Question

What is the boiling point of sugar solution at atmospheric pressure ? How do we calculate boiling point elevation of sugar solution

Answer 1

The boiling point depends on the concentration of the sugar solution.

Explanation:

Assume that you have dissolved 2000 g of sugar in 1 kg water.

The formula for boiling point elevation `ΔT_"b"` is

`color(blue)(bar(ul(|color(white)(a/a)ΔT_"b" = iK_"b"mcolor(white)(a/a)|)))" "`

where

• `i` is the van't Hoff `i` factor
• `K_"b"` is the molal boiling point elevation constant
• `b` is the molality of the solution

We must first calculate the molal concentration `b` of the solution.

`"Moles of sucrose" = 2000color(red)(cancel(color(black)("g sucrose"))) × "1 mol sucrose"/(342.30 color(red)(cancel(color(black)("g sucrose")))) = "5.843 mol sucrose"`

`b = "moles of solute"/"kilograms of solvent" = "5.483 mol"/("1.000 kg") = "5.483 mol/kg"`

In this problem,

`icolor(white)(m) = 1`, because sugar is a nonelectrolyte
`K_text(b) = "0.515 °C·mol·kg"^"-1"`
`b color(white)(m)= "5.483 mol·kg"^"-1"`

`ΔT_"b" = iK_"b"b = 1 × "0.515 °C·"color(red)(cancel(color(black)("kg·mol"^"-1"))) × 5.483 color(red)(cancel(color(black)("mol·kg"^"-1"))) = "2.824 °C"`

`T_"b" = T_"b"^@ + ΔT_"b" = "100 °C +2.824 °C" = "102.824 °C"`

The boiling point of the sugar solution is 102.82 °C.