问题 问答题

请根据下列实验和溶解度曲线回答问题:(已知水的密度约为1g/cm3

实验操作实验结果
取100ml水,加入25g硝酸钾,搅拌,恢复至20℃全部溶解,得溶液①
再加wg硝酸钾,搅拌,恢复到20℃恰好饱和,得溶液②
再加25g硝酸钾,搅拌,恢复到20℃得溶液③
加热全部溶解,得溶液④
冷却至20℃析出晶体,得溶液⑤
(1)③中溶液的质量为______g;一定属于不饱和溶液的是______(填序号,下同);溶质的质量分数一定相等的是______.

(2)析出晶体的质量为______.   

A.25g   B.(w+25)g  C.(w+50)g.

答案

(1)20℃时,硝酸钾的溶解度为31.6g,故取100mL水,加入25g硝酸钾,搅拌,恢复至20°C,所得溶液①为不饱和溶液;再加w g硝酸钾,搅拌,恢复至20°C,恰好饱和,所得溶液②,为饱和溶液;再加25g硝酸钾,搅拌,恢复至20°C,硝酸钾不能继续溶解,故所得溶液③为饱和溶液,③中饱和溶液的质量为131.6g;加热后,全部溶解,溶液④可能恰好饱和,也可能为不饱和溶液;冷却至20°C,有晶体析出,故所得溶液⑤为饱和溶液;

(2)加热后100g水中共溶解了(31.6g+25g)硝酸钾,而20℃时,硝酸钾的溶解度为31.6g,故降温后析出晶体的质量为25g.

故答案为:(1)131.6;①;②③⑤;(2)A.

阅读理解

New rules and behavior standards(行为规范)for the middle school students came out. Middle schools are going to use a new way to decide who the top students are. The following are some of the new rules.

You should not be allowed to dye(染)your hair, smoke or drink. You should not copy others’ work in an exam. Don’t do it again if you did it!

Good students love animals and care for other people. Being kind to animals is being kind to ourselves. Be friendly to the people around you. Try to think of others, not only yourself.

Don’t look down on new ideas. Everyone’s ideas are important. You should welcome them, because new ideas make life better for everyone.

Learn to protect yourselves. If you have to go home late, you should let your mother or your father know.

Use the Internet carefully. The Internet can be very useful for our studies. But some things on the Internet aren’t good for teenagers, so try to look at web pages that are good for you.

小题1:The new school rules will help teenagers by telling them ________.

A.how they can study well

B.what they should do at school

C.what is right and what is wrong

D.how they can pass an exam小题2:Good websites can ________.

A.be a waste of time

B.do homework for children

C.make life busier

D.help children with their studies小题3:According to the passage, which of the following is NOT true?

A.It’s not polite to dye hair for everyone

B.Don’t copy others’ work in an exam

C.Be kind to others and try to think of others

D.Don’t look down on new ideas小题4:The passage mainly tells us how to ________.

A.protect ourselves

B.be the top students

C.care for others

D.use the Internet

单项选择题