# How many moles of HBr are present in 18. mL of a 0.400 M solution?

May 12, 2017

Approx. $7 \cdot m m o l$

#### Explanation:

$\text{Molarity}$ is defined by the quotient,............

$\text{Molarity"="Moles of solute"/"Volume of solution}$, .................

and thus the product...................

$\text{Volume of solution"xx"molarity"="moles of solute}$

And so $\text{moles of HBr} = 18 \times {10}^{-} 3 \cdot \cancel{L} \times 0.400 \cdot m o l \cdot \cancel{{L}^{-} 1} =$

$= 7.20 \times {10}^{-} 3 \cdot m o l$, with respect to $H B r$.

The product is dimensionally consistent; we wanted an answer in moles, and the product gave us an answer in moles. This is good indication that we set the problem up correctly.