StoichiometryEasy

Moles and molar mass

Given 25.0 g of NaOH (M = 40.0 g/mol), calculate the number of moles and the mass corresponding to 0.500 mol.

Given data

m(NaOH) = 25.0 gM(NaOH) = 40.0 g/mol

Steps

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Calculate the moles of NaOH using $n = m/M$ .
Write your working — the numerical result must appear in the text mol
Calculate the mass corresponding to 0.500 mol of NaOH.

Full worked solution

Calculate the moles of NaOH using $n = m/M$ .
$n = \frac{m}{M} = \frac{25.0}{40.0}$
$n = m/M = 25.0/40.0 = \mathbf{0.625\,mol}$ . The number of moles is obtained by dividing the mass by the molar mass.
Calculate the mass corresponding to 0.500 mol of NaOH.
$m = n \cdot M = 0.500 \cdot 40.0$
$m = n \cdot M = 0.500 \cdot 40.0 = \mathbf{20.0\,g}$ . The mass is obtained by multiplying the moles by the molar mass.

Result:n = 0.625 mol; mass for 0.500 mol = 20.0 g.

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