# Question 203c8

Jan 18, 2018

Understand the defenition of Molarity

#### Explanation:

Molarity= no of moles / volume of solution(in litres)
Hence here we have 0.5litre of 0.79M NaOH
So no of moles of NaOH in this will be
$0.5 \cdot 0.79 = 0.395$ moles of NaOH
We know one mole of NaOH weighs 40 grams
Multiply this by no of moles to get the actual weight needed
So weight needed $= 40 \cdot 0.395 g r a m s$

Jan 18, 2018

$x$ = 15.8g

#### Explanation:

molarity = (n)/(volume( L)#; where n is the number of moles of the solute.

$n$ = $\frac{x}{m m}$; where x is the required amount of NaOH and mm is the molar massof NaOH

therefore molarity, M = $\frac{x}{m m}$ x $\frac{1000}{V \left(m L\right)}$

$0.79$ = $\frac{x}{40}$ x $\frac{1000}{500}$

$x$ = $0.79$ x $20$

$x$ = 15.8g