The boiling point of water at 749.2 mmHg is 99.60C. Part A What mass percent suc

ID: 998447 • Letter: T

Question

The boiling point of water at 749.2 mmHg is 99.60C.

Part A

What mass percent sucrose (C12H22O11) should be present in an aqueous sucrose solution to raise the boiling point to 100.00C at this pressure?

Express your answer using two significant figures.

? %

The boiling point of water at 749.2 mmHg is 99.60C.

Part A

What mass percent sucrose (C12H22O11) should be present in an aqueous sucrose solution to raise the boiling point to 100.00C at this pressure?

Express your answer using two significant figures.

? %

In reaction pressure is constant.

Step1.

Calculate the molality of solution.

Tb = (100 – 99.60) °C = 0.40 °C

Kb = 0.512 °C·kg·mol¹

m = Tb / ikb

(Where m = molality, Tb =change in boiling point, i=number of ions into which solute dissociates, kb=boiling point elevation constant.)

=0.40 °C /1 × 0.512 °Ckgmol1

= 0.78 mol·kg¹

Step 2.

Calculate the percent composition.

g of sucrosein0.78 mol =( 0.78 mol sucrose / 1 mol sucrose) x 342.30 g sucrose

= 270 g sucrose

So 270 g sucrose is present in 1 kg water.

% by mass =

mass of sucrose /(mass of sucrose + mass of water) × 100%

=270 g / (270 g + 1000 g) × 100%

=270 g /1270 g × 100%

= 21 %

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