问题 选择题

下列表示对应化学反应的离子方程式正确的是

A.金属钠与水反应:Na+2H2O=Na++2OH+H2

B.Cu与浓硝酸反应制NO2:Cu+4HNO3(浓)=Cu2+2NO3+2NO2↑+2H2O

C.向Na2SiO3溶液中通入过量CO2:SiO32+ CO2 +H2O =H2SiO3↓+ CO32

D.将NaHSO4与Ba(OH)2溶液混合至中性:2H+SO42+Ba2+2OH= BaSO4↓+2H2O

答案

答案:D

题目分析:A、电荷不守恒,错误;B、硝酸为强电解质要拆分,写为离子,错误;C、过量二氧化碳对应产物为HCO3,错误;D、若NaHSO4为2mol,则需Ba(OH)21mol,故参加反应的硫酸根离子为1mol,正确。

单项选择题
单项选择题

Brian arrived at San Francisco airport two hours before the flight to Paris. He was wearing three shirts, a jacket, two pairs of socks, a pair of shorts, and two pairs of jeans. He was carrying one small backpack, which was very full, but he didn’t have any other luggage. Brian needed to meet a man named Tony before he checked in for his flight. He found Tony near the Air France counter. Tony gave him a round trip ticket and a small package.

"Give this package to Jean Paul at the airport in Paris. He will have a sign with your name on it. I think you can find him easily," Tony said," You don’t have any luggage, right"

"Only this backpack," Brian answered. "You said I could bring one carry on bag. "

"That’s right. One carry on bag is fine. Have a good trip. "

"Thanks. "

Is Brian a criminal Not at all. He is an air courier. And he paid only $110 for the round trip ticket to Paris. Air couriers get cheap airline tickets because they take important packages and papers to foreign countries. Businesses sometimes need to get packages and papers to people in foreign countries by the next day. Often, the only way they can do this is to use an air courier company. It is not cheap for a business to send a package with an air courier, but it is quick.

Every year about 80,000 people worldwide travel as air couriers. The number of tickets for courier travel is growing by about 10 percent a year. However, air courier travel isn’t for everyone. But if you have very little money, can be flexible about your travel plans, and don’t mind wearing the same clothes for a week, it can be a great way to take a vacation!

Business choose the air courier service because ().

A.it costs less

B.it is flexible

C.it saves time

D.it grows fast