Question 23 When 793. mg of a certain molecular compound X are dissolved in 85. g of cyclohexane C6H12, the freezing point of the solution is measured to be 4.7 °C. Calculate the molar mass of X. If you need any additional information on cyclohexane, use only what you find in the ALEKS Data resource. Also, be sure your answer has a unit symbol, and is rounded to the correct number of significant digits.

102.7 g/mol is the molar mass for compound X

Explanation:

Colligative property of freezing point depression should be used here:

ΔT = Kf . m . i

We assume compound x is not ionic, so i = 1 (Van't Hoff)

Freezing T° of pure solvent - Freezing T° solution = Kf . molality . i

6.59°C - 4.7°C = 20.8 °C/m . m . 1

1.89°C / 20.8 m/°C = m → 0.0908 mol/kg

Molality refers the moles of solute that corresponds to 1 kg of solvent, but in this case our solvent's mass is 85 g.

We convert the mass to kg in order the know, the moles of solute:

85 g. 1kg/ 1000 g = 0.085 kg

0.0908 mol/kg . 0.085 kg =7.72×10⁻³ moles

These are the moles that corresponds to 0.793 g of compound

(793 mg . 1 g/1000mg = 0.793g)

Molar mass = g/mol → 0.793 g / 7.72×10⁻³ mol = 102.7 g/mol

The molar mass of compound X is 104.8 g/mol

Explanation:

Step 1: Data given

Mass of compound X = 793 mg = 0.793 grams

Mass of cyclohexane = 85 grams = 0.085 kg

freezing point of the solution = 4.7 °C

Freezing point cyclohexane = 6.5 °C

Freezing point depression constant cyclohexane = 20.2 °C/m

Step 2: Calculate molality

ΔT = i*Kf*m

⇒ΔT  = freezing point depression = 6.5 - 4.7 = 1.8 °C

⇒ i = the van't hoff factor = 1

⇒ Kf = Freezing point depression constant cyclohexane = 20.2 °C/m

⇒ m = the molality = ?

1.8 = 20.2 * m

m = 1.8 / 20.2

m = 0.0891 molal

Step 3: Calculate moles of compound X

molality = moles compound X / mass cyclohexane

0.0891 molal = moles compound X / 0.085 kg

moles compound X = 0.0891 molal * 0.085 kg

moles compound X = 0.00757 moles

Step 4: Calculate molar mass compound X

Molar mass = mass / moles

Molar mass = 0.793 grams / 0.00757 moles

Molar mass = 104.8 g/mol

The molar mass of compound X is 104.8 g/mol

answer: the value of enthalpy change will be -152.80 kj.

solution:

pressure = 1atm , temperature = = 298 k

given that pressure and temperature are same in both gases , the number of moles of both gases can be determined by the ideal gas equation.

according to reaction 3 moles no are reacting with 1 mol of ,then 0.49 mol of no will react with moles of ozone that is 0.16 moles of ozone. since, no is limiting reagent and is an excessive reagent.

enthalpy change for the reaction between the given volumes of the gases is :