Question

34.2g of sugar was dissolved in water to produce 214.2g of suger syrup calculate molarity and mole fraction of sugar in the syrup (C=12, H=1, O=16)​

Answer 1

Answer:

1). Mole fraction of sugar in syrup = 1/101

2). Molality of sugar in syrup = 0.5 mol/kg

» NOTE : MOLARITY CAN'T BE CALCULATED WITH GIVEN MASS , IT IS ONLY CALCULATED WITH VOLUME , BUT MOLALITY CAN BE CALCULATED .

Explanation:

1). Mole fraction :

»no. of moles of sugar(solute)/total moles of solution(solution)

(I). sugar = C12H22O11

Weight of sugar = 34.2g (given)

Molar mass of sugar = 342 g/mol

» mole of sugar = 34.2/342 = 1/10 mole

(II). Water = H2O

Weight of water = 214.2-34.2=180 g

Molar mass of water = 18 g/mol

» mole of water = 180/18 = 10 mole

» Total moles of solution = 1/10 +10 = 101/10 moles

Now ,

» Mole fraction = (1/10)/(101/10)

= 1/10 × 10/101

[Answer] = 1/101 [ Mole fraction is a unit less quantity]

2). Molality

» If mass is given in gram then ,

Molality = (weight of solute × 1000)/ (Molar mass of solute × weight of solvent)

Hence ,

weight of solute (Sugar) = 34.2 g (Given)

weight of solvent (water) = 180 g (Given)

Molar mass of solute = 342 g

» (34.2 × 1000)/(342 × 180)

= 34200/61560

≈ 0.5 mole/Kg [Answer]

Regards ,

Ishant Srivastava