0 10 20 30 40 50 60 70 80 90 100 Temperature (TC) 37. A sample of potassium dich

Question

0 10 20 30 40 50 60 70 80 90 100 Temperature (TC) 37. A sample of potassium dichromate (25.0 g) is dissolved in 201 g of water at 7o oc, with precautions taken to avoid evaporation of any water. The solution is cooled to precipitate is observed. This solution is oC and no A) hydrated B) miscible C) saturated D) unsaturated E) supersaturated 38. A solution is prepared by dissolving 2 g of cac, in 375 g of water. The density of g the resulting solution is 1.05 g/mL. The concentration of CT in this solution is M. A) 0.214 B) 0.562 C) 1.12 D) 1.20 E) 6.64 x 10-2

Explanation / Answer

Q37) From the solubility curves shown in the diagram , watch carefully the curve for potassium dichromate (K2Cr2O7). At 70 C, its solubility is aboiut 45 to 50g per100g =100mL of water.

However in the question the amount of dichromate dissolved is 25 g in 201g of water at 70C. Further on cooling to 20 C no precipitate is observed. It clearly shows the solution is unsaturated.

option D is correct.

Q38) mass of solute CaCl2 = 23.7g

mass of solvent water = 375g

total mass of solution = 375 +23.7

= 398.7 g

Given density of solution = 1.05 g/mL

thus volume of solution = mass / density

= 398.7 /1.05

= 379.71 mL

Now Ca Cl2 (aq) -------> Ca+2 (aq) + 2Cl-(aq)

thus molarity of Cl- is twice that of molarity of salt.

Molartiy of salt CaCl2 = ( mass of cacl2/molar mass) x(1000/volmein mL)

= (23.7 /111)(1000/379.71)

= 0.5622M

Thus concentration of Cl- in solution = 2 x 0.5622

=1.125 M

thus Option C is correct.

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