OCR GCSE Combined Science A (Gateway) Chemistry Paper 3 Foundation November 2021 question paper J250/03

The diagrams show two different macromolecules.

Which element are these macromolecules made from?

A Carbon

B Hydrogen

C Oxygen

D Silicon

Which substance is a formulation ?

A Air

B An alloy

C Carbon dioxide

D Distilled water

Which equation shows that the mass of the solid decreases as the solid reacts?

The diagram shows the electrolysis of molten lead bromide.

Which row in the table shows the products formed at the anode and the cathode?

Iron oxide, Fe₂O₃, is heated with carbon, C. Iron, Fe, and another product, X, are made. Look at the equation for the reaction.

What is the formula of X ?

A CO

B CO₂

C FeCO₃

D O₂

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

Which Group of the Periodic Table is the 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.

Copper can form many different compounds.

The table shows the formulae of five different compounds of copper.

Which compound, A, B, C, D or E, is made from copper, carbon and oxygen?

Which compound, A, B, C, D or E, is made when copper is oxidised as copper reacts with oxygen?

Which compound, A, B, C, D or E, reacts with dilute hydrochloric acid to make carbon dioxide?

Calculate the relative formula mass of compound D.

The relative atomic mass, A_r, of Cu is 63.5 and of S is 32.1

A student investigates how the pH of dilute hydrochloric acid changes as sodium hydroxide solution is added to it.

Fig. 13.1 shows the equipment the student uses.

The student:

• Adds 10 cm³ dilute hydrochloric acid to X.

• Adds 0.5 cm³ of the sodium hydroxide solution to the dilute hydrochloric acid.

• Swirls the mixture and measures its pH with a pH probe.

• Repeats adding 0.5 cm³ of the sodium hydroxide solution each time until 10 cm³ of the sodium hydroxide solution has been added.

What is the name of the piece of equipment labelled X ?

The student plots a graph of some of their results.

Look at the table. It shows the rest of the student’s results.

Plot the results on the graph and draw a line of best fit.

Volume of sodium hydroxide solution (cm³)

The dilute hydrochloric acid is exactly neutralised when the pH of the mixture is 7.

Use the graph to work out the volume of sodium hydroxide solution needed to exactly neutralise the dilute hydrochloric acid.

A heating curve shows how the temperature of a substance changes as it is heated.

Fig. 14.1 shows the heating curve for ice.

Look at the sentences, A – D. They describe sections 1, 2, 3 and 4 of the heating curve in Fig. 14.1.

A Heat energy is used to break the forces between the particles.

B Heat energy is used to loosen the forces between the particles.

C Heat energy is used to make the particles move past each other more.

D Heat energy is used to make the particles vibrate faster.

Match the sentences A, B, C or D to the parts of the heating curve labelled 1, 2, 3 and 4 putting the correct letter in each box.

A student wants to produce the heating curve for ice.

Fig. 14.2 shows the equipment the student uses.

The student slowly heats up the ice and measures the temperature every minute.

The student found they could not produce part X of the heating curve in Fig. 14.1.

Explain why.

The table shows the melting points of four different substances, A – D.

State the letter, A, B, C or D, of one pure substance in the table.

State a reason for your answer to (c)(i) using information from the table.

Complete the balanced symbol equation for the reaction of sodium and chlorine to make sodium chloride.

Sodium chloride has a high melting point.

Explain why.

Use ideas about the structure and bonding in sodium chloride in your answer.

Write in the table the state symbol for the solution of sodium chloride.

Tick (✓) one box in each column of the table to show if solid sodium chloride and a

solution of sodium chloride conduct electricity.

Complete the table by writing in the explanation for the student’s results.

Use ideas about the structure and bonding in sodium chloride in your answer.

16* Helium and neon are the first two elements in Group 0 of the Periodic Table.

Look at the symbols for helium and neon.

Describe the similarities and differences in the atomic structures of helium and neon.

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.