a light alloy consists of 70 percent aluminium and 30 percent magnesium by mass calculate density of the alloy given thet density of aluminium is 2700 kilograms

Question

per metre cubed and density of magnesium is 1740 kilograms per metre cubed

Answer 1

On way of working this type of problem is to assume that one starts with an alloy mass of 1 kg = 1000 g.

Then there would be 0.70 x 1000 = 700 g oif Al and  .30 x 1000 = 300 g Mg.

 

Since the Molar Mass of Al is 26.982 g /mole , there are 700/ 26.982 =  25.94 molles of Al, similarly there are

  300 / 24.303  =  12.34 moles of Mg    (Molar mass of Mg is 24.305)

Thus the mole fraction of Al ( f Al )  is  25.94/(25.94 + 12.34) =  0.6776

and the mole fraction of Mg (f Mg ) is   12.34 /(25.98 + 12.34) = 0.3224

 

The density of alloy will then be 0.6776 x 2700 +  0.3324 x 1740  =  2390 kg / m^3