CBSE (Science) Class 12CBSE
Share
Notifications

View all notifications

Boiling point of water at 750 mm Hg is 99.63°C. How much sucrose is to be added to 500 g of water such that it boils at 100°C. - CBSE (Science) Class 12 - Chemistry

Login
Create free account


      Forgot password?

Question

Boiling point of water at 750 mm Hg is 99.63°C. How much sucrose is to be added to 500 g of water such that it boils at 100°C. Molal elevation constant for water is 0.52 K kg mol−1.

Solution 1

Here, elevation of boiling point ΔTb = (100 + 273) − (99.63 + 273)

= 0.37 K

Mass of water, wl = 500 g

Molar mass of sucrose (C12H22O11), M2 = 11 × 12 + 22 × 1 + 11 × 16

= 342 g mol−1

Molal elevation constant, Kb = 0.52 K kg mol−1

We know that:

`triangleT_b = (K_bxx1000xxw_2)/(M_2xxw_1)`

`=>w_2 = (triangleT_bxxM_2xxw_1)/(K_bxx1000)`

`= (0.37xx342xx500)/(0.52xx1000)`

= 121.67 g (approximately)

Hence, 121.67 g of sucrose is to be added.

Solution 2

Given ΔTb = 100 - 96.63 = 3.37º

Mass of water, w1 = 500g

Molar mass of water, M1 = 18g mol-1

Molar mass of sucrose, M2 = 342g mol-1

To find :Mass of sucrose, w2 = ?

Solution: we know, ΔT= Kb x m

= `K_bxxw_2/M_2xx1000/w_1`

`=>w_2 = (M_2xxw_1xxtriangleT_B)/(1000xxK_b)` = `(342xx500xx3.37)/(1000xx0.52)`

w2 = 1108.2g

Mass of solute w2 = 1.11 kg

Solution 3

Here, elevation of boiling point ΔTb = (100 + 273) − (99.63 + 273)

= 0.37 K

Mass of water, wl = 500 g

Molar mass of sucrose (C12H22O11), M2 = 11 × 12 + 22 × 1 + 11 × 16

= 342 g mol−1

Molal elevation constant, Kb = 0.52 K kg mol−1

We know that:

`triangleT_b = (K_bxx1000xxw_2)/(M_2xxw_1)`

`=>w_2 = (triangleT_bxxM_2xxw_1)/(K_bxx1000)`

`= (0.37xx342xx500)/(0.52xx1000)`

= 121.67 g (approximately)

Hence, 121.67 g of sucrose is to be added.

  Is there an error in this question or solution?

APPEARS IN

Solution Boiling point of water at 750 mm Hg is 99.63°C. How much sucrose is to be added to 500 g of water such that it boils at 100°C. Concept: Colligative Properties and Determination of Molar Mass - Elevation of Boiling Point.
S
View in app×