Acids And Bases Book Back Questions 8th Science Lesson 14
8th Science Lesson 14
14] Acids And Bases
Book Back Questions with Answer and Do You Know Box Content
Do You Know?
Swedish chemist Svante Arrhenius proposed a theory on acids. According to him, an acid is a substance which furnishes H+ ions or H3O+ ions in aqueous solution.
We feel hungry due to the corrosive action of hydrochloric acid on the inner lining of the stomach. When the level of hydrochloric acid goes higher, it causes ulcer.
Copper or brass cooking vessels are coated with tin metal (eyam). If it is not coated the organic acids present in the food materials will react with copper and make the food poisonous. The tin isolates the vessel from the action of acids and prevents food poisoning.
Pickles remain in good condition for long time because they contain vinegar (acetic acid) or benzoic acid.
Sodium carbonate (Na2, CO3) is commercially called as washing soda. Similarly sodium bicarbonate (NAHCO3) is commercially called as baking soda. Caustic soda is sodium hydroxide (NaOH) and caustic potash is potassium hydroxide (KOH).
Choose the best answer:
1. Acids are __________ in taste.
(a) Sour
(b) Sweet
(c) Bitter
(d) Salty
2. Aqueous solutions of __________ conduct electricity.
(a) Acid
(b) Base
(c) Salt
(d) All of the these
3. In acidic solutions blue litmus changes into ____________ colour.
(a) Blue
(b) Green
(c) Red
(d) White.
4. Base is a substance that gives ____________ on dissolving in water.
(a) OH
(b) H*
(c) OH
(d) H
5. Sodium hydroxide is a ________________
(a) Acid
(b) Base
(c) Oxide
(d) Alkali
6. Red ant sting contains ______________
(a) Acetic acid
(b) Sulphuric acid
(c) Oxalic acid
(d) Formic acid
7. Magnesium hydroxides are used for treating __________
(a) Acidity
(b) Head pain
(c) Teeth decay
(d) None of these
8. Acid mixed with base forms _____________
(a) Salt and water
(b) Salt
(c) Water
(d) No reaction.
9. We brush our teeth with tooth paste because it is ______________ in nature.
(a) Basic
(b) Acidic
(c) Both a and b
(d) None of these
10. In basic solution turmeric indicator paper changes from yellow to ___________
(a) Blue
(b) Green
(c) Yellow
(d) Red
Fill in the blanks:
1. Benzoic acids are used for __________
2. The word sour refers to ____________ in Latin.
3. Bases are _______________ in taste.
4. Chemical formula of calcium oxide is ___________
5. Wasp sting contains ________
6. Turmeric is used as a _________
7. In acidic solution the colour of the hibiscus indicator paper will change to ____________
State true or false. If false, correct the statement:
1. Most of the acids are not soluble in water.
2. Acids are bitter in taste.
3. Bases are soapy to touch when they are dry.
4. Acids are corrosive in nature.
5. All bases are alkalis.
6. Hibiscus flower is an example for natural indicator.
Answers:
Choose the best answer:
1. Sour 2. Salt and Base 3. Red 4. OH– 5. Alkali 6. formic acid 7. Acidity 8. Salt and water 9. Basic 10. Red
Fill in the blanks:
1. Preservation of foods 2. Acidus 3. Bitter 4. CaO 5. Alkaline substance 6. Indicator 7. Deep pink or deep red
State true or false. If false, correct the statement:
1.True
2.False
Correct answer: Acids are Sour in taste
3.False
Correct answer: Bases are soapy to touch only in aqueous media, not in dry nature
4.True
5.False
Correct answer: All alkali are bases, but not all base is alkali
6.True