Cambridge IGCSE Chemistry - 0620 - Core Paper 3 2018 Winter Zone 1

(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 of a metallic element .......................................................... [1]
(ii) an atom with a proton number of 13 ................................................... [1]
(iii) an atom of phosphorus .......................................................... [1]
(iv) an atom with only two shells of electrons ......................................... [1]
(v) an atom which forms a stable ion with a single negative charge. .................. [1]

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

[Table_1]

$$egin{array}{|c|c|c|c|} \hline & \text{number of electrons} & \text{number of neutrons} & \text{number of protons} \\ \hline ^{14}_6\text{C} & 6 & \text{...} & \text{...} \\ \hline ^{40}_{19}\text{K}^+ & \text{...} & 21 & \text{...} \\ \hline \end{array}$$
[3]

(a) The table shows the ions present in a 1000 cm$^3$ sample of blood plasma.

[Table_1]

Answer these questions using only information from the table.
(i) Which positive ion is present in the lowest concentration?
........................................................................................................................................................................ [1]

(ii) Give the name of the compound formed from K$^+$ and Cl$^-$ ions.
........................................................................................................................................................................ [1]

(iii) Calculate the mass of potassium ions present in 200 cm$^3$ of this blood plasma.

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

(iv) When the 1000 cm$^3$ sample of blood plasma is crystallised, several compounds are formed.
Suggest the name of the compound which forms the greatest mass of crystals.
........................................................................................................................................................................ [1]

(b) Describe a test for potassium ions.
test ..........................................................................................................................................................................................
result ........................................................................................................................................................................................ [2]

(c) Blood plasma also contains proteins. Proteins are present in food.
Which one of the following substances is also present in food? Draw a circle around the correct answer.

carbohydrate hematite poly(ethene) terylene [1]

(d) Compound S is one of the monomer units used to make proteins. Its structure is shown.

compound S



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

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

(a) The apparatus used for distillation is shown.

(i) Complete the box to name the apparatus. [1]
(ii) Describe and explain how the water is separated from the aqueous copper(II) sulfate by distillation. [3]
............................................................................................................................................................
............................................................................................................................................................
............................................................................................................................................................
............................................................................................................................................................
............................................................................................................................................................
(b) A sample of solid hydrated copper(II) sulfate is heated gently in a test-tube.
$$\text{CuSO}_4·5\text{H}_2\text{O} \leftrightarrow \text{CuSO}_4 + 5\text{H}_2\text{O}$$
Solid hydrated copper(II) sulfate is blue.
Describe two observations when the sample of solid hydrated copper(II) sulfate is heated gently in a test-tube. [2]
1 ..........................................................................................................................................................
2 ..........................................................................................................................................................

(c) Copper(II) sulfate can be prepared by heating an excess of copper(II) oxide with dilute sulfuric acid.
(i) Complete the chemical equation for this reaction.
$$\text{CuO} + \text{H}_2\text{SO}_4 \rightarrow \text{CuSO}_4 + \text{.....................}$$ [1]
(ii) What method is used to separate the excess copper(II) oxide from the solution? [1]
..........................................................................................................................................................
(d) Copper(II) oxide can be reduced by hydrogen.
$$\text{CuO} + \text{H}_2 \rightarrow \text{Cu} + \text{H}_2\text{O}$$
How does this equation show that copper(II) oxide is reduced? [1]
..........................................................................................................................................................
..........................................................................................................................................................
(e) The chemical equation for the reaction of copper with concentrated nitric acid is shown.
$$\text{Cu} + 4\text{HNO}_3 \rightarrow \text{Cu}(\text{NO}_3)_2 + 2\text{NO}_2 + 2\text{H}_2\text{O}$$
Complete the word equation for this reaction. [2]

(a) The structure of citraconic acid is shown.

Citraconic acid is an unsaturated compound.

(i) What feature of the structure of citraconic acid shows that it is unsaturated?
............................................................................................................................. [1]

(ii) Describe a test for an unsaturated compound.
test .............................................................................................................................
result ........................................................................................................................... [2]

(b) Ethanoic acid has a carboxylic acid functional group.

Draw the structure of the carboxylic acid functional group. Show all of the atoms and all of the bonds. [1]

(c) Complete the definition of a homologous series using words from the list.

chemical   compounds   elements   functional   hydrocarbons   physical

A homologous series is a family of similar ........................... with similar ..........................
properties due to the presence of the same ........................... group. [3]

(d) The graph shows how the pH of a dilute acid in a conical flask changes as aqueous sodium hydroxide is added to it.

(i) Describe how the pH changes as the aqueous sodium hydroxide is added.
.............................................................................................................................
.............................................................................................................................
............................................................................................................................. [2]

(ii) What is the pH of the dilute acid before the aqueous sodium hydroxide is added?
............................................................................................................................. [1]

(iii) What volume of aqueous sodium hydroxide has been added when the pH reaches pH 7?
............................................................................................................................. [1]

(a) Some of the changes of state of water are shown.
[Image_1: Diagram showing ice to water labelled P, water to water vapour labelled Q]
(i) Give the names of the changes of state represented by P and Q.
P .........................................................................................................
Q ......................................................................................................... [2]
(ii) Use the kinetic particle model to describe the separation and motion of the particles in water when it is:
• a liquid
..............................................................................................................
..............................................................................................................
• a vapour
..............................................................................................................
.......................................................................................................... [4]

(b) When lithium reacts with water, hydrogen is produced and the solution formed is alkaline.
(i) Balance the chemical equation for this reaction.
.....Li + .....H$_2$O → 2LiOH + H$_2$ [2]
(ii) Give the name of the product which causes the solution to be alkaline.
.......................................................................................................... [1]

(c) Dilute sulfuric acid can be electrolysed using the apparatus shown.
[Image_2: Diagram showing dilute sulfuric acid with graphite electrodes]
(i) State the products of this electrolysis at:
the positive electrode (anode) .................................................................
the negative electrode (cathode) ........................................................... [2]
(ii) What observation is made at the electrodes?
.......................................................................................................... [1]
(iii) Suggest one reason why graphite is used for the electrodes rather than magnesium.
.......................................................................................................... [1]

(a) The diagrams show the structures of four substances, R, S, T and U.

(i) Which two of these substances, R, S, T or U, are covalently bonded?
.................................................. and ........................................................ [2]
(ii) Which two of these substances, R, S, T or U, conduct electricity when solid?
.................................................. and ........................................................ [2]
(iii) Which substance, R, S, T or U, has the lowest melting point? ....................................... [1]
(iv) Which one of these substances, R, S, T or U, is soluble in water? ............................... [1]

(b) Phosphorus burns in oxygen to form phosphorus(V) oxide.
(i) Balance the chemical equation for this reaction.
$P_4 + 5O_2 \rightarrow .....P_2O_5$ [1]
(ii) Is phosphorus(V) oxide an acidic oxide or a basic oxide?
Give a reason for your answer.
................................................................................................................ [1]
................................................................................................................ [1]

(c) Phosphate ions are present in many fertilisers.
(i) Which one of the following ions is also present in many fertilisers?
Draw a circle around the correct answer.
Ba$^{2+}$ Cu$^{2+}$ F$^-$ NO$_3^-$ [1]
(ii) Why do farmers put fertilisers on their fields?
................................................................................................................ [1]
................................................................................................................ [1]

(a) A student investigates the reaction of calcium carbonate with dilute hydrochloric acid.

$CaCO_3 + 2HCl \rightarrow CaCl_2 + CO_2 + H_2O$

The student measures the mass of the reaction mixture at 10 second intervals using the apparatus shown.



The graph shows the results when 5.0 g of calcium carbonate is added to an excess of dilute hydrochloric acid.



(i) Suggest why the reaction mixture decreases in mass as the reaction proceeds. ......................................................................................................................................... [1]

(ii) Calculate the loss of mass in grams when the reaction is complete.
loss in mass = ........................... g [1]

(iii) The experiment is repeated using dilute hydrochloric acid of twice the concentration. All other conditions are kept the same.

On the grid, draw a graph to show how the mass changes with time using dilute hydrochloric acid of twice the concentration. [2]

(iv) The original experiment is repeated at three different temperatures. All other conditions are kept the same. The three temperatures are 20 °C, 30 °C and 40 °C.

Complete the table by writing the temperatures in the first column.

[Table_1]

temperature in °C initial rate of reaction in g/s
..................................................................
0.16
..................................................................
0.64
..................................................................
0.32
.................................................................. [1]

(b) Complete the sentences about the use of calcium carbonate in the extraction of iron using words from the list.

bauxite dioxide hematite monoxide silicon slag

The main ore of iron is called ........................ . The main impurity in the iron ore is silicon(IV) oxide.
Calcium carbonate added to the blast furnace decomposes to form calcium oxide and carbon ........................ . The calcium oxide reacts with the silicon(IV) oxide to form ........................ . [3]

(a) (i) Calculate the relative formula mass of sodium carbonate, $Na_2CO_3$. Show all your working. Use your Periodic Table to help you.

relative formula mass = ....................................... [2]

(ii) Sodium carbonate can be manufactured by the reaction between limestone and sodium chloride. The reaction is endothermic.

What is meant by the term endothermic?
............................................................................................................................................................... [1]

(iii) During this glass-making process, limestone decomposes into lime (calcium oxide). Lime is used to treat acidic soils.

What type of chemical reaction occurs when lime reacts with acidic soils? Draw a circle around the correct answer.

addition    neutralisation    oxidation    reduction [1]

(b) Charcoal (carbon) can be burned in an excess of clean, dry air to provide the heat needed to make glass.

(i) Which gas is 21% of clean, dry air?
............................................................................................................................................................... [1]

(ii) Write a word equation for carbon burning in an excess of air.
............................................................................................................................................................... [1]

(iii) Complete the energy level diagram for this reaction by adding these two words:
• reactants
• product

[1]

(c) Argon is also present in clean, dry air.

(i) Give one use of argon.
............................................................................................................................................................... [1]

(ii) Which two of the following statements about argon are correct? Tick two boxes.

□ Argon is unreactive.
□ Argon is diatomic.
□ Argon is monatomic.
□ Argon forms ionic compounds.
□ Argon is a greenhouse gas.
[2]