问题 问答题

向一定量的碳酸钙中加入100克溶质质量分数为7.3%的稀盐酸,恰好完全反应.请计算:

(1)所用碳酸钙的质量;

(2)反应后所得溶液中溶质质量分数是多少?(结果保留到0.1%)

答案

设反应的碳酸钙质量是x   生成氯化钙的质量为y,二氧化碳的质量为z

CaCO3+2HCl═CaCl2+H2O+CO2

100    73    111      44

x  100g×7.3% y        z

100
x
=
73
100g×7.3%
=
111
y
=
44
z

得:x=10g  y=11.1g  z=4.4g

∴反应后所得溶液的质量=10g+100g-4.4g=105.6g.

∴反应后溶液中溶质的质量分数=

11.1g
105.6g
×100%≈10.5%.

答:(1)所用碳酸钙的质量是10g;(2)反应后溶液中溶质的质量分数为10.5%;

完形填空

Section C 

Directions: Read the following text and choose the most suitable heading from A-F for each paragraph. There is one extra heading which you do not need.

A.The factors leading to a good speaker

B.The importance of enunciation

C.Talk with strangers

D.Pronunciation, the other important assistant in conversationE. A famous master of conversation

F. The great use of dictionary

1. _________________________

The ancient Greeks were very good at making conversations, and the greatest talker of them all was philosophers Socrates. His student Plato surpassed some of his supposed conversations, and we read them in The Dialogue of Plato. In many classrooms today, Socrates’ method of teaching is used.

2. _________________________

The best talkers appear to have had a great interest in and love for their follow creatures, a curiosity about the world in general, some powers of observation and tolerance for those of others, and quick thinking. And they talk for the fun of it, not to show off their knowledge.

3. _________________________

A good voice must have the help of good speech, whose two assistants are clear enunciation and correct pronunciation. Poor enunciation may suggest to your listeners that you lack consideration, and that you are not especially concerned about their opinion of you.

4. _________________________

Pronunciation is settled by common agreement of the community of group speaking the particular language or dialect. For standard pronunciations of words, a dictionary is your best friend.

5. _________________________

Think of meeting a stranger as a chance to have a good time to talk, to make a friend. Look with a smile directly into the other’s eyes when you are introduced, and shake hands with a firm, friendly clasp (紧握). This will give you confidence. Then try to have a smooth and pleasant conversation with him.

单项选择题