Aqueous solution of urea is 20% by mass of solution. Then the percentage of urea by mass of solvent is

Options

A. 0.2
B. 0.25
C. 0.4
D. 0.8

Answer

To solve the problem, we need to determine the percentage of urea by mass of the solvent from a 20% by mass aqueous solution of urea. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Given Information
We have a solution that is 20% urea by mass. This means that in every 100 grams of the solution, there are 20 grams of urea.

### Step 2: Calculate the Mass of the Solvent
Since the total mass of the solution is 100 grams and the mass of urea is 20 grams, we can find the mass of the solvent (water) by subtracting the mass of urea from the total mass of the solution.

\[ \text{Mass of solvent} = \text{Mass of solution} - \text{Mass of urea} = 100 \, \text{g} - 20 \, \text{g} = 80 \, \text{g} \]

### Step 3: Calculate the Percentage of Urea by Mass of Solvent
Now, we need to find the percentage of urea by mass of the solvent. The formula for percentage by mass is:

\[ \text{Percentage of urea by mass of solvent} = \left( \frac{\text{Mass of urea}}{\text{Mass of solvent}} \right) \times 100 \]

Substituting the values we have:

\[ \text{Percentage of urea by mass of solvent} = \left( \frac{20 \, \text{g}}{80 \, \text{g}} \right) \times 100 \]

### Step 4: Simplify the Calculation
Calculating the fraction:

\[ \frac{20}{80} = 0.25 \]

Now, multiplying by 100 to convert it to a percentage:

\[ 0.25 \times 100 = 25\% \]

### Step 5: Convert Percentage to Decimal (if required)
If the answer needs to be in decimal form, we convert 25% to a decimal:

\[ 25\% = \frac{25}{100} = 0.25 \]

### Final Answer
The percentage of urea by mass of the solvent is **25%** or **0.25** in decimal form.

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