Question

The density of ethanol is .789 g/mL. How many grams of ethanol should be mixed with 225 mL of water to make 4.5% (v/v) mixture?

Answer 1

Let, the volume of the ethanol be 'V'

Given:

Volume of water=225mL

ρ(ethanol)=0.789g/mL

%V/V=4.5%

♦Solution♦

As,

%v/v=(vol.of solute/vol.of solution)×100

∴ 4.5=[V/(V+225)]×100

⇒0.045(V+225)=V

0.045V+10.125=V

1V–0.045V=10.125

0.955V=10.125

V=10.125÷0.955

⇒V=10.6mL

Now, as, density=mass/vol.

,i.e, ρ=m/V

⇒m=ρ.V

=0.789g/mL×10.6

∴ m=8.363g