Question

120 grams of calcium nitrite ca(no₂)₂ is dissolved in a 240 ml solution. what is the molarity of the solution?
select the correct answer below:
3.4 m
3.6 m
3.8 m
3.1 m

Explanation:

Step1: Calculate molar mass of \(Ca(NO_2)_2\)

Molar mass of \(Ca = 40\space g/mol\), \(N=14\space g/mol\), \(O = 16\space g/mol\).
\(M = 40+(14 + 16\times2)\times2=40+(14 + 32)\times2=40 + 46\times2=40+92 = 132\space g/mol\)

Step2: Calculate moles of \(Ca(NO_2)_2\)

Use formula \(n=\frac{m}{M}\), where \(m = 120\space g\), \(M=132\space g/mol\)
\(n=\frac{120}{132}\space mol\approx0.909\space mol\)

Step3: Convert volume to liters

\(V = 240\space mL=240\times10^{- 3}\space L = 0.24\space L\)

Step4: Calculate molarity

Use formula \(M=\frac{n}{V}\), where \(n = 0.909\space mol\), \(V = 0.24\space L\)
\(M=\frac{0.909}{0.24}\space M\approx3.8\space M\)

Answer:

\(3.8\space M\)