Question

a chemist prepares a solution of nickel(ii) chloride (nicl₂) by measuring out 8.9 g of nickel(ii) chloride into a 200. ml volumetric flask and filling the flask to the mark with water. calculate the concentration in mol/l of the chemists nickel(ii) chloride solution. be sure your answer has the correct number of significant digits.

Explanation:

Step1: Calculate molar mass of NiCl₂

The molar mass of Ni (nickel) is approximately 58.69 g/mol, and the molar mass of Cl (chlorine) is approximately 35.45 g/mol. For NiCl₂, molar mass $M=58.69 + 2\times35.45= 58.69+70.9 = 129.59$ g/mol.

Step2: Calculate moles of NiCl₂

Use the formula $n=\frac{m}{M}$, where $m = 8.9$ g and $M = 129.59$ g/mol. So $n=\frac{8.9}{129.59}\approx0.0687$ mol.

Step3: Convert volume to liters

The volume $V = 200$ mL. Since $1$ L=$1000$ mL, $V=200\div1000 = 0.200$ L.

Step4: Calculate concentration

Use the formula $c=\frac{n}{V}$, where $n = 0.0687$ mol and $V = 0.200$ L. So $c=\frac{0.0687}{0.200}=0.3435\approx0.34$ mol/L (2 significant - digits as 8.9 has 2 significant digits).

Answer:

0.34 mol/L