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3 years ago

What is the value of freezing point depression of a solution of 15.0g of NaCl in 250g of water?

Chemistry

1 answer:

kobusy [5.1K]3 years ago

7 0

Answer:

-3.82ºC is the freezing point of solution

Explanation:

We work with the Freezing point depression to solve the problem

ΔT = m . Kf . i

ΔT = Freezing point of pure solvent - freezing point of solution

Let's find out m, molality (moles of solute in 1kg of solvent)

15 g / 58.45 g/mol = 0.257 moles of NaCl

NaCl(s) → Na⁺ (aq) + Cl⁻(aq)

i = 2 (Van't Hoff factor, numbers of ions dissolved)

m = mol /kg → 0.257 mol / 0.250kg = 1.03 m

Kf = Cryoscopic constant → 1.86 ºC/m (pure, for water)

0ºC - Tºf = 1.03m . 1.86ºC/m . 2

Tºf = -3.82ºC

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Why don't solids change shape?

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3 years ago

Two solutions, initially at 24.60 °C, are mixed in a coffee cup calorimeter (Ccal = 15.5 J/°C). When a 100.0 mL volume of 0.100

yulyashka [42]

Answer:

ΔH = -59.6kJ/mol

Explanation:

The reaction that occurs between Ag⁺ and Cl⁻ ions is:

Ag⁺ + Cl⁻ → AgCl(s) + ΔH

To find ΔH we need to obtain moles of reaction and heat released in the reaction because ΔH is defined as heat released per mole of reaction.

Moles of reaction:

Moles of Ag⁺ and Cl⁻ added are:

Ag⁺: 0.100L * (0.100mol / L) = 0.01moles

Cl⁻: 0.100L * (0.200mol / L) 0 0.02 moles

That means limiting reactant is Ag⁺ and moles of reaction are 0.01 moles

Heat released:

To find heat released we must use coffe cup calorimeter equation:

Q = C*m*ΔT

Where C is specific heat of solution (4.18J/g°C), m is the mass of solution (200g because there are 100 + 100mL = 200mL and density of solution is 1g/mL) and ΔT is change in temperature (25.30°C - 24.60°C = 0.70°C).

Replacing:

Q = C*m*ΔT

Q = 4.18J/g°C * 200g * 0.70°C

Q = 585,2J

Is total heat released.

The calorimeter absorbs:

15.5J / °C * 0.7°C = 10.85

Thus, when 0.01 moles reacts, 585.2J + 10.85 = 596.05J are released (Heat released is heat abosrbed by calorimeter + Heat absorbed by water) and ΔH is:

ΔH = 596.05J / 0.01 moles =

ΔH = 59605J / mol =

As heat is released, ΔH < 0.

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3 years ago