问题 计算题

某抗酸药每片含碳酸钙534 mg、氢氧化镁180 mg。试计算10片该药片理论上可与1. 00 mol·L-1的盐酸溶液多少毫升完全反应?

答案

169ml

考查根据方程式进行的有关计算。

碳酸钙和氢氧化镁的物质的量分别是

CaCO3      +    2HCl=CaCl2+CO2↑+H2O

1mol            2mol

0.0534mol      0.1068mol

Mg(OH)2   +   2HCl=MgCl2+2H2O

1mol            2mol

0.031           0.062mol

所以需要盐酸的体积是(0.1068mol+0.062mol)÷1.0mol/L=0.1688L=0.169L

选择题
单项选择题

Shopping has always been something of an impulse activity, in which objects that catch our fancy while strolling are immediately bought on a whim. Advertisers and sellers have taken advantage of this fact, carefully positioning inexpensive but attractive items on paths that we are most likely to cross, hoping that our human nature will lead to a greater profit for them. With the dawn of the Internet and its exploding use across the world, the same tactics apply.

Advertisers now place "banners", links to commercial web sites decorated with attractive pictures designed to catch our eyes while browsing the webs, on key web sites with heavy traffic. They pay top dollar for the right, thus creating profits for the hosting web site as well. These actions are performed in the hopes that during the course of our casual and leisurely web surfing, we’ll click on that banner that sparks our interest and thus, in theory, buy the products advertised.

Initial results have been positive. Web sites report a huge inflow of cash, both from the advertisers who tempt customers in with the banners and the hosting web sites, which are paid for allowing the banners to be put in place. As trust and confidence in Internet buying increases and information security is heightened with new technology, the volume of buying is increasing, leading to even greater profits.

The current situation, however, is not quite as optimistic. Just as magazine readers tend to unconsciously ignore advertisements in their favorite periodicals, web browsers are beginning to allow banners to slip their notice as well. Internet users respond to the flood of banners by viewing them as annoyances, a negative image that is hurting sales, since users are now less reluctant to click on those banners, preferring not to support the system that puts them in place. If Internet advertising is to continue to be a viable and profitable business practice, new methods will need to be considered to reinvigorate the industry.

With the recent depression in the technology sector and slowing economy, even new practices may not do the trick. As consumers are saving more and frequenting traditional real estate businesses over their Internet counterparts, the fate of Internet business is called into question. The coming years will be the only reliable indication of whether shopping on the world wide web is the wave of the future or simply an impulse activity whose whim has passed.

The author’s attitude toward online advertising can be summarized as()

A. reserved consent but discontent

B. objective analysis void of opinions

C. enthusiastic support but slight contempt

D. approval so far but uncertainty in the future