- The sour and bitter tastes of food are due to acids and bases present in them.
- Acids are sour in taste and change the color of blue litmus to red.
- Litmus solution is a purple dye, which is extracted from lichen. When the litmus solution is neither acidic nor basic, its color is purple.
- Other natural materials like red cabbage leaves, turmeric, coloured petals of some flowers such as Hydrangea, Petunia and Geranium, which indicate the presence of acid or base in a solution.
PROPERTIES OF ACIDS
- The term ‘acid’ has been derived from the Latin word, ‘acidus’ which means sour.
- Acids have sour taste.
- They turn blue litmus solution red.
- They give H+ ions in aqueous solution.
TYPES OF ACIDS
- Strong Acids: HCl, H2 SO4 , HNO3
- Weak Acids: CH3COOH, Oxalic acid, Lactic acid
- Concentrated Acids: More amount of acid + Less amount of water
- Dilute Acids: More amount of water + Less amount of acid
PROPERTIES OF BASES
- These are the substances which are bitter in taste and soapy in touch.
- They turn red litmus solution blue.
- They give OH- ions in aqueous solution.
TYPES OF BASES
- Strong Bases: NaOH, KOH, Ca(OH)2
- Weak Bases: NH4OH
- Alkalis: These are bases which are soluble in water. Examples: NaOH, KOH, Ca(OH)2.
TYPES OF INDICATORS AND ITS PROPERTIES
INDICATORS
Substances which change their colour/smell in different types of substances (like acids and bases).
TYPES OF INDICATORS
(i) Natural indicators: Found in nature in plants. Examples: Litmus, red cabbage leaves extract, flowers of hydrangea plant, turmeric.
(ii) Synthetic indicators: These are chemical substances. Examples: Methyl orange, phenolphthalein.
(iii) Olfactory indicators: These substances have different odour in acid and bases.
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.
- 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 a burning candle near gas bubbles, it bursts with a pop sound.
REACTION OF ACIDS WITH METAL CARBONATES AND HYDROGENCARBONATES
- Acids reacts with Metal Carbonates and Metal Hydrogencarbonates 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
NEUTRALIZATION REACTION
- Reaction of acid with a base is called a 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
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 the 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 give 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 an acid or a base in water is highly exothermic.
STRENGTH OF ACID AND BASE SOLUTIONS
- Strength of acid or base can be estimated using a 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
