NSAA 2021 Section 1, Part C (Chemistry questions)

The following equations represent the reactions of four metals M, Q, R and T:$$\mathrm{M}(\mathrm{s})+\mathrm{HCl}(\mathrm{aq})\to \text{no reaction}$$$$\mathrm{R}(\mathrm{s})+\mathrm{TS}{\mathrm{O}}_4(\mathrm{aq})\to \mathrm{RS}{\mathrm{O}}_4(\mathrm{aq})+\mathrm{T}(\mathrm{s})$$$$\mathrm{M}(\mathrm{s})+\mathrm{QN}{\mathrm{O}}_3(\mathrm{aq})\to \mathrm{MN}{\mathrm{O}}_3(\mathrm{aq})+\mathrm{Q}(\mathrm{s})$$$$\mathrm{T}(\mathrm{s})+2\mathrm{HCl}(\mathrm{aq})\to \mathrm{TC}{\mathrm{l}}_2(\mathrm{aq})+{\mathrm{H}}_2(\mathrm{g})$$Which option lists the order of reactivity of the four metals, from the most to the least reactive?

Consider the following three ions of calcium observed in mass spectrometry:$${}^{40}{\mathrm{Ca}}^{2+}{}^{42}{\mathrm{Ca}}^{2+}{}^{43}{\mathrm{Ca}}^{+}$$Which of the following statements is/are correct?

1 All three ions have the electron configuration 2,8,8

2 ${}^{42}{\mathrm{Ca}}^{2+}$ has more neutrons than ${}^{40}{\mathrm{Ca}}^{2+}$

3 ${}^{42}{\mathrm{Ca}}^{2+}$ has more protons than ${}^{43}{\mathrm{Ca}}^{+}$

The relative isotopic abundances of a sample of magnesium are shown in the table.$$\begin{array}{cc}\text{isotope}& \text{percentage abundance}\\ {}^{24}\mathrm{Mg}& 80\\ {}^{25}\mathrm{Mg}& 10\\ {}^{26}\mathrm{Mg}& 10\end{array}$$What is the relative atomic mass ($A_{\text{r}}$) of the magnesium?

A portion of the Periodic Table is given:

Which one of these trends is correct?

$1.0{\text{ mol dm}}^{-3}$ hydrochloric acid was slowly added from a burette into an insulated flask containing $50{\text{ cm}}^3$ of aqueous sodium hydroxide. The flask was gently swirled and the temperature of the resulting solution measured continuously.

The two solutions had the same initial temperature and a graph was drawn of the temperature of the resulting solution against the volume of hydrochloric acid added.

Which of the following statements explains the shape of the graph?

Which one of the following represents the repeating unit of poly(pent-2-ene)?

The six displayed formulae are labelled A to F in the figure; the options describe them.

X is a gaseous element. X can react explosively with hydrogen to produce a single product. When dissolved in water, this product forms an acidic aqueous solution Y. When aqueous silver nitrate is added to solution Y, a white precipitate forms.

Solution Y reacts with substance Z to form two products only. One of these products forms a white precipitate when aqueous sodium hydroxide is added to it.

Which of the following could be X and Z?

The options list, in order: X and Z.

Some students were trying to assign oxidation numbers to each of the four sulfur atoms in the tetrathionate ion, ${\mathrm{S}}_4{\mathrm{O}}_6^{2-}$.

Which of the following lists gives the possible oxidation states of the four sulfur atoms present?

The table shows the reagents in three organic reactions.

Which of the rows correctly show(s) the product(s) obtained from the specified reactants?

The table lists, for each row, the reactants and then the product(s).

1 $\mathrm{C}{\mathrm{H}}_3\mathrm{CH}=\mathrm{C}{\mathrm{H}}_2$ and HBr; product(s): 1,2-dibromopropane (only)

2 ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{COOH}$ and $\mathrm{C}{\mathrm{H}}_3\mathrm{OH}$, in the presence of an ${\mathrm{H}}^{+}(\mathrm{aq})$ catalyst; product(s): methyl propanoate and water

3 ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}$ and Na; product(s): sodium ethanoate and hydrogen

Chlorine gas reacts with hot concentrated aqueous sodium hydroxide to form sodium chloride, sodium chlorate(V) and water.

The unbalanced ionic equation for this reaction is:$$u\mathrm{C}{\mathrm{l}}_2+v\mathrm{O}{\mathrm{H}}^{-}\to w\mathrm{C}{\mathrm{l}}^{-}+x\mathrm{Cl}{\mathrm{O}}_3^{-}+y{\mathrm{H}}_2\mathrm{O}$$What is the simplest ratio of $w:x$ in the balanced equation?

An experiment was carried out to separate the four amino acids present in a mixture of amino acids.

A spot of this mixture was placed on chromatography paper. The bottom of the paper was placed in solvent 1 and left until the solvent nearly reached the top of the paper.

The paper was then thoroughly dried and turned by $90^{\circ }$. The procedure was then repeated with solvent 2.

The amino acids were then identified with reference to known $R_{\text{f}}$ values in the respective solvents.

The final positions of the amino acids on the chromatograph are shown on the following diagram.

Which of the following statements is correct?

A reaction between copper and nitric acid produces a blue solution of copper(II) nitrate, water and substance X only.

Substance X does not contain copper or hydrogen.

The balanced equation for the reaction shows that 1 mole of copper reacts to produce 2 moles of water.

What is the identity of substance X?

Ethanedioic acid, $(\mathrm{COOH}{)}_2$, is a weak diprotic acid.

What is the minimum volume of a $2.50{\text{ mol dm}}^{-3}$ solution of ethanedioic acid required to neutralise $25.0{\text{ cm}}^3$ of $2.00{\text{ mol dm}}^{-3}$ sodium hydroxide solution?

Propene burns in air. For each mole of propene burned, $2000\text{ kJ}$ of heat is released.

$2.10\text{ g}$ of propene is burned to heat a $1000\text{ g}$ sample of olive oil.

The olive oil has an initial temperature of $23.0{}^{\circ }\text{C}$. It takes $2.00\text{ J}$ to heat one gram of olive oil by $1.0{}^{\circ }\text{C}$.

Assume that all heat is transferred to the olive oil and none is lost to the surroundings.

What is the maximum temperature reached by the oil?

($M_{\text{r}}$ value: ${\mathrm{C}}_3{\mathrm{H}}_6=42.0$)

What is the calculated energy change for the following reaction using appropriate values from the data provided?$$\mathrm{C}{\mathrm{H}}_4(\mathrm{g})+2{\mathrm{H}}_2\mathrm{O}(\mathrm{g})\to \mathrm{C}{\mathrm{O}}_2(\mathrm{g})+4{\mathrm{H}}_2(\mathrm{g})$$$$\begin{array}{cc}\text{bond}& {\text{bond energy / kJ mol}}^{-1}\\ \mathrm{H}-\mathrm{H}& 440\\ \mathrm{O}-\mathrm{H}& 460\\ \mathrm{C}-\mathrm{H}& 430\\ \mathrm{C}-\mathrm{O}& 360\\ \mathrm{C}=\mathrm{O}& 800\\ \mathrm{C}\equiv \mathrm{O}& 1070\end{array}$$

The balanced equation for an oxidation of ammonia is:$$4\mathrm{N}{\mathrm{H}}_3(\mathrm{g})+5{\mathrm{O}}_2(\mathrm{g})\to 4\mathrm{NO}(\mathrm{g})+6{\mathrm{H}}_2\mathrm{O}(\mathrm{g})$$$50.0{\text{ dm}}^3$ of ammonia and $50.0{\text{ dm}}^3$ of oxygen, both at $850{}^{\circ }\text{C}$ and 1 atmosphere pressure, are mixed and allowed to react to form the products shown in the equation. No other reactions occur.

What is the maximum total volume of gases (at $850{}^{\circ }\text{C}$ and 1 atmosphere pressure) after the reaction?

(Assume that all gases have the same volume at the given temperature and pressure.)

The electrolysis of molten potassium chloride in an inert atmosphere produces potassium at the negative electrode and chlorine at the positive electrode.

The electrolysis of aqueous copper(II) sulfate solution deposits copper on the negative electrode.

The masses of potassium, chlorine and copper produced or deposited in these experiments were recorded.

Assume that the same number of electrons is transferred during the electrolysis of molten potassium chloride and aqueous copper(II) sulfate solution.

Which of the following gives the elements arranged in order of the mass produced/deposited during these electrolysis experiments, from lowest mass to highest mass?

($A_{\text{r}}$ values: $\mathrm{Cl}=35.5$; $\mathrm{K}=39.0$; $\mathrm{Cu}=63.5$)

$0.500\text{ g}$ of magnesium (an excess) was added to dilute hydrochloric acid.

The following graph shows the total volume of the gas released over time as the reaction progresses. All volumes were measured in ${\text{cm}}^3$ at room temperature and pressure.

What is the mass of magnesium remaining after two seconds?

($A_{\text{r}}$ value: $\mathrm{Mg}=24$. Assume that the volume of one mole of gas at room temperature and pressure is $24.0{\text{ dm}}^3$.)

A mixture of both sodium nitrate and barium bromide solids, with a combined mass of $6.36\text{ g}$, was stirred into water and completely dissolved.

An excess of aqueous silver nitrate was added and a precipitate formed. The precipitate was filtered and dried. The mass of dry precipitate was $3.76\text{ g}$.

What was the mass of sodium nitrate in the original mixture?

($M_{\text{r}}$ values: $\mathrm{NaN}{\mathrm{O}}_3=85$; $\mathrm{BaB}{\mathrm{r}}_2=297$; $\mathrm{AgBr}=188$)

A spoonful of magnesium carbonate powder was added to excess hydrochloric acid in an open conical flask on an electronic balance.$$\mathrm{MgC}{\mathrm{O}}_3(\mathrm{s})+2\mathrm{HCl}(\mathrm{aq})\to \mathrm{MgC}{\mathrm{l}}_2(\mathrm{aq})+\mathrm{C}{\mathrm{O}}_2(\mathrm{g})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})$$The mass of the flask and its contents was measured initially and at 1-minute intervals. The total mass of gas produced was then calculated.

The reaction stopped at 5 minutes.

Which row in the following table could represent the total mass of gas calculated after each measurement?

The options list, in order: the total mass of gas after 1 minute, 2 minutes, 3 minutes, 4 minutes and 5 minutes.