,
,则
.
B .
C .
D .
,
,则
Today is Sunday. It's ten o'clock in the morning. Mr. Brown's1are all at home. Mrs. Brown is watching TV. She is watching TV shopping. She wants to buy a2, because she likes reading. Mr. Brown is3a newspaper. There is an interesting photo of a panda. It's from China and its4is Mengmeng.
Their son, David, is talking on the phone. He is calling one of his friends. He wants to go to the5to see animals with his friend. Their daughter, Mary, is playing with her pet cat. A(n)6is in her hand: It is her favourite fruit. What's that over there? Oh, it's a bird. It's7in the cage(笼子).“Mary, please be8Don't wake it up (弄醒) ,”Mrs. Brown says.

①巨大的环境压力
②粮食问题尖锐
③社会保障方面面临新挑战
④经济飞速发展
图象的大致形状是( )
B .
C .
D .
求:
[提出问题]烧碱样品中含有哪些杂质?
[建立猜想]猜想1:可能含有碳酸钠,判断依据是氢氧化钠能和二氧化碳反应生成碳酸钠。
猜想2:可能含有氯化钠,判断依据是在化工生产中,原料可能。
[实验探究]
|
实验操作 |
实验现象 |
实验结论 |
|
取少量烧碱样品于试管中,加适量水溶解,加入过量的稀硝酸,再滴加少量硝酸银溶液 |
|
烧碱样品中含碳酸钠和氯化钠 |
(反思评价]除去烧碱样品中含有的少量碳酸钠,可选用的药品是。
A.CuCl2溶液
B.Ba(NO)2溶液
C.Ba(OH)2溶液
D.KOH溶液