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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.

311.

Which of the following metals does not react with water to produce hydrogen?

A.

Copper

B.

Potassium

C.

Sodium

D.

Zinc

Correct answer is A

Most alkali metals and alkaline earth metals react with water to produce hydrogen. The alkali metals comprise Group 1 of the periodic table, and include lithium, sodium, potassium, etc.

- Zinc is not much reactive with cold or room temperature water but reacts with steam to form zinc oxide and liberate hydrogen gas.

- Copper lies below hydrogen in the activity series of metals, therefore it can not displace hydrogen from water

312.

"Electrons always occupy the lowest empty energy level" is a statement of

A.

Aufbau Principle

B.

Hund's rule

C.

Pauli Exclusion Principle

D.

Periodic law

Correct answer is A

- The Aufbau principle states that electrons fill lower-energy atomic orbitals before filling higher-energy ones

313.

If 20 cm3 of sodium hydroxide was neutralized by 20 cm3 of 0.01 mol dm3 tetraoxosulphate(VI) acid, what is the concentration of the solution?

A.

0.010

B.

0.020

C.

0.100

D.

0.150

Correct answer is B

fracCaVaCbVb  = fracNaNb

( 0.01 X 20 ) / (Cb X 20) = 1 / 2

cross multiply → Cb = (0.01 X 20 X 2) / ( 20 X 1) 

Cb = 0.02 mol/dm3

314.

How many moles of H2SO4 are there in 50 cm3 of 0.108 mol dm3 solution of the acid?

A.

5.4x 10

B.

5.4 x 103

C.

5.4 x 102

D.

5.4x 101

Correct answer is B

No. of moles = molarconc×volume1000

No. of moles = 0.108×501000

: No. of moles = 0.0054 moles = 5.4×103

315.

Which of the following statements about the solubility of a salt is correct?

A.

A salt whose solubility increases with temperature would not crystallize easily on cooling

B.

A salt whose solubility is independent of temperature would normally crystallize out on cooling

C.

Crystallization would be efficient in separating out a salt whose solubility increases considerably with temperature

D.

Solubility of a solid does not affect its crystallization

Correct answer is C

Crystallization is based on the principles of solubility: compounds (solutes) tend to be more soluble in hot liquids (solvents) than they are in cold liquids. If a saturated hot solution is allowed to cool, the solute is no longer soluble in the solvent and forms crystals of pure compound.