NSAA 2021 Chemistry S1

• A.M, Q, R, T
• B.M, R, T, Q
• C.Q, M, T, R
• D.Q, R, T, M
• E.R, M, T, Q
• F.R, T, M, Q
• G.T, M, R, Q
• H.T, R, Q, M

Answer: F

• A.none of them
• B.1 only
• C.2 only
• D.3 only
• E.1 and 2 only
• F.1 and 3 only
• G.2 and 3 only
• H.1, 2 and 3

Answer: C

The relative isotopic abundances of a sample of magnesium are shown in the table.

What is the relative atomic mass ($A_r$) of the magnesium?

• A.24.0
• B.24.3
• C.24.5
• D.24.8
• E.25.0

Answer: B

A portion of the Periodic Table is given:

Which one of these trends is correct?

• A.Boiling point: K > Na > Li
• B.Electrical conductivity: NaCl(l) > NaCl(s) > Na(s)
• C.Reactivity: $Br_2 > Cl_2 > F_2$
• D.Melting point: $SiO_2 > H_2O > Na_2O$
• E.Number of double bonds per molecule: $CO_2 > O_2 > H_2O$

Answer: E

$1.0 \text{ mol dm}^{-3}$ 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?

• A.The reaction has reached a state of equilibrium.
• B.An endothermic reaction occurs after $x \text{ cm}^3$ of hydrochloric acid is added.
• C.The reaction rate decreases as the acid is used up.
• D.The sodium hydroxide has been neutralised by $x \text{ cm}^3$ hydrochloric acid.
• E.The sodium hydroxide becomes a weaker base as the volume of the resulting solution increases.

Answer: D

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

• A.Represents a segment of a 5-carbon alkane chain.
• B.Represents the repeating unit of polyethylene, $-[CH_2-CH_2]-$.
• C.Represents a 4-carbon chain with side groups.
• D.Represents the repeating unit of polypropylene, $-[CH(CH_3)-CH_2]-$.
• E.Represents the repeating unit of poly(pent-2-ene), $-[CH(CH_3)-CH(CH_2CH_3)]-$.
• F.Represents the repeating unit of poly(but-1-ene), $-[CH(CH_2CH_3)-CH_2]-$.

Answer: E

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?

• A.$X = Br_2$, $Z = CaCO_3$
• B.$X = Br_2$, $Z = CuO$
• C.$X = Br_2$, $Z = Mg$
• D.$X = Cl_2$, $Z = CaCO_3$
• E.$X = Cl_2$, $Z = CuO$
• F.$X = Cl_2$, $Z = Mg$
• G.$X = O_2$, $Z = CaCO_3$
• H.$X = O_2$, $Z = Mg$

Answer: F

• A.0, 0, +6, +6
• B.+3, +3, +3, +3
• C.0, +2, +6, +6
• D.0, 0, +5, +5
• E.-2, -2, +7, +7

Answer: D

The table shows the reagents in three organic reactions.

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

• A.none of them
• B.1 only
• C.2 only
• D.3 only
• E.1 and 2 only
• F.1 and 3 only
• G.2 and 3 only
• H.1, 2 and 3

Answer: C

• A.1:1
• B.1:2
• C.2:1
• D.1:5
• E.5:1
• F.1:7
• G.7:1

Answer: E

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°. The procedure was then repeated with solvent 2.

The amino acids were then identified with reference to known $R_f$ values in the respective solvents.

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

[Image of a 2D chromatogram. Y-axis: 'distance moved in solvent 1 / cm' from 0 to 10. X-axis: 'distance moved in solvent 2 / cm' from 0 to 20. The solvent front for solvent 1 is at 10 cm. The original spot is at (0,0). The final spots are at approximate coordinates (distance in solvent 2, distance in solvent 1): glycine (6, 8), leucine (14, 8), tyrosine (6, 6), lysine (8, 6).]

Which of the following statements is correct?

• A.Leucine travels further relative to the solvent front in solvent 2 than in solvent 1.
• B.Lysine has a greater $R_f$ value in solvent 1 than it has in solvent 2.
• C.Solvent 1 alone could be used to separate all four amino acids.
• D.Solvent 2 alone could be used to separate all four amino acids.
• E.The $R_f$ value of tyrosine in solvent 1 is 0.6 and in solvent 2 is 0.7.

Answer: B

• A.$N_2$
• B.NO
• C.$NO_2$
• D.$NO_3$
• E.$N_2O_5$

Answer: C

• A.$10.0 \text{ cm}^3$
• B.$12.5 \text{ cm}^3$
• C.$20.0 \text{ cm}^3$
• D.$25.0 \text{ cm}^3$
• E.$100 \text{ cm}^3$

Answer: A

• A.20.0°C
• B.43.0°C
• C.48.0°C
• D.50.0°C
• E.73.0°C
• F.100°C
• G.200 °C
• H.223°C

Answer: E

What is the calculated energy change for the following reaction using appropriate values from the data provided?

$CH_4(g) + 2H_2O(g) \rightarrow CO_2(g) + 4H_2(g)$

• A.+200 kJ mol⁻¹
• B.-200 kJ mol⁻¹
• C.+720 kJ mol⁻¹
• D.-720 kJ mol⁻¹
• E.+1080 kJ mol⁻¹
• F.-1080 kJ mol⁻¹

Answer: A

• A.$100 \text{ dm}^3$
• B.$110 \text{ dm}^3$
• C.$111 \text{ dm}^3$
• D.$125 \text{ dm}^3$
• E.$200 \text{ dm}^3$

Answer: B

• A.chlorine, copper, potassium
• B.chlorine, potassium, copper
• C.copper, chlorine, potassium
• D.copper, potassium, chlorine
• E.potassium, chlorine, copper
• F.potassium, copper, chlorine

Answer: C

0.500 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 $cm^3$ at room temperature and pressure.

What is the mass of magnesium remaining after two seconds?

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

• A.0.024 g
• B.0.036 g
• C.0.048 g
• D.0.452 g
• E.0.464 g
• F.0.476 g

Answer: F

• A.0.42 g
• B.0.85 g
• C.1.70 g
• D.2.97 g
• E.3.39 g
• F.5.94 g

Answer: E

A spoonful of magnesium carbonate powder was added to excess hydrochloric acid in an open conical flask on an electronic balance.

$MgCO_3(s) + 2HCl(aq) \rightarrow MgCl_2(aq) + CO_2(g) + H_2O(l)$

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?

• A.Row A
• B.Row B
• C.Row C
• D.Row D
• E.Row E

Answer: A