Calculations Involving Masses (Edexcel GCSE Chemistry: Combined Science)

Figure 13 shows a model of how particles are arranged in a solid.

Figure 13

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mass of solid = ................................................................. g

Higher Only

Magnesium reacts with water in the form of steam as shown in the equation.

Mg + 2H₂O → Mg(OH)₂+ H₂

2.4 g of magnesium reacts with sufficient steam for a complete reaction to form 5.8 g of magnesium hydroxide and 0.2 g of hydrogen.
Show, by calculation, that the law of conservation of mass applies to this reaction.
(relative atomic masses: H = 1.0, O = 16, Mg = 24)

Higher Only

2.7 g aluminium reacts with 38.1 g of iodine, I₂, to make 40.8 g aluminium iodide, AlI₃.

(Relative atomic masses:     Al = 27        I = 127

Relative formula mass:      AlI₃ = 408)

What coefficients would balance the equation for the reaction?

A student placed a piece of metal P in a test tube containing excess dilute sulfuric acid.
The student repeated this with three other metals, Q, R and S.
All the pieces of all four metals were the same size.

Figure 9

Use this information to put the four metals in order of reactivity from the least reactive to the most reactive.

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Higher Only

When iron reacts with copper sulfate solution, solid copper is formed.
Two possible equations for this reaction are

A    CuSO₄ + Fe → Cu + FeSO₄
B    3CuSO₄ + 2Fe →  3Cu + Fe₂(SO₄)₃

It was found that 10.00 g of iron powder reacted with excess copper sulfate solution to produce 11.34 g of copper.
Carry out a calculation to decide which equation, A or B, represents the reaction taking place.

(relative atomic masses: Fe = 56.0, Cu = 63.5)

Higher Only

Acid solutions contain hydrogen ions.

Aluminium reacts with dilute hydrochloric acid to form a solution containing aluminium ions, Al³⁺.

Complete the balanced ionic equation for this reaction.

................... + .................. H⁺ .................. AI³⁺ + ...................

Higher Only

The hydrogen ion concentration in a solution is decreased by a factor of 10.

State how the pH of this solution changes.

Higher Only

Calculate the mass, in g, of a hydrogen atom, using the data below.
(relative atomic mass: H = 1.00;
Avogadro constant = 6.02 × 10²³)

Sodium hydroxide is added to sulfuric acid.

Name the type of reaction that takes place.

Complete the balanced symbol equation for the reaction.

2NaOH (aq) + H₂SO₄ (aq) → ………… (aq) + ………. (l)

Higher Tier Only

Calculate the mass of sodium hydroxide needed to add to 1 dm³ of water to make solution with a concentration of 0.2 mol dm^-3.

Show your working out.

(relative atomic masses: Na = 23, O = 16, H = 1)

Higher Tier Only

Deduce which reactant is in excess when 100 cm³ of 0.2 mol dm^-3 sodium hydroxide reacts completely with 50 cm³ of 0.5 mol dm^-3 sulfuric acid.

A student reacted calcium carbonate with hydrochloric acid.
They wanted to investigate how the mass changed during the reaction.

Figure 1 shows the equipment they used.

Figure 1

Give the function of the cotton wool.

The symbol equation for the reaction is:

CaCO₃ (s) + 2HCl (aq) → CaCl₂ (aq) + CO₂ (g) + H₂O (l)

Calculate the relative formula mass of calcium carbonate.

(relative atomic masses: Ca = 40, C = 12, O = 16)

Higher Tier Only

They used 0.25 mol of hydrochloric acid.

Calculate the minimum mass of calcium carbonate that must be added to react with all the hydrochloric acid.

The student measures the mass of the contents of the flask at the start and end of the reaction.

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