ACIDS, BASES AND SALTS - pH and importance of pH in everyday life-notes-part-3
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| acids, bases and salts - pH and importance of pH in everyday life |
HOW TO FIND OUT THE STRENGTH OF ACID OR BASE?
How do we find whether the particular acid is strong?
Can we measure
hydrogen ion concentration quantitatively?
Acids give hydrogen
ions and bases give hydroxide ions. The hydrogen ion concentration can be
measured with the help of a pH scale. P
stands for Potenz in German, meaning power.
pH is inversely proportional to hydrogen ion concentration. So if hydrogen ion concentration is more, its pH will be less.
In a basic solution, hydroxide ion concentration will be more and in that case pH will be higher.
pH scale
pH scale has been made from 0 to 14.
pH - 0 -7 - acidic
pH - 7 - neutral
pH - 7 to14- basic
The pH of 0 to 7 indicates the acidic nature of the solution. If the pH of a particular solution is zero, it means it is strongly acidic and as pH increases the acidic nature decreases as hydrogen ion concentration decreases.
pH will be 7 for distilled
water. It means the solution is neutral.
pH from 7 to 14 indicates the basic nature of the solution.
So on this scale, we can find out
whether a particular solution is acidic or basic, strongly acidic
or weakly acidic, concentrated solution or a dilute solution.
Universal indicator is a mixture of several indicators. Different acids at different hydrogen ion concentrations give different colours with universal indicators which can be then compared with standard pH colour charts.
The numbers on the chart indicate the pH values. By matching the
colour, pH can be found.
If pH is zero it will be dark red, if pH is 4 it will be orange, if pH is 7 it will become green if pH is14 it will become violet.
We have discussed the pH of the various solutions. pH is a measure of hydrogen ion concentration. An acid gives hydrogen ions in a solution. More are the hydrogen ions present in the solution, less is the pH and strong is the acid. So pH is a measure of acidic strength of the solution.
An activity can be performed by taking various solutions in daily life and testing their pH and finding out whether these solutions are acidic or basic or neutral.
ACTIVITY
Saliva before a meal is taken and then it is tested with a universal indicator. The colour changes to green. pH is approximately 7.4 and as you know if the pH of the solution is above 7 it is slightly basic. Similarly, saliva after a meal is taken and its colour on the indicator is orange-yellow. The pH is 5. 8 and this is acidic.
You simply need to remember that if pH is below 7 it is acidic, if pH is 7 it is neutral and from 7 to 14 it is basic in nature. Here are the pH value and the colour change of few samples.
Aerated drink - greenish-yellow -6 – acidic
Coffee -orange – 5 - acidic
Tomato juice –orange- 4.1 –acidic
Tap water-greenish- yellow-slightly acidic
Sodium hydroxide- violet- -14- strong base
HCl- dark red - 0 –strong acid
WHAT IS THE IMPORTANCE OF pH IN OUR EVERYDAY LIFE?
pH is very important in our everyday life.
1. Plants and animals are pH-sensitive.
Our body works well at a pH range of 7 to 7.8.
Acid rain- Acidic gases present in the air reacts with rainwater and forms acids. If it falls on plants and animals, it is quite harmful. If the pH of this rain is less than 5.6, it is very harmful to the plants and animals. Acid rain falling in the river is a threat to aquatic animals. pH is a very important factor for plants and animals.
2. pH of the soil
You can collect different samples of soil from different places and also note down what type of plant is growing there.
You can perform an activity. Take 2
grams of soil in a test tube and add about 5ml of water distilled water and
shake it well and then filter it. The impurities or the solid particles will
remain on the filter paper and the solution can be collected. That is called the filtrate.
Test this filtrate with universal
indicators and then compare it with the standard Universal indicator
colour chart. Find out pH by the colour change and find out the pH
of the soil collected from various places. If the pH is less than 7 it will
be acidic, if pH is more than 7 it will be basic.
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| quick lime with soil |
adding quicklime (calcium oxide) or calcium hydroxide. If the soil is basic then it can be neutralized by an acid. Manure or compost is added to the soil for this purpose.
3. pH in our digestive system-
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| acidity |
When food is eaten, the stomach produces dilute HCl which helps in the digestion of the food. This dilute hydrochloric acid does not harm the lining of the stomach. But sometimes dilute HCl is secreted by the stomach in excess. It may be due to overeating or it may be due to indigestion.
Sometimes eating spicy food or mental stress can cause acidity. Then it will harm the stomach walls and it may cause ulcers and the burning sensation. The pain will be there initially, but if it is increased it may cause ulcers also.
So acidity is a serious
problem and it must be removed. As discussed earlier the effect of an acid can be
neutralized by taking either baking soda solution or by using milk of
magnesia (that is a solution of magnesium hydroxide in water)which neutralizes
the acid formed in the stomach. It gives relief from acidity.
4.pH change in tooth decay
If the pH falls below 5.5, the
tooth decay occurs at the hardest part of the tooth – ie, enamel (made up of
calcium phosphate). Always brush your teeth after every meal and that is very
much necessary.
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| toothpaste |
Toothpaste which we use is also basic in nature. So brushing the teeth not only will remove the food particles from the mouth. It will neutralize the acid formed in the mouth thereby preventing the tooth decay.
5. Self-defence- Chemical warfare
Plants and animals defend
themselves by chemical warfare by producing certain acids or bases and
they protect themselves. How do they defend themselves?
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| honey bee |
When
honey bee sting, what do you feel? You feel very much irritated. You feel some
pain because honey bee stings leaves acid on the skin due to which irritation
and pain occurs and this acid which is left on the skin can be neutralized by
baking soda solutions. It gives relief because baking soda will neutralize the
acid left on the skin.
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| stinging nettle leaves |
Also, there is a plant called nettle. It
has very small hair on its leaves which causes stings. If by chance you happen
to touch those leaves you will feel certain irritation because this produces an
acid called methanoic acid. This irritation and pain can be removed by applying
baking soda solution which will neutralize the effect of the acid methanoic
acid.
Nature has provided dock plants which
grow in the neighbourhood of these nettle plants and if you rub that area on
which the nettle sting has occurred, it gives relief. So next time when you
happen to visit someplace where nettle plants are growing. You can identify them and
find that dock plants are also growing there.
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| dock plant |
ORGANIC ACIDS
There are some naturally occurring
acids which are present in plants as well as the animals. Naturally occurring
acids are called organic acids. Vinegar is commonly used in the kitchen for
cooking purposes. It contains acetic acid. Lemon or orange contains citric acid
. Tamarind which is used for cooking purposes contains tartaric acid. Tomatoes also contain oxalic acid. Sour milk or curd contains lactic acid and ant or
bee sting as well as the nettle sting contains methanoic acid. So these are all
organic acids.
In the previous board exams, many questions were there from the topic related to pH. Application-level questions with pH values also can be asked from this topic.
Do you want to learn salts and some important compounds obtained from common salt? You can refer my next blog for that.
YOU MAY ALSO READ: PART 4 ACIDS,BASES AND SALTS
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