问题 选择题

关于溶液配制,下列说法正确的是

A.配制480mL0.1mol/LCuSO4溶液,需要CuSO4·5H2O晶体12.0g

B.用浓硫酸配制稀硫酸时,将浓硫酸稀释后立即转入容量瓶中

C.称量5.3g碳酸钠固体时,若将物质和砝码放反,将会使称量结果偏小

D.定容后发现液面高于刻线,可用胶头滴管将多余的水吸出

答案

答案:C

题目分析:A项配制溶液时没有480mL的容量瓶,所以应配制500mL0.1mol/LCuSO4溶液,需要的CuSO4·5H2O晶体应该为: g。B项浓硫酸稀释放热,应该冷却到室温时再转移到容量瓶中,否则容量瓶的容积受温度影响会变化,使所配溶液浓度不准确。C项正确。D项水加多了,此时用胶头滴管将多余的水吸出,可能也会把溶质吸出,使溶液浓度不准确,此时应该倒掉重新配制。

点评:记住容量瓶的正确使用方法,熟悉配制溶液的操作步骤和注意事项。

问答题
单项选择题

In 1998 consumers could purchase virtually anything over the Internet. Books, compact discs, and even stocks were available from World Wide Web Sites that seemed to spring up almost daily. A few years earlier, some people had predicted that consumers accustomed to shopping in stores would be reluctant to buy things that they could not see or touch in person. For a growing number of time-starved consumers, however, shopping from their home computer was proving to be a convenient alternative to driving to the store.

A research estimated that in 1998 US consumers would purchase $ 7.3 billion of goods over the Internet, double the 1997 total. Finding a bargain was getting easier, owing to the rise of online auctions and Web sites that did comparison shopping on the Internet for the best deal.

For all the consumer interest, retailing in cyberspace was still a largely unprofitable business, however. Internet pioneer Amazon. com, which began selling books in 1995 and later branched into recorded music and videos, posted revenue of $153.7 million in the third quarter, up from $37.9 minion in the same period of 1997. Overall, however, the company’s loss widened to $45.2 million from $9.6 million, and analysts did not expect the company to turn a profit until 2001. Despite the great loss, Amazon. com had a stock market value of many billions, reflecting investors’ optimism about the future of the industry.

Internet retailing appealed to investors because it provided an efficient means for reaching millions of consumers without having the cost of operating conventional stores with their armies of salespeople. Selling online carried its own risks, however. With so many companies competing for consumers’ attention, price competition was intense and profit margins thin or nonexistent. One video retailer sold the hit movie Titanic for $9.99, undercutting the $19.99 suggested retail price and losing about $6 on each copy sold. With Internet retailing still in its initial stage; companies seemed willing to absorb such losses in an attempt to establish a dominant market position.

It can be inferred from the passage that Amazon. com()

A. is making a profit now

B. will probably make a profit in 2001

C. is a company that sells books only

D. suffers a great loss on the stock market