有t℃时浓度相同的两份KNO3溶液A和B，A为100g，B为80g，将其恒温蒸发20g水后，A刚好饱和，则关于B溶液正确的说法是（ ）
A．也刚好是饱和溶液
B．仍是不饱和溶液
C．是饱和溶液，并有晶体析出
D．有晶体析出剩余不饱和溶液
在温度条件不变的情况下，同种溶液的饱和度是不变的．
假设该题中此溶液的浓度是20%．则A中有20g溶质，B中有16g溶质．
A原来是100g，蒸发掉20g水刚好饱和，溶液浓度变为
×100%=25%，20 80
B原来是80g，蒸发掉20g水后，浓度变为
×100%=26.6%，显然大于其饱和度25%，所以要析出，有结晶析出的溶液肯定是饱和溶液了．16 60
故选C
| 阅读理解。 | |
An interview with Benno Nigg, the sports scientist
Nigg's Answer: That is a little bit overstated. But the literature shows that shoes are a minor player in injury development. If you take a group of people and want to injure them, send them out every day for a 20-kilometre run. A lot of them will be injured in three weeks. The major factors are the distance run, the intensity and recovery time, not the shoes. 2. _____ Nigg's Answer: The problem is that if you go to a store and want to find your best shoes, you don't know what to do. Things that are sometimes done, like video analysis of your rear foot movement, may not help. The only way to assess whether a shoe is right for you is how it feels. If you feel comfortable in a shoe, it's likely to be good for you. 3. _____ Nigg's Answer: A shoe may act as a training device, making some muscles to function more effectively for a majority of users. Or it may use materials that last longer. That may have something to do with its price. However, for the average runner it is difficult to distinguish between actual functional designs and unnecessary features. Generally, the more a shoe controls movement, the more it acts like a cast, which means you lose some muscle strength, and your feet are more likely to be injured. 4. _____ Nigg's Answer: Yes, for about 80 per cent of people. The major benefits are training the small muscles crossing the ankle joint, and a reduction of knee and lower back pain. However, some claims for these unstable shoes are overstated, such as the general muscle strengthening that they are claimed to produce. 5. _____ Nigg's Answer: There are claims that there are fewer injuries when you run barefoot, but there is not yet enough evidence, or enough research, to prove that. If you look at performance, most papers suggest an advantage of 3 to 4 per cent. With a few exceptions, people don't run barefoot, so it may be that it's not an advantage, or it may be that we're just not used to it. |