Question

A 30.0-mL sample of an unknown strong base is neutralized after the addition of 12.0 mL of a 0.150 M HNO3 solution. If the unknown base concentration is 0.0300 M, give some possible identities for the unknown base.

Answer 1

The question is incomplete, here is the complete question:

A 30.0-mL sample of an unknown strong base is neutralized after the addition of 12.0 mL of a 0.150 M HNO₃ solution. If the unknown base concentration is 0.0300 M, give some possible identities for the unknown base.  (Select all that apply)

A.)  Ca(OH)₂

B.)  LiOH

C.)  Sr(OH)₂

D.)  Al(OH)₃

E.)  NaOH

F.)  Ba(OH)₂

Answer: The unknown base could be $Ca(OH)_2,Sr(OH)_2\text{ or }Ba(OH)_2$

Explanation:

To calculate the number of moles for given molarity of solution, we use the equation:

       .......(1)

• For nitric acid:

Molarity of solution = 0.150 M

Volume of solution = 12.0 mL

Putting values in equation 1, we get:

$0.150M=\frac{\text{Moles of nitric acid}\times 1000}{12.00}\\\\\text{Moles of nitric acid}=\frac{0.150\times 12.00}{1000}=1.8\times 10^{-3}moles$

• For unknown base:

Molarity of solution = 0.0300 M

Volume of solution = 30.0 mL

Putting values in equation 1, we get:

$0.0300M=\frac{\text{Moles of unknown base}\times 1000}{30.00}\\\\\text{Moles of unknown base}=\frac{0.0300\times 30.00}{1000}=0.9\times 10^{-3}moles$

Mole ratio of acid and base is calculated as: $\frac{\text{Moles of unknown base}}{\text{Moles of nitric acid}}=\frac{0.9\times 10^{-3}}{1.8\times 10^{-3}}=\frac{2}{1}$

Number of $OH^-$ = 2 × number of $H^+$ ions

So, the unknown base is diprotic in nature.

Hence, the unknown base could be $Ca(OH)_2,Sr(OH)_2\text{ or }Ba(OH)_2$