Question

What is the concentration of NO3- ions in a solution prepared by dissolving 20.0 g of Ca(NO3)2 in enough water to produce 300. mL of solution

Answer 1

0.812 M

Step-by-step explanation:

The reaction that takes place is:

• Ca(NO₃)₂ → Ca⁺² + 2NO₃⁻

First we convert grams of Ca(NO₃)₂ to moles, using its molecular weight:

• 20.0 g Ca(NO₃)₂ ÷ 164.088 g/mol = 0.122 mol Ca(NO₃)₂

Then we convert Ca(NO₃)₂ moles to NO₃⁻, keeping in mind the stoichiometry of the reaction:

• 0.122 moles Ca(NO₃)₂ *
  `(2molNO_(3)^-)/(1molCa(NO_3)_2)` = 0.244 mol NO₃⁻

Finally we divide the number of moles by the volume (in L), to calculate the concentration:

(300.0 mL ⇒ 300.0 / 1000 = 0.300 L)

• Molarity = 0.244 mol NO₃⁻ / 0.300 L = 0.812 M