问题 计算题

(2011年浙江温州,35题)在一定量的氢氧化钠稀溶液中逐渐滴加溶质质量分数毒.0.73%的稀盐酸,反应过程中不断搅拌并及时测量不同时刻溶液的温度与pH,记录数据如下表:

反应时间(秒)0255075100125150175200
滴入稀盐酸体积(毫升)048121620242832
pH13.213.012.712.412.17.02.01.61.3
温度(℃)36.937.538.038.538.839.239.038.838.6
 

(1)观察上表发现,当反应时间在__________秒时,氢氧化钠与盐酸恰好中和。

(2)分析上表数据发现,在逐渐滴加稀盐酸的过程中,溶液的温度先升高后降低,请分析原因:________________。

(3)结合上表中滴入稀盐酸体积与pH的变化数据,试计算氢氧化钠稀溶液中溶质的质量。(稀盐酸的密度取l.0克/毫升;化学方程式为:NaOH+HCI=NaCl+H2O)

答案

(1)125    

(2)氢氧化钠与盐酸反应放出热量,导致温度上升;反应停止后,温度下降。

(3)解:HCl的质量=20毫升×1克/毫升×0.73%=0.146g

设NaOH稀溶液中溶质的质量为x

NaOH  +  HCl =  NaCl 十H2O

40    36.5

x    0.146克

40/x=36.5/0.146克

解得x=0.16克; 

答:氢氧化钠稀溶液中溶质的质量为0.16克

单项选择题
阅读理解

C

Telepathy: Mind-to-mind Contact

Telepathy is the ability to communicate without the use of the five senses (sight, hearing, touch, smell, taste). It’s an instinct (本能) which can be woken up in times of emergency or need. When we feel that something is happening or about to happen by instinct, we’re using resources within the unconscious mind. When the resources of two persons’ unconscious minds link together into the same frequency, we call it Telepathy.

We can either send or receive Telepathy. If you know who is calling before you answer the ringing phone, you are probably a good receiver. If you think of a person and he/she calls you, you are most likely to be better at sending.

You can easily put your abilities to the test. Think of somebody and will him or her to contact you. Be patient. The other person may not be a good receiver, but they should contact you much earlier than would normally be expected. Or whenever the phones rings, but try “feeling” who is contacting you. Don’t guess, but try to feel it with your mind. However, if neither of these work for you, that doesn’t mean that you have no ability of telepathy. As mentioned earlier, telepathy is most likely to turn up in case of emergency.

Telepathy dreams often contain telepathic messages. Two people may both dream of the other and find that their dreams had a clear connection. These people are probably linking to each other’s unconscious mind.

Telepathy & Relationships. The more people spend time together, the more likely they are to be able to link up to the other’s mind, specially when separated. There are two reasons for this. One is that they understand the other’s mind through time spent together; the other is that there is usually a strong desire to communicate. A mother will often sense that her child is in danger. This is due to the child’s eagerly wanting his or her mother, knowing that this person who would always want to be there for them, and the mother’s deep desire to protect her child from harm.

64. Telepathy turns up when we ____.

A. sense a close friend in danger              B. use the five senses together

C. recall things from our memory              D. think of a stranger

65. You’re better at sending than receiving Telepathy if you ____.

A. can feel your mom is in danger               B. receive a friend’s call as you wish

C. can tell who knocks at your door             D. dream of a friend dreaming of you

66. Which is not the way to help people gain Telepathy?

A. Help them have a strong desire to communicate.   B. Separate them all the time.

C. Help them link up their unconscious minds.       D. Let them spend much time together.