Which one of the following solutions will have the greatest concentration of hydroxide ions?

a) 0.100 m hydrochloric acid
b) 0.100 m magnesium hydroxide
c) 0.100 m ammonia
d) 0.300 m rubidium hydroxide
e) 0.250 m calcium hydroxide

e = 0.250 M calcium hydroxide

it will produce 0.5 M [OH⁻].

Explanation:

A = 0.100 M HCl

HCl is an acid it would produce negligible amount of OH⁻.

B = 0.100 M magnesium hydroxide

Mg(OH)₂ + H₂O → Mg²⁺ + 2OH⁻

The ration of Mg(OH)₂  and OH⁻ is 1:2.

[OH⁻] = 2× 0.100 = 0.200 M

C =0.100 M ammonia

NH₃ + H₂O → NH₄OH → NH₄⁺ + OH⁻

The Kb expression will be written as,

Kb = [NH₄⁺] [OH⁻] / [NH₃]

Kb = 1.8 ×10 ⁻⁵

Now we will put the values:

1.8 ×10 ⁻⁵ = [NH₄⁺] [OH⁻] / 0.100

[NH₄⁺] [OH⁻]  = x²

1.8 ×10 ⁻⁵ = x² / 0.100

x² = 1.8 ×10 ⁻⁵ × 0.100

x² =  1.8  × 10 ⁻⁶

x = 1.34 × 10 ⁻³

[OH⁻] = 1.34 × 10 ⁻³ M

d = 0.300 M rubidium hydroxide

RbOH + H₂O    →     Rb⁺ + OH⁻

The ratio of RbOH  and OH⁻ is 1:1.

[OH⁻] = 0.300 M

e = 0.250 M calcium hydroxide

Ca(OH)₂ + H₂O → Ca²⁺ + 2OH⁻

The ration of Ca(OH)₂  and OH⁻ is 1:2.

[OH⁻] = 2× 0.250 = 0.5 M

on passing the small ampere of electric current through the tube made of ar and hg of cfl generates uv rays which excites the fluorescent and thus emits the high radiation by consumption of just 5- 12 w in comparison to incandescent light which requires more power such as around 40 - 55 w to lighten.

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