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Grade 12 Chemistry entrance exam, 2018 E.C. (2026), version 1

Real questions from the Grade 12 university entrance exam in Chemistry, as students sat it in 2018 E.C. Every question comes with the correct answer and a worked explanation. The 2018 E.C. exam went out in several versions. This page holds version 1; the others are listed further down.

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  • Natural science stream

    Who sits it

  • 2018 E.C. (2026), version 1

    Exam year

  • 65 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

Who used the 'cathode ray tube' to discover the electron and determine its charge to mass ratio?

  1. A.Robert. A. Millikan
  2. B.James Chadwick
  3. C.J.J. Thomson
  4. D.Ernest Rutherford
Show the answer and explanation

Answer: C J.J. Thomson

Why

Thomson sent a beam through a cathode ray tube and bent it with electric and magnetic fields. From how far the beam bent he worked out the charge to mass ratio of the particles in it, and those particles are the electrons. Millikan is the tempting choice because his oil drop experiment is also about the electron, but he measured the charge on its own, not the charge to mass ratio.

Question 2

Among the following postulates of Dalton's atomic theory, the one that was modified in the modern atomic theory is

  1. A.Atoms are indivisible
  2. B.Atoms are the smallest particle of all elements
  3. C.Atoms of more than one element combine to form compounds
  4. D.Atoms are indestructible
Show the answer and explanation

Answer: A Atoms are indivisible

Why

Dalton said the atom could not be broken down. The discovery of the electron, the proton and the neutron showed that it can, so that postulate had to be changed. B is the tempting one, but an atom is still the smallest particle that keeps the chemical identity of an element, so that idea survives in modern theory.

Question 3

Which of the following statements can be used as an example to describe the law of definite proportion?

  1. A.48g of magnesium ribbon burns in excess oxygen to form 80g of magnesium oxide
  2. B.The mass in gram of oxygen to phosphorus in P4O10 to that in P4O6 is in 3:2 ratio
  3. C.White chalk consists of the elements Calcium, carbon and oxygen which are combined in the mass ratio of 10:3:12 regardless of its source.
  4. D.Water is a colorless liquid at room temperature
Show the answer and explanation

Answer: C White chalk consists of the elements Calcium, carbon and oxygen which are combined in the mass ratio of 10:3:12 regardless of its source.

Why

The law of definite proportion says a pure compound always holds the same elements in the same fixed mass ratio, whatever its source. Chalk always giving calcium, carbon and oxygen in a 10:3:12 mass ratio is exactly that. B is tempting, but comparing two different compounds of the same elements, P4O10P_4O_{10} against P4O6P_4O_6, is the law of multiple proportions.

Question 4

The statement 'The properties of the elements are periodic functions of their atomic masses' is the

  1. A.Law of mass action
  2. B.Mendeleev's periodic law
  3. C.Modern periodic law
  4. D.Law of definite proportion
Show the answer and explanation

Answer: B Mendeleev's periodic law

Why

Mendeleev lined the elements up by increasing atomic mass and saw their properties repeat at regular intervals. That is his periodic law. C is the tempting answer, but the modern periodic law makes properties a function of atomic number, not atomic mass, and that change is what fixed the places where Mendeleev's order broke down.

Question 5

What was the main conclusion of the Rutherford Gold Foil Experiment conducted by Ernest Rutherford?

  1. A.Electrons carry a negative charge.
  2. B.A proton is a hydrogen atom without an electron.
  3. C.Electrons move around the nucleus in fixed orbits.
  4. D.Most of the mass and all the positive charge of an atom are concentrated in a very small nucleus
Show the answer and explanation

Answer: D Most of the mass and all the positive charge of an atom are concentrated in a very small nucleus

Why

Most alpha particles passed straight through the gold foil, but a few came back at sharp angles. Rutherford read that to mean the atom is mostly empty space with all its positive charge and nearly all its mass packed into a very small centre, the nucleus. C is tempting, but the idea of fixed orbits came later from Bohr, not from this experiment.

Question 6

The number of protons, neutrons and electrons respectively in Cd2+ are _____.

  1. A.48, 64, 48
  2. B.48, 64, 46
  3. C.48, 64, 50
  4. D.48, 63, 46
Show the answer and explanation

Answer: B 48, 64, 46

Why

Cadmium has atomic number 48, so every cadmium particle has 48 protons. The isotope in the question has mass number 112, so the neutron count is 112−48=64112 - 48 = 64. The 2+ charge means two electrons were lost, leaving 48−2=4648 - 2 = 46. A is tempting if you keep the electron count equal to the proton count, but that is only true for a neutral atom, not for an ion.

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The other Chemistry papers of 2018 E.C.

2018 E.C. (2026)2018 E.C. (2026), version 22018 E.C. (2026), version 4

Chemistry papers from other years

2017 E.C. (2025)2017 E.C. (2025), round 12017 E.C. (2025), version 22016 E.C. (2024)2016 E.C. (2024), Tigray2016 E.C. model exam2015 E.C. (2023)2014 E.C. (2022)2013 E.C. (2021)2012 E.C. (2020)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 2018 E.C. Chemistry entrance exam questions?

Yes. They come from the national university entrance exam in Chemistry that students sat in 2018 E.C. (2026). Our set holds 65 of its questions, each with its answer and an explanation that points back to the textbook.

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Can I download the Chemistry 2018 E.C. paper as a PDF?

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