问题 单项选择题

碘量法测定维生素C的含量,应选

A.淀粉指示剂
B.喹哪啶红-亚甲蓝混合指示剂
C.二苯胺指示剂
D.邻二氮菲指示剂
E.酚酞指示剂

答案

参考答案:A

解析: 本题考查维生素含量测定方法。
维生素B1分子中含有两个碱性的已成盐的伯胺和季铵基团,在非水溶液中,可与高氯酸作用。通过喹哪啶红-亚甲蓝混合指示剂在终点由无色变为天蓝色。维生素C在醋酸酸性条件下,可被碘定量氧化。根据消耗碘滴定液的体积,计算维生素C的含量。滴定过程中用淀粉指示剂,临到终点时,碘过量,使指示剂由无色变为蓝色。

判断题
阅读理解

阅读理解

     Time and how we experience it have always puzzled us.Physicists have created fascinating theories,

but their time is measured by a pendulum (钟摆) and is not psychological time, which leaps with little

regard to the clock or calendar.As some-one who understood the distinction observed, "When you sit

with a nice girl for two hours it seems like a minute, but when you sit on a hot stove, a minute seems like

two hours."

     Psychologists have long noticed that larger units of time, such as months and years, fly on swifter wings

as we age.They also note that the more time is structured with schedules and appointments, the more

rapidly it seems to pass.For example, a day at the office flies compared with a day at the beach.Since

most of us spend fewer days at the beach and more at the office as we age, an increase in structured tune

could well be to blame for why time seems to speed up as we grow older.

     Expectation and familiarity also make time seem to flow more rapidly.Almost all of us have had the

experience of driving somewhere we've never been before. Surrounded by unfamiliar scenery, with no real

idea of when we'll arrive, we experience the trip as lasting a long time. But the return trip, although exactly

as long, seems to take far less time. The novelty of the outward journey has become routine. Thus taking

a different route on occasions can often help slow the clock.

     When was become as identical as identical as beads(小珠子)on a string, they mix together, and even

months become a single day. To counter this, try to find ways to interrupt the structure of your day-to stop

time, so to speak.

     Learning something new is one of the ways to slow the passage of time. One of the reasons the days

of our youth seems so full and long is that these are the days of learning and discovery. For many of us,

learning ends when we leave school, but this doesn't have to be.

1.The underlined sentence in Paragraph 1 is used to show         .

A.psychological time is quite puzzling

B.time should not be measured by a pendulum

C.physical time is different from psychological time

D.physical theory has nothing to do with the true sense of time

2.Why do units of time fly faster as we grow older?

A.Our sense of time changes.

B.We spend less time at the beach.

C.More time is structured and scheduled.

D.Time is structured with too many appointments.

3.In Paragraph 3 "novelty" probably means         .

A.excitement

B.unfamiliarity

C.imagination

D.amusement

4.The purpose of the passage is to         .

A.give various explanations about time

B.describe how we experience time psychologically

C.show the different ideas of physicists and psychologists on time

D.explain why time flies and how to slow it down psychologically