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氢氧化钠是一种重要的化工原料，广泛应用于肥皂、造纸等工业．现有少量长期暴露在空气中的固体氢氧化钠．

（1）请你说说氢氧化钠是否会变质？原因是什么？写出有关反应的化学方程式．

（2）如果此氢氧化钠已经变质，请你用一种实验方法证明，简要写出实验步骤、现象和有关化学方程式．

答案

（1）氢氧化钠暴露在空气中易于空气中的二氧化碳反应生成碳酸钠和水而变质，反应的化学方程式为：2NaOH+CO2═Na2CO3+H2O

（2）实验方法：检验CO32-的存在，取样品少许放在试管中，向样品中滴加稀盐酸，观察现象．

    实验现象：若样品中有气泡产成，证明样品已变质．

   有关化学方程式：Na2CO3+2HCl═2NaCl+H2O+CO2↑

故答案为：（1）变质；NaOH潮解与空气中的CO2反应；2NaOH+CO2═Na2CO3+H2O

（2）取少量上述NaOH，滴加盐酸，有气泡产生；Na2CO3+2HCl═2NaCl+H2O+CO2↑

填空题

Part 3


Questions 19-25


·Read the following passage and answer questions 19-25.
·For questions 19-25, choose the correct answer A, B, C and D.
·Mark your answers on the Answer Sheet.
While still in its early stages, welfare reform has already been judged a great success in many states, at least UN is getting people off welfare, lt’s estimated that more than two million have left the roles since 1994.
In the past four years, welfare in rolls in Athens country has been cut in half. But 70 percent of the people who left in the past two years took jobs that paid less than $6 an hour. The result: The Athens country poverty rate still remains at more than 30 percent—twice the national average.
For advocates for the poor, that’s an indication that much more needs to be done.
"More people are getting jobs, but it’s not making their lives any better," says Kathy Lairn, a policy analyst at the center in budget and policy priorities in Washington.
Canter analysis of US census data nationwide found that between 1995 and 1996, a great percentage of single, fame-headed household were earning money on their own, but that average income for these households actually went down.
But for many, the fact that poor people are able to support themselves almost as well without government aid as they did with it is in itself a huge victory.
"Welfare was a poison. It was a toxin that was poisoning the family," says Rector, a welfare reform is changing the moral climate in low-income communities. It’s beginning to rebuild the work ethic, which is much more important.
Mr. Rector and others argued that once "the habit of dependency is cracked," then the country can make other policy changes aimed at improving living standards.

From the passage we can infer that before 1994 ______.

A．most of the people depended on government

B．most of the people took jobs

C．we don’t know as the passage didn’t say

D．most of the people live a richer life
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