问题 计算题

小明的妈妈经常为小明蒸碱面馒头吃,有一次小明仔细查看了包装说明,发现此品牌纯碱中碳酸钠含量大于98%。他从家里带了一包样品来学校实验室检验其中的碳酸钠含量是否属实。现准确秤取6g试样放在烧杯中,并向其中滴加稀盐酸至恰好完全反应(忽略CO2溶于水)。共用去盐酸36.5g,此时烧杯内溶液总质量为40.3g(杂质溶于水,且不与稀盐酸反应)。试计算:

(1)生成CO2的质量是           

(2)样品中碳酸钠的质量分数是多少?并判断样品中碳酸钠含量与标签是否相符。

(3)所用稀盐酸中溶质的质量分数是多少?

答案

(1)2.2g (2)88.3% 与标签不相符 (3)10%

题目分析:(1)根据重量守恒定律可得:6g+36.5g-40.3g=2.2g

(2)设6g样品中含有碳酸钠的质量为x,

2HCl+Na2CO3═2NaCl+H2O+CO2

106                  44

x                    2.2g

则:x=5.3g

×100%=88.3% ∵88.3%<98% ∴与标签不相符

(3)设所用盐酸的溶质质量分数为y,

2HCl+Na2CO3═2NaCl+H2O+CO2

73                      44

36.5gXy                2.2g

y=10%

阅读理解

阅读理解。

                                                              Making them sweeter

         JAPANESE scientists have developed a special kind of tomato.  It can change an eater's sense of

taste,says a report in Science News.  For about an hour after a person eats one of the tomatoes,sour foods taste sweet.

         Say you eat one of the tomatoes before lunch.  Then you take a bite of a lemon (柠檬).  You will

find that the lemon tastes like super-sweet lemonade.

           How magical is that !  The key ingredient in the taste-changing tomatoes is " miraculin (非洲奇果蛋白 ) ". Miraculin is found in berries that grow in West Africa.  These fruits are sometimes sold as "

Miracle(奇迹)  Fruit"  berries.

        People have long known about the ability of miracle berries to change taste.  In some countries,the

berries are used  as a way to help people lose weight:  For example,a dieter can eat a berry and then eat

low-calorie sour foods that will

taste wonderfully sweet.

      Scientists found miraculin in the miracle berry in 1968. Since then,people have wondered how to

manufacture it. One way could be to harvest the berries.  The problem was that if demand got too large,

the berry plants could be driven to extinction.

      That's where the Japanese scientists came in.  Professor Kazuhisa Kato and his team at the University of Tsukuba studied the DNA of the miracle berry.  They found a gene(基因)  that contained the

instructions for how to make miraculin.

       Kato and other researchers put the gene for miraculin into the DNA of a tomato. As a result,the

tomatoes started to make miraculin. Those tomatoes had just as much miraculin as miracle berries do.

These "miracle" tomatoes could be grown in large numbers.  If scientists can grow other foods with

miraculin inside,then there won't be any need to harvest all the miracle berries.

      The researchers don't know yet how the tomato-based miraculin can be used. Perhaps it could be sold as a dieting food,to be taken before meals.

1. The tomato is special in that___.

A. it tums all tastes sweet      

B. it can only be eaten before lunch

C.  it changes a sour taste to a sweet one    

D. it has a magical ingredient

2. According to the article,the Japanese scientists____.    

A. found a gene that contained instructions for making miraculin

B. discovered the secrets of miracle fruit berries in 1968

C.  have planted miracle tomatoes in large numbers

D. invented the miraculin gene and put it into the tomato=

3.  According to the article,which of the following statements is TRUE?   

A. It was a latest discovery that miracle berries could change taste.

B. The tomato is a low-calorie fruit that tastes wonderfully sweet.

C. Scientists have already found many uses for mariculin.

D. The tomato-based miraculin might help people lose weight,so it might be used as a dieting food.

问答题 简答题