Grade 7 STEM
CBSE Grade 7 Science
NCERT Chapter 4
Chemistry & Indicators
Acids, Bases & Indicators Lab
Explore natural indicators (Litmus, Turmeric, China Rose), dropwise neutralization reactions, and everyday pH chemistry.
Testing Bench
Dip natural indicators into household substances to observe chemical color transitionsLive Result & Inference:
Acidic
Observation: Blue Litmus turns Red. Red Litmus remains Red.
Scientific Takeaway: Acids turn blue litmus red. Contains citric acid naturally found in citrus fruits.
NCERT Table 4.2 Log
Your tested substances automatically record here just like the practical notebook in school.
| Substance | Indicator | Color Change | Inference |
|---|
NCERT Key Rule: Neutral substances (like sugar, salt, and pure water) do NOT change the color of either red or blue litmus paper!
Dropwise Neutralization Apparatus
NCERT Activity 4.5: Neutralizing Sodium Hydroxide (Base) with Hydrochloric Acid using PhenolphthaleinReaction Dynamics
pH Meter Probe:
13.0
0 (Strong Acid)
7 (Neutral)
14 (Strong Base)
Exothermic Heat:
25.0 °C
Notice the flask becomes warm! Heat is always liberated during neutralization.
Acid (HCl) Added:
0 drops
Neutralization Equation:
Acid + Base → Salt + Water + Heat
HCl + NaOH → NaCl + H2O + ΔHeat
Everyday Neutralization Clinic
NCERT Section 4.3: Real-world problems where chemical neutralization saves the day1. Ant Sting Remedy
An ant bit Mohan while playing in the garden. The area is burning and swollen due to Formic Acid injection.
2. Stomach Indigestion
After eating spicy food, Ananya suffers from acidity caused by excessive Hydrochloric Acid in her stomach.
3. Acidic Farm Soil
Due to heavy chemical fertilizers, the farmer's soil has turned excessively acidic, stunting plant growth.
4. Turmeric Curry Stain
Ravi dropped turmeric curry on his white shirt. When his mother rubbed it with soap bar, the yellow stain turned bright red!
NCERT Table of Natural Acids & Bases
Common Acids & Their Natural Sources:
| Name of Acid | Found In (Natural Source) |
|---|---|
| Acetic Acid | Vinegar |
| Formic Acid | Ant's sting |
| Citric Acid | Citrus fruits (oranges, lemons) |
| Lactic Acid | Curd / Yogurt |
| Oxalic Acid | Spinach |
| Ascorbic Acid (Vitamin C) | Amla, citrus fruits |
| Tartaric Acid | Tamarind, grapes, unripe mangoes |
Common Bases & Where They Are Found:
| Name of Base | Found In (Common Use) |
|---|---|
| Calcium Hydroxide | Lime water |
| Ammonium Hydroxide | Window cleaner |
| Sodium Hydroxide / Potassium Hydroxide | Soaps |
| Magnesium Hydroxide | Milk of Magnesia (Antacid) |