Cambridge IGCSE Chemistry - 0620 - Core Paper 3 2018 Winter Zone 2

(a) The electronic structures of five atoms, A, B, C, D and E, are shown.



Answer the following questions about these structures. Each structure may be used once, more than once or not at all. State which structure, A, B, C, D or E, represents:
(i) an atom in Group VIII of the Periodic Table ............................................................... [1]
(ii) an atom of a reactive non-metal ............................................................... [1]
(iii) an atom with a proton number of 11 ............................................................... [1]
(iv) an atom with only three shells of electrons ............................................................... [1]
(v) an atom which forms a stable ion with a single positive charge .................................. [1]

(b) Complete the table to show the number of electrons, neutrons and protons in the nitrogen atom and chromium ion shown.

[Table_1]

$$\begin{array}{|c|c|c|c|} \hline & \text{number of} & \text{number of} & \text{number of} \\ & \text{electrons} & \text{neutrons} & \text{protons} \\ \hline \phantom{^{15}_7}N^{15}_7 & 7 & \text{.....................} & \text{.....................} \\ \hline \phantom{^{52}_{24}}Cr^{2+}_{52,24} & \text{.....................} & 28 & \text{.....................} \\ \hline \end{array}$$ [3]

(a) The table shows the concentrations of the ions present in a solution obtained from cells in the body.

[Table_1]

Answer these questions using only information from the table.

(i) Which negative ion is present in the highest concentration?
.............................................................................................................................. [1]

(ii) Calculate the mass of potassium ions present in 250 cm³ of this solution.

mass of potassium ions = .............................. mg [1]

(iii) Calculate the total mass of positive ions present in 1000 cm³ of this solution.

total mass of positive ions = .............................. mg [1]

(iv) Give the name of the compound formed from Na⁺ and HCO₃^- ions.
.............................................................................................................................. [1]

(b) Describe what is observed in these two reactions.

• An excess of aqueous sodium hydroxide is added to a solution containing Ca²⁺ ions.
.........................................................................................................................

• An excess of aqueous ammonia is added to a solution containing Ca²⁺ ions.
......................................................................................................................... [2]

(c) Lactic acid can build up in muscle cells during exercise.
The structure of lactic acid is shown.



(i) On the structure, draw a circle around the carboxylic acid functional group. [1]

(ii) Deduce the molecular formula of lactic acid showing the number of carbon, hydrogen and oxygen atoms.
.............................................................................................................................. [1]

(d) Lactic acid can form a polymer.
Complete the sentence about polymers using words from the list.

atomic large molecular monomers polymers small

During polymerisation .............................. molecules called .............................. join together to form long-chain molecules with a very high relative .............................. mass. [3]

(a) The table gives information about the solubility of copper and selenium in an organic solvent and in water. The organic solvent boils at 30°C.

[Table]

(i) Use the information in the table to suggest how you could obtain pure, dry samples of copper and selenium from a mixture of copper powder and selenium powder.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
................................................................................................................................. [4]

(ii) Ethanol is an organic solvent.
Draw the structure of ethanol. Show all of the atoms and all of the bonds.

[Image]

[2]

(iii) Selenium reacts with fluorine to form selenium(VI) fluoride.
Balance the chemical equation for this reaction.
$\text{Se} + .....\text{F}_2 \rightarrow \text{SeF}_6$ [1]

(b) The chemical equation for the reaction of copper with hot concentrated sulfuric acid is shown.
$\text{Cu} + 2\text{H}_2\text{SO}_4 \rightarrow \text{CuSO}_4 + \text{SO}_2 + 2\text{H}_2\text{O}$

(i) Complete the word equation for this reaction.
[Image]

[2]

(ii) One of the compounds in this equation is a pollutant gas which contributes to acid rain.
Identify the pollutant gas and state a common source of it.
pollutant gas ...............................................................................................................
source ............................................................................................................................ [2]

(c) Solid hydrated copper(II) sulfate decomposes to anhydrous copper(II) sulfate when it is continuously heated.
Is this an endothermic or an exothermic reaction? Explain your answer.
........................................................................................................................................
........................................................................................................................................ [1]

This question is about acids.
(a) The structure of fumaric acid is shown.

Fumaric acid is an unsaturated compound.
(i) What feature of the structure of fumaric acid shows that it is unsaturated?
.......................................................................................................................................................... [1]
(ii) Describe a test for an unsaturated compound.
test ...............................................................................................................................................
result ............................................................................................................................................. [2]

(b) Hydriodic acid can be used for the reduction of some carboxylic acids.
(i) What is meant by the term \textit{reduction}?
.......................................................................................................................................................... [1]
(ii) Hydriodic acid is oxidised by oxygen.
Balance the chemical equation for this reaction.
......HI + O$_{2}$ \rightarrow 2H$_{2}$O + ......I$_{2}$ [2]
(iii) What percentage of clean, dry air is oxygen?
......................................................................................................................................... [1]

(c) The concentration of a dilute acid can be found by reacting it with aqueous sodium hydroxide using the apparatus shown.

(i) What piece of apparatus should be used to add exactly 25.0cm$^{3}$ of dilute acid to the conical flask?
.......................................................................................................................................................... [1]
(ii) A few drops of litmus solution are added to the conical flask.
Explain why litmus solution is added to the conical flask.
.........................................................................................................................................
......................................................................................................................................... [1]
(iii) Aqueous sodium hydroxide is then added to the dilute acid until it is in excess.
Describe the change in the colour of the litmus solution in the conical flask.
from ..................................................... to .............................................................. [2]

Bromine is a volatile liquid. Potassium bromide is a compound made from bromine.
(a) Use the kinetic particle model to describe the arrangement and motion of the particles in bromine when it is:
• a liquid
....................................................................................................................................................
....................................................................................................................................................
• a gas
....................................................................................................................................................
....................................................................................................................................................

(b) Molten potassium bromide can be electrolysed using the apparatus shown.

(i) On the diagram, label:
• the anode
• the electrolyte
[2]
(ii) Predict the products of this electrolysis at:
the positive electrode ..........................................................................................................................
the negative electrode .........................................................................................................................
[2]
(iii) Give one observation that is made at the positive electrode.
.................................................................................................................................................... [1]
(iv) Suggest why the electrodes are made of graphite and not of magnesium.
.................................................................................................................................................... [1]

(c) Aqueous potassium bromide reacts with aqueous chlorine.
(i) Complete the word equation for this reaction.
potassium bromide + chlorine → .......................... + .......................... [2]
(ii) Using ideas about the reactivity of the halogens, explain why aqueous potassium bromide does not react with aqueous iodine.
....................................................................................................................................................
.................................................................................................................................................... [1]
(iii) Describe what you would observe when aqueous silver nitrate is added to aqueous potassium bromide.
.................................................................................................................................................... [2]

(a) The diagrams show the structures of four substances, R, S, T and U.
[Image_1: Diagrams of substances R, S, T and U]
State which one of these substances, R, S, T or U:
(i) is an element $= \text{........................}$ [1]
(ii) contains ionic bonds $= \text{........................}$ [1]
(iii) is a gas at room temperature $= \text{........................}$ [1]
(iv) is a polymer $= \text{........................}$ [1]

(b) Ammonium chloride is present in some fertilisers.
Which two of the following compounds are also present in many fertilisers?
Tick two boxes.
[ ] hydrogen sulfide
[ ] calcium phosphate
[ ] copper(II) fluoride
[ ] nickel(II) oxide
[ ] potassium nitrate [2]

(c) A mixture of ammonium chloride and aqueous sodium hydroxide is heated as shown.
[Image_2: Diagram of apparatus]
The filter paper changes colour from red to yellow. Explain why.
............................................................................................................
............................................................................................................ [2]

(a) The graph shows the effect of temperature on the rate of reaction of dilute hydrochloric acid with zinc powder. temperature / °C
rate of reaction in cm³ gas/minute (i) Determine the rate of reaction at 40 °C.
rate of reaction = ..................... cm³ gas/minute [1] (ii) The experiments were repeated using small lumps of zinc instead of zinc powder. All other conditions were kept the same.
On the grid, draw a graph to show how the rate of reaction changes with temperature when small lumps of zinc are used instead of zinc powder. [2]

(b) What effects do these factors have on the rate of a chemical reaction? (i) decreasing the concentration of a reactant ......................................................................................................................... [1] (ii) adding a catalyst ......................................................................................................................... [1]

(c) Zinc and iron are both metals. Give two physical properties which are characteristic of metals. 1 ......................................................................................................................... 2 ......................................................................................................................... [2]

(d) Stainless steel is an alloy of iron. (i) What is meant by the term alloy? ......................................................................................................................... [1] (ii) Give one common use of stainless steel. ......................................................................................................................... [1]

The table shows the properties of some Group I elements.

[Table_1]

(a) (i) Describe the trend in the relative hardness of the Group I elements.
.................................................................................................................. [1]

(ii) Predict the melting point of rubidium.
.................................................................................................................. [1]

(iii) Explain why it is difficult to predict the density of caesium.
..................................................................................................................
.................................................................................................................. [1]

(b) When potassium reacts with water, it floats and melts into a ball. A flame is observed.

(i) What colour does potassium give to the flame?
.................................................................................................................. [1]

(ii) Use the information in the table to suggest why potassium floats on water.
.................................................................................................................. [1]

(iii) Hydrogen is produced when potassium reacts with water.
Complete the dot-and-cross diagram to show the electron arrangement in a molecule of hydrogen.


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