Question

A chemist makes a solution of Ca(NO3)2 by dissolving 21.3 g Ca(NO3)2 in water to make 100.0 mL of solution. What is the concentration of NO3− ions in the solution? Assume that Ca(NO3)2 is the only solute in the solution. The molar mass of Ca(NO3)2 is 164.10 g/mol.

Answer 1

[NO₃⁻ ] = 2.596 M

Step-by-step explanation:

Ca(NO₃)₂ dissolves in water according to the following equation:

Ca(NO₃)₂ ⇒ Ca²⁺ + 2NO₃⁻

The moles of Ca(NO₃)₂ that dissolve is found as followed:

(21.3 g) / (164.10 g/mol) = 0.1298... mol

The number of NO₃⁻ ions are related to the above quantity by the molar ratio:

(0.1298 mol Ca(NO₃)₂) (2NO₃⁻/Ca(NO₃)₂) = 0.2596...mol NO₃⁻

The concentration of the nitrate ions is then calculated:

[NO₃⁻ ] = (0.2596...mol) / (100.0ml) x (1000mL/L) = 2.596 M