Question

7. If a 3.0 M solution of glucose (C H202), a 2.0 M solution of Na SO, and a 1.0 M solution of (NH4)3PO4, is made, which solution will have the lowest vapor pressure, highest boiling point, and lowest freezing point?

Answer 1

Answer of Question No.-7:

Lowering of vapour pressure, elevation of boiling point and depression of freezing point are known as colligative properties of a solution. These properties depend only on the number of solute particles, irrespective of their nature.

This implies, higher the number of solute particles in a solution, higher will be the changes of these colligative properties.

Thus, lowering of vapour pressure of a solution having 3 mole solutes, will be less than a solution having 6 mole solutes.

Now 3.0 M glucose will have 3.0 M solute particles.

2.0 M Na₂SO₄ will furnish {2.0 x (2 sodium ion + 1 sulphate ion)} M = 6.0 M solute particles

1.0 M (NH₄)₃PO₄ will furnish {1.0 x (3 ammonium ion + 1 phosphate ion)} M = 4.0 M solute particles

Thus, 2.0 M Na₂SO₄ will have lowest vapour pressure, highest boiling point and lowest freezing point.

Answer of question no. 10:

a) No, all the atoms of cyclohexanone are not in the same plane, because, apart from the carbonyl group, all other carbons of cyclohexane are SP³ hybridised and therefor have tetrahedral 3-dimensional orientation.

b) Molecular mass of benzophenone is higher than cyclohexanone. Thus benzophenone has higher van der wall attraction between the molecules, leading to its solid nature at room temperature. Such attractive force is less in cyclohexanone and therefore, it is liquid at room temperature.

Answer of Question No. 11:

Since benzophenone and cyclohexanone are organic hydrophobic compounds, they are soluble only in organic solvents (methanol, chloroform, acetone etc.). So, in order to wash the test tubes we can use these organic solvents.