Question

how many grams of water should be added to 4.00 grams NaOH to create a 2.00% by mass NaOH solution

Answer 1

Given:

Mass of solute NaOH = 4.00 grams

Percentage by mass of solution = 2.00%

To find:

Quantity of water in grams to be added to make a solution of 2.00% by mass =?

Solution:

The numerical is based on the concept of mass per cent of solution.

The mass per cent of solute means the particular amount of solute in terms of percentage is present in the solution.

Grams of solvent required to make the solution is to be calculated.

Let "Y" be the mass of water in g.

Mass percent of solution = $\frac{Mass of solute (g)}{Mass of solute + Mass of solvent}$} × 100

2 % =  $\frac{4.00 g}{4.00 g + Y g}$

$\frac{2}{100}$ =   $\frac{4.00 g}{4.00 g + Y g}$

2 (4.00 g + Y g) = 4.00 g(100)

8.00 g + 2 Y = 400

2 Y = 400 - 8

2 Y = 392

Y = $\frac{392}{2}$

Y = 196 g

Hence, the 196 g of water is to be added to 4.00 g of NaOH to make 2.00% by mass NaOH solution.