Галогендердің және оның қосылыстарының қолданылуы. Химия, 10 сынып, қосымша материал.

APX 1

Trends in chemical properties

The halogens can all act as _____________________ agents. (an _______________ agent is an electron _______________). When a halogen acts as an __________________ agent, each halogen gains an electron to form the corresponding halide ion:

The halogen atom itself is _________________. For example:

I₂ + 2e^- → 2I^-

Down Group VII the ability of the halogen to act as an ________________ agent decreases.

Can you think of an explanation why?

APX 2

Uses of chlorine and chlorate (I)

• a) Write an equation to show the reaction between chlorine and water to

 make chloric (I) acid

• State what is oxidized and what is reduced in this reaction

• State an application of this reaction

• a) State what happens when chlorine is added to water in the presence of bright

 sunlight

• State what is oxidized and what is reduced in this reaction

• Explain why chlorine is added to the water supply

• State one advantage and one disadvantage of adding chemicals to the water supply

• a) Write an equation to show the reaction between chlorine and sodium

 hydroxide to make sodium chlorate (I)

• State what is oxidized and what is reduced in this reaction

• State an application of this reaction

APX 3

Chlorine and public health

• Divide the paragraphs between the people in your group.
• Read the paragraph and then each person must summarise the paragraph so the group can fill the table and questions below.

Questions: (In your book)

• Why do we put chlorine in out drinking water?

• What are the disadvantages of chlorinated water?

• Who do you think wrote this article?

• Give three pieces of evidence to support your claim.

• Would you trust this source? Why?

• 6 mark question:

Chlorinating water introduced in 1904

‘Should chlorine be used to purify drinking water?’ Use the data to help you answer.

1.

The addition of chlorine in drinking water has been the standard in water treatment in the United States since 1904. For over 100 years we have trusted and relied on chlorine to purify our water and kill off any waterborne pathogens.

2.

The good news is that chlorine has done a good job in killing off most microorganisms in the water. In fact, the United States has one of the safest water supplies in the world, and I am truly grateful for this. Without chlorine (or some other form of water disinfection treatment), millions of people would die from devastating infections such as cholera, salmonella, and others.

3.

The bad news is that chlorine treatment does not absolutely ensure that by the time our drinking water comes out of our home faucet it is free of unhealthy microorganisms. Dangerous bacteria (such as e-coli and coliform) are still found in chlorinated tap water on occasion. When this happens it is primarily due to problems related to the treatment system itself or to the transport of the water to our homes. Even minimal exposure to these types of bacteria can cause symptoms similar to the flu, such as headaches, diarrhoea, cramps, nausea or vomiting. Thus, I highly recommend a tap water filter at the point-of-use (your water faucet) to ensure adequate filtration of unhealthy micro-organisms, as well as other many other contaminants, that could end up in your drinking water.

4.

The ugly side of drinking chlorinated water has only recently been documented. And it has to do with the long-term health effects of chlorine and its disinfection by-products (DBPs). What the studies have found is that chlorine itself is not the main problem; rather it has to do with what happens when the chlorine mixes with any type of organic matter in the water. In the 1970s scientists discovered that when chlorine is added to water, it forms Trihalomethanes (THMs), one of which is chloroform. THMs increase the production of free radicals in the body and are highly carcinogenic (cancer causing). Chlorine and THMs has been linked to various types of cancer, kidney and liver damage, immune system dysfunction, disorders of the nervous system, hardening of the arteries, and birth defects.

5.

What most people don’t realize is that chlorine in drinking water is not the only problem. According to the Journal of Public Health, “Up to two-thirds of the harmful effects of chlorine are due to inhalation and skin absorption while showering.” Even though I had filtered my drinking water for chlorine and other contaminants for many years, it took me a while longer to realize how much chlorine I was being exposed to in an unfiltered shower. We just don’t think about it. The inhalation of chlorine and other chemical vapors into our lungs means that these chemicals enter directly into our bloodstream. Thus, removing chlorine and other volatile chemicals with a quality shower filter is just as important as removing these chemicals from your drinking water with a tap water filter.

6.

The primary reason adding chlorine to water for disinfection has become so widely accepted is not because it is the safest or most effective way to disinfect water — it is the cheapest. Is there a better way? The most powerful and cost-effective way to get chlorine-free water is to invest in a whole house water filter or to purchase a drinking and shower combo pack for your home.