Question

22. A waiter added two teaspoons (10 g) of table sugar into a cup containing 200 cm3 of coffee. The chemical formula of sugar is C12H22011.
(a) Calculate the number of sugar molecules in two teaspoons of sugar.​

Answer 1

Answer:

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Correct option is

B

(a)210.65,(b)68.2%

(a) 10% w/w solution means 10 kg of solute and 90 kg of solvent.

ΔT

b

=100.27

o

C−100

o

C=0.27

o

C

M

2

=

ΔT

b

W

1

K

b

W

2

=

0.27×90

0.512×10

=0.21065kg/mol=210.65g/mol

Hence, the average mass of the dissolved materials is 210.65 g/mol.

(b) Sucrose+Water→Glucose+Fructose

The molar masses of sucrose, glucose and fructose are 342 g/mol, 180 g/mol and 180 g/mol respectively.

Assume initially 1 mole of sucrose is present and x moles of sucrose undergo inversion to form x moles of glucose and x moles of fructose. (1−x) moles of sucrose remain unreacted.

The average molar mass of the mixture is

1−x+x+x

342(1−x)+180x+180x

=210.65.

1+x

342+18x

=210.65

342+18x=210.65+210.65x

131.35=192.65x

x=0.682

Hence, the fraction of sugar that has inverted is

1

0.682

×100=68.2.