Question

What amount Na2co3 dissolved in 250 ml water to prepare Semimolar solution

Answer 1

semi molar is the solution whose molarity is 1/2 or 0.5

means, question indirectly said “ find the amount of Na2CO3 dissolved in 250ml of water to prepare concentration of solution 0.5M”

we know, number of mole of solute = concentration × volume in L

= 0.5M × (250/1000)L = 0.5/4 = 0.125

now, number of mole of Na2CO3 = weight of Na2CO3 in solution/molar weight of Na2CO3

[ molar weight of Na2CO3 = 2 × 23 + 12 + 3 × 16 = 46 + 12 + 48 = 106g/mol]

or, 0.125 = weight of Na2CO3 in solution/106

or, 106 × 0.125 = weight of Na2CO3 in solution

or, weight of Na2CO3 in solution = 13.25g