Edexcel IGCSE Chemistry E Chemical Formulae Equations and Calculations Questions

This question is about magnesium metal and its compounds.

Crude oil is a mixture of hydrocarbons.

One of the hydrocarbons in the refinery gas fraction is an alkane with the structural formula $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}$

Calculate the relative molecular mass $\left(M_{\mathrm{r}}\right)$ of this alkane.

The diagram shows the positions of some elements in part of the Periodic Table.

Na Al S Cl
K Xe
In

A teacher adds a small piece of sodium to a glass trough containing water and universal indicator.

The universal indicator changes colour.
The equation for the reaction is

The reaction with sodium produces 0.036 g of hydrogen gas.

One mole of hydrogen gas contains $6.0 \times 10^{23}$ molecules.
Calculate the number of molecules of hydrogen gas produced in the reaction with sodium.

Give your answer to two significant figures.
number of molecules of hydrogen gas =

This question is about magnesium metal and its compounds.

Magnesium burns in oxygen gas to form solid magnesium oxide.

Complete the chemical equation for the reaction by balancing the equation and adding the state symbols.

A sample of iron(III) oxide reacts with excess carbon monoxide.

This is the equation for the reaction.

Calculate the minimum mass of iron(III) oxide needed to produce a theoretical yield of 28 g of iron.
[for $\mathrm{Fe}_{2} \mathrm{O}_{3} \quad M_{\mathrm{r}}=160$ ]
minimum mass of iron(III) oxide =

A sample of iron(III) oxide reacts with excess carbon monoxide.

This is the equation for the reaction.

The actual yield of iron from this sample is 21 g .

Calculate the percentage yield of iron.

Sodium sulfate can be prepared by the reaction between sodium hydroxide solution and sodium hydrogensulfate ( $\mathrm{NaHSO}_{4}$ ) solution.

This is the equation for the reaction.

Sodium hydrogensulfate solution is acidic.
A student adds $25.0 \mathrm{~cm}^{3}$ of sodium hydroxide solution to a conical flask and adds two drops of indicator.

The student does a titration.

Crystals of hydrated sodium sulfate decompose when heated.

This is the equation for the decomposition.

A student uses this apparatus to find the value of x .
hydrated sodium sulfate

The student heats the crystals until the decomposition is complete.
The table shows the student's results.

Use the results to calculate the value of x .
[for $\mathrm{Na}_{2} \mathrm{SO}_{4}, M_{\mathrm{r}}=142$ for $\mathrm{H}_{2} \mathrm{O}, M_{\mathrm{r}}=18$ ]


value of x=

Ocimene is an organic compound that gives some plants their particular smell.
The molecular formula of ocimene is $\mathrm{C}_{10} \mathrm{H}_{16}$

Using ocimene as an example, explain what is meant by the term empirical formula.

The table shows the structures of six organic compounds.

This question is about magnesium metal and its compounds.

A student uses this method to make a solution of magnesium chloride.

Step 1. measure $25 \mathrm{~cm}^{3}$ of dilute hydrochloric acid into a beaker
Step 2 add magnesium powder a little at a time
Step 3 keep adding magnesium powder until it is in excess
Step 4 remove the excess magnesium powder by filtration

This is the equation for the reaction.

Calculate the minimum mass of magnesium needed to react with $25.0 \mathrm{~cm}^{3}$ of $2.00 \mathrm{~mol} / \mathrm{dm}^{3}$ hydrochloric acid.
[for $\mathrm{Mg}, \mathrm{A}_{\mathrm{r}}=24$ ]

mass = g

This question is about octane $\left(\mathrm{C}_{8} \mathrm{H}_{18}\right)$ which is produced in the gasoline fraction during fractional distillation of crude oil.

A car is driven at constant speed for 4.00 km .

The exhaust gases are collected and their volume at room temperature and pressure (rtp) is $5.02 \times 10^{5} \mathrm{~cm}^{3}$.

The exhaust gases include carbon dioxide and oxides of nitrogen.
The carbon dioxide is removed from the exhaust gases. The volume of the remaining gases at rtp is $2.96 \times 10^{5} \mathrm{~cm}^{3}$.

Show that the car produces less than 100 g of carbon dioxide per km.
[molar volume of carbon dioxide at rtp $=24000 \mathrm{~cm}^{3}$ ]