NSAA 2017 Section 1, Part C (Chemistry questions)

Consider the atoms/ions below:$${}_{12}^{24}{\mathrm{Mg}}^{2+}{}_8^{16}{\mathrm{O}}^{2-}{}_8^{18}\mathrm{O}{}_{16}^{32}{\mathrm{S}}^{2-}$$Which of the following statements is/are correct?

1 Both ${}_8^{16}{\mathrm{O}}^{2-}$ and ${}_{12}^{24}{\mathrm{Mg}}^{2+}$ have the same electronic configuration.

2 ${}_{16}^{32}{\mathrm{S}}^{2-}$ has double the number of neutrons that are in ${}_8^{18}\mathrm{O}$.

3 The sum of the numbers of electrons in ${}_8^{16}{\mathrm{O}}^{2-}$ and ${}_8^{18}\mathrm{O}$ is equal to the number of electrons in ${}_{16}^{32}{\mathrm{S}}^{2-}$.

Which two of the following reactions involve oxidation?

1 $\mathrm{Ca}\to {\mathrm{Ca}}^{2+}+2{\mathrm{e}}^{-}$

2 $\mathrm{C}{\mathrm{l}}_2+2{\mathrm{e}}^{-}\to 2\mathrm{C}{\mathrm{l}}^{-}$

3 $\mathrm{F}{\mathrm{e}}_2{\mathrm{O}}_3+3\mathrm{CO}\to 2\mathrm{Fe}+3\mathrm{C}{\mathrm{O}}_2$

4 $\mathrm{MgC}{\mathrm{O}}_3+2\mathrm{HCl}\to \mathrm{MgC}{\mathrm{l}}_2+\mathrm{C}{\mathrm{O}}_2+{\mathrm{H}}_2\mathrm{O}$

Hydrochloric acid (HCl) is a strong acid. Properties of a solution of $1.00{\text{ mol dm}}^{-3}$ hydrochloric acid include:

1 It turns blue litmus indicator red.

2 On reaction with sodium carbonate gaseous carbon dioxide is evolved.

3 $25.0{\text{ cm}}^3$ of this acid solution neutralises $25.0{\text{ cm}}^3$ of $1.00{\text{ mol dm}}^{-3}$ sodium hydroxide solution.

Ethanoic acid ($\mathrm{C}{\mathrm{H}}_3\mathrm{COOH}$) is a weak acid.

Which of the three properties is/are also correct for a $1.00{\text{ mol dm}}^{-3}$ solution of ethanoic acid?

Consider the following reactions:

Reaction Q: $\mathrm{C}{\mathrm{H}}_2=\mathrm{C}{\mathrm{H}}_2(\mathrm{g})+{\mathrm{H}}_2\mathrm{O}(\mathrm{g})\rightleftharpoons \mathrm{C}{\mathrm{H}}_3\mathrm{C}{\mathrm{H}}_2\mathrm{OH}(\mathrm{g})$, $\Delta H$ is $-$ve

Reaction R: $\mathrm{PC}{\mathrm{l}}_5(\mathrm{g})\rightleftharpoons \mathrm{PC}{\mathrm{l}}_3(\mathrm{g})+\mathrm{C}{\mathrm{l}}_2(\mathrm{g})$, $\Delta H$ is $+$ve

The following actions could be applied independently to each reaction (Q and R) above:

1 increase the pressure

2 increase the temperature

3 use a suitable catalyst

Assuming that all other conditions remain constant, which of these actions will increase the initial rate of reaction and increase the yield of products for both reactions Q and R?

Study the chromatogram below showing the spots obtained, labelled (i) to (v), from two sweets and pure samples of the food additives, labelled Q, R and S.

Which of the following statements about the chromatogram is/are correct?

1 Both sweet 1 and 2 contain additives R and S.

2 The $R_{\mathrm{f}}$ value for spot (iv) is half that for spot (iii).

3 The $R_{\mathrm{f}}$ value for spot (v) is 0.7.

Element X has atomic number 20. Consider only the simple oxide of X.

Which of the following options identifies the formula, the type of bonding and the acid-base character of the oxide of element X?

The options list, in order: the formula of the oxide, the type of bonding in the oxide and the acid-base character of the oxide.

Solid copper(II) chloride contains ${\mathrm{Cu}}^{2+}$ ions and $\mathrm{C}{\mathrm{l}}^{-}$ ions only.

Solid lithium phosphate(V) contains $\mathrm{L}{\mathrm{i}}^{+}$ ions and $\mathrm{P}{\mathrm{O}}_4^{3-}$ ions only.

Aqueous solutions of copper(II) chloride and lithium phosphate(V) are mixed to produce a precipitate of copper(II) phosphate(V) and an aqueous solution of lithium chloride.

Which of the following represents the balanced ionic equation for this process?

Which of the following statements about the reaction of lithium with water are correct?

1 The reaction is a redox reaction.

2 $7\text{ g}$ of lithium will react with excess water to produce $2\text{ g}$ of hydrogen gas.

3 The reaction produces a solution with a pH greater than that of water.

4 $14\text{ g}$ of lithium will exactly react with $36\text{ g}$ of water.

($A_{\mathrm{r}}$ values: H = 1; Li = 7; O = 16)

Consider this electrochemical cell containing an aqueous copper(II) chloride electrolyte:

Which row in the following table identifies the reactions occurring at the electrodes?

The options list, in order: the reaction at the cathode (negative electrode) and the reaction at the anode (positive electrode).

A fluorocarbon has a relative molecular mass which is twice that of its empirical formula mass.

$81\text{ g}$ of the compound contains $57\text{ g}$ of fluorine.

What is the molecular formula of the compound?

($A_{\mathrm{r}}$ values: C = 12; F = 19)

In which of the following reactions is there a change in volume of $24{\text{ dm}}^3$, when measured at room temperature and pressure?

1 $56\text{ g}$ of carbon monoxide completely reacts with an excess of oxygen $2\mathrm{CO}(\mathrm{g})+{\mathrm{O}}_2(\mathrm{g})\to 2\mathrm{C}{\mathrm{O}}_2(\mathrm{g})$

2 $36\text{ g}$ of steam is fully decomposed $2{\mathrm{H}}_2\mathrm{O}(\mathrm{g})\to 2{\mathrm{H}}_2(\mathrm{g})+{\mathrm{O}}_2(\mathrm{g})$

3 $30\text{ g}$ of nitrogen monoxide completely reacts with an excess of oxygen $2\mathrm{NO}(\mathrm{g})+{\mathrm{O}}_2(\mathrm{g})\to 2\mathrm{N}{\mathrm{O}}_2(\mathrm{g})$

($A_{\mathrm{r}}$ values: C = 12; O = 16; H = 1.0; N = 14. Assume that one mole of gas occupies a volume of $24{\text{ dm}}^3$ at room temperature and pressure.)

Magnesium reacts with sulfuric acid according to the following chemical equation:$$\mathrm{Mg}(\mathrm{s})+{\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4(\mathrm{aq})\to \mathrm{MgS}{\mathrm{O}}_4(\mathrm{aq})+{\mathrm{H}}_2(\mathrm{g})$$Line P on each graph shows how the volume of hydrogen formed changes with time when $1.2\text{ g}$ of magnesium reacts with $40{\text{ cm}}^3$ of $1.0{\text{ mol dm}}^{-3}$ sulfuric acid at $20{}^{\circ }\text{C}$.

($A_{\mathrm{r}}$ value: Mg = 24)

Two further experiments were carried out and the volumes of hydrogen formed were plotted.

Experiment Q: $1.2\text{ g}$ of magnesium + $40{\text{ cm}}^3$ of $2.0{\text{ mol dm}}^{-3}$ sulfuric acid at $20{}^{\circ }\text{C}$

Experiment R: $1.2\text{ g}$ of magnesium + $40{\text{ cm}}^3$ of $0.5{\text{ mol dm}}^{-3}$ sulfuric acid at $20{}^{\circ }\text{C}$

Which lines show how the volume of hydrogen formed will change with time in each experiment?

The options list, in order: the line for experiment Q and the line for experiment R.

Nitrogen and hydrogen react together to form ammonia as shown below:$${\mathrm{N}}_2(\mathrm{g})+3{\mathrm{H}}_2(\mathrm{g})\to 2\mathrm{N}{\mathrm{H}}_3(\mathrm{g})$$The energy released by this reaction is $93{\text{ kJ mol}}^{-1}$.

What is the bond energy in the nitrogen molecule?

(Bond energies: $\mathrm{H}-\mathrm{H}=436{\text{ kJ mol}}^{-1}$; $\mathrm{N}-\mathrm{H}=391{\text{ kJ mol}}^{-1}$)

Consider the following two electrolytic processes:

electrolysis of molten lead(II) chloride

electrolysis of brine (sodium chloride solution)

Which of the following statements is/are correct?

1 In both processes, reduction takes place at the negative electrode.

2 If $20.0\text{ g}$ of product is formed at the negative electrode in each process, then both processes produce the same volume of chlorine gas, measured at room temperature and pressure.

3 In both processes, a metal is produced at the negative electrode.

($A_{\mathrm{r}}$ values: Cl = 35.5; H = 1.00; Na = 23.0; Pb = 207. Assume that one mole of gas occupies $24.0{\text{ dm}}^3$ at room temperature and pressure.)

Silver nitrate solution reacts with zinc powder in an exothermic reaction:$$2\mathrm{AgN}{\mathrm{O}}_3(\mathrm{aq})+\mathrm{Zn}(\mathrm{s})\to 2\mathrm{Ag}(\mathrm{s})+\mathrm{Zn}(\mathrm{N}{\mathrm{O}}_3{)}_2(\mathrm{aq})$$The graph shows the maximum temperature rise as different masses of zinc react with separate $50.0{\text{ cm}}^3$ samples of $0.100{\text{ mol dm}}^{-3}$ silver nitrate solution.

What is the mass of zinc at the position labelled Y?

($A_{\mathrm{r}}$ value: Zn = 65)

Natural samples of copper contain two isotopes: ${}^{63}\mathrm{Cu}$ which has a relative isotopic mass of 62.93, and ${}^{65}\mathrm{Cu}$ which has a relative isotopic mass of 64.93.

The relative atomic mass of a sample of elemental copper is 63.55.

What is the percentage abundance of each of the two isotopes to the nearest whole number?

The reaction between calcium carbonate and hydrochloric acid was used to measure the effect of changing conditions on the mass of $\mathrm{C}{\mathrm{O}}_2$ produced and the rate of $\mathrm{C}{\mathrm{O}}_2$ production.$$\mathrm{CaC}{\mathrm{O}}_3(\mathrm{s})+2\mathrm{HCl}(\mathrm{aq})\to \mathrm{CaC}{\mathrm{l}}_2(\mathrm{aq})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})+\mathrm{C}{\mathrm{O}}_2(\mathrm{g})$$The experiment was carried out five times with different conditions at a constant temperature.

The following conditions were varied:

$\mathrm{CaC}{\mathrm{O}}_3$ as chips or powder

mass of $\mathrm{CaC}{\mathrm{O}}_3$

volume of HCl

concentration of HCl

Which experiment (A-E) in the following table will produce $8.8\text{ g}$ of carbon dioxide in the shortest time?

($M_{\mathrm{r}}$ values: $\mathrm{CaC}{\mathrm{O}}_3=100$; $\mathrm{C}{\mathrm{O}}_2=44$)

The options list, in order: the type of $\mathrm{CaC}{\mathrm{O}}_3$, the mass of $\mathrm{CaC}{\mathrm{O}}_3$ in g, the volume of HCl in ${\text{cm}}^3$ and the concentration of HCl in ${\text{mol dm}}^{-3}$.

An atom of ${}_1^1\mathrm{H}$ has a radius of 0.05 nanometres.

The radius of the nucleus of this atom is approximately 50 000 times smaller.

What is the approximate radius of the nucleus in femtometres?

(1 femtometre $=10^{-15}\text{ m}$)