OCR GCSE Combined Science A (Gateway) Chemistry Paper 9 Higher November 2021 question paper J250/09

An atom of an element forms an ion with the formula X^2–. 1

Which Group of the Periodic Table is this element found in?

A Group 0

B Group 2

C Group 6

D Group 7

The diagram shows the ‘ball and stick’ model for an ionic compound.

Which statement about the ‘ball and stick’ model is correct?

A It shows all the forces between the ions.

B It shows the arrangement of the ions.

C It shows the charges on the ions.

D It shows the sizes of the ions.

Look at the symbol for boron.

Which is the symbol for the element with an atom that contains 1 more proton and 2 more neutrons than an atom of boron?

A scientist wants to find out the amount of each chemical in a mixture.

Which row in the table shows the chromatographic techniques that the scientist could use?

Which equation shows the ionisation of a weak acid ?

A student completely reacts 0.403 g of magnesium oxide with an excess of carbon.

What is the mass of magnesium made?

The relative atomic mass, A_r, of O is 16.0 and of Mg is 24.3

A 0.1215 g

B 0.243 g

C 0.486 g

D 0.668 g

Look at the ionic equation.

Which species is reduced ?

A Cu(s)

Cu²⁺(aq) B

C Mg(s)

Mg²⁺(aq) D

A solution has a hydrogen ion concentration of 1 × 10^–6 mol / dm³. The solution has a pH of 6. 9

What is the hydrogen ion concentration of a solution with a pH of 3?

1 × 10^–9 mol / dm³ A

1 × 10^–6 mol / dm³ B

1 × 10^–3 mol / dm³ C

1 × 10^–1 mol / dm³ D

Which term is defined as ‘The sum of the relative atomic masses of all the atoms in a chemical formula’?

A Mass number

B Molecular formula

C Relative formula mass

D The Avogadro constant

The reaction between solid citric acid and sodium hydrogen carbonate solution is an endothermic reaction.

A student investigates the temperature change for the reaction.

The diagram shows the equipment the student uses.

50 cm³ of sodium hydrogen carbonate solution

The student adds 0.65 g of solid citric acid to an excess of sodium hydrogen carbonate solution.

The student measures the temperature change. The temperature change is 3.5 °C.

How does a temperature change show that a reaction is endothermic?

How should the student have written the temperature change to show that this reaction is endothermic?

Describe how the student performed the experiment so that they could calculate the temperature change.

The student repeats the experiment using a different mass of citric acid. This time the student measures a larger temperature change.

The temperature change is 10.0 °C.

If 0.65 g of citric acid gives a temperature change of 3.5 °C, calculate the mass of citric acid, in milligrams, that gives a 10.0 °C temperature change.

1 g = 1000 mg

Give your answer to 3 significant figures.

When the student washed out the plastic cup at the end of the second experiment they saw some excess solid left.

Explain how this affected the student’s result and describe how the student could have improved their experiment.

Citric acid and sodium hydrogen carbonate react to form sodium citrate.

Sodium citrate contains sodium ions, Na⁺, and citrate ions, C₆H₅O₇^3–.

Write the formula of sodium citrate.

Solder is a mixture of lead and tin. Solder can be used to join two electrical wires together as shown in Fig. 13.1.

Electrical wire

The table shows how the melting point of solder changes with the percentage of tin it contains.

Plot the data on the grid shown in Fig. 13.2.

On Fig. 13.2 draw a line of best fit through the first three points and a second line of best

fit through the last two points.

Use the lines of best fit to work out the percentage of tin in solder with the lowest melting point.

Solder conducts electricity like a typical metal.

Explain why.

Use knowledge of the properties of metals in your answer.

Look at Fig. 13.3. It shows how the atoms are arranged in pure lead and in solder.

Solder is an example of a formulation.

What name is given to a formulation which is a mixture of metals such as solder?

Suggest whether solder is harder, softer or the same hardness as pure lead.

Explain your answer using your knowledge of the properties of metals.

Carbon dioxide, CO₂, is a covalently bonded molecule.

Explain what is meant by a covalent bond.

Look at the diagram. It shows the structure of carbon dioxide.

Complete the dot and cross diagram for carbon dioxide.

The equation shows the formation of 1 mole of carbon dioxide from carbon monoxide and oxygen.

The table shows the bond energies of some bonds.

Calculate the energy change for the formation of 1 mole of carbon dioxide.

Energy change =........ kJ / mol

Explain the term activation energy.

Look at your calculation in (c).

Suggest a value for the activation energy for the formation of 1 mole of carbon dioxide in this reaction.

The mole is a unit of measurement used in chemistry for the amount of a substance.

Define the term mole.

Iron, Fe, reacts with steam, H₂O. An oxide of iron and hydrogen, H₂, are made.

The oxide of iron has the formula Fe_xO_y where x and y are whole numbers.

In a reaction 1.67 g of iron, Fe, reacts with 0.72 g of steam, H₂O. 0.08 g of hydrogen, H₂, are made.

Calculate the number of moles of iron, steam and hydrogen.

Give your answers to 2 decimal places.

The relative atomic mass, A_r, of H is 1.0, of O is 16.0 and of Fe is 55.8

Look at the reaction equation. It shows the formation of 1 mole of the oxide of iron, Fe_xO_y.

Use your answers to (b)(i) to balance the reaction equation and work out the formula of the oxide of iron, Fe_xO_y.