Class 10 Science Chapter-2 notes
Chapter- 2 Acids, Bases and Salts
The sour and bitter tastes of food are due to acids and bases are present in them.
Indicators:
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.
2. Olfactory Indicator:
Substances which change their smell when mixed with acid or base are known as Olfactory Indicators. For example; Onion, vanilla etc.
3. Synthetic Indicator:
Indicators that are synthesized in the laboratory are known as Synthetic Indicators. For example; Phenolphthalein, methyl orange, etc.
| 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:
1. Acids have a sour taste.
2. Turns blue litmus red.
3. Acid solution conducts electricity.
4. Release H+ ions in aqueous solution.
Types of acids
On the basis of origin, acids are classified as:
Organic acids:
Acids derived from living organisms like plants and animals. For example citric acid is present in fruits, acetic acid present in vinegar, oxalic acid present in tomato, tartaric acid present in tamarind, lactic acid present in sour milk and curd.
Mineral acids:
They are also called inorganic acids. They are dangerous Example sulphuric acid (H2504), hydrochloric acid (HCI) etc.
On the basis of their strength, acids are classified as:
Strong acids:
Completely dissociate into its ions in aqueous solutions
Example: Nitric acid (HNO3), sulphuric acid (H504). hydrochloric acid (HCI)
Weak acids:
Weak acids are those acids which do not completely dissociate into its ions in aqueous solutions. For example: carbonic acid (H2CO), acetic acid (CH3COOH)
On the basis of their concentration, acids are classified as:
Dilute acids:
Have a low concentration of acids in aqueous solutions.
Concentrated acids:
Have a high concentration of acids in aqueous solutions
On the basis of number of hydrogen ion, acids can be classified as:
Monoprotic acid -
Such type of acid produces one mole of H+ ions per mole of acid, e.g.. HCl. HNO3
Diprotic acid -
They can produce two males of H ions per mole of acid, e.q.. H2So4
Triprotic acid -
They produce three moles of H ions per mole of acid, e.g.. H3PO4
Polyprotic -
They can produce more than three H+ ions per mole of acid.
Bases:
Bases are bitter in taste, have soapy touch, turn red litmus blue and give hydroxide ions (OH–) in aqueous solution.
Examples: Sodium hydroxide (caustic soda) – NaOH
Calcium hydroxide – Ca(OH)2
Potassium hydroxide (caustic potash) – (KOH)
Properties of Bases:
1. Have a bitter taste.
2. Soapy to touch.
3. Turns red litmus blue.
4. Conducts electricity in solution.
5. Release OH– ions in Aqueous Solution
Reaction of Acids and Bases with Metals
Reaction of Acids with Metals
• Acids react with metal to form metal salt and releases Hydrogen Gas.
Acid + Metal → Salt + Hydrogen Gas
• Example: Zinc granules react with dilute Hydrochloric acid in a test tube.
2HCl + Zn → ZnCl2 + H2
→ Reaction of Bases with Metals
Bases react with metal to evolve hydrogen Gas. Also, note that all metals do not react with bases. The metal must be more reactive than the metals present in the base for the reaction to take place.
Base + Metal → Salt + Hydrogen gas
Example: Zinc granules react with NaOH solution to form sodium zincate and evolve hydrogen gas.
2NaOH + Zn → Na2ZnO2 + H2
• Hydrogen gas released can be tested by bringing burning candle near gas bubbles, it burst with pop sound.
Reaction of Acids with Metal Carbonates and Metal Hydrogen carbonates
• Acids reacts with Metal Carbonates and Metal Hydrogen Carbonates to form Salt, Carbon dioxide and water.
Metal carbonate/Metal hydrogen carbonate + Acid → Salt + Carbon dioxide + Water
• Examples: (i) 2HCl + Na2CO3 → 2NaCl + CO2 + H2O
(ii) HCl + NaHCO3 → NaCl + CO2 + H2O
• CO2 can be tested by passing it through lime water. It turns lime water milky.
Ca(OH)2 + CO2 → CaCO3 + H2O
• When excess CO2 is passed, milkiness disappears.
CaCO3 + CO2 + H2O → Ca(HCO)3
• Bases do not react with Metal Carbonates and Metal Hydrogencarbonates.
Base + Metal Carbonate/Metal Hydrogen Carbonate → No Reaction
Reaction of Acids and Bases with each other
• Acids and Bases react to form salt and water.
Acid + Base → Salt + H2O
• Neutralisation Reaction: Reaction of acid with a base is called as neutralization reaction.
Example: HCl + NaOH → NaCl + H2O
• Strong Acid + Weak Base → Acidic salt + H2O
• Weak Acid + Strong Base → Basic salt + H2O
• Strong Acid + Strong Base → Neutral salt + H2O
• Weak Acid + Weak Base → Neutral salt + H2O
Reaction of Metallic Oxides with Acids
→ Metallic oxides are basic in nature.
Example: CaO, MgO are basic oxides.
Metallic Oxide + Acid → Salt + H2O
CaO + 2HCl → CaCl2 + H2O
Reaction of Non-metallic Oxides with Bases
→ Non-metallic oxides are acidic in nature.
→ Non-metallic Oxide + Base → Salt + H2O
CO2 + Ca(OH)2 → CaCO3 + H2O
Reaction of Acid
(i) Acid + Metal Carbonate → Salt + CO2 + Water
(ii) Acid + Metal → Salt + H2
(iii) Acid + Metal Hydrogen Carbonate → Salt + CO2 + H2O
(iv) Acid + Metallic oxide → Salt +H2O
(v) Acid + Base → Salt + H2O
Reaction Of Base
(i) Base + Metal → Salt + H2
(ii) Base + Metal Carbonate → No Reaction
(iii) Base + Metal Hydrogen Carbonate → No Reaction
(iv) Base + Acid → Salt + H2O
(v) Base + Non Metallic oxide → Salt + H2O
For example:-
Ca(OH)2(aq)+CO2(g)→CaCO3(aq)+H2O
When CO2 is passed through lime water ( calcium hydroxide) for short interval of time, it turns milky due to the formation of insoluble calcium carbonate.
Similarities between all Acids and all Bases
→ All acids have H+ ions in common. All acids produce H+ ions
→ Acids produce H+ ions in solution which are responsible for their acidic properties.
→ All bases have OH- (hydroxyl ions) in common. All bases produce OH- ions
Acid or Base in Water Solution
→ Acids produce H+ ions in presence of water.
→ H+ ions cannot exist alone, they exist as H3O+ (hydronium ions).
H+ + H2O → H3O+
HCl + H2O → H3O+ + Cl-
→ Bases when dissolved in water gives OH − ions.
→ Bases soluble in water are called alkali.
→ While diluting acids, it is recommended that the acid should be added to water and not water to acid because the process of dissolving a acid or a base in water is highly exothermic.
Strength of Acids and Base solutions
→ Strength of acid or base can be estimated using universal indicator.
→ Universal indicator: It is a mixture of several indicators. It shows different colours at different concentrations of H+ ions in the solution.
→ pH Scale: A scale for measuring H+ ion concentration in a solution. p in pH stands for ‘potenz’ a German word which means power.
• If value of ph is equal to 7 → neutral solution
• If value of pH is less than 7 → acidic solution
• If value of pH more than 7 → basic solution