Page 46 - Science Class 07

Its main uses are as follows: Other Bases
v To manufacture soap.
v To manufacture several industrial
chemicals such as sodium hypochlorite.
v To manufacture paper, rayon, tex les
medicines, etc.
The strength of an acid or an alkali is
measured by a scale called the pH scale.
This scale has a range from 1 to 14. On
this scale, pure water is neutral with
pH=7. Find out the range of pH for acids
and bases. Also, find out about the
rela on between pH value and strength
of an acid or a base.
Acid Neutral Alkali
Ba ery Acid Gastric Acid Hydrochloric Acid Acid Rain Black Coffee Urine/Saliva Pure Water Sea Water Baking Soda Milk of Magnesium Ammoria Soapy Water Bleach Drain Cleaner solu ons. These chemicals have a pH of 7.0 on
Ammonium Hydroxide
Its main uses are as follows:
v To manufacture fer lizers, such as
ammonium nitrate.
v To manufacture nylons, plas cs, dyes, etc.
v As ‘ink remover’ to remove ink spots from
clothes.
1. Why does milk turn sour a er some me?
2. What do you mean by organic acid?
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Hydrochloric acid present in our stomach helps
in diges on of food. However, too much of acid
causes indiges on and pain in stomach.
Magnesium hydroxide is used as an antacid to
neutralize the excessive acidity in the stomach.
It is sold as ‘milk of magnesia’.
Sodium carbonate is used as washing soda and
sodium hydrogen carbonate as baking soda.
Baking soda is also used to treat ant s ngs.
When an ant s ngs, it injects formic acid into
the skin. This irritates the skin. Baking soda or
calamine solu on (zinc carbonate) is used to
neutralize the acid and provide relief.
NEUTRAL SUBSTANCES
Neutral substances are chemicals that have no
proper es of either acids or bases, have equal
parts of hydrogen and hydronium ions and
don’t change the colour of litmus paper or
other acid-base indicators. Neutral substances
include water, glucose solu ons and salt
a scale of 14. In terms of toxicity, neutral
substances are generally harmless to the touch.
For example: Sugar, common salt, alcohol,
water, etc.
The complete reac on of an acid with a base to
form a salt and water is called neutraliza on.
Common salt is a neutral substance which is
prepared by the following method.
It can be prepared by the reac on of sodium
hydroxide with hydrochloric acid.
NaOH + HCl NaCl + H O
2
(Sodium (Hydrochloric Sodium C hloride (Water)
hydroxide) Acid) (common salt)
Science-7