搜题请搜索小程序“爱下问搜题”
问题 选择题

下列物质敞口放置在空气中较长时间后，质量会减少的是（　　）

A．浓硫酸

B．酒精

C．烧碱

D．熟石灰

答案

A、浓硫酸具有吸水性，溶液质量会变大，故此选项错误．

B、酒精具有挥发性．溶液质量会不断减小，故此选项正确．

C、氢氧化钠固体会吸收空气中的二氧化碳和水．固体质量会不断变大，故此选项错误．

D、熟石灰会吸收空气中的二氧化碳，固体质量会不断变大，故此选项错误．

故选B

完形填空

根据短文内容，从短文后的选项中选出适当的选项补全短文，并将选项的编号依次填人下边表格内。(共5小题，每小题1分；计5分)

It is my 12th birthday today．When I’m having my breakfast，my friends come with presents (礼物) for me．I am so happy to see them．We go to the sports club (俱乐部) to play．Then we have lunch at Mc Donald’s．

At about 5:00 in the afternoon we come back home．Mum makes a big birthday cake and  the cake has my name on it．I get (收到) many birthday presents --- a blue T-shirt from mum，sports shoes from dad，a book from my sister Lucy，a basketball from Georgina and a bag from Devin．

I have a happy birthday today!

小题1:--- How old am I today．

--- I am twelve ____________ old．

小题2:We have lunch at ____________．

小题3:--- When (什么时候) do we come back home?

--- At ___________．

小题4:My mum gives a blue ____________  to me as a present．

小题5:--- Who buys me a book?

--- My ___________．
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选择题

过量的NaHCO3和Na2O2混合，在密闭容器中充分混合加热后，最后排出气体，残留的固体是                                                           

A．Na2O

B．Na2CO3

C．Na2O2和Na2CO3

D．Na2O2和Na2O
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