问题 选择题

镁粉、锌粉的混合物m克与一定量的某浓度的稀硫酸恰好完全反应,蒸发水分后得固体(不含结晶水)n克,则反应中生成的氢气的质量为(  )

A.

n-m
48
g

B.

n-m
49
g

C.

m-n
48
g

D.

m-n
49g

答案

由题意可知,蒸发后的n克固体为硫酸镁与硫酸锌的混合物,反应前的固体是镁与锌,共m克;根据质量守恒定律可知,(n-m)g为硫酸根的质量,再除以硫酸根的摩尔质量96g/mol,即可得出硫酸根的物质的量,也就是硫酸的物质的量,也是氢气的物质的量.因此,

(n-m)g
96g/mol
后乘以氢气的摩尔质量2g/mol,即可得出氢气的质量.从而推算出得出A选项是正确的.

另解(用差量法):

Mg+H2SO4=MgSO4+H2

Zn+H2SO4=ZnSO4+H2

两式合并

Mg+Zn+2H2SO4═ZnSO4+MgSO4+2H2↑△M(硫酸根的质量)

24+65           65+96+24+96    4          96+96

 m                  n          x            n-m

则:x=

n-m
48

故选A.

判断题
阅读理解

阅读理解。

     Just how comfortable is your sofa? Would you be prepared to let a stranger crash out there for the

night? And, on the basis of a bit of email correspondence and seeing a photo of the sofa belonging to

"An Unknown", would you travel halfway across the world to do the same? It might sound crazy, but

this is exactly what millions of people have done whilst participating in an activity known as couch

surfing.

     Couch surfing is travelling on a budget, using a broad network of contacts in order to get overnight

accommodation for free, or at as little cost as possible. Participants, also called couch surfers, join

dedicated websites, providing as much information about themselves as possible in order to make others

feel comfortable hosting them, or using them as a host. Various safety features are generally available in

such online networks, like verification (核实) of names and addresses,, personal references, and "vouching

(担保) for" a particular member; a reliable host or guest.

     As well as the financial advantages of couch surfing, participants also claim that the practice gives them

a more unique, authentic (真正的) travel experience, allowing them to experience culture and cuisine through

the locals, rather than from the confines of sanitized tourist accommodation. "We open our minds and lives

and welcome the knowledge that becomes available through cultural exchange." said Casey Fenton, founder

of Couch Surfing. com. "Couch Surfing wants to change not only the way we travel, but how we relate to

the work."

1. What is the right order of couch surfing?

    a. Provide personal information.

    b. Travel to the host's house.

    c. Join dedicated websites.

    d. Check photos of sofas by emails.

A. d-b-a-c

B. b-c-a-d

C. a-d-c-b

D. c-a-d-b

2. Which is NOT a safety feature of online network?

A. Verification of identity.

B. A copy of the passport.

C. Personal references.

D. Vouching for the member as reliable.

3. From the text we can know that _____.

A. participants can be hosted or a host

B. couch surfing tests people's patience

C. couch surfing leads to trust between people

D. people couch surf simply for financial reasons

4. What can be the best title of the test?

A. Touring the World on the Internet.

B. Unique Advantages of Local Travelling.

C. Around the World from Sofa to Sofa.

D. Cultural Exchange by Correspondence.