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Grade 6 (age 11-12)

grade 6 Acids & Bases

Solutions around us can be sorted by their properties into acidic, neutral and basic. Vinegar and lemon juice are acidic; soapy water and water with baking soda dissolved in it are basic. How acidic or basic something is can be shown with a number called pH: pH 7 is neutral, and the further below 7 the stronger the acid, the further above 7 the stronger the base. Indicators such as litmus paper and BTB solution change color depending on the solution, so we can tell acids from bases without tasting or touching them. Move the pH to see everyday examples, pick a solution to compare the indicator colors, then add a basic solution to an acid little by little and follow how it is neutralized.

Acidic, neutral and basic

7
🧪 Acidic and basic
①Acidic solutions: many taste sour, like vinegar, lemon juice and fizzy drinks.
②Basic solutions: many feel slippery, like soapy water or detergent.
③Neutral: neither acidic nor basic, like pure water.
④pH 7 is neutral; lower is acidic, higher is basic.
⑤Never taste or touch lab solutions with bare hands; check them with an indicator.

Telling them apart with indicators

🔬 Indicators
①Blue litmus paper turns red in an acidic solution.
②Red litmus paper turns blue in a basic solution.
③In a neutral solution, both kinds of litmus paper stay the same color.
④BTB solution turns yellow in acid, green when neutral and blue in a base.
⑤Phenolphthalein is colorless in acidic and neutral solutions and turns pink only in a base.

Neutralization

20%
💡 Neutralization
①H⁺ from the acid and OH⁻ from the base meet and become water (H₂O).
②As more basic solution is added, H⁺ runs low and the acid gets weaker, until the two match exactly and the solution is neutral.
③Add more after that, and the leftover OH⁻ makes it basic.
④A substance called a salt is formed along with the water.
⑤The counts in the picture are just to help you understand; a real solution holds countless particles.

Summary

How acidic or basic
pH 0–6: acidic / pH 7: neutral / pH 8–14: basic
The further the pH is from 7, the stronger the acid or base.
Neutralization
Acid(H⁺) + Base(OH⁻) → Water(H₂O) + Salt
When an acid and a base meet, they weaken each other.
🎯 Key points
①Acidic: pH below 7, turns blue litmus paper red.
②Basic: pH above 7, turns red litmus paper blue.
③Neutral: pH 7, litmus paper stays the same color.
④BTB solution is yellow in acid, green when neutral and blue in a base.
⑤Neutralization: acid + base → water + salt.

Examples and Unit Test

Example 1
A solution has a pH of 3. Is it acidic, neutral or basic?
1
pH 7 is neutral; below 7 is acidic and above 7 is basic.
2
3 is less than 7, so the solution is acidic.
▸ Acidic
Set the pH to 3 in the first picture and lemon juice and vinegar appear as examples.
Example 2
BTB solution added to a liquid turns yellow. What kind of liquid is it, and what happens if you dip blue litmus paper in it?
1
BTB solution turns yellow in acid, green when neutral and blue in a base.
2
It is yellow, so the liquid is acidic, and an acid turns blue litmus paper red.
▸ Acidic / blue litmus paper turns red.
Choose vinegar in the second picture: the BTB turns yellow and the dipped part of the blue litmus paper turns red.
Unit-test style
Which statement about acids and bases is correct?
①The higher the pH, the stronger the acid.
②An acidic solution turns blue litmus paper red.
③Pure water has a pH of 14.
④When an acid and a base meet, they make a stronger acid.
⑤BTB solution turns blue in an acid.
▸ ② An acidic solution turns blue litmus paper red.
1
An acid turns blue litmus paper red, and a base turns red litmus paper blue.
2
A higher pH means more basic (①), pure water has a pH of 7 (③), an acid and a base neutralize each other (④), and BTB turns yellow in an acid (⑤).
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Various Gases
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Combustion & Fire Extinguishing

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