NSAA 2023 Section 1, Part C (Chemistry questions)

An experiment is carried out at two different pressures by changing the volume of the reaction vessel.

The experiment measures the rate of the reaction between molecules X and Y to form Z:$$\mathrm{X}(\mathrm{g})+\mathrm{Y}(\mathrm{g})\to \mathrm{Z}(\mathrm{s})$$Assume that the experiments are carried out under exactly the same conditions apart from the difference in pressure.

How will the rate of the reaction change with pressure, if at all, and what is the reason for this?

The options list, in order: the difference in rate of reaction and the reason.

Which of the following represents the structure of the addition polymer formed from but-1-ene?

The six candidate repeat units are drawn in the diagram; each option below gives the same repeat unit as a condensed formula.

The chart shows the relative abundances of the isotopes of an element.

What is the relative atomic mass ($A_{\mathrm{r}}$) of this element?

In this question, all solutions have the same concentration in ${\text{mol dm}}^{-3}$.

Three separate experiments were set up using the same volume of each solution:

experiment 1: $\mathrm{LiCl}(\mathrm{aq})$ and $\mathrm{AgN}{\mathrm{O}}_3(\mathrm{aq})$

experiment 2: $\mathrm{NaCl}(\mathrm{aq})$ and $\mathrm{AgN}{\mathrm{O}}_3(\mathrm{aq})$

experiment 3: $\mathrm{KCl}(\mathrm{aq})$ and $\mathrm{AgN}{\mathrm{O}}_3(\mathrm{aq})$

For each experiment, the solid formed was filtered, washed, dried, and weighed.

Which of the following statements is/are correct?

1 Experiment 3 forms the greatest mass of solid.

2 Experiment 3 has a noticeably greater rate of reaction than the others.

3 The reaction taking place in each experiment is a redox reaction.

How many moles of ions are present in $20{\text{ cm}}^3$ of $0.15{\text{ mol dm}}^{-3}$ magnesium nitrate solution?

(Ignore ions produced by dissociation of water.)

Silicon is directly below carbon in the Periodic Table and has a melting point of $1414{}^{\circ }\text{C}$.

Which of the following statements explains why silicon has a high melting point?

Atoms of element Q have two full shells of electrons and the third shell requires one more electron to gain a noble gas configuration.

Which row of the table correctly describes the elements near to Q in the Periodic Table?

The options list, in order: the element immediately above Q, the element immediately below Q, the element immediately to the left of Q, and the element immediately to the right of Q.

A simple ion of an element has a mass number $x$, an atomic number $\frac{x-1}{2}$ and a charge of $-1$.

How many protons, neutrons and electrons are present in this ion?

The options list, in order: the number of protons, the number of neutrons and the number of electrons.

Titanium metal can be extracted from titanium(IV) chloride, $\mathrm{TiC}{\mathrm{l}}_4$.

Titanium(IV) chloride is heated to $1000{}^{\circ }\text{C}$ with either sodium or magnesium metal in an atmosphere of argon.

Which one of the following statements is correct?

($A_{\mathrm{r}}$ values: $\mathrm{Na}=23$; $\mathrm{Mg}=24$; $\mathrm{Cl}=35.5$; $\mathrm{Ti}=48$)

Ethene gas and hydrogen gas react to form ethane gas.

The energy change for this reaction is $-150{\text{ kJ mol}}^{-1}$.

Using the provided data, what is the mean $\mathrm{C}-\mathrm{H}$ bond energy?

(Bond energy data: $\mathrm{H}-\mathrm{H}=430{\text{ kJ mol}}^{-1}$; $\mathrm{C}-\mathrm{C}=350{\text{ kJ mol}}^{-1}$; $\mathrm{C}=\mathrm{C}=600{\text{ kJ mol}}^{-1}$)

A water treatment unit processes $355000{\text{ dm}}^3$ of drinking water each day.

$0.4\text{ mg}$ of chlorine gas is used to kill the bacteria in $1{\text{ dm}}^3$ of the source water.

What volume of chlorine gas, if measured at room temperature and pressure, is used each day at the water treatment unit?

($A_{\mathrm{r}}$ value: $\mathrm{Cl}=35.5$. Assume that one mole of a gas occupies $24{\text{ dm}}^3$ at room temperature and pressure.)

Element X is in Group 13, Period 4. It consists of atoms of two isotopes with mass numbers 69 and 71. The relative atomic mass of element X is 69.7.

Which of the following statements is/are correct about element X?

1 75% of the atoms of element X have mass number 69.

2 An atom of element X has three electrons in its outer shell.

3 Element X forms an oxide with formula ${\mathrm{X}}_2{\mathrm{O}}_3$ that reacts with acids.

One mole of copper reacts completely with an excess of concentrated nitric acid.

A gaseous oxide of nitrogen is one of the products of the reaction. The volume of this gas is $48{\text{ dm}}^3$ when measured at room temperature and pressure.

The oxidation state of the nitrogen in the gaseous oxide is one less than the oxidation state of the nitrogen in the nitric acid.

Which of the following could be the equation for this reaction?

(Assume that one mole of any gas occupies $24{\text{ dm}}^3$ at room temperature and pressure.)

Two experiments were carried out using separate samples of a solution of an acid of concentration $0.40{\text{ mol dm}}^{-3}$ ($36{\text{ g dm}}^{-3}$) and the following observations were made.

- $25{\text{ cm}}^3$ of the acid solution exactly neutralised $100{\text{ cm}}^3$ of $0.20{\text{ mol dm}}^{-3}$ sodium hydroxide solution.

- Bubbles of gas were given off when magnesium ribbon was added to the acid solution.

Which of the following statements can be deduced from this information?

1 It is a monoprotic acid.

2 It is a strong acid.

3 The acid has a relative molar mass ($M_{\mathrm{r}}$) of 90.

When methanol is burned in the apparatus shown it gives out $720{\text{ kJ mol}}^{-1}$. However, only 80% of the energy released is transferred into the water.

The starting temperature of the water is $12{}^{\circ }\text{C}$.

What mass of methanol would need to be burned to give a $60{}^{\circ }\text{C}$ temperature rise in the water?

($M_{\mathrm{r}}$ value: methanol $=32$. Assume that the specific heat capacity of water $=4{\text{ J g}}^{-1}{}^{\circ }{\text{C}}^{-1}$)

A student electroplates a solid metal ball with copper.

The student dissolves $80.0\text{ g}$ of anhydrous copper(II) sulfate in water and makes up the solution to exactly $500{\text{ cm}}^3$ to use as the electrolyte.

Two electrodes are placed in this solution. One electrode is the ball to be electroplated and the other electrode is an inert graphite electrode. The electrodes are connected to a battery.

After some time, the ball is removed and is found to be coated with $8.00\text{ g}$ of copper. Water is added to the remaining solution to give a final volume of exactly $500{\text{ cm}}^3$.

What is the final concentration of the copper(II) ions in solution?

($A_{\mathrm{r}}$ values: $\mathrm{O}=16$; $\mathrm{S}=32$; $\mathrm{Cu}=64$)

The structure of cyclohexa-1,4-diene is shown in the diagram.

Bromine is dissolved in inert organic solvent to form $0.250{\text{ mol dm}}^{-3}$ of bromine solution.

What is the minimum volume of this bromine solution required to react completely with $0.10{\text{ cm}}^3$ of cyclohexa-1,4-diene?

($M_{\mathrm{r}}$ value: cyclohexa-1,4-diene $=80$. Density of cyclohexa-1,4-diene $=0.84{\text{ g cm}}^{-3}$)

The relative tendency for metals to form positive ions in solution can be measured using the following apparatus.

Electrons can pass from metal 1 to metal 2 via the external circuit. The difference in the tendency of the metals to form positive ions is given by the reading on the voltmeter. The higher the reading on the voltmeter the greater the difference in the tendency of the pair of metals to form positive ions.

Results from three experiments are given in the following table.$$\begin{array}{cccc}\text{experiment}& \text{metal 1}& \text{metal 2}& \text{reading on voltmeter / V}\\ 1& \mathrm{P}& \mathrm{Q}& +0.62\\ 2& \mathrm{S}& \mathrm{Q}& +0.30\\ 3& \mathrm{S}& \mathrm{R}& +1.24\end{array}$$Using the information in the table, what is the order of reactivity of the four metals P, Q, R and S, from most reactive to least reactive?

A sample of aluminium ore (bauxite) contains 75.0% by mass of hydrated aluminium oxide.

Hydrated aluminium oxide is one mole of aluminium oxide combined with two moles of water.

What is the minimum mass of this sample of bauxite that is required to produce 108 tonnes of aluminium?

(1 tonne $=1\times 10^6\text{ g}$. $A_{\mathrm{r}}$ values: $\mathrm{H}=1$; $\mathrm{O}=16$; $\mathrm{Al}=27$)

Equal amounts of carbon dioxide and carbon monoxide are produced when $2.0\text{ mol}$ of propanol, ${\mathrm{C}}_3{\mathrm{H}}_7\mathrm{OH}$, are reacted with a limited supply of oxygen. Water is the only other product in this reaction.

How many moles of oxygen molecules are used in this reaction?