測知含一種雜質(zhì)的Fe2O3粉末中含氧32.5%,則這種雜質(zhì)不可能是( )
A.MgO
B.Fe(OH)3
C.FeO
D.Al2O3
【答案】
分析:假定該物質(zhì)為純凈物,求出Fe
2O
3中氧元素的質(zhì)量分數(shù),與題給數(shù)據(jù)為是氧化鐵中氧元素的質(zhì)量分數(shù)與雜質(zhì)中氧元素的質(zhì)量分數(shù)(不含氧元素的質(zhì)量分數(shù)為0)平均值,做比較.根據(jù)物質(zhì)中某元素的質(zhì)量分數(shù)=
![](http://thumb.zyjl.cn/pic6/res/czhx/web/STSource/20131030161429840395629/SYS201310301614298403956028_DA/0.png)
×100%,進行解答本題.
解答:解:純凈的Fe
2O
3氧元素的質(zhì)量分數(shù)為:
![](http://thumb.zyjl.cn/pic6/res/czhx/web/STSource/20131030161429840395629/SYS201310301614298403956028_DA/1.png)
×100%=30%,題目給的數(shù)據(jù)為是氧化鐵中氧元素的質(zhì)量分數(shù)與雜質(zhì)中氧元素的質(zhì)量分數(shù)(不含氧元素的質(zhì)量分數(shù)為0)平均值,由于32﹒5%>30%,則雜質(zhì)中必須含有氧元素,且氧元素的質(zhì)量分數(shù)必須要大于32﹒5%.
A、MgO中氧元素的質(zhì)量分數(shù)=
![](http://thumb.zyjl.cn/pic6/res/czhx/web/STSource/20131030161429840395629/SYS201310301614298403956028_DA/2.png)
=40%,故A正確;
B、Fe(OH)
3中氧元素的質(zhì)量分數(shù)=
![](http://thumb.zyjl.cn/pic6/res/czhx/web/STSource/20131030161429840395629/SYS201310301614298403956028_DA/3.png)
=44.9%,故B正確;
C、FeO中氧元素的質(zhì)量分數(shù)=
![](http://thumb.zyjl.cn/pic6/res/czhx/web/STSource/20131030161429840395629/SYS201310301614298403956028_DA/4.png)
=22.2%,故C錯誤;
D、Al
2O
3中氧元素的質(zhì)量分數(shù)=
![](http://thumb.zyjl.cn/pic6/res/czhx/web/STSource/20131030161429840395629/SYS201310301614298403956028_DA/5.png)
=47%,故D正確.
故選:C.
點評:混合物成分的確定用極值法,也就是先假定該物質(zhì)為純凈物,算出相關(guān)的量,再與題給量相比較,就能得出正確的結(jié)論.