问题 计算题

水垢的主要成分是CaCO3和Mg(OH)2,为了测定其中CaCO3的含量,取100g水垢,加入过量稀盐酸,测量5min内生成的CO2的质量,绘出如下图所示曲线,请问:

(1)该水垢中CaCO3的质量分数为多少?

(2)假定水垢不含其他杂质,若要计算反应消耗的稀盐酸的质量,还需知道什么信息?

答案

解:(1)由图可知共生成33gCO2

设1009水垢中含碳酸钙的质量为x

CaCO3+2HCl==CaCl2+CO2↑+H2O

100        44

x        33g

x=75g

75g/100g×100%= 75%

(2)还要知道稀盐酸的质量分数

填空题
单项选择题

(四)

With only about 1 000 pandas left in the world, China is desperately trying to clone the animal and save the endangered species. That’s a move similar to what a Texas A & M University researchers have been undertaking for the past five years in a project called "Noah’s Ark’.

Noah’s Ark is aimed at collecting eggs, embryos, semen and DNA of endangered animals and storing them in liquid nitrogen. If certain species, should become extinct, Dr. Duane Kraemer, a professor in Texas A & M’s College of Veterinary Medicine, says there would be enough of the basic building blocks to reintroduce the species in the future.

It is estimated that as many as 2000 species of mammals, birds reptiles will become extinct in over 100 years. The panda, native only to China, is in danger of becoming extinct in the next 25 years.

This week, Chinese scientists said they grew an embryo by introducing cells from a dead female panda into the egg cells of a Japanese white rabbit. They are now trying to implant the embryo into a host animal.

The entire procedure could take from three to five years to complete.

"The nuclear transfer of one species to another is not easy, and the lack of available(capable of being used) panda eggs could he a major problem," Kraemer believes. "They will probably have to do several hundred transfers to result in one pregnancy(having a baby). It takes a long time and it’s difficult, but this could be groundbreaking science if it works. They are certainly not putting any live pandas at risk, so it is worth the effort," adds Kraemer, who is one of the leaders of the Project at Texas A & M, the first-ever attempt at cloning a dog.

"They are trying to do something that’s never been done, and this is very similar to our work in Noah’s Ark. We’re both trying to save animals that face extinction. I certainly appreciate their effort and there’s a lot we can learn from what they are attempting to do. It’s a research that is very much needed. \

From the passage we know that ().

A.Kraemer and his team have succeeded in cloning a dog

B.scientists try to implant a panda’s egg into a rabbit

C.Kraemer will work with Chinese scientists in clone researches

D.about two thousand of species will probably die out in a century