问题 计算题

将等物质的量的两种氧化物溶于100mL硫酸,而后逐滴加入1.00mol·L-1的NaOH溶液。当加入的NaOH的体积V1=650mL时,沉淀量达最大值,继续滴加NaOH时,沉淀量逐渐减小。当V3≥750mL时,沉淀量不再改变。

(1)最初加入的50mL NaOH溶液的作用是什么?

(2)计算所用硫酸的浓度。

(3)试判断两种氧化物各是什么,并计算其物质的量。

答案

(1)中和过量的硫酸

(2)沉淀量最大时所用OH-的物质的量与100mL强酸中H+的物质的量相等,n(OH-)=1.00mol·L-1×

0.650L=0.650mol,故n(H+)也为0.650mol 硫酸的浓度为3.25mol·L-1

(3)在“考试说明”规定的内容范围内,由题意知,其中一种氧化物为Al2O3,根据Al(OH)3+OH-=AlO2-+2H2O,该反应用去的n(NaOH)=1.00mol·L-1×(0.750-0.650)L=0.100mol

故Al(OH)3为0.100mol,而Al2O3为0.0500mol

根据Al3++3OH-==Al(OH)3 生成Al(OH)3用去0.300mol NaOH。而生成另一种氢氧化物也用去0.300mol

NaOH,且已知两种氧化物的物质的量相等,故另一种氧化物也是三价金属的氧化物,且不溶于过量碱溶液中,可知其为Fe2O3

Fe2O3的物质的量为0.0500mol。

阅读理解

High school students need “cool” jobs in summer holidays. Working at popular retail chains(零售连锁店) and ice-cream shops are good choices. The U.S. Department of Labor(美国劳工部) says that about two-thirds of the teenager workers are in fast food business. 1/5 of cooks and food workers are between 16 and 19 years old and 2/5 of food workers are part-time workers.

If you think taking a part-time job is easier, you are wrong. For young people, whatever you do, do your jobs well. Because a good work record will be useful for higher-paid jobs in the future. Let’s share my story.

Unless with my family members, I would go to eat fast food. That doesn’t mean I don’t like working in a fast food restaurant. My first part-time job, at age 16, was at the McDonald’s in Bloomington, Indiana. It was very hard work. Especially on Indiana University football weekends, we had no time to rest, but we still had a lot of fun. Finally I got a higher-paid job.

A future manager believes that difficult work encourages success. The growing U.S. population will bring more restaurants. While many people can’t deal with the pressure(压力) to fill orders quickly, the people who really do a great job will get plenty of rewards in the workplace.

小题1:According to the U.S. Department of Labor, ______.

A.more than half of teenager workers are in fast food business

B.teenagers in America like to work in a fast food restaurant

C.teenagers like to take a part-time job in summer holidays

D.almost all teenagers are interested in fast food小题2:The author uses his own story mainly to tell us that ______.

A.he never liked fast food and would never eat it

B.he didn’t like working in a fast food restaurant at all

C.he did a great job, which enabled him to find a better one

D.he never went to the fast food restaurant with his family小题3:The underlined phrase “A future manager” in Paragraph 4 means the person who ______.

A.will become a manager in the future

B.wants to be a manager in the future

C.doesn’t like his job at present

D.worries about his future小题4:From the last paragraph, we can learn that ______.

A.a manager will do less work and get more money

B.not all the people are suitable for the job in fast food business

C.a hardworking waiter has few chances to be a manager

D.the growing U.S. population can bring higher-paid jobs

单项选择题