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SCIENCE
What is pH?
You may have heard of pH testing for aquariums or swimming pools or perhaps you’ve
seen commercials that advertise pH balanced products? What exactly does pH mean?
What kinds of things have a pH? Who needs to know about pH?
Read the article below and highlight what you think is important. Be ready to discuss
the information and answer some questions.
Scientists can divide almost all substances into two groups-acids and bases. Acids taste
sour and contain many hydrogen atoms. Some acids like orange juice and vitamin C are
harmless and can even help us stay healthy. Others, like hydrochloric and sulfuric acids,
are very dangerous and can dissolve skin and damage eyes. Bases have a bitter taste and
feel slippery in water. They contain a combination of hydrogen and oxygen atoms
called hydroxyl groups. Strong bases can cause serious burns. Some are used to make
soaps and other cleaning products. Weak bases can be used to make medicines like
antacids for acid indigestion.
Chemists use a special scale to measure how strong each acid or base is. This scale is
called the pH scale. Battery acid is one of the strongest acids with a pH of about 1. Lye
is a base of pH 13.5 and is used in manufacturing soap. Any substance with a pH from
6.9 to 1 is acidic. If the substance has a pH from 7.1 to 14 they are basic or alkaline. If a
substance has a pH of 7.0 they are chemically neutral. These substances have an equal
number of hydrogen (H) and hydroxyl (OH) groups. Distilled water is one of the few
substances with a pH of exactly 7.0.
What does it mean for a product to be pH balanced? We’ve all heard or read the
advertisement claim, “gentle on hands but tough on grease”. Shampoo and body soaps
start out with a pH above 7.0 they are bases. Some people have sensitive skin and the
chemicals in soap can burn or irritate them. We still need to clean ourselves using base
products so manufactures are adding citric acid to help lower the pH to make it more
neutral and gentle on our skin. Every morning you are battling tooth decay by brushing
your teeth. Tooth decay is caused by bacteria that grows in your mouth. This bacteria
releases acid that slowly dissolves teeth causing cavities. When you brush your teeth the
toothpaste is a base and it raises the pH killing the bacteria. This neutralizes your mouth
temporarily but, as the day goes on the bacteria begin to grow again and the pH of your
saliva drops becoming acidic again.
Chemists use electronic test meters to measure pH. Litmus paper is a paper soaked
with an indicator chemical that changes colors in an acid or base. There are also test kits
using liquid indicators to measure the pH of hot tubs, swimming pools or fish aquariums.
Bromothymol blue (BTB) is a blue liquid used in fish aquariums to test the pH of the
water. Fish are very sensitive to changes in pH. The pH scale for a healthy aquatic
environment only ranges from 6.2 to 7.4.
If an aquariums pH level drops from pH 7 to pH 6 the water is ten times more acidic. If
it drops to pH 5 it’s 100 times more acidic and so on… The pH scale changes by powers
of ten!!!
There are many natural indicators that change colors in acids or bases. Grape juice and
cabbage juice can be used to test acids and bases. Some purple flowers such as wild
violets will change in color if placed in an acid or base. Many color changeable markers
use acid and base substances in their mixtures to cause color changes. Next time you
observe a color change perhaps you’ve seen a change in pH with an indicator substance.
USE THE TEXT TO ANSWER THESE QUESTIONS:
1. What causes a substance to be acidic?
2. What causes a substance to be basic?
3. Why is water neutral?
4. If you have acid indigestion why does antacid help you feel better?
5. What is an indicator?
6. Give three examples of indicators:
7. Why should you brush your teeth more than once daily?
8. What is another word for basic substances ?
9. How many times more acidic is a pH 4 compared to pH 7 ?
10. Ask me a question ?