A student dissolved 3.00 g of Co(NO 3) 2 in enough water to make 100. mL of stock solution. He took 4.00 mL of the solution then diluted it with water to give 275 mL of a final solution. How many grams of NO 3 - ion are there in the final solution?

0.0812 grams of nitrate ions are there in the final solution.

Explanation:

Mass of cobalt (II) nitrate = 3.00 g

Moles of cobalt(II) nitrate =

Volume of the solution = 100 mL = 0.100 L

1 mL = 0.001 L

Molarity of the solution =

Cobalt (II) nitrate in its aqueous solution gives 1 mole of cobalt(II) ion and 2 moles of nitrate ions.

Molarity of the nitrate ion before solution =

Volume of the  nitrate ion  before solution =

Molarity of the  nitrate ion after solution =

Volume of the  nitrate ion after solution =

( Dilution)

Moles of nitrate ions in 275 ml = n

Molarity of the  nitrate ion after solution =0.00477 M

volume of the final solution = 275 mL = 0.275 L

Mass of 0.00131 moles of nitrate ions:

0.00131 mol × 62 g/mol = 0.0812 g

0.0812 grams of nitrate ions are there in the final solution.

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