Limiting reactants

A student investigates the reaction of magnesium carbonate and dilute sulfuric acid.

The student wants to measure the pH of the dilute sulfuric acid.

Suggest the pH of dilute sulfuric acid.

Name an indicator that the student could use to measure the pH of dilute sulfuric acid.

State the colour of the indicator after it has been added to the dilute sulfuric acid.

Name of indicator........

Name a piece of equipment the student could use to measure the pH more accurately.

When magnesium carbonate reacts with dilute sulfuric acid, it forms a salt, water and carbon dioxide.

What is the name of the salt?

The student adds an excess of magnesium carbonate to dilute sulfuric acid until no more of it reacts.

magnesium carbonate(s) + sulfuric acid(aq) salt(aq) + water(l) + carbon dioxide(g)

Magnesium carbonate is a white powder that is insoluble in water.

A colourless solution of the salt is formed.

Describe two observations the student would see as the reaction is happening.

The student separates the salt from the solution formed at the end of the reaction.

Step 1: They remove the excess magnesium carbonate.

Step 2: They remove the water from the salt solution.

State the names of the separation techniques used in Step 1 and Step 2.

The student measures the mass of the salt obtained when different masses of magnesium carbonate are added to the same volume of dilute sulfuric acid.

The table shows their results.

Describe the relationship between the mass of magnesium carbonate and the mass of the salt.

A student thinks that when 6.0 g of magnesium carbonate has been added it is in excess.

Explain why the student is correct.

Copper can be made by reacting copper oxide, CuO, with carbon, C.

When 2.00 g of copper oxide reacts with 1.00 g of carbon, copper oxide is the limiting reactant.

Explain the effect of a limiting reactant on a reaction.

Calculate the number of moles in 2.00 g of copper oxide and 1.00 g of carbon.

Give your answers to 3 decimal places.

Relative atomic mass (A_r): C = 12.0 O = 16.0 Cu = 63.5

Use your answers in part (b) to explain why copper oxide is the limiting reactant.

The number of moles in a different mass of copper oxide is 0.045.

Calculate the maximum mass of copper, Cu, that can be made from 0.045 moles of copper oxide.

Give your answer to 2 significant figures.

Relative atomic mass (A_r): Cu = 63.5

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.

The gradient of the tangent gives the rate of reaction. Use the tangent to calculate the rate of reaction at the start of the reaction.

Give your answer to 1 decimal place.

Rate of reaction =........ cm³ / minute

What happens to the rate of reaction as the reaction progresses?

Explain your answer using ideas about particles and collisions.

Another student repeats the experiment.

They increase the concentration of the dilute hydrochloric acid. They keep everything else in the experiment the same.

Does the gradient of the graph at the start of this student’s reaction decrease, increase or stay the same compared to the first student’s experiment?

Tick (✓) one box.

Give a reason for your answer.

Write down the volume of hydrogen gas that is produced at the end of this reaction.

A student investigates how to make a sample of a pure salt.

His method is shown in Fig. 14.1.

React an excess of copper oxide with 50 cm³ dilute hydrochloric acid. Stage 1

Stage 2 Heat the solution from Stage 1.

Copper oxide is an insoluble compound that neutralises dilute hydrochloric acid.

Name the type of insoluble compound that neutralises an acid to form a salt and water.

Dilute hydrochloric acid is a hazardous chemical.

Describe one safety precaution the student should take when using dilute hydrochloric acid.

Stage 1 uses an excess of copper oxide.

Give a reason why.

Calculate the number of moles of copper oxide, CuO, in 0.500 g.

Give your answer to 3 significant figures.

Use your answer to (d)(i) and the balanced symbol equation to explain why the copper oxide is in excess.

Another student thinks that the method in Fig. 14.1 will not make pure copper chloride.

Explain why this student is correct.

Carbon is an element which can form a very wide range of compounds.

This is partly due to the number of bonds that a carbon atom can form.

State the type and maximum number of bonds that a carbon atom forms.

Maximum number of bonds........

Hex-1-ene is a carbon-based compound with the formula C₆H₁₂.

20.0 g of hex-1-ene is burned in oxygen. Carbon dioxide and water are made. Look at the equation for this reaction.

Calculate the number of molecules in 20.0 g of hex-1-ene.

Avogadro’s constant = 6.02 × 10²³ mol^–1

Give your answer to 3 significant figures.

Number of molecules of C₆H₁₂ =........

Hex-1-ene was burned using a spirit burner in the laboratory.

The diagram shows the spirit burner.

Burning 20.0 g of hex-1-ene should produce 62.9 g of carbon dioxide.

The actual mass of carbon dioxide produced in the reaction was 48.4 g.

What conclusion can be made about the mass of oxygen available for combustion?