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3 years ago

What is the molality of a solution of water and kcl if the freezing point of the solution is –3mc030-1.jpgc?

1 answer:

4 0

We will use the expression for freezing point depression ∆Tf
∆Tf = i Kf m
Since we know that the freezing point of water is 0 degree Celsius, temperature change ∆Tf is
∆Tf = 0C - (-3°C) = 3°C
and the van't Hoff Factor i is approximately equal to 2 since one molecule of KCl in aqueous solution will produce one K+ ion and one Cl- ion:
KCl → K+ + Cl-
Therefore, the molality m of the solution can be calculated as
3 = 2 * 1.86 * m
m = 3 / (2 * 1.86)
m = 0.80 molal

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3 years ago

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Consider the calculation of the pressure in kilopascals exerted by 1.25 g of nitrogen gas in a flask of volume 250 mL (0.250 dm3

Harrizon [31]

The amount of the nitrogen gas, N₂ molecules present is 2.68×10²² molecules

<h3>Avogadro's hypothesis </h3>

1 mole of N₂ = 6.02×10²³ molecules

<h3>How to determine the mole of N₂</h3>

We'll begin by calculating the number of mole of N₂. This can be obtained as follow:

Mass of N₂ = 1.25 g
Molar mass of N₂ = 28.02 g/mol
Mole of N₂ =?

Mole = mass / molar mass

Mole of N₂ = 1.25 / 28.02

Mole of N₂ = 0.0446 mole

<h3>How to determine the molecules of N₂ present</h3>

From Avogadro's hypothesis,

1 mole of N₂ = 6.02×10²³ molecules

Therefore,

0.0446 mole N₂ = 0.0446 × 6.02×10²³

0.0446 mole N₂ = 2.68×10²² molecules

Thus, the molecules of N₂ present is 2.68×10²² molecules

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2 years ago

The molal boiling point elevation constant Kb = 1.97 C .Kg.Mol-1 for a certain substance X. When 31.98 g of urea are dissolved i

Ipatiy [6.2K]

Answer:

Boiling point of pure liquid is 135.4°C

Explanation:

The boiling point elevation (Colligative property of solutions) follows the formula:

ΔT = Kb×m×i

<em>ΔT is equal to increase in boiling point (Boililng point solution - boiling point pure liquid), Kb is boiling point elevation constant of the liquid, m is molality of solution and i is Van't Hoff factor.</em>

<em>Molality of solution (Moles urea / Kg X):</em>

Moles urea: 31.98g * (1mol / 60.06g) = 0.53247 moles

-60.06g/mol = Molar mass urea-

In 650g = 0.650kg:

0.53247 moles urea / 0.650kg = 0.8192m

Van't Hoff factor of urea is 1

Replacing in the equation:

ΔT = Kb×m×i

ΔT = 1.97°CKgMol⁻¹×0.8192m×1

ΔT = 1.6

As the solution boils at 137°C:

ΔT = Boililng point solution - boiling point pure liquid

ΔT = 1.6°C = 137.0°C - boiling point pure liquid

Boiling point of pure liquid is 135.4°C

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4 years ago