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Question
Why does tooth decay start when the pH of mouth is lower than 5.5?
Solution
Tooth enamel is made up of calcium phosphate and is the hardest part of the body. When the pH in the mouth goes down and becomes 5.5, it is strong enough to corrode the enamel of the tooth. The mouth turns acidic because the bacteria present in it produce acids by breaking down sugar and food particles left behind in it after eating.
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RELATED QUESTIONS
Five solutions, A, B, C, D and E, when tested with universal indicator, showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is
- neutral?
- strongly alkaline?
- strongly acidic?
- weakly acidic?
- weakly alkaline?
Arrange the pH in increasing order of hydrogen-ion concentration.
The indicators which turn red in acid solution are:
(a) turmeric and litmus
(b) phenolphthalein and methyl orange
(c) litmus and methyl orange
(d) phenolphthalein and litmus
The pH values of six solutions A to F are given below:
A = 0, B = 11, C = 6, D = 3, E = 13, F = 8
Which of the above solutions are (i) acids (ii) alkalis?
What colour would the universal indicator show in an aqueous solution of sugar? Why?
Separate the following into substances having pH values above and below 7. How do these influence litmus paper?
(i) Lemon juice
(ii) Solution of washing soda
(iii) Toothpaste
(iv) Vinegar
(v) Stomach juices
A group of students measured the pH of some substances they found in their homes. Their results are given in the following table:
| Substance | pH | Substance | pH |
| Apples | 3.0 | Salt | 7.0 |
| Baking soda | 8.5 | Sugar | 7.0 |
| Black coffee | 5.0 | Toothpaste | 9.0 |
| Household ammonia | 12.0 | Vinegar | 3.0 |
| Lemon juice | 2.5 | Washing soda | 11.5 |
| Milk | 6.5 |
(a) What would the students have used to measure the pH?
(b) Which solution is the most acidic?
(c) Which solution is the most alkaline?
(d) Which solutions are neutral?
(e) Which solution can be used to treat wasp stings?
(f) Which solutions can be used to treat bee stings?
Methyl orange gives ______ colour in an acidic solution.
Write a note on:
Litmus
Write a note on:
Phenolphthalein
Take some lemon juice in a tumbler and add baking soda slowly. What do you see? What do you infer from this?
