Question

What mass of `NaOH` is contained in 250.0 mL of a 0.400 M sodium hydroxide solution?

Answer 1

`"Approx. 4 g of NaOH."`

Explanation:

`"Concentration"` `=` `"Moles"/"Volume of solution"`

`"Number of moles"` `=` `"Volume"xx"concentration "=`

`0.250*Lxx0.400*mol*L^-1`

`=` `0.100*mol`

`"Mass of sodium hydroxide"` `=` `0.100*molxx40.0*g*mol^-1`

`=??*g`

Answer 2

3.998 grams NaOH

Explanation:

The Molarity of a solution is determined by the comparison of the moles of the solute compared to the volume of the solution in liters.

The equation of the formula is `M = (mol)/L`

In order to find the mass we first need to solve for the moles.

`mol = M/L`

M = 0.400
moles = ?
L = 250.0 mL or 0.25 L

`0.400 M (0.25 L) = (? mol)`

`0.100 mol of NaOH`

Now we can calculate the grams be converting moles to grams.

`Na = 22.98 g`
`O = 15.99 g`
`H = 1.01 g`

`NaOH = 39.98 g`

`0.100 cancel(mol NaOH) x (39.98 g NaOH)/( 1 cancel(molNaOH)`

3.998 grams NaOH