问题 问答题

有一无色气体,可能由SO2、SO3、O2中的一种或几种混合而成,现测知该气体中氧元素的质量分数是60%,则该气体的组成可能是(1)______,(2)______,(3)______,(4)______.(可不填满,不够可添线).

答案

SO2中氧元素的质量分数为

16×2
32+16×2
×100%=50%;

SO3中氧元素的质量分数为

16×3
32+16×3
×100%=60%;

O2中全部是氧元素,氧元素的质量分数为100%.

若含有一种气体,应为SO3

若是混合气体,要满足氧元素的质量分数为60%,若是两种气体,则一种气体中氧元素质量分数大于60%,另一种小于60%,因此可以是SO2和O2

若是三种气体,则可以是SO2、SO3、O2

故答案为:(1)SO3,(2)SO2和O2,(3)SO2、SO3、O2

阅读理解

阅读理解。

     Lily has a penfriend in America. Her name is Alice. They write to each other every week. They tell each

other about their lives. Here is a letter from Lily.

Dear Alice,

    Thank you for your letter and telling me about your best friend.In this letter,I'm going to tell you about my

friend.Her name is Cathy. She has long brown hair and blue eyes. She is the same age as me,but a little taller.

She is always happy. We sit together in class and help each other with our homework. We always play

together after school and play computer games for an hour. Cathy thinks quickly (迅速地) and does better

than me. She is learning to play the piano (钢琴).I am learning to play the piano,too.We play together every

day. It's fun. We always have a good time.

     Please write to me soon. 

                                                                                                                                                   Love, 

                                                                                                                                                   Lily

1. How often does Lily write to Alice? [ ]

A. Every two weeks.

B. Every week.

C. Every day.

D. Every three weeks.

2. Who is Lily's best friend? [ ]

A. She doesn't have one.

B. Cathy.

C. Alice.

D. Tommy.

3. What is Cathy's hair like? [ ]

A. Long and green.

B. Long and brown.

C. Short and brown.

D. Short and black.

4. When do they play computer games? [ ]

A. Before school.

B. At school.

C. After school.

D. At the weekend.

5. What other things do they do together every day? [ ]

A. Write letters.

B. Sing.

C. Play the piano.

D. Use the computer.

单项选择题