问题 问答题

有一包固体粉末,可能由Ba(NO32、NaCl、Na2CO3、CuSO4、CaCO3、NaOH中的一种或几种组成.现进行如下实验:

(1)取少量该粉末,向其中加入足量水,充分搅拌后过滤,得到白色沉淀和无色滤液.

(2)在上述沉淀中加入足量稀盐酸,沉淀全部溶解,并放出无色气体.

(3)用pH试纸测得(1)中无色滤液pH为14.

(4)取少量(1)中无色滤液,加入适量稀硫酸,无明显现象.

(5)另取少量(1)中无色滤液,加入稀硝酸和硝酸银溶液,无白色沉淀产生.

根据以上现象,判断该固体粉末的所有可能组成(可不填满,也可补充):

第一组______;

第二组______;

第三组______;…

答案

由(1)现象可得:混合物中一定不含硫酸铜.因硫酸铜溶液为蓝色.

由(2)现象可得:混合物中可能含有碳酸钙或碳酸钠和硝酸钡.

由(3)现象可得:溶液为碱性,所以溶液中可能含有氢氧化钠和碳酸钠中的一种或两种.

由(4)现象可得:混合物中可能含有的碳酸钠和硝酸钡恰好完全反应,或不含碳酸钠.

由(5)现象可得:混合物中一定不含氯化钠.

由以上现象我们可得在混合物中一定不含:硫酸铜和氯化钠.其它物质可能同时存在,也可能存在其中的一部分.若不含碳酸钙时,硝酸钡和碳酸钠一定同时存在,且氢氧化钠可能不存在,也可能存在.

故答案为:NaOH、CaCO3

NaOH、Na2CO3、Ba(NO32

NaOH、Na2CO3、Ba(NO32、CaCO3

判断题
单项选择题

Work looks a better cure for poverty than welfare Especially as fewer and fewer countries will be able to afford to pay potential workers to stay at home a Victorian idea is back in favour: many poor people are better off when they are pulled back into the labour market. The idea revived first in the United States. There, in its harshest form, the unemployed work in exchange for welfare. But countries with governments to the left of America’s, including Labour Australia and Socialist France, are now also exploring ways to link income support and employment policy.

Coming from different directions, the right and the left are gradually finding new common ground. For the right, it seems deplorable to encourage the poor to rely on the state for cash, because they get hooked on government help and accustomed to being poor. For the left, it seems deplorable to allow workers to drop out of the job market for long periods, because it makes it harder for them to find new jobs. For both, the answer is to get the poor to work.

Most industrial countries have a two-tier system of social protection: a social-security scheme, where workers and their bosses make regular contributions in exchange for payments to workers when they are unemployed, sick or retired; and a safety-net, to give some income to those poor people who have exhausted their social insurance or who have none The former is usually not means-tested but, for the unemployed, is of limited duration; the latter is almost always tied to income The public tends to approve of contributory benefits, which is what designers of such schemes intended.

Safety-net benefits carry no such sense of entitlement, and are less popular. Yet they have grown more rapidly in large part because the 1980-82 recession increased the number of people of working age who had exhausted their right to contributory benefits. And an increasing proportion of the poor are people for whom the contributory systems were never designed: the young and lone mothers. In consequence, payments which carry a clear entitlement have become less significant, compared with those which appear to depend purely on state charity.

The rise in the bill for the unpopular kind of social protection comes at a time when governments want to curb state spending. It comes, too, at a time when many countries have done almost everything they can think of to protect the poor. A decade ago many on the left argued that poverty was usually caused by circumstances outside the control of the poor—a lack of jobs, disability, old age, racial discrimination, broken marriages. One way or another, governments have tried to tackle most of these problems. Still the poor remain.

Existing social security systems are increasingly expensive to operate because()

A. more people have lost their jobs

B. many countries have done all they call for the poor

C. poverty has increased uncontrollably

D. more people are in the safety-net category