Calculations Involving Masses (Edexcel GCSE Chemistry)

The diagram shows the displayed formula of succinic acid. 

What is the empirical formula for this compound?

The apparatus in Figure 7 shows a piece of magnesium ribbon being heated.

Figure 7

During the heating, the magnesium reacts with oxygen from the air. The lid of the crucible was raised slightly from time to time. Magnesium oxide was formed as a white powder. The experiment was repeated with different masses of magnesium. The results are shown in Figure 8.

Figure 8

i) Draw a graph of the mass of oxygen in magnesium oxide against the mass of magnesium used.

(3)

ii) The result for experiment 5 is anomalous. The masses were all measured accurately.

Suggest a reason for this anomalous result.

(1)

Balance the equation for the reaction of magnesium with oxygen to form magnesium oxide.

....................... Mg + ....................... O₂→ ........................ MgO

Calcium nitrate contains calcium ions and nitrate ions.

Calculate the relative formula mass of calcium nitrate, Ca(NO₃)₂. (relative atomic masses: Ca = 40, N = 14, O = 16)

relative formula mass = .....................................................

Two oxides of lead, R and S, were analysed.

The empirical formula of oxide R was found to be PbO.

The results of the analysis of oxide S showed it contained 0.207 g of lead combined with 0.032 g of oxygen.

Show, by calculation, that the two oxides had different empirical formulae. (relative atomic masses: O = 16, Pb = 207)

A company produces tin from an ore called cassiterite, which is mainly tin oxide.

What is the relative formula mass (M_r) of tin oxide, SnO₂?

Relative atomic masses (A_r):   Sn= 119 O= 16

Higher Only

Avogadro's constant has a value of 6.02 x 10²³.

How many hydrogen atoms are in 0.05 moles of hydrogen molecules?

The molecular formula of butene is C₄H₈.

Which of the following is the empirical formula of butene?

Calculate the relative formula mass of butene, C₄H₈.

(relative atomic masses: H = 1, C = 12)

relative formula mass ................................

When burnt completely in air, butene forms carbon dioxide and water.

i) Balance the equation for this reaction by putting numbers in the spaces provided. C₄H₈ + 6O₂  ................ CO₂ + ................ H₂O (2)

ii) Describe the test to show that a gas is carbon dioxide. (2)

Substance X is a gas at room temperature. It is a simple molecular, covalent substance. Which row of the table shows the properties that substance X is most likely to have?

Diamond has a giant covalent structure.

State one property of diamond that is the result of its giant covalent structure.

A piece of iron wool is left in moist air and goes rusty.

Which graph shows how the mass of the iron wool changes?

Higher Only

A student wanted to make 15.0 g of zinc chloride. The equation for the reaction is:

ZnCO₃ + 2HCl →  ZnCl₂ + CO₂ + H₂O

What mass of zinc carbonate should the student add to the hydrochloric acid to make 15.0 g of zinc chloride?

Relative atomic masses (A_r): C = 12    Zn = 65   O= 16    Cl = 35.5     H= 1

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

Figure 13

 i) State two ways in which this model fails to accurately represent a crystal of sodium chloride.

(2)

ii) Magnesium oxide has a melting point of 2852 °C. Explain why magnesium oxide has such a high melting point.

(3)

i) Carbon dioxide can be formed by the reaction of calcium carbonate, CaCO₃ with dilute hydrochloric acid.

Write the balanced equation for this reaction.

(3)

ii) The thermal decomposition of copper carbonate forms copper oxide and carbon dioxide.

CuCO₃(s) → CuO(s) + CO₂(g)

15.0 g of pure copper carbonate is decomposed completely.

Calculate the mass of solid produced.

(relative atomic masses: C = 12.0; O = 16.0; Cu = 63.5)

Give your answer to two significant figures.

(2)

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.

i) The student recorded the observations until each metal had reacted with the acid for two minutes. The observations are shown in Figure 9.

Figure 9

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

(2)

ii) Complete the diagram below to show how the student could add to the apparatus to measure the volume of gas produced in the two minutes.

(2)

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)

mass of hydrogen atom = ......................................g

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.

i) Describe one way they could tell the reaction was over.

[1]

ii) Explain why the results from this experiment do not appear to support the law of conservation of mass.

[3]