What mass (in g) of NH3 must be dissolved in 475 g of methanol to make a 0.250 m

Question

What mass (in g) of NH3 must be dissolved in 475 g of methanol to make a 0.250 m solution?

A. 2.02 g B. 4.94 g C. 1.19 g D. 8.42 g E. 1.90 g

Determine the vapor pressure of a solution at 25°C that contains 76.6 g of glucose (C6H12O6.) in 250.0 mL of water. The vapor pressure of pure water at 25°C is 23.8 torr and the density of water is 1 g/mL.

A. 70.8 torr B. 72.9 torr C. 23.1 torr D. 22.9 torr E. 7.29 torr

Determine the freezing point of a solution that contains 78.8 g of naphthalene (C10H8, molar mass = 128.16 g/mol) dissolved in 722 mL of benzene (d = 0.877 g/mL). Pure benzene has a melting point of 5.50°C and a freezing point depression constant of 4.90°C/m.

A. 4.76°C B. 4.17°C C. 0.74°C D. 1.33°C E. 1.68°C

Choose the aqueous solution with the smallest osmotic pressure. Assume ideal van't Hoff factors where applicable.

A. 0.120 M C2H6O2 B. 0.040 M (NH4)2SO4 C. 0.060 M K2CO3 D. 0.030 M LiC2H3O2

Explanation / Answer

Post one more question to get the remaining answers

1)

molality = number of moles of solute/mass of solvent in Kg

0.250 = number of moles of solute/0.475

number of moles of solute = 0.11875 moles

Molar mass of NH3 = 14 + 3 * 1 = 17 gm/mol

Mass of NH3 = 0.11875 mol * 17 gm/mol = 2.01875 grams

The correct answer is Option A

2)

Number of moles of water = 250/18 = 13.888 moles

Number of moles of glucose = 76.6/180 = 0.42555 moles

Vapor Pressure of solution = mole fraction of water * Pressure of Pure H2O

=> (13.888/(13.888+0.42555) * 23.8

=> 23.09 torr

Hence the correct answer is Option C

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