溶質(zhì)質(zhì)量分數(shù)定義：溶質(zhì)質(zhì)量占溶液質(zhì)量(溶質(zhì)質(zhì)量與溶劑質(zhì)量之和)的百分率，溶液中溶質(zhì)的質(zhì)量分數(shù)是溶質(zhì)質(zhì)量與溶液質(zhì)量之比。溶質(zhì)質(zhì)量分數(shù)表達式:% (百分率符號)。注意：1、溶質(zhì)的質(zhì)量分數(shù)只表示溶質(zhì)質(zhì)量與溶液質(zhì)量之比，并不代表具體的溶液質(zhì)量和溶質(zhì)質(zhì)量。2、溶質(zhì)的質(zhì)量分數(shù)計算式中溶質(zhì)質(zhì)量與溶液質(zhì)量的單位必須統(tǒng)一。3、計算式中溶質(zhì)質(zhì)量是指被溶解的那部分溶質(zhì)的質(zhì)量，沒有被溶解的那部分溶質(zhì)質(zhì)量不能計算在內(nèi)。