题干

除去下列物质中的少量杂质,所选试剂及操作方法正确的是(  )

 选项

 物质(括号内为杂质)

除杂质的方法及操作

 A

 硫酸钠溶液(氯化钠)

加适量稀硫酸

 B

硫酸铜溶液(硫酸)

 加过量的铜,过滤

 C

 氢氧化钠溶液(硫酸钠)

 加适量氢氧化钙溶液,过滤

 D

 氧化钙(碳酸钙)

 加足量水,过滤

A:A

B:B

C:C

D:D

上一题 下一题 0.0难度 选择题 更新时间:2018-04-02 07:01:26

答案(点此获取答案解析)

C

同类题2

课外阅读

                                    李广巧计退兵

     西汉时期,北方匈奴势力逐渐强大,不断兴兵进犯中原。飞将军李广任上郡太守,奉命抵挡匈奴南进。

一天,有三名匈奴兵又来侵扰,李广大怒,亲自率领一百名骑兵前去追击,一直追了几十里地,终于追上三名匈奴兵,杀了两名,活捉一名。

    李广的队伍正准备回营时,忽然发现有数千名匈奴骑兵正向他们这边前进。匈奴队伍也发现了李广,但看见李广只有百名骑兵,以为他们是为大部队诱敌的前锋,不敢攻击,急忙上山摆开阵势,观查动静。

    李广沉着地对部下说:“我们只有百余骑,离大营还有几十里远。如果我们逃跑,匈奴部将必定追杀我们。如果我们按兵不动,敌人反倒疑心我们有大部队埋伏在附近,他们决不敢轻易进攻。所以我们只能进,不能退。”

    部将们听了李广的话,依计而行,跟着李广继续前进。

    到距离敌阵仅二里地光景的地方,李广又下令:“全体下马休息。”李广的士兵卸下马鞍,悠闲地躺在草地上休息,战马在一旁津津有味地吃草。

    匈奴部将感到十分奇怪,派了一名军官出阵观查形势。李广立即命令士兵上马,冲杀过去,一箭射死了这个军官。然后他们又回到原地,继续休息。

匈奴部将见此情形,更加恐慌,料定李广胸有成竹,附近定有伏兵。天黑以后,李广的人马仍无动静。匈奴部将怕遭到大部队的袭击,慌慌张张地领兵逃跑了。

    李广的百余骑兵安全返回大营。

同类题3

阅读填空。先通读下面的短文,然后根据短文内容,在文章后表格的空格内填入一个最恰当的单词,每个空格只能填一个单词。

    It is difficult to find true friends these days. A lot of people would backstab(背后伤人). Some make friends just to use them. Others promise to be your friends but they are never there when you need them the most. They appear only when they need something from you.

    Once you find a friend who is worth keeping, make sure to take care of what you have with that person. How? Here are some tips on how to make friendship last forever:

    1).Call for no reason. Call just to say “Hi” or just to ask “What's up?” You don't need a huge or an important reason to call a friend. If you can't call, just send an e-mail. This would send a message that you remember your friends at any time of the day.

    2).Know when to say I'm sorry and thank you. Don't let pride get in the way, especially when you are wrong. The word “sorry” already has saved a lot of friendships. Show praise for the things, big or little, which your friend does for you. Did she listen to you when you were complaining about that physics exam? Did he offer his shoulders for you to cry on when somebody broke your heart? Say thank you. It's that easy.

    3).Avoid hurtful words. If you have nothing good to say, don't talk at all. Don't hurt your friend's feelings by saying hurtful words that, most of the time, you don't really mean. If you're a true friend, you will be careful with your words.

    4).Don't lie to a friend. Trust is the first thing for building up true friendship. Write them a note from time to time. Also, try to be thoughtful. Give simple gifts that will make their day.

    5).Know how to keep a secret. Show your friends that they can depend on you to be there whatever happens. If you promise to keep the secrets for your friends, just do it.

    6).Be generous with your time. Spare some time to see your friends however busy you are. You can always spare an hour or two after school or work to visit them.

    If you are the type of person who knows how to take care of friendship, you are certainly a keeper!

How to treat your friendship in a right way

Reasons for being difficult to find true friends

●Some will backstab or treat friends as____  .

●Some never give you a helping hand when you are in____  but only take something from you.

Ways of making friendship last forever

●Call for no reason or just e-mail your friend to show that you remember him at any time.

●Say sorry when you are wrong and express thanks for his help at the right time.

●Be ____  with your words so that you won't hurt your friend's feelings.

●Be an____  person and care about friends with simple gifts.

●Don't ____  your promises by letting out your friends' secrets, but show that you are a believable person.

●Be generous with your time and visit your friends although you are very busy.