NSAA 2018 Section 1, Part C (Chemistry questions)

Which row in the following table gives the numbers of protons, neutrons and electrons in ${}_{29}^{64}{\mathrm{Cu}}^{2+}$?

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

The following exothermic reaction reaches equilibrium at room temperature.$${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}(\mathrm{l})+\mathrm{C}{\mathrm{H}}_3\mathrm{COOH}(\mathrm{l})\rightleftharpoons \mathrm{C}{\mathrm{H}}_3\mathrm{COO}{\mathrm{C}}_2{\mathrm{H}}_5(\mathrm{l})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})$$Which of the following changes, when applied independently, will alter the position of the equilibrium?

1 increasing the temperature by $25{}^{\circ }\text{C}$

2 adding $20{\text{ cm}}^3$ of water to the equilibrium mixture

3 adding a catalyst

4 adding an extra $0.5\text{ mol}$ of ethanol (${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}$)

What is the overall process that takes place at the cathode (negative electrode) in the electrolysis of dilute aqueous sodium sulfate?

A mass spectrum of a sample of element X with atomic number 5 is shown.

Using the data, which row in the following table best describes the position of X in the Periodic Table and the relative atomic mass of this sample of X?

The options list, in order: the Period, the Group and the relative atomic mass.

The gases nitrogen, oxygen and argon can be separated from liquefied air by fractional distillation.

Given the data in the table, in which order would the gases be collected?$$\begin{array}{ccc}& \text{melting point / }{}^{\circ }\text{C}& \text{boiling point / }{}^{\circ }\text{C}\\ \text{nitrogen}& -210& -196\\ \text{oxygen}& -218& -183\\ \text{argon}& -189& -186\end{array}$$

Concentrated aqueous sodium chloride was electrolysed. After a few minutes, the remaining electrolyte solution was tested with a pH probe at $25{}^{\circ }\text{C}$.

The gases produced at the electrodes were collected and tested with a colourless aqueous solution of sodium bromide.

Which row in the following table best describes the observations in these tests?

The options list, in order: the pH of the remaining solution, the test of gas from the anode (positive electrode) and the test of gas from the cathode (negative electrode).

The following equations show the main reactions that take place in a blast furnace during the extraction of iron and the removal of the impurities:$$\mathrm{C}+{\mathrm{O}}_2\to \mathrm{C}{\mathrm{O}}_2$$$$[[U]]\mathrm{C}{\mathrm{O}}_2[[/U]]+\mathrm{C}\to 2\mathrm{CO}$$$$\mathrm{F}{\mathrm{e}}_2{\mathrm{O}}_3+3\mathrm{CO}\to 2\mathrm{Fe}+3\mathrm{C}{\mathrm{O}}_2$$$$[[U]]\mathrm{CaC}{\mathrm{O}}_3[[/U]]\to \mathrm{CaO}+\mathrm{C}{\mathrm{O}}_2$$$$[[U]]\mathrm{CaO}[[/U]]+\mathrm{Si}{\mathrm{O}}_2\to \mathrm{CaSi}{\mathrm{O}}_3$$Which row in the following table correctly identifies whether the underlined substance is oxidised, or reduced, or neither?

The options list, in order: $\mathrm{C}{\mathrm{O}}_2$, $\mathrm{CaC}{\mathrm{O}}_3$ and $\mathrm{CaO}$.

X, Y and Z have the same electron configuration.

X is an atom, Y is a monatomic anion and Z is a monatomic cation.

Which of the following statements is always correct?

In the Contact process, sulfur dioxide reacts with oxygen to make sulfur trioxide in a reversible reaction.$$\mathrm{S}{\mathrm{O}}_2(\mathrm{g})+\frac{1}{2}{\mathrm{O}}_2(\mathrm{g})\rightleftharpoons \mathrm{S}{\mathrm{O}}_3(\mathrm{g})$$When $5.00\text{ mol}$ of $\mathrm{S}{\mathrm{O}}_2$ and $11.0\text{ mol}$ of ${\mathrm{O}}_2$ are allowed to reach equilibrium at $450{}^{\circ }\text{C}$, 80.0% of the $\mathrm{S}{\mathrm{O}}_2$ is converted to $\mathrm{S}{\mathrm{O}}_3$.

What is the volume of the resulting mixture?

(Assume that temperature and pressure are constant, and that at this temperature the volume of one mole of gas is $60.0{\text{ dm}}^3$.)

The non-metallic element phosphorus forms two stable chlorides: $\mathrm{PC}{\mathrm{l}}_3$ (boiling point $76{}^{\circ }\text{C}$) and $\mathrm{PC}{\mathrm{l}}_5$ (boiling point $161{}^{\circ }\text{C}$).

Which of the following statements explain(s) the difference in boiling points?

1 There are more covalent bonds in $\mathrm{PC}{\mathrm{l}}_5$ so more energy is required to break them.

2 The forces between the molecules in liquid $\mathrm{PC}{\mathrm{l}}_5$ are stronger.

3 The covalent bonds in $\mathrm{PC}{\mathrm{l}}_3$ are weaker so less energy is required to break them.

A student calculated the mass of anhydrous copper(II) sulfate ($\mathrm{CuS}{\mathrm{O}}_4$) required to make $250{\text{ cm}}^3$ of an aqueous solution of concentration $0.200{\text{ mol dm}}^{-3}$.

However, the student mistakenly made the solution using the same mass of hydrated copper(II) sulfate ($\mathrm{CuS}{\mathrm{O}}_4\cdot 5{\mathrm{H}}_2\mathrm{O}$) instead.

What is the concentration, in ${\text{mol dm}}^{-3}$, of the solution made with the hydrated copper(II) sulfate?

($A_{\text{r}}$ values: Cu = 64; S = 32; O = 16; H = 1.0)

Bromine is an element in Group 17 of the Periodic Table.

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

1 Bromine will oxidise chloride ions in aqueous solution to form chlorine.

2 Bromine has a lower boiling point than chlorine.

3 Bromine reacts with calcium (Group 2) to form a compound containing 80% bromine by mass.

($A_{\text{r}}$ values: Cl = 35.5; Ca = 40; Br = 80)

Paper chromatography was used to separate three mixtures of amino acids. The mixtures were labelled P, Q and R.

Each mixture contains some of the five amino acids in the following table. The $R_{\text{f}}$ values were measured for each amino acid with the solvent used to produce the chromatogram.$$\begin{array}{cc}\text{amino acid}& R_{\text{f}}\text{ value}\\ \text{asparagine}& 0.50\\ \text{glutamic acid}& 0.30\\ \text{glycine}& 0.26\\ \text{leucine}& 0.71\\ \text{valine}& 0.61\end{array}$$Which of the following statements is/are correct?

1 Mixture P contains valine and glycine.

2 Leucine is found in all three mixtures.

3 Glutamic acid is the least mobile amino acid with this solvent.

4 Mixtures P and Q both contain asparagine.

Dilute hydrochloric acid and magnesium were mixed and the total volume of gas released was measured over time.

What is the average rate of reaction, in ${\text{g s}}^{-1}$, with respect to the magnesium over the first two seconds?

($A_{\text{r}}$ value: Mg = 24. Assume that the volume of one mole of gas is $24{\text{ dm}}^3$.)

Copper can react with concentrated nitric acid to form the gas nitrogen monoxide.$$3\mathrm{Cu}+a\mathrm{HN}{\mathrm{O}}_3\to b\mathrm{Cu}(\mathrm{N}{\mathrm{O}}_3{)}_2+c{\mathrm{H}}_2\mathrm{O}+d\mathrm{NO}$$What is the value of $a$ when the equation is balanced?

A small amount of a solid mixture, containing calcium carbonate and an inert substance, was added to $50.00{\text{ cm}}^3$ dilute hydrochloric acid of concentration $0.1000{\text{ mol dm}}^{-3}$.$$\mathrm{CaC}{\mathrm{O}}_3+2\mathrm{HCl}\to \mathrm{CaC}{\mathrm{l}}_2+\mathrm{C}{\mathrm{O}}_2+{\mathrm{H}}_2\mathrm{O}$$After all of the calcium carbonate had reacted, the solution was heated to drive off the carbon dioxide.

The resulting solution was neutralised by $12.50{\text{ cm}}^3$ of $0.1000{\text{ mol dm}}^{-3}$ sodium hydroxide solution.

What was the mass of calcium carbonate in the mixture added to the hydrochloric acid?

($M_{\text{r}}$ value: $\mathrm{CaC}{\mathrm{O}}_3$ = 100.0)

$2.80\text{ g}$ of lithium metal is placed in a closed system with $1.20{\text{ dm}}^3$ of pure oxygen gas (volume measured at room temperature and pressure).

If a complete reaction occurs between the lithium and the oxygen, what is the maximum mass of lithium oxide that can be formed?

($A_{\text{r}}$ values: Li = 7; O = 16. Assume that one mole of gas occupies $24.0{\text{ dm}}^3$ at room temperature and pressure.)

The following reaction between nitrogen oxide and oxygen releases $116\text{ kJ}$ of energy as heat for each mole of oxygen that reacts.$$2\mathrm{NO}(\mathrm{g})+{\mathrm{O}}_2(\mathrm{g})\rightleftharpoons 2\mathrm{N}{\mathrm{O}}_2(\mathrm{g})$$An excess of NO and $y$ moles of oxygen are mixed in a sealed container. The reaction reaches equilibrium in one hour.

At equilibrium, there are $z$ moles of $\mathrm{N}{\mathrm{O}}_2$.

Assume that the pressure is constant throughout the experiment.

How much heat will be released over this hour?