Question

A solution of ethanol in water is 10% by volume. if the solution and pure ethanol have densities of 0.9866 g/cc and 0.785 g/cc respectively, find the per cent by weight ...

Answer 1

Take 100cc of solution

Volume of ethanol = 10cc

Mass of ethanol = volume x density

                          = 10x0.9866 = 9.866 g

Mass of solution = 100 x 0.785 = 78.5 g

Percent of ethanol by weight = 9.866/78.5  x 100

                                              = 12.568%

Answer 2

Hello Dear.



Let the Volume of the Solution be 100 cm³.

According to the Question,

Volume of the Ethanol = 10% of 100 cm³.
                                    = 10 cm³.

Now, Volume of the Ethanol = 10 cm³.
Density of the Pure Ethanol = 0.785 g/cc.

Using the Formula,

 Density = Mass/Volume
     Mass =  0.785 × 10
              = 7.85 grams.


Now, Density of the Solutions = 0.9866 g/cc.
   Volume of the Solutions = 100 cm³

∴ Mass = 0.9866 × 100
             = 98.66 grams.


% Of the Ethanol by Weight =
 (Mass of the Ethanol/Mass of the Solutions) × 100%
= (7.85/98.66) × 100%
= 0.0795 × 100%
= 7.95 %

Thus, the % of the Ethanol by the Weight in the solution is 7.95%.



Hope it helps.