Chemistry 9701/21 — May/June 2022

Cambridge AS Level · AS Level Structured Questions · worked solutions for every part, with the mark scheme

questions

marks

minutes

Topics Atoms, Molecules and Stoichiometry · Introduction to Organic Chemistry · Hydrocarbons · Carbonyl Compounds · Atomic Structure · Group 2 · +10 more

Q1Atomic StructureGroup 2Atoms, Molecules and StoichiometryChemical EnergeticsReaction KineticsFree sample

Calcium, magnesium and radium are Group 2 elements. Radium follows the same trends as the other members of Group 2.

(a)

Identify the highest energy orbital which contains electrons in a calcium atom. Sketch the shape of this orbital.

identity of highest energy orbital in Ca .............................

shape

(b)

(i)

Write the equation for the thermal decomposition of calcium nitrate.

(ii)

Suggest which of the Group 2 nitrates, calcium, magnesium or radium, requires the highest temperature to decompose. Explain your answer.

(c)

Predict what you would observe when aqueous radium chloride is added to aqueous sodium sulfate.

Do not refer to temperature changes in your answer.

(d)

(i)

$^{25}_{12}\text{Mg}$ is an isotope of magnesium.

Determine the number of protons and neutrons in an atom of $^{25}_{12}\text{Mg}$ .

number of protons ..............................................................................................................

number of neutrons ............................................................................................................

(ii)

State the full electronic configuration of an atom of $^{25}_{12}\text{Mg}$ .

(e)

A sample of magnesium contains three isotopes, $^{25}\text{Mg}$ , $^{26}\text{Mg}$ and $\mathbf{X}$ .

The percentage abundance of the three isotopes is shown in Table 1.1.

Table 1.1

isotope of Mg	mass / a.m.u.	percentage abundance / %
$\mathbf{X}$		78.99
$^{25}\text{Mg}$	24.99	10.00
$^{26}\text{Mg}$	25.98	11.01

(i)

The relative atomic mass, $A_r$ , is calculated by comparing the average mass of the isotopes of an element to the unified atomic mass unit.

Define the unified atomic mass unit.

(ii)

Calculate the mass of $\mathbf{X}$ . Use data from Table 1.1 and $A_r$ (magnesium) = 24.31 in your calculation. Show your working.

mass of $\mathbf{X}$ = ..............................

(iii)

State one similarity and one difference in the properties of these isotopes of magnesium. Explain your answer.

(f)

Magnesium, Mg, burns in oxygen, $\text{O}_2$ .

The activation energy, $E_a$ , for this reaction is $+148\text{ kJ mol}^{-1}$ .

(i)

State one observation when magnesium burns in oxygen.

Do not refer to temperature changes in your answer.

(ii)

On Fig. 1.1:

sketch a reaction pathway diagram for the reaction that occurs when Mg burns in $\text{O}_2$
label the diagram to show the enthalpy change, $\Delta H$ , and the activation energy, $E_a$ , for the reaction.

Fig. 1.1

(g)

Cold water reacts slowly with a piece of Mg to produce bubbles of $\text{H}_2(\text{g})$ .

Cold water reacts rapidly with burning Mg to produce $\text{H}_2(\text{g})$ in an explosive mixture.

\text{Mg} + 2\text{H}_2\text{O} \rightarrow \text{Mg(OH)}_2 + \text{H}_2

Explain why the rate of reaction of cold water with burning magnesium is greater.

The rest of this paper

3 more questions

Q2Chemical Bonding · Nitrogen and Sulfur · Equilibria12M
Q3Introduction to Organic Chemistry · Hydrocarbons · Carbonyl Compounds · Hydroxy Compounds · Halogen Compounds · Chemical Periodicity17M
Q4Atoms, Molecules and Stoichiometry · Carboxylic Acids and Derivatives · Hydrocarbons · Carbonyl Compounds · Introduction to Organic Chemistry · Analytical Techniques14M

Loading the full paper…