NSAA 2022 Section 1, Part C (Chemistry questions)

The following pairs of $0.1{\text{ mol dm}}^{-3}$ solutions are mixed separately in test tubes.

1 $\mathrm{AgN}{\mathrm{O}}_3(\mathrm{aq})$ with $\mathrm{NaI}(\mathrm{aq})$

2 $\mathrm{C}{\mathrm{l}}_2(\mathrm{aq})$ with $\mathrm{NaI}(\mathrm{aq})$

3 $\mathrm{HCl}(\mathrm{aq})$ with $\mathrm{NaOH}(\mathrm{aq})$

4 $\mathrm{MgC}{\mathrm{l}}_2(\mathrm{aq})$ with $\mathrm{NaBr}(\mathrm{aq})$

Which pair(s) of solutions, when mixed, would produce a visible chemical change?

Some reactions of metal M and its compounds are shown in the following diagram.

Which one of the following could be the identity of metal M?

Consider the following properties of compound X:$$\begin{array}{lc}\text{melting point}& -114{}^{\circ }\text{C}\\ \text{boiling point}& -85{}^{\circ }\text{C}\\ \text{conductivity as a solid}& \text{poor}\\ \text{conductivity as a liquid}& \text{poor}\\ \text{conductivity in aqueous solution}& \text{good}\end{array}$$Which one of the following could be the identity of compound X?

Which of the following statements about losing electrons is/are correct?

1 During the electrolysis of a molten binary compound the ions attracted to the cathode (negative electrode) lose electrons at that electrode.

2 Descending Group 1 of the Periodic Table from lithium to caesium, the atoms of the elements lose electrons more easily.

3 When a substance is acting as a reducing agent it loses electrons.

Which of the following chemical reactions is/are redox reactions?

1 $\mathrm{B}{\mathrm{a}}^{2+}(\mathrm{aq})+\mathrm{S}{\mathrm{O}}_4^{2-}(\mathrm{aq})\to \mathrm{BaS}{\mathrm{O}}_4(\mathrm{s})$

2 $\mathrm{PC}{\mathrm{l}}_5(\mathrm{s})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})\to \mathrm{POC}{\mathrm{l}}_3(\mathrm{l})+2\mathrm{HCl}(\mathrm{aq})$

3 $\mathrm{Kr}{\mathrm{F}}_2(\mathrm{s})\to \mathrm{Kr}(\mathrm{g})+{\mathrm{F}}_2(\mathrm{g})$

Three samples of calcium of different masses were added separately to excess dilute hydrochloric acid and the volume of gas released, measured at room temperature and pressure, was monitored.

One sample was powdered calcium, one was granules of calcium, and one was a solid piece of calcium.

The results are shown on the graph.

What is the mass of powdered calcium used in this experiment?

($A_{\text{r}}$ value: Ca = 40. Assume that one mole of gas occupies a volume of $24{\text{ dm}}^3$ at room temperature and pressure.)

Concentrated aqueous solutions of three compounds are electrolysed with inert electrodes.

The constituent elements of which of the following compounds may be collected using this process?

1 copper(II) bromide

2 hydrogen chloride

3 potassium chloride

$50{\text{ cm}}^3$ of $0.100{\text{ mol dm}}^{-3}$ hydrochloric acid has a pH of 1.0.

What is the pH of the mixture formed when $450{\text{ cm}}^3$ of $0.010{\text{ mol dm}}^{-3}$ calcium hydroxide solution is added?

Carboxylic acid X reacts with propanol in the presence of an acid catalyst to form compound Y.

Compound Y has a relative molar mass of 116.

What is the relative molar mass ($M_{\text{r}}$) of X?

($A_{\text{r}}$ values: C = 12; H = 1; O = 16)

Element Z is in Group 1 of the Periodic Table.

A pure sample of element Z consists of two isotopes with mass numbers 85 and 87, and has a relative atomic mass of 85.5.

Which of the following statements is/are correct about element Z in this sample?

1 Element Z reacts with bromine to form an ionic compound with formula $\mathrm{ZB}{\mathrm{r}}_2$.

2 Element Z forms a basic oxide.

3 More than 70% of the atoms of element Z have mass number 85.

Three mixtures (P, Q and R) of amino acids were separated using paper chromatography.

The test was repeated with the same mixtures, paper and solvent but this time the distance travelled by the common component of the mixtures was $7.5\text{ cm}$.

How far did the most mobile component of mixture Q travel in the second test?

A typical sample of dry air is at room temperature and pressure. There is a total of $25.0\text{ mol}$ of gas in this sample.

One of the gases in the sample, X, contributes $1.50\times 10^{23}$ separate particles to the mixture.

A second gas in the sample, Y, would, if alone, occupy a volume of $468{\text{ dm}}^3$ at room temperature and pressure.

What are the identities of gases X and Y, and what would be the total amount of all of the remaining gases in the sample?

(Take Avogadro's number as $6.00\times 10^{23}$. Assume that one mole of any gas occupies a volume of $24.0{\text{ dm}}^3$ at room temperature and pressure.)

The options list, in order: the identity of gas X, the identity of gas Y, and the total amount of all of the remaining gases in the sample in moles.

The atomic number of fluorine is 9.

An element X forms a fluoride with the formula $\mathrm{X}{\mathrm{F}}_3$. Each molecule of $\mathrm{X}{\mathrm{F}}_3$ has 32 electrons in total.

Element X has two isotopes. One isotope has the same number of neutrons as protons and the other isotope has a number of neutrons one greater than the number of protons.

The relative abundance of the heavier isotope is 0.80 (80%).

What is the relative atomic mass of element X?

1 mol of compound X undergoes complete combustion to produce $144{\text{ dm}}^3$ of carbon dioxide (measured at room temperature and pressure).

1 mol of X can also undergo an addition reaction with 1 mol of hydrogen to form a saturated compound that has one branch.

X undergoes addition polymerisation. A section of the addition polymer containing three repeating units has an $M_{\text{r}}$ value greater than 200 but less than 300.

Which one of the following structural formulae could be that of compound X?

($A_{\text{r}}$ values: C = 12; H = 1; F = 19. Assume that one mole of any gas occupies a volume of $24{\text{ dm}}^3$ at room temperature and pressure.)

The five structures are drawn in the figure, labelled A to E. The options below give the same structures as condensed formulae, reading across the carbon-carbon double bond.

The equation shows the complete combustion of an alkane.$$\text{alkane}+a{\mathrm{O}}_2\to b\mathrm{C}{\mathrm{O}}_2+c{\mathrm{H}}_2\mathrm{O}$$$100{\text{ cm}}^3$ of a gaseous alkane requires $650{\text{ cm}}^3$ of oxygen for complete combustion. The volumes of both gases were measured at the same temperature and pressure.

What is the value of $a+b+c$?

A sample of magnesium carbonate, $\mathrm{MgC}{\mathrm{O}}_3$, was reacted completely with $50{\text{ cm}}^3$ of $0.10{\text{ mol dm}}^{-3}$ hydrochloric acid, which is an excess.

The remaining hydrochloric acid was titrated with $0.20{\text{ mol dm}}^{-3}$ sodium hydroxide solution. $5.0{\text{ cm}}^3$ of sodium hydroxide was required for complete neutralisation.

What was the original mass of magnesium carbonate used, in mg?

($M_{\text{r}}$ value: $\mathrm{MgC}{\mathrm{O}}_3=84$)

A student mixed together $30.0{\text{ cm}}^3$ of $3.0{\text{ mol dm}}^{-3}$ hydrochloric acid and $20.0{\text{ cm}}^3$ of $4.0{\text{ mol dm}}^{-3}$ aqueous ammonia in an insulated container.

The initial temperatures of both solutions were $20.0{}^{\circ }\text{C}$.

The maximum temperature observed was $40.0{}^{\circ }\text{C}$.

Assume that the specific heat capacity of any aqueous solution is $4.0{\text{ J g}}^{-1}{}^{\circ }{\text{C}}^{-1}$ and that the density of the reaction mixture is $1.0{\text{ g cm}}^{-3}$.

Using this information, what is the molar enthalpy change, in ${\text{kJ mol}}^{-1}$, for the reaction of hydrochloric acid and aqueous ammonia?

An oxide of nitrogen can be prepared by the reaction of copper with hot nitric acid.

The other products of the reaction are copper(II) nitrate and water.

$0.060\text{ mol}$ of copper reacted exactly with $40.0{\text{ cm}}^3$ of $4.00{\text{ mol dm}}^{-3}$ nitric acid.

What is the empirical formula of the oxide of nitrogen produced in the reaction?

One mole of an unsaturated hydrocarbon reacts with exactly one mole of bromine to form a compound that contains $\frac{6}{15}$ carbon, $\frac{1}{15}$ hydrogen and $\frac{8}{15}$ bromine by mass.

What is the relative molar mass ($M_{\text{r}}$) of this product?

($A_{\text{r}}$ values: C = 12; H = 1; Br = 80)

Airbags in cars contain sodium azide ($\mathrm{Na}{\mathrm{N}}_3$) as a primary reagent, and potassium nitrate ($\mathrm{KN}{\mathrm{O}}_3$) as a secondary reagent.

The sodium azide decomposes according to the following equation to form nitrogen gas, which rapidly fills the airbag:$$2\mathrm{Na}{\mathrm{N}}_3\to 2\mathrm{Na}+3{\mathrm{N}}_2$$The sodium by-product of this first reaction then reacts with excess potassium nitrate according to this second equation:$$10\mathrm{Na}+2\mathrm{KN}{\mathrm{O}}_3\to {\mathrm{K}}_2\mathrm{O}+5\mathrm{N}{\mathrm{a}}_2\mathrm{O}+{\mathrm{N}}_2$$Assume that both reactions go to completion.

An airbag contains $130\text{ g}$ of sodium azide.

What is the total volume of nitrogen gas formed in this airbag, measured at room temperature and pressure?

($A_{\text{r}}$ values: N = 14.0; Na = 23.0. Assume that one mole of gas occupies $24.0{\text{ dm}}^3$ at room temperature and pressure.)