Acids, Bases and Salts

Class 10 Science • Chapter 02 (Deep Detail)

1. Acid-Base Indicators

Natural: Litmus (Lichen), Turmeric, Red Cabbage.

Synthetic: Methyl Orange, Phenolphthalein.

Olfactory: Onion, Vanilla, Clove (Smell vanishes in Base).

Indicator	Color in Acid	Color in Base
Blue Litmus	Turns Red	No Change
Red Litmus	No Change	Turns Blue
Phenolphthalein	Colorless	Pink
Methyl Orange	Red	Yellow
Turmeric	No Change (Yellow)	Reddish-Brown

2. Chemical Properties

METAL REACTION $$ Acid + Metal \to Salt + H_2 \uparrow $$ $$ 2HCl + Zn \to ZnCl_2 + H_2 $$ Pop Sound Test: Burning candle near $H_2$ gas causes a "Pop".

SAFETY: DILUTION Always add Acid to Water slowly with stirring.
Never add Water to Acid! The reaction is highly Exothermic. Adding water to conc. acid can cause the mixture to splash out and cause burns.

Carbonate Test (Lime Water)

$Acid + Carbonate \to Salt + H_2O + CO_2$.
Pass $CO_2$ through Lime Water $Ca(OH)_2$:

Short Duration: Turns Milky (White ppt $CaCO_3$).
Excess Duration: Milkiness Disappears (Soluble $Ca(HCO_3)_2$).

NEUTRALIZATION $$ Acid + Base \to Salt + Water + Heat $$ $$ HCl + NaOH \to NaCl + H_2O $$

3. pH in Everyday Life

Human Body: 7.0 to 7.8.
Acid Rain: pH < 5.6.
Stomach: Hydrochloric Acid aids digestion. Antacids ($Mg(OH)_2$ Milk of Magnesia) neutralize excess.
Tooth Decay: Starts when mouth pH < 5.5. Enamel (Calcium Hydroxyapatite, hardest substance) corrodes.
Self Defense:
- Ant/Bee Sting (Methanoic Acid) $\to$ Use mild Base (Baking Soda).
- Nettle Leaves (Methanoic Acid) $\to$ Rub Dock Plant leaf (Basic, found nearby).

4. The Salt Family

1. Chlor-Alkali Process (NaCl $\to$ NaOH)

Electrolysis of Brine.

$$ 2NaCl(aq) + 2H_2O(l) \to 2NaOH(aq) + Cl_2(g) + H_2(g) $$

Anode ($Cl_2$): PVC, Pesticides, Water Treatment.
Cathode ($H_2$): Fuels, Ammonia for fertilizers.
NaOH: Soaps, Paper making.

2. Bleaching Powder ($CaOCl_2$)

Chlorine on Dry Slaked Lime.

$$ Ca(OH)_2 + Cl_2 \to CaOCl_2 + H_2O $$

Use: Disinfecting water, Oxidizing agent.

3. Baking Soda ($NaHCO_3$)

Uses: Antacid, Fire Extinguisher (Soda-acid).

Heating: $2NaHCO_3 \xrightarrow{\Delta} Na_2CO_3 + H_2O + CO_2$ (Makes cake fluffy).

4. Washing Soda ($Na_2CO_3 \cdot 10H_2O$)

Uses: Glass/Soap industry, Removing Permanent Hardness of water.

PLASTER OF PARIS Gypsum ($CaSO_4 \cdot 2H_2O$) heated at 373K $\to$ POP ($CaSO_4 \cdot \frac{1}{2}H_2O$).
Use: Fractured bones, Toys.
Reaction: $CaSO_4 \cdot \frac{1}{2}H_2O + 1\frac{1}{2}H_2O \to CaSO_4 \cdot 2H_2O$ (Hard Solid).

5. Water of Crystallization

Fixed number of water molecules present in one formula unit of a salt.

ACTIVITY: HEATING CRYSTALS Heat Blue Copper Sulphate Crystals in a test tube.
$$ CuSO_4 \cdot 5H_2O (\text{Blue}) \xrightarrow{\Delta} CuSO_4 (\text{White}) + 5H_2O $$ Droplets of water appear. Adding water back restores Blue colour.

Examples:

Blue Vitriol: $CuSO_4 \cdot 5H_2O$
Green Vitriol: $FeSO_4 \cdot 7H_2O$
Gypsum: $CaSO_4 \cdot 2H_2O$
Washing Soda: $Na_2CO_3 \cdot 10H_2O$

[IMAGE PLACEHOLDER: SALT FAMILY MAP]

Create a flowchart/mindmap. Center node: "NaCl (Common Salt)". Branches pointing to:
1. NaOH (via Chlor-Alkali)
2. Baking Soda (via Solvay)
3. Washing Soda (from Baking Soda)
4. Bleaching Powder (from Chlorine of Chlor-Alkali)
Use icons for uses (e.g. soap for NaOH, bread for Baking Soda).