问题 填空题

空气是人类赖以生存的自然资源。测定空气中氧气体积分数的实验装置如下图所示。

集气瓶中的燃烧匙内放有一定量的红磷,用弹簧夹夹紧乳胶管。点燃红磷,立即伸入瓶中并把塞子塞紧。待红磷熄灭后,打开弹簧夹。

(1)写出红磷在空气中燃烧的符号表达式:_______________________

(2)该实验的现象是___________________________________________,可代替红 磷测定空气中氧气含量的药品是__________(填序号)。

A.木炭

B.铜丝

C.铁粉

D.蜡烛(3)红磷熄灭后,集气瓶内剩下的气体主要是________(填化学式),由此实验可推知该气体具有___________________________________ 性质。

(4)造成测量结果偏小的原因可能是___________________________________ 。(任写一条)

答案

(1)P +  O2P2O5    

(2)红磷燃烧、产生大量白烟、烧杯中的水进入集气瓶约占总体积的1/5 , B 

(3) N2 , 难溶于水、不燃烧也不支持燃烧  

(4) 红磷的量不足或未冷却至室温或装置气密性不好等

题目分析:(1)红磷燃烧,生成五氧化二磷;(2)红磷燃烧,产生大量白烟,冷却后打开止水夹,烧杯中的水倒吸入集气瓶中,约占集气瓶剩余体积的1/5;木炭燃烧时会产生二氧化碳,使集气瓶中的压强变化不大,故A错误;铜可与氧气反应生成氧化铜,故B正确;铁不能在空气中燃烧,生锈时会与水反应,故C错误;蜡烛燃烧会产生大量的二氧化碳,故D错误;(3)红磷燃烧时与氧气反应,集气瓶中剩下的是氮气,从实验中可知氮气不能燃烧,也不支持燃烧,不能溶于水;(4)造成测量结果偏小的原因主要是集形瓶内的压强减小太少,原因可能有:装置气密性差、红磷量不足等。

阅读理解

阅读理解。

     Between school, homework, sports, your afterschool job, and hanging out with friends, it may feel

like there's no time for healthy eating. And when you do stop to eat, it's probably tempting to go the

quick and easy route by grabbing a burger and fries, potato chips, or candy.

     Even if you take time to eat three meals a day, you may still feel hungry at times.  This is natural-during

teens, a person's body demands more nutrients to grow. What's the answer? Healthy snacks. Snacking

on nutritious food can keep your energy level high and your mind alert without taking up a lot of your

time. Snacks are a great way to satisfy that hunger and get all the vitamins and nutrients your body

needs.

     But you need to pay attention to what you eat. Filling your face with a large order of fries after class

may give you a temporary help, but a snack high in fat and calories will only slow you down in the long

run.

     To keep energy levels going-and avoid weight gain-keep clear of foods with lots of simple

carbohydrates (sugars) like candy bars or soda. Look for foods that contain complex carbohydrates

like wholegrain breads and cereals and combine them with proteinrich snacks such as peanut butter or

lowfat yogurt (酸奶) or cheese.

     Choosing healthy snacks means shopping smart. Be careful of the health claims on food packages.

Just because something is "all natural" or "pure" doesn't necessarily mean that it's nutritious. For example, "all natural" juice drinks or sodas can be filled with sugar (which is, after all, a natural ingredient) but all

that sugar means they'll be high in calories and give you little nutrition.

     A granola (麦片) bar is a good example of a snack that people think is healthy. Although granola

bars can be a good source of certain vitamins and nutrients, many also contain a great deal of fat,

including a particularly harmful type of fat called trans fat (反式脂肪酸). Check the Nutrition Facts label

on the package to be sure.

1. People think that granola bar is healthy because ________.

A. it is a good source of calories                        

B. it provides trans fat

C. it contains some vitamins          

D. it is natural

2. In choosing healthy snacks, we should try to make sure that ________.

A. they are all natural or pure                          

B. they are high in nutrition

C. their packages are good                  

D. they contain harmless fat

3. Teens need snacks to ________.

A. keep a good figure            

B. gain weight

C. help grow                  

D. keep healthy

4. According to the passage, all the following snacks are good EXCEPT ________.

A peanut butter                        

B. fries

C. lowfat yogurt                        

D. wholegrain bread

填空题