Maharashtra Board solution 8th science topic -12 Introduction to Acid and Base.

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Q.1. Fill in the blank and rewrite the completed statements :

1. the Main constituent of alkali is …………… .

Ans Main constituent of alkali is hydrogen ion.

2. The substances which change their colors in presence of acid or base are called …………… .

Ans The substances which change their colors in presence of acid or base are called ‘Indicators’.

3. Main constituent of acid is …………… .

Ans Main constituent of acid is hydrogen ion.

4 .Proteins which are part of our body cell are made up of …………… .

Ans Proteins which are part of our body cell are made up of amino acids.

5. Tartaric acid is a acid.

Ans Tartaric acid is a natural (organic) acid.

6. is used for sterilization of water.

Ans Dil. HCl is used for sterilization of water.

7. Metal oxides are generally in nature.

Ans Metal oxides are generally alkaline in nature.

8. is used for the preparation of different types of chloride salts.

Ans Hydrochloric acid is used for the preparation of different types of chloride salts.

Q.2. Find the odd one out:

1. Tamarind, Tomato, Lemon, water

Ans Tamarind, Tomato, Lemon, water

2. Sodium hydroxide, Potassium hydroxide, Calcium hydroxide, Methyl red.

Ans Sodium hydroxide, Potassium hydroxide, Calcium hydroxide, Methyl red.

3. Litmus paper Blue, Litmus paper Red, Phenolphthalein , Vinegar.

Ans Litmus paper Blue, Litmus paper Red, Phenolphthalein, Vinegar.

Q. 3. Find co-related terms :

  1. Flowering plants : Angiosperms :: Non-flowering plants : ?

Ans Flowering plants : Angiosperms :: Non-flowering plants : Gymnosperms

Q .4. Extra data :

  1. Acid and Base.
Ans
Acid Base
Acid molecules contain hydrogen ion (H+) as a main constituent. Alkali contains hydroxide (OH-) as a main constituent.

Q.5. Match the pair :

1.

Group A Group B
i. Lemon a. Acetic acid
ii. Vinegar b. Citric acid
c. Tartaric acid
d. Lactic acid

Ans

i. Lemon Citric acid
ii. Vinegar Acetic acid

2.

Group – A Group – B
i. Tamarind i. Acetic acid
ii. Curd ii. Citric acid
iii. Tartaric acid
iv. Lactic acid

Ans

i. Tamarind Tartaric acid
ii. Curd Lactic acid

3.

Column – A Column – B
1. Magnesium Hydroxide a. Ca(OH)2
2. Calcium Hydroxide b. Mg(OH)2
c. NaOH

Ans

Column – A Column – B
1. Magnesium Hydroxide b. Mg(OH)2
2. Calcium Hydroxide a. Ca(OH)2

Q.6. State True or False:

1.. Salt is acidic.

Ans False – Salt is neutral

2. Metal oxides are generally acidic in nature

Ans False – Metal oxides are generally alkaline in nature.

3. Blue litmus turns red in acid.

Ans True

4. Acid reacts with metal to form hydrogen gas.

Ans True

5. Oxides of metals are alkaline in nature.

Ans True

6. Salts are neutral.

Ans True

7. Metal corrodes due to salts.

Ans False – Metal corrodes due to water and oxygen.

Q.7. Name the following :

1. Write chemical name for given formula: NH4OH

Ans Ammonium hydroxide

2. Write chemical name for given formula: NaOH

Ans Sodium hydroxide

3. Write chemical name from given formula: H2SO4

Ans Sulphuric acid

4. Write chemical name from given formula: KOH

Ans Potassium hydroxide

5. Write chemical name for given formula. HCl

Ans Hydrochloric acid

6. Write chemical name for given formula. Ca(OH)2

Ans Calcium hydroxide

Q. 7. Multiple Choice Questions (Activity) :

1. Name the acid present in our body decides heredity property?

a. DNA b. Acetic acid

c. Amino acids d. none of the above

Ans Option a.

2. What do you observe on addition of baking soda solution in the fruit juice?

a. Bubbles formed c. Effervescence and bubbles formed

b Effervescence formed d. None of the above

Ans Option c.

3. Antacids are used to control its ?

a. Hyper acidity b. Hypoacidity

c. Hyper alkalify d. Hypo alkalify

Ans Option c.

Q.8. Answer in one sentence :

1. Define Acid

Ans i. Acid is such a substance which gives H+ ions in solution state.

ii. E.g. HCl dissociates in water solution

2. Define : Neutralization

Ans i. Salt and water are formed by combination of acid and alkali.

ii.We have seen that acid contains (H+) hydrogen ions and alkali contains(OH-) hydroxide ions.

Q.9. Multiple Choice Questions (Experiment) :

1. Methyl orange indicator becomes in acid.

a. Pink b. Red c. Yellow d. No change

Ans Option a.

2. Hydrochloric acid is used for the preparation of different types of chloride salts.

a. Sodium salts b. Chloride salts c. Fertilizers d. Dyes

Ans Option b.

3. is used for sterilization of water.

    1. Dil. H2SO4 b. Dil. HCL c. H2SO4 d. CO2

Ans Option b.

Q.10. Write Short Notes :

1. Classify following substances into acidic, basic and neutral group – HCl, NaCl, MgO, KCl, CaO, H2SO4 , HNO3 , H2O, Na2CO3

Ans

Acidic Basic Neutral
HCI MgO NaCI
H2SO4 CaO KCI
HNO3 Na2CO3 H2O

Q. 11. Distinguish between:

1 Acid and Base

Ans

Acid Base
i. Acid are sour in taste. a. Base are bitter in taste.
ii. Blue litmus turns red in acid. b. Red litmus turns blue in base.
iii. Acid molecules contain hydrogen ion as a main constituent. c. Alkali contains hydroxide as main constituent.
d. Metals oxides are generally alkaline in nature.
iv. Acid react with metals to form hydrogen gas.

Q.13. Write properties, uses, inferences, important factors, examples :

1. Writing properties of Base and explain Base with reaction? (Minimum 4 points).

Ans Alkali is a substance whose water solution gives hydroxide (OH-) ion

e.g. NaOH (aq) ⇒ Na+(aq) + OH- (aq)

(Sodium Hydroxide) (Sodium ion) (Hydroxide ion)

Properties of alkali

i. . Alkali has bitter taste.

ii. They are slippery.

iii. Alkali contains hydroxide (OH-) as a main constituent.

iv. Metal oxides are generally alkaline in nature.

Q.14. Give scientific reasons :

1. Which acid is used for getting chloride salt?

Ans i. Salt is formed by the combination of acid and alkali.

ii. In a chloride salt, the chloride ion comes from hydrochloric acid. Hence, hydrochloric acid (HCI) is used for getting chloride salt.

2. By squizzing lemon on a piece of rock the gas liberated turned lime water milky. which compound is present in the rock?

Ans The compound present in rock is calcium carbonate. Lemon juice contains citric acid. Acids react with metal carbonates to liberate carbon dioxide (CO2) gas, which turns lime water milky.

3. The label on the bottle of chemical is spoiled. How will you find whether the chemical is acidic or not?

Ans i. We can identify whether the chemical is acidic or not by using indicators such as litmus paper.

ii. If the chemical turns blue litmus red, it is acidic and if it turns red litmus blue, it is basic. Thus, based on the colour change of the indicator, we can find our whether the chemical is acidic or not.

Q.15. Activity based questions. (2 mks) :

1. Classify the following into natural acids and alkali.

Sodium hydroxide, Potassium hydroxide, Calcium hydroxide, Tomato, Lemon, Curd, Orange, Ammonium hydroxide.

Ans Natural acids (Tomato, Lemon, Curd, Orange)

Alkali (Sodium hydroxide, Potassium hydroxide , Calcium hydroxide, Amonium hydroxide)

2. . Complete the table:

Name of indicator Colour of indicator Colour in acid
Litmus paper Blue ……………
Methyl orange Orange ……………
Phenolphthalein …………… ……………

Ans

Name of indicator Colour of indicator Colour in acid
Litmus paper Blue Red
Methyl orange Orange Pink
Phenolphthalein Colourless Colourless

Q.16. Activity based question (3 mks):

1. .Identify the following solutions, whether they are acid or alkali.

Change in indicator
Solution Acid/Alkali
Litmus Phenolphthalein Methyl orange
i. …………… No change …………… ……………
ii. …………… …………… Orange colour turns red ……………
iii. Red litmus turns blue …………… …………… ……………

Ans

Change in indicator
Solution Acid/Alkali
Litmus Phenolphthalein Methyl orange
Blue litmus turns red Orange colour turns red
i. No change Acid
Blue litmus turns red Orange colour turns red
ii. No change Acid
Red litmus turns blue Colourless solution turns Pink
iii. Yellow Alkali

2. Complete the table:

Sr. No. Substances/sources Acids (Natural/Organic)
1. Vinegar ……………
2. Orange ……………
3. Tamarind ……………
4. Tomato ……………
5. Curd ……………
6. Lemon ……………

Ans

Sr. No. Substances/sources Acids (Natural/Organic)
1. Vinegar Acetic acid
2. Orange Citric acid
3. Tamarind Tartaric acid
4. Tomato Oxalic acid
5. Curd Lactic acid
6. Lemon Citric acid
  1. Complete the paragraph:

(Alkalies, Heat, caustic, H2SO4, water, dangerous, sulphuric acid)

Dissolution of conc. …………… in water generates large amount of …………….. Therefore for dilution of

concentrated acid, it is slowly added to ……………. Never add water in the concentrated It will

produce enormous heat and cause explosion. like sodium hydroxide and potassium hydroxide are

strong and in nature. Their concentrated solution burns skin as it decomposes the proteins in skin.

Ans Dissolution of conc. H2SO4 in water generates large amount of Heat. Therefore for dilution of concentrated acid, it is slowly added to water. Never add water in the concentrated sulphuric acid. It will produce enormous heat and cause explosion. Alkalies like sodium hydroxide and potassium hydroxide are strong and caustic in nature. Their concentrated solution burns skin as it decomposes the proteins in skin.

4. Under the guidance of teacher take vinegar, lime juice, ammonium hydroxide (NH4OH) and dil. hydrochloric acid (dil.HCl) in different test-tubes. Add drops of following indicators in them. Also dip litmus papers in the solutions.

i. What happens to blue litmus paper?

ii.What happens to phenolphthalein in alkali solution?

Iii . What happens to red litmus in alkali?

Ans i. Blue litmus turns red in acidic solution.

ii.Colurless to pink.

iii.Red litmus turns blue.

  1. Complete the paragraph:

(Chemical reaction, domestic, Alkaline, natural indicators, Yellow , soap, water)

On non availability of laboratory indicator, ‘……………………’ can be made by using several

………………… substances. You must have seen …………………… food stain turning Red after washing with

……………….. This colour change is a result of …………….. between Turmeric and material of soap. Here turmeric acts as on …………………… Natural indicators can also be prepared from radish, red cabbage and similarly from tomato and hibiscus and rose.

Ans On non availability of laboratory indicator, ‘natural indicators’ can be made by using several domestic substances. You must have seen Yellow food stain turning Red after washing with soap. This colour change is a result of Chemical reaction between Turmeric and material of soap. Here turmeric acts as on Alkaline. Natural indicators can also be prepared from radish, red cabbage and similarly from tomato and hibiscus and rose.

Q.17. Explain the statement. :

1. Litmus paper is used to test alkali and acid.

Ans i. . This paper is made by an extract of licane plant. It is red or blue coloured.

ii. Blue litmus paper turns red on dipping in acid and red litmus turns blue by alkali.

iii. . Similarly phenolphthalein, methyl orange and methyl red are used in laboratory in solution form.

Iv Methyl orange indicator becomes pink in acid and yellow in alkali.

v. Phenolphthalein remains colourless in acid and becomes pink in alkali.

vi. Universal indicator which are in liquid state change their colour in the presence of acid and base.

2.. Acid is such a substance which gives H+ ions in solution state.

Ans i. Acids present in food stuffs are called natural acids or carbonic acids.

ii. These acids being weak in nature are called weak acids

iii. HCl dissociates in water solution.

iv. HCl (aq) ⇒ H+ + Cl(Hydrochloric acid)

(Hydrogen ion) (Chloride ion)

v. They are caustic / inflammatory.

Q.18. Answer the following:

1. Sulphuric acid has highest importance in chemical Industry. Why?

Ans i. Sulphuric acid (H2SO4) is used in the manufacturing of number of other chemicals. It is used in making fertilizers, detergents, pigments, medicines, insecticides, explosives, etc.

ii. Medicines, insecticides, explosives, etc.

iii. Dilute sulphuric acid is used in the batteries (electric cell).

iv. It is used in iron and steel industry to remove rust from products.

v. Sulphuric acid is referred to as ‘king of chemicals’ due to its numerous applications. Thus, sulphuric acid has the highest importance in chemical industry.

2. Explain the difference between Acid and Alkali.

Ans

Acid Alkali
i. Acids are sour to taste. i. Alkalies are bitter to taste.
ii. Acid molecules contain hydrogen ion (H+) as the main constituent. ii. Alkali molecules contain hydroxide ion (OH+) as the main constituent.
iii. Acids turn blue litmus paper to red. iii. Alkalies turn red litmus paper to blue.
iv. Nonmetal oxides are generally acidic in nature. iv. Metal oxides are generally alkaline in nature.
E.g. – HCI, H2SO4, etc. E.g. – NaOH, Mg(OH)2, etc.

2. Which are the industrial uses of acids?

Ans i. Acids are used in the manufacturing of chemical fertilizers.

ii. Acids are used in the manufacturing of explosives, oil purification, medicines, dyes and paints.

iii. Hydrochloric acid (HCI) is used in preparing different chloride salts.

iv. Dilute sulphuric acid (H2SO4) is used in the batteries (electric cell).

v. Dilute HCI is used for sterilization of water.

vi. Acid is used for making of white paper from wood pulp.

2. Hydrochloric acid is present in our stomach. It helps to ease digestion process. However excessive acid leads to indigestion. Antacids are used to control this hyper acidity. This medicine contains milk of magnesia [Mg(OH)2]. Such alkaline medicine neutralises excess acid present in stomach.

i. Excessive acid leads to?

ii. Antacids are used to control ?

Ans i. Indigestion

ii. Hyper acidity

3. Explain properties and uses of Acid.

Ans Properties of acid :

i. Acids are sour in taste.

ii. Acid molecules contain hydrogen ion (H+) as a main constituent.

iii. Acid reacts with metal to form hydrogen gas.

iv. Acid reacts with carbonates and liberates CO2 gas.

v. Blue litmus turns red in acid.

Use of acids :

i. Acid are used in the production of chemical fertilizers.

ii. Acids are used in the production of explosives, oil purification, medicines, dyes and paints.

iii. Hydrochloric acid is used for the preparation of different types of chloride salts.

iv. Dil. H2SO4 acid is used in the batteries. (electric cell).

v. Dil. HCl is used for sterilization of water.

vi. Acid is used for making of white paper from wood pulp.

4. Which substances are produced by neutralization process ?

Ans In neutralization process, acid and alkali combine to produce salt and water.

5. Why indicator does not get affected by salt?

Ans i. Indicators change their colour in the presence of acid or alkali.

ii. Common salt (sdium chloride) is formed by the combination of acid (hydrochloric acid) and alkali (sodium hydrosice). This chemical reaction is called neutralization reaction.

iii. As a result, common salt is neutral in nature, that is, it is neither acidic nor alkaline. Hence, indicator does not get affected by common salt.

Q. 19 . Answer the following in detail :

1. What are acid explain in details.

Ans i. . Acids present in food stuffs are called natural acids or carbonic acids.

ii. These acids being weak in nature are called weak acids. Some acids are strong in nature.

ii. The skin gets burnt when their concentrated solution falls on skin, similarly their vapours if inhaled can be harmful to health.

iv. Strong concentrated acids are converted into their dilute acids by slowly adding them into water.

v. Such dilute acids are less harmful than their corresponding strong acids.

vi. We know that the distilled water is tasteless. Water is neither acidic nor basic.

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