Question

a chemist adds 0.15 l of a 2.33 mol/l nickel(ii) chloride (nicl2) solution to a reaction flask. calculate the mass in grams of nickel(ii) chloride the chemist has added to the flask. be sure your answer has the correct number of significant digits.

Explanation:

Step1: Calculate the number of moles

Use the formula $n = c\times V$, where $c$ is the concentration and $V$ is the volume. Given $c = 2.33\ mol/L$ and $V=0.15\ L$.
$n = 2.33\ mol/L\times0.15\ L= 0.3495\ mol$

Step2: Find the molar - mass of $NiCl_2$

The molar - mass of $Ni$ is approximately $58.69\ g/mol$, and the molar - mass of $Cl$ is approximately $35.45\ g/mol$. For $NiCl_2$, $M = 58.69\ g/mol+2\times35.45\ g/mol=58.69\ g/mol + 70.9\ g/mol = 129.59\ g/mol$

Step3: Calculate the mass

Use the formula $m=n\times M$. Substitute $n = 0.3495\ mol$ and $M = 129.59\ g/mol$ into the formula.
$m=0.3495\ mol\times129.59\ g/mol\approx45\ g$ (rounded to two significant digits as 0.15 L has two significant digits)

Answer:

45 g