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JAMB Chemistry Past Questions 2020

10 questions from the JAMB 2020 Chemistry paper, with answers and explanations. Tap "Show answer" under each one when you are ready.

JAMB 2020Question 1 · Acids, Bases, and Salts
A few drop of conc HCL are added to about of a solution of PH 3.4. The PH of the resulting mixture is?
  1. A.less than 3.4
  2. B.greater than 3.4
  3. C.unaltered
  4. D.the same as that of the pure water
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Answer: A. less than 3.4

Adding concentrated HCl increases [], lowering the pH below 3.4.

JAMB 2020Question 2 · Atomic Structure and Chemical Bonding
How many valence electrons are contained in the element ?
  1. A.3
  2. B.4
  3. C.15
  4. D.31
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Answer: A. 3

Phosphorus (atomic number 15) commonly shows a valency of 3 (as in and ).

JAMB 2020Question 3 · Chemistry of Metals
Duralumin consists of aluminum, copper?
  1. A.Zinc and Gold
  2. B.Lead and Manganese
  3. C.Nickel and Silver
  4. D.Manganese and Magnesium
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Answer: D. Manganese and Magnesium

Duralumin is an alloy of aluminium, copper, manganese and magnesium.

JAMB 2020Question 4 · Chemistry of Non-metals and Gases
Which of the following gases will rekindle a brightly burning splint?
  1. A.
  2. B.NO
  3. C.
  4. D.
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Answer: C.

Nitrogen(I) oxide supports combustion similarly to oxygen and rekindles a glowing splint.

JAMB 2020Question 5 · Electrochemistry and Redox Reactions
What are the possible oxidation numbers of an element if its atomic number is 17?
  1. A.-1 and 7
  2. B.-1 and 6
  3. C.-3 and 5
  4. D.-2 and 6
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Answer: A. -1 and 7

Chlorine (atomic number 17) commonly shows oxidation states of -1 (as chloride) and +7 (as in perchlorates), among its range of possible states.

JAMB 2020Question 6 · Organic Chemistry
An example of a polysaccharide is?
  1. A.Dextrose
  2. B.Mannose
  3. C.Glucose
  4. D.Starch
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Answer: D. Starch

Starch is a polysaccharide, a large polymer of glucose units, unlike the monosaccharides dextrose, mannose and glucose.

JAMB 2020Question 7 · Organic Chemistry
An organic compound that does not undergo a reaction with both hydrogen cyanide and hydroxylamine can be?
  1. A.Alkene
  2. B.Alkanal
  3. C.Alkanone
  4. D.Alkanoic Acid
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Answer: D. Alkanoic Acid

Unlike aldehydes and ketones, a carboxylic acid's carbonyl carbon is deactivated by resonance donation from the -OH group, so it does not undergo the typical nucleophilic addition reactions with HCN or hydroxylamine.

JAMB 2020Question 8 · Organic Chemistry
The general formula for the Alkanals is?
  1. A.RCO
  2. B.RCHO
  3. C.ROH
  4. D.RCOOR
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Answer: B. RCHO

Alkanals (aldehydes) have the general formula RCHO.

JAMB 2020Question 9 · Physical Chemistry
Chromatography is used to separate components of mixture which differ in their rates of ?
  1. A.diffusion
  2. B.migration
  3. C.reaction
  4. D.sedimentation
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Answer: B. migration

Chromatography separates mixture components based on their differing rates of migration through the stationary phase.

JAMB 2020Question 10 · Quantitative Chemistry
The volume occupied by of a gas at S.T.P is . What is the relative molecular mass of the gas? [ G.M.V at S.T.P = ]
  1. A.28
  2. B.32
  3. C.44
  4. D.71
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Answer: D. 71

Moles = / = . Molar mass = = 71.

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