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Chemistry questions and answers

Chemistry Questions and Answers

Learn more about the properties, composition, and structure of substances (elements and compounds) with these Chemistry questions and answers. This Test can be used by students preparing for Chemistry in JAMB, WAEC, NECO or Post UTME.

631.

The hydrogen ion concentration of a sample of orange juice is 2.0 X 1011moldm3. What is its pOH? [log102 = 0.3010]

A.

3.30

B.

13.00

C.

10.70

D.

11.30

Correct answer is A

PH+POH=14
pH = Log [H+]

p[H+ ] = 2.0 X 1011moldm3

  pH = Log [2.0 X 1011]

  pH = 10.70

10.70+ pOH =14
pOH = 14 -10.70

= 3.30

632.

An element X forms the following compounds with chlorine; XCl4, XCl3, XCl2. This illustrates the

A.

law of multiple proportions

B.

law of chemical proportions

C.

law of simple proportions

D.

law of conservation of mass

Correct answer is A

The law of multiple proportion states that when element A and B combine to form more than one chemical compound then the various masses of sample A react with a fixed mass of sample B are in a simple multiple ratio.

633.

The figure above shows the electrolysis of molten sodium chloride. Z is the

A.

anode where the Cl ions are oxidized

B.

cathode where the Cl ions are reduced

C.

anode where the Na+ ions are reduced

D.

cathode where the Na+ ions are oxidized

Correct answer is A

During the electrolysis of brine, the chlorine ions are discharged at the anode and are oxidized. While at the cathode Hydrogen ion is discharged.

634.

Which of the following produces relatively few ions in solution?

A.

NaOH

B.

Ca(OH)2

C.

KOH

D.

AI(OH)3

Correct answer is D

Aluminium hydroxide is not soluble in water because it is polymeric and it also has high lattice energy and therefore it is hard to break bonds in this compound. So, water cannot dissolve such types of compounds.

Al(OH)3 is not soluble in water

635.

The choice of method for extracting a metal from its ores depends on the

A.

strength of the core

B.

position of the metal in the electrochemical series

C.

source of the core

D.

position of the metal in the periodic table

Correct answer is B

The method used to extract a metal from its ore depends upon the stability of its compound in the ore, which in turn depends upon the reactivity of the metal:

  • The oxides of very reactive metals, such as aluminum, form stable oxides and other compounds. A lot of energy is needed to reduce them to extract the metal.

  • The oxides of lesser reactive metals, such as iron, form less stable oxides and other compounds. Relatively little energy is needed to reduce them to extract the metal.

  So, the method of extraction of a metal from its ore depends on the metal's position in the reactivity series.