Question

15.77 mg libr in 198.6 ml of solution. express the molarity in moles per liter to four significant figures. molarity = m

Explanation:

Step1: Calculate molar mass of LiBr

The molar mass of Li (lithium) is approximately $6.94\ g/mol$ and Br (bromine) is approximately $79.90\ g/mol$. So molar mass of LiBr, $M_{LiBr}=6.94 + 79.90=86.84\ g/mol$.

Step2: Convert mass of LiBr to moles

Given mass of LiBr is $m = 15.77\ mg=15.77\times10^{- 3}\ g$. Using the formula $n=\frac{m}{M}$, we have $n=\frac{15.77\times10^{-3}\ g}{86.84\ g/mol}=1.816\times10^{-4}\ mol$.

Step3: Convert volume of solution to liters

Given volume of solution $V = 198.6\ mL = 198.6\times10^{-3}\ L$.

Step4: Calculate molarity

Molarity $M=\frac{n}{V}$. Substituting the values of $n$ and $V$, we get $M=\frac{1.816\times10^{-4}\ mol}{198.6\times10^{-3}\ L}=9.144\times10^{-4}\ M$.

Answer:

$9.144\times10^{-4}$