问题 填空题

(1)pH=3的醋酸和pH=11的氢氧化钠溶液等体积混合后溶液呈______,溶液中c(CH3COO-)______c(Na+).(填大于、小于、等于)

(2)将pH=3的硫酸溶液和pH=12的氢氧化钠溶液混和,若使混和后溶液的pH=7,则硫酸溶液和氢氧化钠溶液的体积比是______

(3)某酸性化工废水中含有浓度约为0.01mol.L-1的Ag+、Pb2+等重金属离子.有关数据如下:

难溶电解质AgIAgOHAg2SPbI2Pb(OH)2PbS
Ksp8.3×10-125.6×10-86.3×10-507.1×10-91.2×10-153.4×10-28
(i)在废水排放前,用沉淀法除去这两种离子,最好加入______(填字母序号)

A.Na2S、B.NaOH、C.KI、D.Ca(OH)2

(ii)某工程师用CaO处理上述废水后Pb2+的浓度为1.2×10-3则此溶液的pH=______.

答案

(1)pH=3的醋酸,c(醋酸)>0.001mol/L,pH=11的氢氧化钠,c(NaOH)=0.001mol/L,等体积混合,醋酸过量,溶液呈酸性,c(OH-)<c(H+),由电荷守恒为c(CH3COO-)+c(OH-)=c(Na+)+c(H+),则c(CH3COO-)>c(Na+),

故答案为:酸性;大于;

(2)混和后溶液的pH=7,则酸中n(H+)=碱中n(OH-),则V×10-3=V×10-2,硫酸溶液和氢氧化钠溶液的体积比是10:1,故答案为:10:1;

(3)(i)用沉淀法除去这两种离子,由表格中溶度积数据可知,硫化物的溶度积小,易转化为沉淀,则最后选择硫化钠,故答案为:A;

(ii)用CaO处理上述废水后Pb2+的浓度为1.2×10-3,由Pb(OH)2的Ksp可知,c(OH-)=

1.2×10-15
1.2×10-3
=10-6mol/L,则c(H+)=10-8mol/L,所以pH=8,

故答案为:8.

单项选择题
单项选择题

The Federal Government


联邦政府


The Constitution
When America broke away from Britain in 1775, she did not adopt a British Constitution. The British have always had an unwritten constitution, whereas every item of the American Constitution is clearly written down and numbered, and can only be changed by a two-thirds majority vote of Congress.
Yet in their different ways, the American and British forms of government did have one thing in common. They were both democratiC.As for American society, it was more democratic than British society, in that it paid less attention to class or wealth.
Political Parties
There are two major political parties in the USA, the Democratic Party and the Republican Party. The policies of the two parties are not basically opposed to one another. Inside both parties there moderates and right-wringers, though the Democrats still have the reputation of being somewhat more liberal than the Republicans. Voters are influenced by family traditions, but there are plenty of ordinary people who vote according to their hopes, fears and beliefs.
There are no other political parties that can compete with the two big parties, though there are occasionally independents who stand for the presidency and manage to collect quite a few votes. There are no left-wing parties. Most Americans are in favor of free enterprise, believing that it may one day help them fulfill the American Dream.
The President and Congress
The President of the USA has more power than any other president in the democratic world- except the French President. It is he who formulates foreign policy and prepares laws for the home front. He is leader of the nation and Commander-in-Chief of the Armed Forces. He represents the USA and, since the USA is a super power, the eyes of the whole world are on him. The fate of the world is in his hands, or so many people believe, and one careless, ill-prepared speech by him could precipitate a crises.
Actually, a great deal of the President’s power is controlled by Congress, the American name for "parliament". It is Congress that declares war, not the President. Unlike the Prime Minister of Great Britain, or of Germany, he can make a treaty with a foreign power. But this treaty must be debated and agreed by Congress before it comes into force. The same control applies to laws at home. Congress has (on several occasions) refused to ratify treaties or given approval to laws proposed by the President. The USA is the only country, apart from France, where a president can rule with a parliament, the majority of whose members do not belong to his own political party.
Some Americans have the feeling that idealism has gone out of politics and that personal ambition and money have taken its place. The election campaign fro the Presidency is unique in the amount of money poured into it. The wooing of voters lasts for months. But before the campaign for the election of the President can begin, each political party has to choose its candidate for the Presidency. This can lead to some very close contests. Men aspiring to be elected as the party candidate employ top public relations and advertising men, who invent clever catch phrases and set about "selling" their man. There are whistle stop tours by train, by plane, by car. The candidate delivers countless speeches and shakes countless hands. This razzamatazz typifies American enthusiasm and extravagance.
Big money is necessary to support a presidential candidate’s campaign and the candidate himself must be rich enough to pay his share. An attractive wife is an advantage, too. Money is also needed to become the Governor of a state, or a successful Senator, or member of the House of Representatives. Yet from this small group many excellent men have become President, and the same is true of members of Congress.
It is very unlikely that the President could ever become a dictator. Congress, the press and the people between them rule out such a possibility.
The Supreme Court
Perhaps the most effective safeguard of democracy is the Supreme Court, for one of its objects is to protect the individual against the government. It has the authority to cancel a law which it considers violates the Constitution. The Court sits for at least four days a week and any individual who has a grievance against the government can apply to it for help.
The Supreme Court goes way back to 1787, the days of the Founding Fathers, and is one of the cornerstones of American democracy. It gives judgement in disputes between States, or between a State and the Federal Government, and without invitation can declare a law made by Congress to be unconstitutional. The great Jefferson, who drew up the Declaration of Independence, saw to it, too, that there was a Bill of Rights which every American could thrust under the nose of anyone who tries to rob him of his freedom as a democratic citizen.

One thing in common between the American and British form of government is that they were both______.

A.constitutional


B.unconstitutional
C.democratic


D.interested in class and wealth