问题 选择题

下列方法不能将饱和石灰水和氢氧化钠溶液区别开的是(  )

A.分别升高温度

B.分别通入CO2

C.分别滴加碳酸钠溶液

D.分别滴加稀盐酸

答案

A、饱和石灰水是氢氧化钙的水溶液,氢氧化钙的溶解度随着温度的升高而减小,升高温度饱和石灰水会析出氢氧化钙,而氢氧化钠溶液没有明显现象,现象不同,可以鉴别.

B、二氧化碳能与氢氧化钠溶液反应生成碳酸钠和水,但无明显变化;二氧化碳能使饱和石灰水变浑浊;能出现两种明显不同的现象,故可以鉴别.

C、碳酸钠溶液能与饱和石灰水反应生成碳酸钙白色沉淀,与氢氧化钠溶液不反应,能出现两种明显不同的现象,故可以鉴别.

D、饱和石灰水和氢氧化钠溶液分别与稀盐酸反应生成氯化钙和水、氯化钠和水,均无明显变化,不能鉴别.

故选:D.

判断题
阅读理解

阅读理解

     Competition. It's a simple word, yet a very complex word that covers many angles when it comes to

how gasoline prices are determined. It seems so easy to explain, but don't let that trick you-it's incredibly

difficult to explain and adequately understand.

     Say you're on a Sunday afternoon drive, and notice a gas station near you charging $3.50. Down the

road a few miles, that price could easily be 10 or more cents higher or lower. The question is "how" or

"why" is that? Think of it this way. Are you more likely to get a better deal on a car if there are two similar car dealers next to each other? Perhaps, because the dealers are too close. Say there is a third similar car dealer miles away. Is he going to be at the same level of competition and sell his cars for the same price as the two dealers next to each other? Likely not. He may charge more or less. Maybe people don't know

there are two other dealers down the road. Maybe the dealer is almost outside of the city and the land

value isn't as high, so his taxes aren't as high.

     These situations do take place at gas stations. And more factors can impact what a station will charge. Timing can greatly impact what price a station charges as well! Many motorists fail to realize that the price a station pays for gasoline changes daily. If one station gets lucky and buys gas on Monday and the cost

goes up Tuesday, the station that bought on Monday doesn't necessarily have to raise prices like the

station that bought on Tuesday. Maybe the station that got caught buying for a higher price on Tuesday

will pass that higher cost on by raising its gas price.

      Perhaps the difference is what brand the station is-branded stations usually pay a slightly higher cost

for their gasoline. In return for paying a higher cost, those stations are guaranteed first supply in case of

emergency situations. Independent stations don't pay as much, but aren't guaranteed supply.

     While competition sounds easy to understand, there are always a large number of factors that could

influence what one station charges. Keep in mind how many variables (变数) there are next time you fill

up.

1. What could be the best title for the passage?

A. How Competition Impacts Gas Prices 

B. Gas Prices Go Up or Down

C. Competition---a Very Complex Word 

D. We Can't Stress Enough the Need for Competition  

2. The example of car dealers is used to show ________.  

A. car prices are determined by car dealers

B. location is an important factor in pricing

C. the quality of service matters most

D. dealing strategy should be flexible

3. The gas prices of a station always change partly because _______. 

A. a gas station always wants to charge more

B. the gasoline is in great demand

C. the cost of the gas the station buys varies daily

D. gas is in greater need on Monday

4. According to the passage, branded stations _______.

A. spend less money on their gasoline        

B. have more staff than independent stations

C. charge less for high quality oil            

D. offer a steady oil supply