问题 选择题

下列说法正确的是(  )

A.稀溶液一定是不饱和溶液

B.不饱和溶液转化为饱和溶液后,质量分数一定增大

C.同种物质的饱和溶液一定比它的不饱和溶液要浓

D.饱和溶液中析出溶质后,溶质质量分数不一定变小

答案

A、溶液的浓与稀和溶液是否饱和没有必然的联系,故A错误;

B、将不饱和溶液转化为饱和溶液的方法有多种,若是通过改变温度的方法则溶液的溶质的质量分数则不一定改变,故B错误;

C、不同温度下的同种溶质的饱和溶液不一定比不饱和溶液的浓度大,故C错误;

D、根据溶质的质量分数的计算公式可以知道,当饱和溶液中溶质析出时,溶液中溶质的质量分数要减小,但是如果是保持温度不变的情况下,通过蒸发溶剂的方法而析出了溶质,则溶液中溶质的质量分数不变,故D正确.

故选D.

多项选择题
阅读理解

任务型阅读。根据短文内容,从下框的A-F选项中选出能概括每一段的主题最佳选项。选项中有一项

为多余选项。

1. _____

     With the development of society, unwanted sound is the most widespread nuisance (厌恶的事) in America.

But noise is more than just a nuisance. It constitutes a real and present danger to people's health. Day and night,

at home, at work, and at play, noise can produce serious physical and psychological stress. No one escapes

being affected by this stress. Though we seem to adjust to noise by ignoring it, the ear, in fact, never closes

and the body still responds-sometimes with extreme tension, as to a strange sound in the night.

2. _____

     The annoyance we feel when faced with noise is the most common outward symptom of the stress building

up inside us. Indeed, because irritability (易怒) is so obvious, legislators (立法人员) have made public

annoyance the basis of many noise limit programs. But the more unnoticeable and more serious health hazards

(harm and danger) associated with stress caused by noise traditionally have been given much less attention.

3. _____

     Nevertheless, when we are annoyed or made irritable by noise, we should consider these symptoms fair

warning that other things may be happening to us, some of which may be damaging to our health. Of many

health hazards to noise, hearing loss is the most clearly observable and measurable by health professionals. The

other hazards are harder to pin down (说清). For many of us, there may be a risk that exposure to the stress of

noise increases susceptibility to disease and infection. The more susceptible among us may experience noise as

a complicating factor in heart problems and other diseases. Noise that causes annoyance and irritability in health

persons may have serious consequences for these already ill in mind or body.

4. _____

     Noise affects us throughout our lives. For example, there are indications of effects on the unborn child when

mothers are exposed to industrial and environmental noise. During infancy and childhood, youngsters exposed

to high noise levels may have trouble falling asleep and obtaining necessary amounts of rest.

5. _____

     Why, then, is there not greater alarm about these dangers? Perhaps it is because the link between noise and

many disabilities or diseases has not yet been conclusively demonstrated. Perhaps it is because we tend to

dismiss annoyance as a price to pay for living in the modern world. It may also be because we still think of

hearing loss as only an occupational hazard.

A. Noise affects us from birth even embryo (胚胎) to death.

B. Less attention to more unnoticeable and serious hazards in spite of the most common annoyance caused by

    noise.

C. The reasons for there being no greater alarm about these dangers.

D. Noise is more a real and present danger than a nuisance to people's health.

E. How much do we know about annoyance caused by noise?

F. How much do we know about the possible hazards to people's health caused by noise?