问题 问答题

菠菜营养丰富,素有“蔬菜之王”之称,在营养价值上还是一种高效的补铁剂.长期以来民间流传着“菠菜根比菠菜茎叶更有营养”、“菠菜不能与豆腐同食”等说法.

某校化学兴趣小组的同学拟通过实验来探究以下问题:

(1)菠菜中是否含有丰富的铁.

(2)菠菜中是否含有某种酸类物质.

(3)菠菜根中铁的含量是否比菠菜茎和叶高.

(4)菠菜为什么与豆腐不能同食.

该小组同学通过上网查询,获得以下资料:

①菠菜中确实含有一种有机酸,其化学名称为乙二酸(化学式为C2H2O4),俗称草酸.②草酸的酸性比醋酸强.③豆腐中含有丰富的钙元素. ④草酸钙是一种无色晶体,不溶于水,是 * * 结石的主要成分.⑤Fe2+遇氧化性物质能转化为Fe3+.⑥含Fe3+的溶液遇KSCN(硫氰化钾)溶液呈血红色,而含 Fe2+的溶液则不能.

该小组设计了如下实验方案:

实验Ⅰ:

实验Ⅱ:

取有根菠菜ag使用相同仪器和试剂,重复实验Ⅰ的过程,观察现象时发现溶液B的红色比实验Ⅰ中得到的溶液红色深.

实验Ⅲ:

另将菠菜在少量开水中煮沸2~3分钟,滤去菠菜,得滤液C.向滤液C中加入足量的Ca(OH)2溶液,再加入足量的醋酸,观察现象.

请回答下列问题:

(1)操作①中加入的浓硝酸具有强氧化性.由此推知溶液A中含有______(填“Fe2+”或“Fe3+”).操作②的名称为______,操作过程中所需使用的玻璃仪器有______、______、______.

(2)操作③中加入活性炭的作用______.

(3)实验Ⅱ中得到的溶液B的红色比实验Ⅰ中溶液B的红色深,可以说明菠菜根中铁元素的含量与菠菜茎、叶相比______(填“高”、“低”或“相同”).

(4)实验Ⅲ中向滤液C加入Ca(OH)2溶液后,再加入足量的醋酸,其目的是排除碳酸钙的干扰.若醋酸的化学式可用HAc表示,写出碳酸钙与醋酸发生反应的化学方程式______.在加入醋酸后发现仍有不溶性物质存在,你认为该物质可能是______,则菠菜中______(选填“含有”、“不含有”或“无法证明”)草酸.

(5)试解释菠菜不能与豆腐同食的理由:______.

答案

(1)菠菜中含有铁元素,浓硝酸具有强氧化性,可以将亚铁离子氧化为铁离子,通过操作②,得到了沉淀物和溶液,说明此步操作是过滤,在过滤操作中用到的玻璃仪器主要有烧杯、玻璃棒和漏斗,所以本题答案为:Fe3+,过滤,烧杯,玻璃棒,漏斗;

(2)活性炭具有吸附性,可以吸附水中的杂质,所以本题答案为:吸附水中的可溶性杂质;

(3)含Fe3+的溶液遇KSCN(硫氰化钾)溶液呈血红色,含量越高,则颜色越深,实验Ⅱ中得到的溶液B的红色比实验Ⅰ中溶液B的红色深,可以说明菠菜根中铁元素的含量与菠菜茎、叶相比要高,所以本题答案为:高;

(4)碳酸盐遇酸化气,故与醋酸反应后会生成二氧化碳,同时生成醋酸钠和水,由于草酸的酸性比醋酸强,所以草酸钙不会与醋酸反应,仍然会以沉淀的形式存在,所以本题答案为:CaCO3+2HAc═CaAc2+H2O+CO2↑,草酸钙,含有;

(5)通过题干提供的信息可以看出,菠菜中含有草酸,豆腐中含有丰富的钙元素,会结合生成不溶于水的草酸钙,所以本能同食,故本题答案为:与豆腐中含有丰富的钙反应产生草酸钙.

单项选择题 B型题
阅读理解

阅读理解。

      American children and teenagers have increased their use of entertainment media by more than one hour

a day in the last five years. On an average day they now spend seven and a half hours using media.

     These are the findings of a new survey. It included not only devices like TVs, computers, mobile phones

and MP3 players, but also media like books and magazines. It did not count media use for school.

     Vicky Rideout at the Kaiser Family Foundation, a health re- search group, wrote the report. She was

surprised that kids could fit even more media time into their day.

     She found that they spent ten hours and fortyfive minutes if you counted each device individually. But

children multi-task a lot, and Vicky Rideout says this is not necessarily a good thing. "

     People who study the brain will tell you that you can't actually multitask in that way. You're really

switching back and forth in order from different tasks, just doing it rapidly, and that you don't really do either

task as well as you would do them if. you did them one at a time." she added.

     The study suggests a link between heavy media use and lower performance in school. About one-fourth of

those who used media the least reported that their grades were mostly average or below. But that was true of

half the heavy media users.

     So where are the parents? Children who had any rule limiting the use of any kind of media were exposed to

an average of about three hours less media a day. But only one-third of children had to follow any rules.

     Girls spent more time than boys on social networking sites, lis tening to music and reading. Boys spent

more time on video games-an average of forty eight minutes more a day than girls.

     Vicky said "It looks like the girls just sort of lose interest in the games and they drop off and start doing

other things, whereas the boys' interest remains strong."

     Some other findings: Time spent reading books has not dropped in the last five years. But time with

newspapers and magazines has, though some reading now takes place online.

1. What is worrying about American children and teenagers according to the survey?

A. The burden and pressure of study after school.

B. The money spent on the entertainment media.

C. Their increased time spent on entertainment media.

D. The lost control of their entertainment activities.

2. What does the underlined word "multitask" mean?

A. Doing different tasks without being permitted.

B. Carrying many tasks at the same time.

C. Doing some illegal things out of school.

D. Only doing one task in the limited time.

3. The underlined sentence in Paragraph 7 means____.

A. Parents should watch children while they are using media

B. Parents shouldn't allow children use media at all

C. Parents should hide and give children free space

D. Parents should play an important part as a director