Question

How many grams of NaOH must be dissolved in 5 litre solution, so that the molarity of

solution will be 2.5 ?​

Answer 1

Answer:

Molarity= number of moles ÷ volume of solution (in Litres)

=> 0.5 = n ÷ 5

=> n = 0.5 × 5

=> n = 2.5 moles

Since n = given weight ÷ Molecular weight

=> 2.5 = w ÷ 40

=> w = 2.5 × 40

=> w = 100g

So you need 100g of NaOH to make 0.5 M 5L solution.

Answer 2

Answer:

Let the no. of moles of NaOH be x

Molarity = no. of moles of solute/ volume of solution (in L)

2.5 = x/5

2.5×5 = x

12.5 = x

x = 12.5

Therefore, no. of moles of NaOH = 12.5

Molar mass of NaOH = 23+16+1 = 40

No. of moles of NaOH = Mass/ Molar mass

12.5 = Mass/ 40

12.5×40 = Mass

500 = Mass

Therefore, Mass of NaOH is 500 g.