A KNO_3, solution containing 45 g of KNO_3 per 100.0 g of water is cooled from 4

Question

A KNO_3, solution containing 45 g of KNO_3 per 100.0 g of water is cooled from 40 degree C and 0 degree C. What happens during cooling? (Refer to Figure 12.10.) A KCl solution containing 42 g of KCl per 100.0 g of water is cooled from 60 degree C to 0 degree C. What happens during cooling? (Refer to Figure 12.10.) Some laboratory procedures involving oxygen-sensitive reactants or products call for using preboiled (and then cooled) water. Explain why this is so. A person preparing a fish tank uses boiled (and then cooled) water to fill it. Explain why this is so. Scuba divers breathing air at increased pressure can suffer from oxygen toxicity - too much oxygen in their blood-stream-when the partial pressure of oxygen exceeds about 1.4 atm. What happens to the amount of oxygen in a diver's blood-stream when he or she breathes oxygen in a diver's blood-stream when he or she breathes oxygen at elevated pressures? How can this be reversed?

Explanation / Answer

15. Solubility of KNO3 at 40 oC = 65 g/100 g water

solubility of KNO3 at 0 oC = 13 g/100 g water

So, when a solution of 45 g KNO3 (completely soluble, unsaturated) solution was cooled to 0 oC, 32 g of KNO3 precipitates out of the solution.

22. Henry's law constant for Helium = 3.7 x 10^-4 M/atm

so solubility at 1 atm = 3.7 x 10^-4 x 1 = 3.7 x 10^-4 M

23. Aqueous solution of NaCl

moles of NaCl = 145 g/58.44 g/mol = 2.48 mols

molarity of solution = 2.48 mol/1 L = 2.48 M

mass of solution = 1000 ml x 1.08 g/ml = 1080 g

mass of solvent = 1080 - 145 = 935 g

molality of solution = 2.48 mol/0.935 kg = 2.65 m

mass percent NaCl in solution = 145 x 100/1080 = 13.426%

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