8gof caustic soda is dissolved in 50 g of water with continuous stirring and the volume is made to 100 mL by adding more water to the solution. Molarity of the solutionand volume of the water required to add to reduce its molarity
by 50% respectively will be
Answers
Molar mass of NaOH = 23 + 16 + 1=> 40 grams per mole.
Hence, 8 grams of NaOH is 8/40 => 1/5 =>0.2 moles of NaOH
Hence, in the end, 0.2 moles of NaOH will be present in 100 mL or 0.1 L of solution.
Molarity = (moles of NaOH)/(litres of solution)
=> 0.2 / 0.1
=> 2 M
Hence, the molarity of solution is 2 M (molar).
If its molarity is to be reduced by 50% from 2 molars.
The new molarity will be 2-(50/100 x 2) => 2 -1 => 1 M
Initial Volume of solution is 0.1 litres.
Volume of water to be added to reduce its molarity to 1 M =?
New molarity = 1 M
Moles of NaOH = 0.2 moles (8 grams)
Volume of solution = ?
Molarity = (moles of solute) / (litres of solution)
1 = 0.2/(liters of solution)
liters of solution = 0.2/1 => 0.2 liters
Final volume of solution will be 0.2 liters.
hence, amount of water to be added = final volume - initial volume
=> 0.2 - 0.1 L => 0.1 L or 100 mL of Water will have to be added.