Question

You have a 0.7 M solution. Your job is to produce 50 mL of a 0.4 M solution.

Answer 1

Answer: A. 28.6 ml of the 0.7 M solution we need to start with.

B. There are 0.02 moles of solute were in the 0.7 M solution.

C. Amount of water to be added is 21.4 ml

D. The resulting solution will have concentration of 0.28 M

Explanation:

According to the dilution law,

$M_1V_1=M_2V_2$

where,

$M_1$ = molarity of stock solution = 0.7 M

$V_1$ = volume of stock solution = ?

$M_1$ = molarity of diluted solution = 0.4 M

$V_1$ = volume of  diluted solution = 50 ml

Putting in the values we get:

$0.7\times V_1=0.4\times 50$

$V_1=28.6ml$

A. 28.6 ml of the 0.7 M solution we need to start with.

B. Molarity of a solution is defined as the number of moles of solute dissolved per liter of the solution.

$Molarity=\frac{n\times 1000}{V_s}$

where,

n = moles of solute

$V_s$ = volume of solution in ml

$0.7=\frac{n\times 1000}{28.6}$

$n=0.02$

Thus there are 0.02 moles of solute were in the 0.7 M solution.

C. Amount of water to be added = (50-28.6 ) ml = 21.4 ml

D. If water added is $2\times 21.4=42.8 ml$

$0.7\times 28.6=M_2\times 71.4$

$M_2=0.28M$

If volume of concentrated solution will be more , the resulting solution will have lesser concentration of 0.28 M