Question

How much water is required to dilute 0.5 M (500 ml solution) to dilute it to 0.25 M solution?
1) 1000 ml
2) 500 ml
3) 250 ml
4) None of these

provide the answer with solution or else please don't answer.

Answer 1

We know that molarity (M) = n/V
where 'n' is number of moles of solute and 'V' is volume of soln.
as we are not adding any solute hence n doesn't change.
then applying,
MV= constant
note : MV = n = constant,
=> MV= M'V',
0.5×500= 0.25× V'
=> V' ( final volume of solution ) = 1000 ml
hence water to be added in existing solution = 1000-500= 500ml

Answer 2

you can apply a formula to find the ans.     or,  simply this way:

   0.5 M solution volume: 500 ml  =>  0.25 moles in 500 ml solution.

  To make it 0.25 M in 1000 ml, just add 500 ml of water.