Chemistry 9701/21 — October/November 2022

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

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Topics Chemical Bonding · Introduction to Organic Chemistry · Group 17 · Atomic Structure · Atoms, Molecules and Stoichiometry · Group 2 · +12 more

Q1Atomic StructureAtoms, Molecules and StoichiometryFree sample

Atoms with nuclei containing an odd number of protons tend to have fewer isotopes than those with an even number of protons.

(a)

Gallium has two stable isotopes, $^{69}\text{Ga}$ and $^{71}\text{Ga}$ .

(i)

Complete Table 1.1 to show the numbers of protons, neutrons and electrons in the two stable isotopes of gallium.

Table 1.1

isotope	number of protons	number of neutrons	number of electrons
$^{69}\text{Ga}$
$^{71}\text{Ga}$

(ii)

Define relative atomic mass.

(iii)

The relative atomic mass of gallium, $A_r$ , is 69.723.
The relative isotopic masses of $^{69}\text{Ga}$ and $^{71}\text{Ga}$ are:

$^{69}\text{Ga}$ , 68.926; $^{71}\text{Ga}$ , 70.925.

Use this information to calculate the percentage abundance of $^{69}\text{Ga}$ in elemental gallium.
Show your working.
Assume that the element contains only the $^{69}\text{Ga}$ and $^{71}\text{Ga}$ isotopes.
Give your answer to four significant figures.

(b)

Potassium also has two stable isotopes. Both isotopes have the same chemical properties.

(i)

Explain why both isotopes of potassium have the same chemical properties.

(ii)

State the full electronic configuration of an atom of potassium.

(iii)

The first, second and third ionisation energies of potassium are 418, 3070 and $4600\text{ kJ mol}^{-1}$ , respectively.

Use this information to explain why potassium is in Group 1.

The rest of this paper

4 more questions

Q2Chemical Bonding · Group 2 · Group 179M
Q3Chemical Periodicity · Group 17 · Halogen Compounds · Hydroxy Compounds · States of Matter · Chemical Bonding · Chemical Energetics · Equilibria · Introduction to Organic Chemistry18M
Q4Introduction to Organic Chemistry · Organic Synthesis · Chemical Bonding · Polymerisation14M
Q5Hydrocarbons · Carbonyl Compounds · Introduction to Organic Chemistry · Carboxylic Acids and Derivatives · Analytical Techniques9M

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