JAMB Chemistry Past Questions & Answers - Page 46

226.

The oxidation state(s) of nitrogen in ammonium nitrite is/are

A.

-3, +3

B.

+5

C.

-3, +5

D.

-3

Correct answer is A

Ammonium nitrite = NH\(_4\)NO\(_2\)

NH\(_4 ^+\): Let the oxidation number of Nitrogen = x

x + 4 = 1 \(\implies\) x = 1 - 4

x = -3

NO\(_2 ^-\): x - 4 = -1

x = -1 + 4 \(\implies\) x = +3.

The oxidation numbers for Nitrogen in Ammonium Nitrite = -3, +3.

227.

Which quantum divides shells into orbitals?

A.

Spin

B.

Principal

C.

Azimuthal

D.

Magnetic

Correct answer is C

The azimuthal quantum number determines an atom's orbital angular momentum and the shape of the orbital. The principal quantum number determines its number of shells. Magnetic quantum number determines how many orbitals there are as well as their orientation within a subshell.

228.

The shapes of water, ammonia, carbon (iv) oxide and methane are respectively

A.

linear, tetrahedral, angular and pyramidal

B.

angular, pyramidal, linear and tetrahedral

C.

pyramidal, linear, tetrahedral and angular

D.

tetrahedral, angular, pyramidal and linear

Correct answer is B

Ammonia \((NH_3\)) has a trigonal pyramidal structure with a bond angle of approximately 107 degrees. Methane (\(CH_4\)) has a tetrahedral structure with a bond angle of 109.5 degrees. Carbon dioxide is a linear molecule, with a 180-degree bond angle. Water \((H_2O\)) has a bent or V-shaped structure with a bond angle of approximately 104.5 degrees.

229.

A cell shorthand notation can be written as A / A\(^+\) // B\(^{2+}\) /B. The double slash in the notation represents the 

A.

electrolyte

B.

electrodes

C.

salt bridge

D.

solid - liquid interface

Correct answer is C

No explanation has been provided for this answer.

230.

Consider the reaction: A + 2B\(_{(g)} \rightleftharpoons \) 2C + D\(_{(g)}\) (\(\Delta\)H = +ve)

What will be the effect of decrease in temperature on the reaction?

A.

Rate of backward reaction will increase

B.

The equilibrium constant will shift

C.

Rates of forward and backward reactions are not affected

D.

Rate of forward reaction will increase

Correct answer is A

The given reaction is endothermic, hence, a decrease in temperature will favor the exothermic side which is the backward reaction.