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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.

421.

How many valence electrons are contained in the element 3115P?

A.

3

B.

4

C.

15

D.

31

Correct answer is A

The element is Phosphorus in group 5 with valencies of 3 and 5.

422.

The products of the thermal decomposition of ammonium trioxonitrate(v) are?

A.

Nitrogen (I) Oxide and Water

B.

Ammonia and Oxide

C.

Nitrogen and Water

D.

Nitrogen (IV) Oxide and Water

Correct answer is A

NH4NO3 Ammonium Trioxonitrate(V) , unlike all other metallic trioxonitrates(v), decomposes on heating to give nitrogen(i)oxide N2O and water.

423.

Four elements P, Q, R and S have atomic numbers of 4, 10, 12 and 14 respectively. Which of these elements is noble gas? 

A.

P

B.

Q

C.

R

D.

S

Correct answer is B

They are the most stable due to having the maximum number of valence electrons their outer shell can hold. Therefore, they rarely react with other elements since they are already stable.

424.

If the quantity of oxygen occupying 2.76L container at a pressure of 0.825 atm and 300k is reduced by one-half, what is the pressure exerted by the remaining gas?

A.

1.650atm

B.

0.825atm

C.

0.413atm

D.

0.275atm

Correct answer is A

Using the combined gas law formula,

Given that P1 = 0.825,   V1 = 2.76 L, V2 = 1.38 L, P2 = ?

And T1 = T2; we would have P2 = [ P1 X V1 ] ÷ V2

: [0.825 X 2.76]  ÷ 1.38

= 1.650atm

425.

When water drops are added to calcium carbide in a container and the gas produced is passed through a jet and lighted, the resultant flame is called an?

A.

Oxyethene

B.

Oxyhydrocarbon flame

C.

Oxyacetylene flame

D.

Oxymethane flame

Correct answer is C

The reaction of calcium carbide with water, producing acetylene and calcium hydroxide, was discovered by Friedrich Wöhler in 1862. This reaction was the basis of the industrial manufacture of acetylene, and is the major industrial use of calcium carbide.