问题 计算题

(本题共6分)

某学生课外兴趣小组为了测定镁铝合金中铝的含量,进行了如下实验。将合金3.0克投入到足量的100 mL 1.5 mol•L-1的烧碱溶液中,充分反应后分离出未反应的镁,然后在溶液中滴加1.0 mol•L-1的盐酸,加入盐酸的体积与得到沉淀的数据如下表:

实验次数加入盐酸的体积沉淀质量
160 mL0
280 mL0.78 g
3180 mL5.46 g
(1)开始沉淀时加入的盐酸体积必须大于             mL;若得到沉淀的量最大时,加入的盐酸体积为            mL。 

(2)合金中铝的质量分数为              

答案

(1)70(2分),150(2分)  (2)72 %(2分)

(1)根据表中数据可知,前60ml盐酸是中和过量的氢氧化钠的。0.78g沉淀是0.01mol,所以根据方程式H+AlO2+H2O=Al(OH)3↓可知,需要盐酸是0.01mol,其体积是10ml,因此开始沉淀时加入的盐酸体积必须大于80ml-10ml=10ml。当沉淀最大时,溶液中生成氯化钠是0.1L×1.5mol/L=0.15mol,需要盐酸是150ml。

(2)生成的氢氧化铝是(0.15L-0.07L)×1.0mol/L=0.08mol,则铝的质量是0.08mol×27g/mol=2.16g,其质量分数为

阅读理解

阅读理解。

     American Idol is a singing competition on TV in America. There is one competition every year. People usually

watch the show on Tuesday and Wednesday nights. American Idol is also televised on Fox and CTV in Canada. Its first season was on June 11th, 2002. Until now, it has altogether 7 seasons. This program is to find the best

singer in the country by a series of competition. Audience determines (决定) the result of every competition on

the stages through public voting (投票) by telephone. There are also three judges (裁判) beside the stages. They

watch the performances of the contestants. Then they give some suggestions to the contestants. All the

contestants must be American citizens. They must have full-time jobs. In the first three seasons, they had to be

16 to 24 years old. Since the fourth season, the upper age limit has been 28 years old. So it attracts different

ages of audience. Some TV stations like Hunan TV also have this kind of program. And we can see Super Girl's

Voice and Super Boys' Voice on TV.

1. What does the underlined word "contestants" mean?

A. 参赛者

B. 评委

C. 观众

D. 主持人

2. How many times has American Idol been on TV?

A. Once

B. Seven times.

C. Three times.

D. Four times.

3. What's the age limit of American Idol now?

A. 13-18

B. 16-30

C. 15-36

D. 16-28

4. Which of the following TV stations is not mentioned in the passage?

A. FOX

B. CTV

C. CCTV

D. Hunan TV

5. Which of the following is TRUE?

A. American Idol is showed only in America.

B. American Idol was first shown on July 11th, 2002.

C. American Idol judges beside the stages.

D. American Idol is a program similar to Super Girl's Voice.

选择题