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Grade 12 Chemistry entrance exam, 2012 E.C. (2020)

Real questions from the Grade 12 university entrance exam in Chemistry, as students sat it in 2012 E.C. Every question comes with the correct answer and a worked explanation.

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  • Natural science stream

    Who sits it

  • 2012 E.C. (2020)

    Exam year

  • 77 questions with answers

    In this set

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Answer each question yourself before opening the answer. The explanations point to the exact place in the textbook, so you know which page to reread when you miss one.

Question 1

According to World Health Organization (WHO), the standard for the concentration of alcohol used to prevent COVID-19 virus is 70%. How much water has to be added to prepare the standard alcohol for 1L of 96% alcohol?

  1. A.1371.4 ml
  2. B.371.4 L
  3. C.371.4 ml
  4. D.30 ml
Show the answer and explanation

Answer: C 371.4 ml

Why

Using the dilution formula C1V1=C2V2C_1 V_1 = C_2 V_2, the final volume required is V2=(96%×1000 mL)/70%=1371.4 mLV_2 = (96\% \times 1000\text{ mL}) / 70\% = 1371.4\text{ mL}. Thus, the volume of water that must be added to the 1 L1\text{ L} of alcohol is 1371.4 mL−1000 mL=371.4 mL1371.4\text{ mL} - 1000\text{ mL} = 371.4\text{ mL}.

Question 2

In which of the following solvents would you expect the solubility of NaCl to be greatest?

  1. A.Carbon tetrachloride (CCl4)
  2. B.Water (H2O)
  3. C.Methanol (CH3OH)
  4. D.Methanol (CH3OH)
Show the answer and explanation

Answer: B Water (H2O)

Why

NaCl is an ionic compound and dissolves best in highly polar solvents that can effectively solvate its ions through strong ion-dipole interactions. Water has a much higher dielectric constant and polarity compared to carbon tetrachloride and methanol.

Question 3

Which of the following substances might stabilize a colloidal suspension of oil in water?

  1. A.Sodium stearate NaCO2(CH2)16CH3
  2. B.Sodium bicarbonate (NaHCO3)
  3. C.H2O
  4. D.CaCl2
Show the answer and explanation

Answer: A Sodium stearate NaCO2(CH2)16CH3

Why

Sodium stearate is an emulsifying agent (soap) containing a hydrophobic non-polar hydrocarbon tail that interacts with the oil and a hydrophilic polar head group that interacts with water, thereby stabilizing the colloidal suspension of oil in water.

Question 4

How many moles of unknown weak acid (HA) in a 100 L solution are required to produce a solution with pH = 2? Ka of the unknown weak acid (HA) = 5×10^-3.

  1. A.3×10^-3
  2. B.0.3×10^-3
  3. C.3
  4. D.0.3
Show the answer and explanation

Answer: C 3

Why

A pH of 2 corresponds to [H+]=10−2 M=0.01 M[\text{H}^+] = 10^{-2}\text{ M} = 0.01\text{ M}. Since Ka=[H+]2[HA]0−[H+]K_a = \frac{[\text{H}^+]^2}{[\text{HA}]_0 - [\text{H}^+]}, we have 5×10−3=(0.01)2[HA]0−0.015 \times 10^{-3} = \frac{(0.01)^2}{[\text{HA}]_0 - 0.01}, giving [HA]0=0.03 M[\text{HA}]_0 = 0.03\text{ M}. For a 100 L100\text{ L} solution, the required amount is 0.03 M×100 L=3 moles0.03\text{ M} \times 100\text{ L} = 3\text{ moles}.

Question 5

If different processes are used to bring about the same change the enthalpy changes during these processes are the same, this is the statement of

  1. A.Hess's law
  2. B.Standard Enthalpy
  3. C.1st law thermodynamics
  4. D.2nd law thermodynamics
Show the answer and explanation

Answer: A Hess's law

Why

Hess's law states that the total enthalpy change for a chemical reaction is the same regardless of whether the reaction takes place in one step or in several steps.

Question 6

Which of the following 0.1 M solutions has the lowest pH?

  1. A.NaNO2
  2. B.KClO4
  3. C.NH4Cl
  4. D.NH3
Show the answer and explanation

Answer: C NH4Cl

Why

NH4Cl\text{NH}_4\text{Cl} is a salt of a strong acid (HCl\text{HCl}) and a weak base (NH3\text{NH}_3). Its cation, NH4+\text{NH}_4^+, undergoes hydrolysis in water to produce hydronium ions, making the solution acidic (%pH<7\%\text{pH} < 7), which is lower than the neutral KClO4\text{KClO}_4 or basic NaNO2\text{NaNO}_2 and NH3\text{NH}_3 solutions.

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Chemistry papers from other years

2018 E.C. (2026)2017 E.C. (2025)2016 E.C. (2024)2015 E.C. (2023)2014 E.C. (2022)2013 E.C. (2021)2011 E.C. (2019)2010 E.C. (2018)2009 E.C. (2017)2008 E.C. (2016)2007 E.C. (2015)2006 E.C. (2014)2005 E.C. (2013)

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Are these the real 2012 E.C. Chemistry entrance exam questions?

Yes. They come from the national university entrance exam in Chemistry that students sat in 2012 E.C. (2020). Our set holds 77 of its questions, each with its answer and an explanation that points back to the textbook.

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