【题目】某化学学习小组为了探究新制备的饱和氯水的组成和性质进行了科学实验:先观察了氯水的外观后,再用滴管将新制备的氯水逐滴滴入含有酚酞的红色NaOH溶液中,边滴加边振荡,并观察现象,结果溶液中的红色逐渐褪去,得到无色溶液。请回答:
(1)写出新制的氯水中含氯元素的物质的化学式_________________________。
(2)根据预测,实验中溶液红色褪去的原因可能有两种。请用简要的文字说明:
①__________________________________;
②__________________________________。
(3)为了探究溶液红色褪去的原因是上述原因中的①还是②,请叙述相应的实验方法、现象和结论。
____________________________________。
【答案】 (1)Cl2、HCl、HClO
(2)①HCl中和了NaOH溶液而使红色褪去
②HClO氧化了酚酞而使红色褪去
(3)取无色溶液少许于另一支洁净的试管中,加过量NaOH溶液,振荡,观察现象。若溶液又变为红色,则证明溶液红色褪去的原因是①而不是②;若溶液仍为无色,则证明溶液红色褪去的原因是②而不是①
【解析】 氯水中含氯元素的物质有Cl2、HClO、HCl。溶液的红色是酚酞与氢氧化钠相互作用的结果,若是氯水中的酸中和了氢氧化钠而使红色褪去,则再加入氢氧化钠溶液后还会变红;若是氯水中的HClO氧化了酚酞而使红色褪去,则溶液中就不存在酚酞了,即使加入过量NaOH溶液也不会再变红。
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【题目】书面表达(满分20分)
假如你是李华,收到笔友Mary的如下来信。
Dear Li Hua,
How are you?
I am having trouble with my deskmate Jenny at the moment. Last week, we had a maths test. The test was important and everyone had prepared for it except Jenny.
During the test, she asked me to help her. I refused and didn’t let her copy from my paper. As a result, she failed the test. She is angry with me and hasn’t talked to me since then. Now I don’t know how to deal with this problem. Can you give me some advice?
I’m looking forward to your reply.
Yours,
Mary
请你给Mary回信,给她提出建议。
注意:
1. 词数100左右;
2. 短文的开头和结尾已为你写好,但不计入总词数。
Dear Mary,
I’m sorry you are having trouble with your friend. Here are some tips that may help you.
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Selfie
Social media and the mobile web have given rise to a strange phenomenon called the selfie.It refers to a picture of yourself, usually shared on any social networking website.
【1】 Some selfies are extreme close-ups, and others show part of an arm held straight outward.A few of them even feature the subject standing in front of a bathroom mirror.
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【题目】B
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【2】 How did the author form her view of life?
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B. By learning from her friends.
C. Through an unfortunate experience.
D. From her children and husband.
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