Question

ACIDS BASES AND SALTS NOTES IN 2 PAGES 10th class
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Answer 1

Answer:

ndicators: Indicators are substances which indicate the acidic or basic nature of the solution by the colour change.

Types of Indicator: There are many types of indicators. Some common types of indicators are:

1. Natural Indicators: Indicators obtained from natural sources are called Natural Indicators. Litmus, turmeric, red cabbage, China rose, etc., are some common natural indicators used widely to show the acidic or basic character of substances.

Litmus: Litmus is obtained from lichens. The solution of litmus is purple in colour. Litmus paper comes in two colours- blue and red.

An acid turns blue litmus paper red.

A base turns red litmus paper blue.

Turmeric: Turmeric is another natural indicator. Turmeric is yellow in colour. Turmeric solution or paper turns reddish brown with base. Turmeric does not change colour with acid.

Red Cabbage: The juice of red cabbage is originally purple in colour. Juice of red cabbage turns reddish with acid and turns greenish with base.

2. Olfactory Indicator: Substances which change their smell when mixed with acid or base are known as Olfactory Indicators. For example; Onion, vanilla etc.

Onion: Paste or juice of onion loses its smell when added with base. It does not change its smell with acid.

Vanilla: The smell of vanilla vanishes with base, but its smell does not vanish with an acid.

Olfactory Indicators are used to ensure the participation of visually impaired students in the laboratory.

3. Synthetic Indicator: Indicators that are synthesized in the laboratory are known as Synthetic Indicators. For example; Phenolphthalein, methyl orange, etc.

Phenolphthalein is a colourless liquid. It remains colourless with acid but turns into pink with a base.

Methyl orange is originally orange in colour. It turns into the red with acid and turns into yellow with base.

Indicator Original

Colour        Acid                         Base

Red litmus Red No Change Blue

Blue litmus Blue                  Red No change

Turmeric Yellow No Change Reddish brown

Red cabbage juice Purple Reddish Greenish yellow

Phenolphthalein Colourless Colourless Pink

Methyl Orange Orange Red Yellow

Onion n/a No change Smell vanishes

Vanilla n/a No change Smell vanishes

Acids: Acids are sour in taste, turn blue litmus red, and dissolve in water to release H+ ions.

Example: Sulphuric acid (H2SO4), Acetic Acid (CH3COOH), Nitric Acid (HNO3) etc.

Properties of Acids:

Acids have a sour taste.

Turns blue litmus red.

Acid solution conducts electricity.

Release H+ ions in aqueous solution.

Types of Acids: Acids are divided into two types on the basis of their occurrence i.e., Natural acids and Mineral acids.

(i) Natural Acids: Acids which are obtained from natural sources are called Natural Acids or Organic Acids.

Examples:

Methanoic acid (HCOOH)

Acetic acid (CH3COOH)

Oxalic acid (C2H2O4) etc.

Explanation:

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Answer 2

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What Is an Acid and a Base?

An ionisable compound when dissolved in water or in its molten state, dissociates into ions almost entirely. Example: NaCl, HCl, KOH, etc.

A non-ionisable compound does not dissociate into ions when dissolved in water or in its molten state. Example: glucose, acetone, etc.

Examples

• Acids

1. Hydrochloric acid (HCl)
2. Sulphuric acid (H2SO4)
3. Nitric acid (HNO3)

• Bases

1. Sodium hydroxide (NaOH)
2. Potassium hydroxide (KOH)
3. Calcium hydroxide (Ca(OH)2)

Physical test

Given are two possible physical tests to identify an acid or a base.

a. Taste

An acid tastes sour whereas a base tastes bitter.

The method of taste is not advised as an acid or a base could be contaminated or corrosive.

b. Effect on indicators by acids and bases

An indicator is a chemical substance which shows a change in its physical properties, mainly colour or odour when brought in contact with an acid or a base.

Below mentioned are commonly used indicators and the different colours they exhibit:

a) Litmus

In a neutral solution – purple

In acidic solution – red

In basic solution – blue

Litmus is also available as strips of paper in two variants – red litmus and blue litmus.

An acid turns a moist blue litmus paper to red.

A base turns a moist red litmus paper to blue.

b) Methyl orange

In a neutral solution – orange

In acidic solution – red

In basic solution – yellow

c) Phenolphthalein

In a neutral solution – colourless

In acidic solution – remains colourless

In basic solution – pink

Acid-Base Reactions

Reactions of acids and bases

a) Reaction of acids and bases with metals

Acid + active metal → salt + hydrogen + heat

2HCl+Mg→MgCl2+H2 (↑)

Base + metal → salt + hydrogen + heat

2NaOH+Zn→Na2ZnO2+H2 (↑)

A more reactive metal displaces the less reactive metal from its base.

2Na+Mg (OH) 2→2NaOH+Mg

b) Reaction of acids with metal carbonates and bicarbonates

Acid + metal carbonate or bicarbonate → salt + water + carbon dioxide.

2HCl+CaCO3→CaCl2+H2O+CO2

H2SO4+Mg (HCO3)2→MgSO4+2H2O+2CO2

Effervescence indicates liberation of CO2 gas.

c) Neutralisation reaction

1. Reaction of metal oxides and hydroxides with acids

Metal oxides or metal hydroxides are basic in nature.

Acid + base → salt + water + heat

H2SO4+MgO→MgSO4+H2O

2HCl+Mg (OH) 2→MgCl2+2H2O

2. Reaction of non-metal oxides with bases

Non-metal oxides are acidic in nature

Base + Non-metal oxide → salt + water + heat

2NaOH+CO2→Na2CO3+H2O

Water

Acids and bases in water

When added to water, acids and bases dissociate into their respective ions and help in conducting electricity.

Difference between a base and an alkali

Base-

Bases undergo neutralisation reaction with acids.

They are comprised of metal oxides, metal hydroxides, metal carbonates and metal bicarbonates.

Most of them are insoluble in water.

Alkali –

An alkali is an aqueous solution of a base, (mainly metallic hydroxides).

It dissolves in water and dissociates to give OH− ion.

All alkalis are bases, but not all bases are alkalis

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