a) Given data
M1 = 16 M
V1 = ?
M2 = 0.5 M
V2 = 1.0 L
For dilution M1V1 = M2V2
∴ The volume of "concentrated" (16 M) HNO3 (aq) required to prepare 0.5 M 1.0 L solution
V1 = M2V2 / M1
= (0.5M)(1.0L) / (16 M)
= 0.03125 L
= 31.25 mL
Take the 31.25 mL of concentrated acid and dilute it to 1000 mL then you will get 0.5 M solution.
b) HNO3 (aq) + NaOH (aq) --------------> NaNO3(aq) + H2O(l)
M1V1/n1 = M2V2/n2
Here n1 = n2 = 1
M1V1 = M2V2
V2 = M1V1/M2
= (100 mL)(0.5M)/ (0.2 M)
= 250 mL
The volume of NaOH required to neutralized by 100. mL of the diluted solution = 250 mL