质量分数为a%，物质的量浓度为c mol·L－1的KOH溶液，蒸发溶剂，恢复到原来的温度，若质量分数变为2a%，则物质的量浓度变为
A．等于2c mol·L－1
B．大于2c mol·L－1
C．小于2c mol·L－1
D．在c～2c mol·L－1之间
答案：B
KOH溶液的密度大于水，浓度越大密度越大，设原溶液的密度为ρ1 g/L，蒸发后密度为ρ2 g/L，物质的量浓度为y mol/L
由公式得：c=
，y=
，两式相比得：y=2c×
＞2c mol/L
故答案为B
| 完形填空。 | |||
| Richard found work in a big office after he had finished college. He liked to use his (1)____and was good (2)_____ his work. So he was often paid more than his workmates and he worked (3)______. But something was wrong with the young man one month. He couldn't fall (4)____ at night. So he was always (5)_____ in the daytime and often made mistakes. He had to go to a hospital.The (6)______ looked him over and (7)_____ him to buy some highly effective sleeping pills(高效安眠药). He took them (8)_____ the went to bed. Soon after that he went to (9)_____. Richard (10)_____ in the morning, he had a look at the (11)_____ on the wall. It was a quarter to seven. He got up and went to work after (12)____ . As soon as he went in the office, he said to the head of the office, "Good morning, Mr. Clarke! I've(13)_____ had a good sleep like last night's. And I'm feeling (14)_____better now!" "Skunk(混蛋)!" the head (15)_____ loudly.”We've looked for you for two days! I wanted you to do something important, but it's too late now!" | |||
| ( )1. A. hand ( )2 A. for ( )3. A. hard ( )4. A. asleep ( )5. A. well ( )6. A. doctor ( )7. A. tell ( )8. A. after ( )9. A. asleep ( )0. A. stood up ( )11. A. o’clock ( )12. A. meal ( )13. A. always ( )14. A. much ( )15. A. laughed | B. head B. in B. fast B. alone B. hungry B. policeman B. say B. since B. sleeping B. woke up B. map B. dinner B. usually B. more B. shouted | C. ear C. with C. harder C. afraid C. thirsty C. driver C. ask C. before C. sleep C. at down C. picture C. party C. never C. most C. smiled | D. nose D. at D. faster D. behind D. tired D. nurse D. told D. because D. slept D. lay down D. clock D. breakfast D. often D. than D. asked |