SELECT * FROM question_mgmt as q WHERE id=1772 AND status=1 SELECT id,question_no,question,chapter FROM question_mgmt as q WHERE courseId=3 AND subId=9 AND chapterId=57 and ex_no='1' AND status=1 ORDER BY CAST(question_no AS UNSIGNED) CBSE Free NCERT Solution of 12th chemistry Solutions calculate a molality b molarity and

Question:

Calculate

(a) molality

(b) molarity and

(c) mole

fraction of KI if the density of 20% (mass/mass) aqueous KI is 1.202 g mL-1.

Answer:

(a) Molar mass of KI = 39 + 127 = 166 g mol - 1

20% (mass/mass) aqueous solution of KI means 20 g of KI is present in 100 g of solution.

That is,

20 g of KI is present in (100 - 20) g of water = 80 g of water

Therefore, molality of the solution = Moles of KI / Mass of water in kg

= 20/166 / 0.08 m

= 1.506 m

= 1.51 m (approximately)

 

(b) It is given that the density of the solution = 1.202 g mL - 1

∴Volume of 100 g solution = Mass /  Density

= 100g / 1.202g mL-1

= 83.19 mL

= 83.19 × 10 - 3 L

Therefore, molarity of the solution = 20/166 mol / 83.19 × 10 - 3 L

= 1.45 M

 

(c) Moles of KI = 20/166 = 0.12 mol

Moles of water = 80/18 = 4.44 mol

Therefore, mole fraction of KI = Moles of KI / (Moles of KI + Moles of water)

= 0.12 / (0.12+4.44)

= 0.0263


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