解：設(shè)氫氧化鈉溶液中溶質(zhì)的質(zhì)量為x
?$\ \text {NaOH~~~~+~~~~HCl}\xlongequal[\ \ \ \ \ \ ]{}\ \text {NaCl+H}_2\ \text {O}$?
40 36.5
x 20mL×1.0g/mL×0.73％
?$\mathrm{ \frac { 40}{ x }=\frac { 36.5 }{ 20mL×1.0g/mL×0.73％ } }$? x = 0.16 g
答：氫氧化鈉溶液中溶質(zhì)的質(zhì)量為0.16g。
