Q. 24. (a) Write the name given to bases
that are highly soluble in water. Give an
example.
(b) How is tooth decay related to pH ?
How can it be prevented?
(c) Why does bee sting cause pain and
irritation ? Rubbing of baking soda on the
sting area gives relief. How?
Or
(a) Name the compound which is
obtained from baking soda and is used to
remove permanent hardness of water.
(b) Write its chemical formula.
(c) What happens when it is
recrystallised from its aqueous solution?
Answers
Explanation:
(a) Water soluble bases are called alkalis, e.g., NaOH, KOH.
(b) Tooth decay starts when the pH of the mouth is lower than 5.5. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. This can be prevented by clearing the mouth and teeth using tooth pastes which are generally basic and can neutralize the excess acid.
(c ) Bee sting pain, a mild base like baking soda is rubbed on stung area as the mild base neutralizes the acid.
a) Sodium carbonate is obtained from baking soda and is used to remove hardness of water.
(b) Its chemical formula is Na2CO3
(c) When it is recrystallized with water, it changes to washing soda, hydrated salt
Na2CO3.10H2O
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Answer:
1.alkalis...eg., Sodium hydroxide(NaOH)
2.when the ph of the inner side of the mouth is less than 5.5, the decay of teeth starts. the outer layer of teeth is made up of a hard enamel like substance that is calcium phosphate.it does not dissolve in water, but gets corroded when ph of inner side of mouth becomes less than 5.5. the tooth paste which are used for teeth cleaning possesses basic nature. they neutralise the acid produced inside the mouth and prevent tooth decay.
3.when we are stung by honeybee then sting of bee releases formic acid due to which we experience pain and irritation. to get relief in the effect of bee sting basic substances such as an aqueous solution of baking soda is applied around the place of bite which neutralise the acidic poison.
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