碳酸氫鈉是焙制糕點(diǎn)所用發(fā)酵粉的主要成分之一.小明的母親從商場買回一包碳酸氫鈉,包裝袋上標(biāo)有“NaHCO3質(zhì)量分?jǐn)?shù)≥95%”字樣.小明為了判斷包內(nèi)NaHCO3質(zhì)量分?jǐn)?shù)是否達(dá)到要求,從包內(nèi)取出4.5g樣品充分溶于水,再加入足量的澄清石灰水,發(fā)生如下反應(yīng)(雜質(zhì)不參加反應(yīng)):NaHCO3+Ca(OH)2═CaCO3↓+NaOH+H2O,測得生成5g碳酸鈣.計算并回答:
(1)NaHCO3中鈉元素的質(zhì)量分?jǐn)?shù)是(精確到0.1%).
(2)4.5g樣品中含有NaHCO3的質(zhì)量.
(3)包內(nèi)碳酸氫鈉的質(zhì)量分?jǐn)?shù)與標(biāo)簽上所標(biāo)的數(shù)據(jù)相符嗎?
解:(1)NaHCO
3中鈉元素的質(zhì)量分?jǐn)?shù)為:
×100%=27.4%
(2)設(shè)4.5 g樣品中NaHCO
3的質(zhì)量為x
NaHCO
3+Ca(OH)
2═CaCO
3↓+NaOH+H
2O
84 100
x 5g
x=4.2g
(3)樣品中NaHCO
3的質(zhì)量分?jǐn)?shù)為:
×100%=93.3%
所以包內(nèi)NaHCO
3的質(zhì)量分?jǐn)?shù)與標(biāo)簽上所標(biāo)的數(shù)據(jù)不符.
答:(1)NaHCO
3中鈉元素的質(zhì)量分?jǐn)?shù)為27.4%
(2)4.5g樣品中含有NaHCO
3的質(zhì)量為4.2g.
(3)包內(nèi)碳酸氫鈉的質(zhì)量分?jǐn)?shù)與標(biāo)簽上所標(biāo)的數(shù)據(jù)不相符
分析:(1)根據(jù)物質(zhì)中某元素的質(zhì)量分?jǐn)?shù)=
×100%,進(jìn)行解答;
(2)根據(jù)化學(xué)方程式和碳酸鈣的質(zhì)量可求得4.5g樣品中含有NaHCO
3的質(zhì)量;
(3)NaHCO
3的質(zhì)量與樣品的質(zhì)量的百分比為實(shí)際NaHCO
3質(zhì)量分?jǐn)?shù),然后確定包內(nèi)碳酸氫鈉的質(zhì)量分?jǐn)?shù)與標(biāo)簽上所標(biāo)的數(shù)據(jù)是否相符;
點(diǎn)評:本題主要考查學(xué)生運(yùn)用化學(xué)方程式和質(zhì)量分?jǐn)?shù)公式進(jìn)行計算的能力.