1. the concentration of all salts present in sea water is 3.52% mv.calculate the volume of sea water which on evaporation  will produce 5kg of salts.
  2. 18-carat gold contains 18 parts of gold and 6 parts of copper by mass.calculate the concentration of gold ana copper in 18-carat gold in % (mv).

1) We are given that the concentration of sea water is 3.52 % (mass by volume). This means that 3.52 g of salt is present in 100 ml of solution. The mass by volume percent of a solution is given as 

   ......  (a)

Let x ml be the volume of solution that gives 5Kg or 5000 g of salt. Hence

 3.52 = (5000 X 100) / x = 1420.45 X 100 ml

 = 142.045 L

Hence 142.054 litres of solution would give 5 Kg of saly=t.

2) 18 carat gold is an alloy (homogeneous mixture) of gold and copper in which 18 parts of gold and 6 parts of copper are present. The concentration of gold and copper in terms of mass by mass is

 

Mass percentage of gold = parts of gold / (parts of gold + parts of copper) X 100

 = 18 / (6 + 18) X 100 =75 %

Mass percentage of copper = parts of copper / (parts of gold + parts of copper) X 100

 = (6/ 24) X 100 = 25 %

To calculate the mass by volume percentage, we need the density of both gold and copper. We will use the relation

 Density = mass / Volume

and calculate the volume of gold and copper. Then in will be used as the volume of solution in relation (a)

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