1.2 Formulae, Equations & Calculations

A student reacted copper metal with excess sulfuric acid and collected 35.9 g of the hydrated copper sulfate crystals, CuSO₄●5H₂O crystals. The yield of crystals was 80.0%.

What was the original mass of copper used?

What is the empirical formula of an oxide of vanadium that contains 57.7% vanadium by mass?

Magnesium sulfate can be made by the reaction of magnesium oxide with sulfuric acid

MgO + H₂SO₄ → MgSO₄ + H₂O

1.96 g of magnesium sulfate was produced in a reaction which had a percentage yield of 87.5%.

What mass of magnesium oxide, in mg, was used in the reaction?

Which reaction has the highest atom economy for the production of the carbon containing product?

4.900 g of a carbohydrate contains 2.063 g of carbon. The carbohydrate also contains 6.43% hydrogen by mass and the remainder of the carbohydrate is oxygen.

The relative molecular mass of the carbohydrate is 342 g mol^-1.

What is the molecular formula of the carbohydrate?

A 250 cm³ solution was made by dissolving 3.56 g of Na₂CO₃●nH₂O in pure water.

26.70 cm³ of 0.150 mol dm^-3 hydrochloric acid were required to neutralise a 25.0 cm³ of the solution.

What is the value of n in the Na₂CO₃●nH₂O?

In a thermal decomposition reaction, 6.27 g of calcium oxide is produced from calcium carbonate. The percentage conversion of calcium carbonate is 84.2%.

What mass of calcium carbonate underwent thermal decomposition? 

Aspirin is a common analgesic used for the relief of aches and pains.

Which row correctly describes aspirin?

Refer to the unbalanced equation below when answering this question.

2KMnO₄ + 5H₂C₂O₄ + _HCl → 2MnCl₂ + _H₂O + 10CO₂ + 2KCl

In the balanced equation, the simplest mole ratio for hydrochloric acid to water is

When heated magnesium carbonate, MgCO₃, will decompose to a white solid and a gas, X.

6.90 g of anhydrous magnesium carbonate is heated until no further reaction takes place.

What is the mass of X produced?

2.12 g of a metal element reacts with 300 cm³ of oxygen at 298 K and 100 kPa, to form a metal oxide containing O^2- ions.

The gas constant R = 8.31 J K^–1 mol^–1.

Identify the metal.

An additive in petrol is composed of lead, carbon and hydrogen only. The compound contains 64.11% lead and 29.7% carbon by mass.

What is the empirical formula of the additive?

A student completes a titration experiment to determine the percentage by mass of iron in steel wire.

Their titration results are shown in the table.

Calculate the mean titre.

15.0 g of a compound contains 6.105 g of carbon, 0.765 g of hydrogen and 8.130 g of oxygen. The relative molecular mass of the compound is 118.0 g mol^-1.

What is the molecular formula of the compound?

Calcium carbonate undergoes thermal decomposition according to the following equation

CaCO₃ (s)  → CaO (s) + CO₂ (g)

If 6.00 g of calcium carbonate is heated and produces 2.73 g of calcium oxide, what is the percentage yield of calcium oxide?

The anti-cancer drug cisplatin has the chemical name dichlorodiamineplatinum (II). It is produced from a multi-step reaction. The first step in this reaction is shown in the following equation.

KPtCl₄ + 4KI → KPtI₄ + 4KCl

What is the percentage atom economy for the formation of the potassium tetraiodoplatinate (II), KPtI₄, in this reaction?

A 13.81 g sample of magnesium sulphate, MgSO₄.xH₂O, was heated until no further change in mass was recorded. 6.75 g of the solid remained after strong heating.

What is the value of x?

A thermometer was used to measure the temperature change in a calorimetry experiment. 

The initial temperature was 19.0 C and the final temperature was 26.5 C.

Each reading of the thermometer has an uncertainty of ± 0.5 C.

What is the percentage uncertainty in the temperature change?