Question

A student dissolved 5.00 g of Co(NO3)2 in enough water to make 100. mL of stock solution. He took 4.00 mL of the stock solution and then diluted it with water to give 275. mL of a final solution. How many grams of NO3- ion are there in the final solution?

Answer 1

Answer:

0.136g

Explanation:

A student dissolved 5.00 g of Co(NO3)2 in enough water to make 100. mL of stock solution. He took 4.00 mL of the stock solution and then diluted it with water to give 275. mL of a final solution. How many grams of NO3- ion are there in the final solution?

$Co(NO_3)_2(aq)\rightarrow Co^{2+}(aq)+2NO_3^{-}(aq)$

Initial mole of Co(NO3)2  $=\frac{mass}{molar mass}$

$=\frac{5.00}{182.94} \\\\=0.02733mol$

Mole of Co(NO3)2 in final solution

$=\frac{4.00}{100}\times 0.02733\\\\=0.04\times 0.02733\\\\= 0.001093mol$

Mole of  NO3- in final solution = 2 x Mole of Co(NO3)2

$=2\times 0.001093\\\\=0.002186mol$

Mass of  NO3- in final solution is mole x Molar mass of NO3

$=0.002186\times62.01\\\\=0.136g$