Question

Concentration of urea in an aqueous solution is 45% by mass. Calculate the mass of urea in 100g of water.

Answer 1

Explanation:

Mass of urea in 100 g of 10% solution =

<br> Mass of urea in 150 g of 15% solution

<br> Total mass of urea 10+22.5=32.5 g <br> Total mass of solution = 100+150=250 g <br>

Answer 2

Answer:

The mass of urea dissolved in 100g of water is equal to 81.8g to get aqueous solution of 45% by mass.

Explanation:

Given, the mass percentage of the aqueous solution of urea =45%

The mass of water (solvent) =100g

The mass percentage of a solution is obtained from mass of solute divided by the mass of the solution.

Mass % of the solution  $=\frac{Mass \; of \; solute}{Mass \; of \; solution}*100$                   .............(1)

Consider that the mass of the urea in dissolved in water $=x$

Mass of the aqueous solution of urea $=100+x$

Put all the values in equation (1):

⇒   $45=\frac{x}{100+x}*100$

⇒  $\frac{45}{100}=\frac{x}{100+x}$

⇒  $0.45(100+x)=x$

⇒   $45+0.45x=x$

⇒   $x(1-0.45)=45$

⇒   $0.55x=45$

∴    $x=81.8g$

Therefore, the mass of urea dissolved in 100g of water is equal to 81.8g.