Q4 of 35 Page 149

Solve the following problems :

1. [OH-] in aqueous solution A is = 4.3 x10-4M and [H3O + ] in aqueous solution of B is 7.3 x 10-10 M, pH of which solution will be less? Which solution will be more basic?


2. Calculate the concentration of OH- in aqueous solution having pH value 9.3.


3. 8 gram NaOH is dissolved in water and the aqueous solution is made to 5 litres. Find pH of this solution.

1. In distilled water: [H3O + ] × [OH-] = 10-14

For solution A, [H3O + ] = 10-14 ÷ [OH-]


= 10-14 ÷ (4.3 × 10-4)


= 2.32 × 10-11 M


For solution B, [H3O + ] = 7.3 × 10-10 M


•Since the hydronium ion concentration of solution B is more, so its pH will be less.


•The solution having the more pH will be more basic. As solution A will have more pH so it will be more basic.


2. using the relation, pOH + pH = 14


pOH = 14 – pH


= 14 – 9.3


= 4.7


Using, pOH = -log10[OH-]


4.7 = -log10[OH-]


log10[OH-] = -4.7


log10[OH-] = 5 -4.7 -5


log10[OH-] = -5 + 0.3


log10[OH-] = + 0.3


[OH-] = antilog


[OH-] = 1.99 × 10-5


3. molar mass of NaOH = atomic mass of Na + Atomic mass of O + atomic mass of H = 23 + 16 + 1 = 40g/ mol.


Volume of solution = 5 litres


Given weight = 8g


No. of moles = given weight ÷ molar mass


= 8g ÷ 40 g/mol


= 0.2 mole


Molarity = no. of moles ÷ volume in litres


= 0.2 ÷ 5


= 0.04 M


Therefore, the hydroxide ion concentration [OH-] = 0.04 M


pOH = -log10[OH-]


pOH = -log10[ 4 × 10-2]


pOH = 2 -log10[ 4]


pOH = 2- 0.6020 = 1.39


using, pOH + pH = 14


pH = 14 – pOH


pH = 14 - 1.39 = 12.61


More from this chapter

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3

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.

 4

Answer the following questions in detail :

1. Explain giving example, Arrhenius acid-base theory, Mention the limitations of this theory.


2. Discuss Bronsted-Lowry Acid-base theory.


3. Discuss methods to measure the pH of the aqueous solution.

 5

Answer the following question in detail:

1. With reference to PH scale,


I. i.Write formula of pH and pOH


ii Mention pH and concentration of H3O + or OH- in acidic, basic and neutral aqueous solutions.


iii Mention limitations of pH scale.


2. Explain the importance of pH in everyday life.


3. “The aqueous solution of the salt produced by neutralization of weak acid and strong base possesses basic nature, while an aqueous solution of salt produced by neutralization of a weak base and strong acid possesses acidic nature” – Explain.

 5

Solve the following problems:

1. pH of an aqueous solution of potassium hydroxide at 298 K temperature is 11.65. The initial volume of this solution is made 6 times by addition of water. What will be the pH of the diluted solution ?


2. What will be the change in the value of pH if the concentration of the aqueous solution of HNO3is increased to 0.05 M from 0.03 M ?