问题 问答题

如图是空气中氧气含量的测定装置.试回答:

(1)盛在仪器A中的物质常用______,该物质燃烧现象是______.

(2)在实验中,钟罩内的水面起变化的原因是______.

(3)实验中,若仪器A中的物质的质量太少,测得氧气的体积分数会______.

答案

(1)磷与氧气在点燃条件下反应生成五氧化二磷,观察的现象是:红磷在空气中燃烧发出黄色火焰,冒出大量白烟,充分反应并冷却后水被倒吸入钟罩中,约占其容积的

1
5

(2)试验中,钟罩内的水面先下降后上升,最终约占其容积的

1
5
;因为:红磷与氧气反应放出大量的热,会使分子运动速率加快,气体体积膨胀,使钟罩内压力增大,所以水面下降;红磷在空气中燃烧会消耗空气中的氧气,空气中氧气的体积分数约为
1
5
,冷却后空气的体积会减少,减少的就是空气中氧气的体积,所以水面又上升;

(3)为了使集气内的氧气完全消耗完在做实验时红磷要过量,若反应中红磷不足,燃烧时钟罩内氧气没有消耗完,水倒吸入装置内的量就占不到其容积的

1
5
,使测得氧气的体积分数会偏低.

故答案为:

(1)红磷,红磷在空气中燃烧发出黄色火焰,冒出大量白烟,充分反应并冷却后水被倒吸入钟罩中,约占其容积的

1
5

(2)因为反应时放出大量的热,分子运动速率加快,使钟罩内压力增大,所以水面下降;当反应结束,温度降低时,由于氧气参加了反应,钟罩内压强减小,所以水面又上升;

(3)偏低.

阅读理解
Reading comprehension.
      Not long ago I was invited out to dinner by a girl called Jane. I have met Jane only twice, and she was
very beautiful.
      I was very pleased. "She loves me" I thought. "I am sorry at such short notice." She said when I arrived,
"but we suddenly knew there were going to be thirteen people at the table,so we had to find someone else."
Believing that the number 13 is unlucky is a typical of superstition. Recently I came across a little group of
worried people.They gathered round a man lying on the pavement (人行道)beside a road in London. They
were waiting for an ambulance, for the man had been knocked down by a passing taxi. He had stapped off
the pavement and into the street in order not to walk under a ladder (梯子). To see a black cat in England is
lucky. But if you see a black cat in India, it is considered very unlucky. There, if you are about to set out on
a long journey, and someone sneezes, you should not go. If you break a mirror, you will have seven year's
bad luck. Just superstition, of course.
1. Jane invited the writer out to dinner because ____.
[ ]
A: she liked him
B: she wanted to have twelve people at the table
C: she wanted to marry him
D: she wanted to have fourteen people at the table
2. A man was knocked down by a passing taxi as a result of his ____.
[ ]
A: slow speed
B: bad luck
C: carelessness
D: superstition
3. To walk under a ladder is considered unlucky in ____.
[ ]
A: England
B: India
C: the U.S.A
D: Japan
4. In ____, if someone sneezes when you start on a journey, you might be unlucky.
[ ]
A: England
B: India
C: the U.S.A
D: Japan
5. The writer ____ superstition.
[ ]
A: believes in
B: likes
C: disbelieves in
D: makes others believe in
6. The word "superstition" means ____.
[ ]
A: 迷信
B: 信仰
C: 笃信
D: 敬重
7. The phrase"come across" means ____.
[ ]
A: 来到
B: 遇到
C: 经过
D: 横过
8. The word "ambulance" means ____.
[ ]

A: 公安人员
B: 救治
C: 专用车
D: 救护车

单项选择题