问题 选择题

下列各项中的两个量,其比例2∶1的是

A.硫酸铵固体中n(NH4+)与n(SO42—)

B.相同温度下,0.01 mol/L的醋酸溶液与0.02 mol/L 醋酸溶液中的c(H+)

C.液面均在“0”刻度时,50 mL酸式滴定管和25 mL酸式滴定管内所盛溶液的体积

D.40℃时pH=7的(NH4)2SO4与NH3·H2O的混合液中,c(NH4+)与c(SO42—)

答案

答案:A

题目分析:根据硫酸铵的化学式(NH4)2SO4可知,硫酸铵固体中n(NH4+)与n(SO42—)=2∶1,A正确;醋酸是弱酸存在电离平衡,由于稀释促进电离,所以相同温度下,0.01 mol/L的醋酸溶液与0.02 mol/L 醋酸溶液中的c(H+)之比不是1∶2,而是大于1︰2;根据滴定管构造可知,C中所盛溶液的体积大于2∶1;D中溶液的温度不是常温下,此时溶液溴解析,所以溶液中c(NH4+)与c(SO42—)大于2∶1,答案选A。

点评:该题容易错选D。这是由于审题不清导致的,因为只有在常温常压下,pH=7的溶液才能显中性。

阅读理解

阅读理解。

     The ostrich (鸵鸟) is the largest bird in the world. From far away , it looks more like a camel than a

bird. It has a long neck, long legs and a walk like a camel. Its eyes are very large and sharp . Like the

camel ,  the ostrich can go for a long time without water . It lives in sandy desert , too .

Its wings are too short for flying , but they do help the ostrich to run fast. The wind gets under the wings

and lifts the bird off the ground . In this way , it can take very long steps. An ostrich can run faster than a

horse .

     Ostriches are  big and strong , but sometimes they do not seem very smart.

     When they are afraid, they run around in circles.

     Ostrich eggs are large . The shells are very strong . They are so strong that they can be used for cups

and bowls.

1.The ostrich ________

A. is larger than a camel

B. is as large as a camel

C. is larger than any other bird

D. looks like each other

2. The ostrich and camel both have ________

A. sharp eyes            

B. long legs

C. short wings            

D. to go without water

3. The ostrich ________

A. can fly fast with the help of its wings 

B. can run fast with the wind

C. can’t fly because it has such short wings 

D. can run fast with the help of its wings

4. What can lift the ostrich off the ground?

A. its wings    

B. its legs    

C. The wind    

D. its long neck

5. People can use ________ for cups and bowls.

A. the shells of ostrich eggs        

B. ostrich eggs 

C. ostrich itself                  

D. ostrich wings

计算题