chemistry 102 college

Question

You wish to prepare 203 grams of 12.3 % Co(NO₃)₂. 

You will need   grams of cobalt(II) nitrate and   mL of water.

Assume that the density of water is 1.00 g / ml.

Answer 1

The question doesn't state % w/w or % w/v. Since the density of water is provided, I'll assume % w/w.

12.3% (w/w) Co(NO₃)₂ = 12.3 g Co(NO₃)₂ / 100 g solution

12.3 g / 100 g soln x 203 g soln = 24.969 g = 25.0 g Co(NO₃)₂

203 g - 25.0 g = 178 g H₂O

178 g H₂O x 1 ml / g = 178 mls H₂O