To prepare 100 g of a 92% by weight solution of NaOH, how many g of H₂O is needed?

$\text{ Weight of }\mathrm{NaOH}=\left(\frac{92 \mathrm{g}}{100\mathrm{g}\text{ solution }}\right)\times (100 \mathrm{g}\text{ solution })=92 \mathrm{g} \mathrm{NaOH}$

Solution weight is 100 g and NaOH is 92 g, so solvent (water) weight is:

$\text{ Weight of }{\mathrm{H}}_2\mathrm{O}=100-92=8.0 \mathrm{g} {\mathrm{H}}_2\mathrm{O}$.