Question

Four liquids are described in the table below. Use the second column of the table to explain the order of their freezing points, and the third column to explain the order of their boiling points. For example, select '1' in the second column next to the liquid with the lowest freezing point. Select '2' in the second column next to the liquid with the next higher freezing point, and so on. In the third column, select '1' next to the liquid with the lowest boiling point, '2' next to the liquid with the next higher boiling point, and so on. Note: the density of water is 1.00 g/mL solution freezing pointboiling point (choose one) (choose one) (choose one) (choose one) (choose one) (choose one) (choose one) (choose one) 4.3 g of hydroiodic acid (HI) dissolved in 200. mL of water 4.3 g of glycerin (C3Hg03) dissolved in 200. mL of water 4.3 g of calcium chloride (CaCl2) dissolved in 200. mL of water 200. mL of pure water

Answer 1

No' of moles of HI = [wt of HI] / [Gram.Mol.Wt of HI ] = 4.3 g / 128 g = 0.0362

In Aqueous solutions HI on dissociation gives H⁺ and I^-( total 2 Ions).

so the total number of moles of ions in the HI Aq solution = 2 x 0.0362 moles = 0.0672 moles

No' of moles of glycerin = [wt of glycerin] / [Gram.Mol.Wt of glycerin ] = 4.3 g / 92 g = 0.0467 moles

note: glycerin does not dissociates in water.

No' of moles of CaCl₂ = [wt of CaCl₂] / [Gram.Mol.Wt of CaCl₂] = 4.3 g / 111 g = 0.0387

In Aqueous solutions CaCl₂ on dissociation gives Ca²⁺ and 2 Cl^-(total 3 Ions).

so the total number of moles of ions in the CacCl₂ Aq solution = 3 x 0.0387 moles = 0.1162 moles

As the number of moles of ions/particles in water increases , the freezing point of solution decreases and the boiling point of solution increases.

Order of freezing point :   water    >     glycerin     >      HI     >    CaCl₂

       (Highest FP) (4)               (3)                  (2)          (1) (lowest FP)

Order of Boiling Point : CaCl₂     >   HI          > glycerin    >     water

                   (Highest BP) (4)               (3)                  (2)                (1) (lowest BP)