Acidic, Basic & Neutral | Science Grade 7 CBSE

Play with it

Test a substance

Tap a substance and watch the indicators react. Red litmus, blue litmus and turmeric each give a clue — together they tell you if it's acidic, basic or neutral.

Explore · Indicator labtap a substance

Learn

The three big ideas

Acidic substances taste sour — lemon, vinegar, tamarind, curd.
Basic substances feel soapy and taste bitter — soap, baking soda, lime water.
Neutral substances are neither — pure water, salt solution.

Safety: never taste or touch unknown chemicals to test them — that's exactly what indicators are for.

An indicator changes colour to reveal an acid or a base:

Litmus — acids turn blue litmus red; bases turn red litmus blue; neutral leaves both unchanged.
Turmeric — yellow normally, turns red in a base (why a turmeric stain reddens with soap).
China rose & red cabbage — natural indicators that shift colour with acids/bases.

Common mistake: thinking "no colour change = the test failed". For a neutral substance, no change is the answer — it's neither acidic nor basic.

Mix an acid and a base in the right amounts and they cancel out — neutralisation — giving a neutral product.

Worked example. You have too much acid in your stomach (acidity). Why does an antacid help?

An antacid is a mild base. It neutralises the excess stomach acid, bringing things back toward neutral and easing the burning.

Ant/nettle sting (an acid) → soothe with a mild base like baking soda.
Acidic soil → farmers add lime (a base) to neutralise it.

Where you'll meet it

Acids & bases at home

The kitchen is a lab

Lemon and vinegar (acids) cut through soapy grease (a base) — that's neutralisation cleaning your dishes. Red cabbage water makes a free indicator for testing them.

Antacids & stings

Acidity tablets and a dab of baking soda on an ant sting are the same idea: a mild base neutralising an acid so it stops hurting.

Check yourself

Competency quiz

Modelled on the competency-based pattern — MCQ, assertion–reason and a case study, testing whether you can use the ideas, not just recall them.

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Acidic, Basic& Neutral