Question

the grams of water that must be added to 4.00 g KI in the preparation of 2.00 % KI solution.

Answer 1

Given:-

→ Mass of KI = 4.00g

→ Concentration of the solution = 2.00%

To find:-

→ Mass of water required [grams]

Solution:-

Let the required mass of water be 'x' grams.

Here, KI [Potassium Iodide] is solute and water is solvent. We are given with the mass of solute and concentration of solution. So firstly, let's calculate the total mass of the solution :-

Mass of solution :-

= Mass of solute + Mass of solvent

= [4 + x]g

Now, we know that:-

Concentration of a solution [m/m %]

= Mass of solute/Mass of solution × 100

By substituting values in the above formula, we get:-

=> 4/[4 + x] × 100 = 2

=> 400 = 2[4 + x]

=> 400 = 8 + 2x

=> 2x = 400 - 8

=> 2x = 392

=> x = 392/2

=> x = 196g

Thus, 196g of water must be added.

Answer 2

We have,

Mass of solute = 4 g

w/w% of solution = 2%

Let, mass of water required = (x) g

∴ Mass of Solution = (4 + x) g

We know,

w/w% of solution = (Mass of Solute)/(Mass of Solution) • 100%

∴ (4)/(4 + x) × 100 = 2

⇒2x + 8 = 400

⇒2x = 400 - 8 = 392

⇒x = ½ × 392 = 196 g {Answer}.