问题 实验题

用2.4 mol/L的H2SO4溶液配制100mL浓度为0.2 mol/L的稀H2SO4,回答下列问题:

(1)需用量筒量取2.4 mol/L的H2SO4溶液的体积是         mL。

(2)溶液配制的所需的基本步骤如下:

将上述实验步骤A到F按实验过程先后次序排列___________________         

(3)上述实验步骤A、B、E、F都用到的仪器名称为__________。  

(4)取上述所配溶液10mL与足量BaCl2溶液反应,生成白色沉淀0.48 g。则该溶液

浓度       0.2 mol/L(填“大于”“等于”或“小于”),造成此误差的操作可能

      。 

a. 定容时俯视容量瓶;  b. 用量筒取2.4 mol/LH2SO4溶液时俯视读数;

c. 容量瓶使用前未干燥;d. 使用的烧杯和玻璃棒未洗涤彻底;

e. 定容时将蒸馏水洒在容量瓶外面

答案

(8分)(1)8.3(2分)

(2)CBDFAE;(2分)

(3)100mL容量瓶;(1分)

(4)大于(1分)   a(2分)

题目分析:(1)根据稀释定律,稀释前后溶质硫酸的物质的量不变,设浓硫酸的体积为xmL,所以xmL×2.4mol/L=100mL×0.2mol/L,解得:x≈8.3,所以应量取的硫酸体积是8.3mL;故答案为:8.3mL。

(2)配制步骤有量取、稀释、移液、洗涤、定容、摇匀等操作,用10mL量筒量取(用到胶头滴管)硫酸,在烧杯中稀释,并用玻璃棒搅拌,冷却后转移到100mL容量瓶中,并用玻璃棒引流,洗涤烧杯与玻璃棒2~3次,并移入容量瓶内,当加水至液面距离刻度线1~2cm时,改用胶头滴管滴加,盖好瓶塞,反复颠倒摇匀,故操作顺序为CBDFAE。

(3)从图中观察得到,A、B、E、F都用到的仪器名称为100mL容量瓶。

(4)白色沉淀是硫酸钡,硫酸钡的物质的量为0.48g÷233g/mol="0.48/233" mol,所以n(H2SO4)=n(BaSO4)="=0.48/233" mol,故所配硫酸溶液的浓度为0.48/233 mol÷0.01L=0.21mol/L>0.2mol/L;

a.定容时俯视容量瓶,所配溶液体积偏小,配制人一样的浓度偏大,故a符合;

b.用量筒取2.4mol/LH2SO4溶液时俯视读数,量取硫酸溶液的体积偏小,所配溶液的浓度偏小,故b不符合;

c.配制需加水定容,使用容量瓶前未干燥,对所配溶液浓度无影响,故c不符合;

d.使用的烧杯和玻璃棒未洗涤彻底,移入容量瓶内溶质硫酸的物质的量偏小,所配溶液浓度偏小,故d不符合;

e.定容时将蒸馏水洒在容量瓶外面,可以继续加水,对所配溶液浓度无影响,故e不符合;

故答案为:大于,A.

点评:本题考查了一定物质的量浓度溶液的配制,难度不大,注意从c= n/V理解溶液配制与误差分析。

综合
填空题

Why must we pay taxes The answer is that the government needs money for many things, for example, to pay its soldiers, sailors and airmen, to build roads, bridges, offices, schools, etc, and to buy goods from abroad ; and only the people of the country can supply the money. One of the most important taxes is income-tax which a person pays according to the amount of his income, whether he is a merchant, a doctor, a lawyer, a shopkeeper, a miner or anything else. This is called a "direct" tax, because it is paid in money directly to the government. Another tax is paid on goods such as watches, jewelry, new clothes, tobacco, wine, etc, when they are brought into a country. Such a tax is paid as part of the price of these goods if they are late sold in shops. We call it "indirect" tax, because it is paid indirectly through the shopkeepers. People usually complain about having to pay taxes, but they forget that the money is spent on things that they and their families need. We need policemen to catch thieves, to see that men obey the laws, to direct traffic, etc, and they must be paid what they earn; children need education, and there must be schools and teachers; we want our streets to be kept clean, and the wages of men who do this kind of work have to be paid. Above all, the country must always be ready to defend itself against attacking enemies, and we can’t have an army without paying for it. Besides, if a country wants to develop, there are many other things to do... Taxes, therefore, cannot be avoided. We buy our food and clothes and pay for our amusements; but, there are several things that the State finds the money for, and that is necessary for us if our society is to continue. We have no real reason to complain, therefore, when we are asked to supply money to be spent for the good of ourselves and for our fellow-citizens.

Title: (46)
Governments need (47)
for many things to do
  • a. (48) its soldiers, sailors and airmen
  • b. (49) roads, bridges, offices, schools, etc
  • c. (50) goods from abroad
Kinds of taxes and tax-payers a. (51) , which is paid by people whose income is over a certain amountb. (52) , which is paid through the shopkeepers
The function of tax Guarantee the (53) and the (54) of a country
(55) Taxes can not be avoided