问题 问答题

为测定某大理石样品中碳酸钙(杂质不溶于水也不参与反应)的质量分数,某小组的同学进行了如下实验(水和氯化氢的挥发忽略不计):取12.5g样品研碎放入烧杯中,每次加入20.8g稀盐酸后并用电子天平称量,记录实验数据如下.

加入稀盐酸次数12345
烧杯及所称物质总质量/g72.291.9111.6131.3152.1
请计算:

(1)大理石样品中碳酸钙的质量分数.

(2)恰好完全反应时烧杯内溶液的溶质质量分数.

答案

【解】由表中实验数据分析可知,生成二氧化碳的质量为4.4 g.

设:大理石中碳酸钙的质量为x,恰好反应时生成氯化钙的质量为y.

CaCO3+2HCl=CaCl2+H2O+CO2

100         111      44

x           y       4.4g

100
x
=
44
4.4g

111
y
=
44
4.4g

x=10 g              y=11.1g

样品中碳酸钙的质量分数=

10g
12.5g
×100%=80%

氯化钙溶液的溶质质量分数=

11.1g
10g+20.8g×4-4.4g
×100%=12.5%

答:(1)大理石样品中碳酸钙的质量分数为80%.

(2)恰好完全反应时烧杯内溶液的溶质质量分数为12.5%.

单项选择题

The days of elderly women doing nothing but cooking huge meals on holidays are gone. Enter the Red Hat Society--a group holding the belief that old ladies should have fun.

"My grandmothers didn’ t do anything but keep house and serve everybody. They were programmed to do that," said Emily Cornette, head of a chapter of the 7-year-old Red Hat Society.

While men have long spent their time fishing and playing golf, women have sometimes seemed to become unnoticed as they age. But the generation now turning 50 is the baby boomers(生育高峰期出生的人), and the same people who refused their parents’ way of being young are now trying a new way of growing old.

If you take into consideration feminism(女权主义), a bit of spare money, and better health for most elderly, the Red Hat Society looks almost inevitable(必然的). In this society, women over 50 wear red hats and purple(紫色的) clothes, while the women under 50 wear pink hats and light purple clothing.

"The organization took the idea from a poem by Jenny Joseph that begins: When I am an old woman, I shall wear purple. With a red hat which doesn’ t go," said Ellen Cooper, who founded the Red Hat Society in 1998. When the ladies started to wear the red hats, they attracted lots of attention.

"The point of this is that we need a rest from always doing something for someone else," Cooper said, "Women feel so ashamed and sorry when they do something for themselves. " This is why chapters are discouraged from raising money or doing anything useful. "We’ re a ladies’ play group. It couldn’ t be more simple," added Cooper’ s assistant Joe Heywood.

Women join the Red Hat Society because()

A. they want to stay young

B. they would like to appear more attractive

C. they would like to have fun and live for themselves

D. they want to be more like their parents

判断题