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The freezing point of pure water is 0.0°C. How many grams of ethylene glycol (C2H6O2) must be mixed in 100.0 g of water to lower the freezing point of the solution to -8.8°C? g

Sagot :

Answer:

17.54 g

Explanation:

the freezing point of the solution to -8.8°C

depression in freezing point = 8.8°C

Molal freezing point depression constant of ethylene glycol  Kf = 3.11⁰C /m

ΔTf = Kf x m , m is no of moles of solute per kg of solvent .

Let gram of ethylene glycol required be x .

moles = m / mol weight of ethylene glycol

= x / 62

100 g of water = .1 kg

moles of solute dissolved in 1 kg of water

m = x / 62 x .1

m = 10 x / 62

Using the above equation for depression in freezing point

8.8 = 3.11 x 10 x / 62

x = 17.54 g .

The mass of ethylene glycol required to lower the freezing point is 17.54 g.

The given parameters:

  • Freezing point of a pure water, = 0⁰C
  • Mass of water, m = 100 g
  • Freezing point of the solution, = -8.8⁰C

Molar freezing point depression constant of ethylene glycol  Kf = 3.11⁰C /m

Let the mass of ethylene glycol required be x .

The number of moles of the ethylene is calculated as follows;

[tex]n = \frac{x}{M} \\\\n = \frac{x}{62 \times 100 g \ of H_2 O}\\\\n = \frac{x}{6.2}[/tex]

Apply the following equation for depression in freezing point as follows;

[tex]\Delta T_f = n Kf\\\\8.8 = 3.11 \times \frac{x}{6.2} \\\\3.11 x = 54.56\\\\x = \frac{54.56}{3.11} \\\\x = 17.54 \ g[/tex]

Thus, the mass of ethylene glycol required to lower the freezing point is 17.54 g.

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