题干

KI在经酸化的溶液中被空气氧化生成I2.该反应的速率受温度、酸度、溶剂、试剂浓度等影响,可用淀粉与碘的显色反应来观测该反应的速率.已知,淀粉与碘的显色反应在温度升高时灵敏度会降低,高于75℃则不能显色;淀粉浓度越高显色越灵敏、颜色也越深.

实验小组拟用0.8mol•L﹣1 KI溶液、0.1mol•L﹣1H2SO4溶液、淀粉溶液等来探究温度、酸度对上述反应速率的影响,他们做了A﹣C三组实验,部分实验数据如表:

编号

温度/℃

H2SO4体积/mL

KI溶液体积/mL

H2O体积/mL

淀粉溶液

/mL

出现蓝色时间/s

A

40

10

5

5

1

5

B

TB

10

5

5

1

没出现蓝色

C

5

10

5

5

1

39

D

t

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    Most people say that most people have not more than 30 friends at any given time, and 400 over the whole of their lives. However, on social networking sites, most users have about 150 friends. If these numbers are correct, then friendship means different things in different situations.

    Also, there are no rules about friendship. There are no instructions about how to make friends, how to keep friendships going, and how to finish friendships if we want to move on. People have very different opinions about this: some people would die for their friends and they value them more than family. Others say that friends are temporary, only there to help each other until they are no longer needed. If people with such different views become friends, this can lead to problems.

    Because of these different definitions of friendship, it is easy to be unhappy about our friendships. We may want them to be deeper or closer, or we may want to have more friends in our lives. Sometimes we simply do not have the time to develop our friendships, or we fear we have left it too late in life to start. If we move to another country or city, we have to find ways, to make new friends again.

    This dissatisfaction shows us how important friendships are for most of us. We should not think that it could be too late to build friendships. We also need to understand that the need to be around other people is one that is shared by many. Therefore, we should not be too frightened about starting to talk to people who in the future may become our friends: it is likely that they too would like to get closer to us. Remember what people say: strangers are friends we have not met yet.