Solve the following problems:

1. Calculate pH of an aqueous solution having H₃O ⁺ concentration equal to 7.9 x 10^-11 M. Which nature, acidic basic or neutral will be possessed by this aqueous solution.

2. Calculate pH of 0.00424 M aqueous solution of KOH.

3. How many times concentrated will be the aqueous solution having pH 11.9 as compared to aqueous solution having pH 8?

4. How will you prepare 500ml aqueous solution of 0.2 M H₂SO₄?

5. How will you prepare 125 ml 0.03 M aqueous solution of KOH.

1. [H₃O ⁺ ] = 7.9 x 10^-11 M

The pH can be calculated using the formula:

pH = -log₁₀[H₃O ⁺ ]

putting the value of hydronium ion concentration in above equation, we get:

pH = -log₁₀[7.9 x 10^-11]

pH = 11 - log₁₀[7.9]

using the log table, we get:

pH = 11-0.8976 = 10.10

Since the pH of the solution comes out to be greater than 7, thus the solution is basic in nature.

2. [OH^-] = 0.00424 M

The formula to calculate pOH is:

pOH = -log₁₀[OH^-]

Putting the value of hydroxide ion concentration in above equation:

pOH = -log₁₀[0.00424]

= -log₁₀[4.24 × 10^-3]

= 3 - log₁₀[4.24]

= 3 – 0.6274

= 2.37

Using the relation, pH + pOH = 14

pH = 14- 2.37 = 11.63

3. A) for solution of pH = 11.9, pOH = 2.1

We know that, pOH = -log₁₀[OH^-]

Putting given pOH value in above equation we get:

2.1 = -log₁₀[OH^-]

log₁₀[OH^-] = -2.1

log₁₀[OH^-] = 3 – 2.1 – 3

log₁₀[OH^-] = -3 + 0.9

[OH^-] = antilog = 7.943 × 10^-3 M

B) solution with pH = 8, pOH = 6

6 = - log₁₀[OH^-]

[OH^-] = 10^-6

Dividing the hydroxide ion concentration of s by Ist solution by second solution, we get: (7.943 × 10^-3 ÷ 10^-6 ) = 7943 times.

4. the formula used to find molarity is:

Putting the value of molarity = 0.2 M

Volume in mL = 500 mL

Molar mass = 98 g/mol

Weight = 9.8 g.

So, by adding 9.8 g of H₂SO₄ in the 500mL water, we can prepare its 0.2M solution.

5. the formula used to find molarity is:

Molarity = 0.03 M

Volume in mL = 125 mL

Molar mass of KOH = 56g/ mol

Weight = 0.21 g.

So by adding 0.21 g of KOH in 125 mL water, its 0.03 solution can be prepared.