实验室需1.0 mol/LNaOH溶液480mL，若用固体NaOH进行配制，则应称NaOH多少克？
应称NaOH 20.0 g。
480mL1.0 mol/LNaOH溶液中的NaOH为19.2g，但实验室无480mL容量瓶，应该用比480mL大的容量瓶，1000mL的大得太多，故用500mL容量瓶，以此计算所需NaOH的质量。则0.5L溶液需NaOH质量为： m(NaOH) ＝ 0.5L × 1.0mol/L × 40g/mol ＝ 20.0g。
| A total of 4.6 million digital televisions have been sold, and the sales of HDTV sets have quadrupled since last year. Consumers have bought HDTVs to play their DVDs and to have clearer pictures and wide screens. Only a small percentage of the people who have purchased HDTVs, however, have actually hooked their TVs up to receive high-definition television digital signals. Perhaps television viewers are having trouble keeping up with the changes in technology. Even the manufacturers of HDTVs, like Mitsubishi, Thomson Multimedia, Sony, and Samsung seem to have a tough time learning how to make their sets work with the various digital TV formats because little standardization has been required or implemented in the industry. Some of the HDTVs Weigh over 200 lbs., and a variety of retailers offer a delivery service to the buyer’s home to help install the heavy sets. This is known as a white-glove service and usually comes with an extra fee. After HDTV purchasers get their sets home and hook them up, they will still need to Work to get the digital signals to their systems. Most of the industry’s cable providers do not yet offer high-definition programing, and only about 15% of commercial television stations have switched over to even the lowest improved digital pictures. Worse yet, viewers may need to install antenna before they can even get the digital signals to their new HDTV sets. Another frustration for home-theater seekers is that the current HDTV sets allow owners only to watch high-definition programs, not to record them. |
A majority of HDTV consumers could not enjoy high-quality digital pictures because______.
A．they did not tune in to the right channel
B．they did not install the system
C．the market retailers created the confusion on purpose
D．the manufacturers did not have a uniform standard for their sets