问题 选择题

水热法制备Fe3O4纳米颗粒的反应是3Fe2++2S2O32-+O2+xOH-=Fe3O4+S4O62-+2H2O,关于该反应下列说法中正确的是(  )

A.H2O和S4O62-都是还原产物

B.Fe2+和S2O32-都是还原剂

C.1molFe2+被氧化时,转移2mol电子

D.x=2

答案

在3Fe2++2 S2O32-+O2+xOH-=Fe3O4+S4O62-+2H2O中,化合物中铁元素、硫元素用平均化合价,铁元素的化合价变化:+2→+

8
3

硫元素的化合价变化为:+2→+

5
2
;氧元素的化合价变化:0→-2,

所以氧化剂是O2还原剂是Fe2+、S2O32-,还原产物是Fe3O4

A、还原产物是Fe3O4,故A错误;

B、还原剂是Fe2+、S2O32-,故B正确;

C、设失电子xmol,由3Fe2+--Fe3O4-失2e-,1molFe2+被氧化时失去的电子为

2
3
mol,故C错误;

D、根据氢原子守恒,水的化学计量数为2,则OH-的化学计量数为4,即x=4,故D错误;

故选B.

阅读理解

阅读理解。

     Sometimes, people are not clear about what kind of food is healthy, and what kind of food may do

harm to our health. The USDA has prepared a food guide to help people learn about which kind of food

is the healthiest to eat. The food guide describes six main food groups: meat (like fish and chicken), dairy

(like milk and cheese), grains (like bread and rice), fruit, and vegetables. The last group is fats and sweets.

The USDA also suggests (建议) how much of each food group is healthy to eat daily. Though this guide

was prepared by the US government, it is very useful for people all over the world.

     As a result of years of study, we know that too much animal fat is bad for our health. For example,

Americans eat a lot of meat and only a small amount (量) of grains, fruit and vegetables. Because of the

way they eat, they have a high rate (率) of cancer (癌症) and heart disease. In Japan, people eat large

amounts of grains and very little meat. The Japanese also have a very low rate of cancer and heart disease.

The Japanese live longer than anyone else in the world. However, when Japanese people move to the US,

the rate of heart disease and cancer goes up as their eating habit changes. And as hamburgers, ice creams

and other high-fat foods become popular in Japan, the rate of heart disease and cancer is going up there

as well. People are also eating more meat and dairy food in other countries, in which the disease rate is

going up along with the change of the way people eat. Doctors everywhere suggest people eat more

grains, fruit and vegetables and less meat and dairy food.

     Eating healthily is important for children as well as their parents. When parents have poor eating habits,

their children usually do, too. After all, children eat the same way as their parents. When parents eat

healthy food, the children will learn to enjoy it, too. Then they will develop good eating habits. Doctors

suggest parents give their children healthier food such as fruit, vegetables and juice.

     Everyone wants to live a long, healthy life. We know that the food we eat affects (影响) us in different

ways. For example, doctors believe that fruit and vegetables can really protect people from many different

diseases. On the other hand, animal fat can cause (引起) diseases. We can change our eating habits now

and enjoy many years of healthy living.

1. What is the USDA in the passage?

A. A group of doctors in the US.

B. An office of the US government.

C. A report on diseases in the US.

D. An order given by the US president.

2. The second paragraph mainly tells us that _____.

A. Japanese are always healthier than Americans

B. living in the US is not good for people's health

C. if you eat too much fat you will have cancer

D. the way we eat may cause some health problems _____.

3. Which of the following is true according to the passage?

A. More and more people have good eating habits now.

B. Parents' eating habits are important to their children.

C. Good eating habits develop only when you are young.

D. The more fruit and vegetables we eat, the longer we will live.

4. The greatest help the passage gives us is _____.

A. to introduce a food guide to the world

B. to provide us with knowledge of six food groups

C. to suggest a way of eating for a healthy life

D. to find the main cause of some serious diseases

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