree$C, very little carbonyl chloride is formed. Explain why.
..........................................................................................................................
................................................................................................................. [2]
(iii) Explain why a catalyst is used.
................................................................................................................. [1]
(c) The structural formula of carbonyl chloride is given below.

Draw a diagram showing the arrangement of the outer (valency) electrons in one molecule of this covalent compound.
Use $\circ$ to represent an electron from a carbon atom.
Use $\times$ to represent an electron from a chlorine atom.
Use $\bullet$ to represent an electron from an oxygen atom. [3]

A sandwich contains three of the main constituents of food.

(a) (i) These constituents of food can be hydrolysed by boiling with acid or alkali. Complete the table.

[Table_1]
constituent of food | product of hydrolysis
protein |
fat |
complex carbohydrate |
[3]
(ii) What type of synthetic polymer contains the same linkage as
fats, ..................................................
proteins? ..................................................
[2]
(b) An incomplete structural formula of a protein is given below. Complete this diagram by inserting the linkages.


insert linkage
insert linkage
[2]
(c) Butter contains mainly saturated fats. Fats based on vegetable oils, such as olive oil, contain mainly unsaturated fats.

A small amount of fat was dissolved in an organic solvent. Describe how you could determine if the fat was saturated or unsaturated.
..........................................................................................................................................................................................
..........................................................................................................................................................................................
..........................................................................................................................................................................................
[3]

Both strontium and sulfur have chlorides of the type $XCl_2$. The table below compares some of their properties.

[Table_1]

(a) (i) Use the data in the table to explain why sulfur chloride is a liquid at room temperature, 25°C.
..........................................................................................................................................
.......................................................................................................................................... [2]

(ii) Strontium is a metal and sulfur is a non-metal. Explain why both have chlorides of the type $XCl_2$.
The electron distribution of a strontium atom is $2 + 8 + 18 + 8 + 2$.
..........................................................................................................................................
.......................................................................................................................................... [2]

(iii) Deduce the name of the acidic compound formed when sulfur chloride reacts with water.
.......................................................................................................................................... [1]

(iv) Explain the difference in the electrical conductivity of liquid strontium chloride and liquid sulfur chloride.
..........................................................................................................................................
..........................................................................................................................................
.......................................................................................................................................... [3]

(b) Strontium chloride-6-water can be made from the insoluble compound, strontium carbonate, by the following reactions.

$$\begin{align} \text{SrCO}_3(s) + 2\text{HCl}(aq) & \rightarrow \text{SrCl}_2(aq) + \text{CO}_2(g) + \text{H}_2O(l) \\ \text{SrCl}_2 (aq) + 6\text{H}_2O(l) & \rightarrow \text{SrCl}_2.6\text{H}_2O(s) \end{align}$$

The following method was used to prepare the crystals.

1 Add excess strontium carbonate to hot hydrochloric acid.
2 Filter the resulting mixture.
3 Partially evaporate the filtrate and allow to cool.
4 Filter off the crystals of $\text{SrCl}_2.6\text{H}_2O$.
5 Dry the crystals between filter papers.

(i) How would you know when excess strontium carbonate had been added in step 1?
..........................................................................................................................................
.......................................................................................................................................... [1]

(ii) Why is it necessary to filter the mixture in step 2?
.......................................................................................................................................... [1]

(iii) In step 3, why partially evaporate the filtrate rather than evaporate to dryness?
.......................................................................................................................................... [1]

(c) In the above experiment, $50.0cm^3$ of hydrochloric acid of concentration $2.0mol/dm^3$ was used. $6.4g$ of $\text{SrCl}_2.6\text{H}_2O$ was made. Calculate the percentage yield.

number of moles of $\text{HCl}$ used = .........................................
number of moles of $\text{SrCl}_2.6\text{H}_2O$ which could be formed = .........................................
mass of one mole of $\text{SrCl}_2.6\text{H}_2O$ is $267g$
theoretical yield of $\text{SrCl}_2.6\text{H}_2O$ = .........................................g
percentage yield = .........................................%

.......................................................................................................................................... [4]