Acids, Bases and Neutral Substances: 26 flashcards
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1. What does the pH scale measure?
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How acidic or basic a substance is, on a scale from 0 to 14.
2. What ion do acids release in water?
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Hydrogen ions ($H^+$)
3. What ion do bases release in water?
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Hydroxide ions ($OH^-$)
4. What is the pH of a neutral substance?
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Exactly 7
5. What colour change does an acid cause in blue litmus?
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Blue litmus turns red.
6. What colour change does a base cause in red litmus?
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Red litmus turns blue.
7. What happens to litmus paper in a neutral substance?
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No colour change occurs in either blue or red litmus.
8. From which organism is litmus extracted?
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Lichens
9. What colour does methyl orange turn in an acid and in a base?
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Red in acids, yellow in bases.
10. What colour is phenolphthalein in an acid and in a base?
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Colourless in acids, pink in bases.
11. What colour does turmeric turn in a base?
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Reddish-brown
12. What colour does china rose indicator turn in an acid and in a base?
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Dark pink in acids, green in bases.
13. What is the general word equation for neutralisation?
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Acid + Base → Salt + Water
14. What ions combine to form water during neutralisation?
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$H^+$ ions from the acid and $OH^-$ ions from the base.
15. What are the products when hydrochloric acid reacts with sodium hydroxide?
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Sodium chloride and water.
16. Which acid is present in the stomach, and what is its approximate pH?
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Hydrochloric acid, with a pH of about 1.5–3.5.
17. How do antacids relieve acidity?
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They contain mild bases like magnesium hydroxide that neutralise excess stomach acid.
18. What is the approximate pH of blood?
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About 7.4, which is slightly basic.
19. Why do farmers add quicklime or slaked lime to soil?
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To raise the pH of acidic soil so crops can grow better.
20. What is the difference between a strong acid and a weak acid?
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A strong acid ionises completely in water; a weak acid ionises only partially.
21. Why is it dangerous to taste or touch unknown substances to test acidity?
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Strong acids and bases are corrosive and can burn skin or damage eyes.
22. Why is toothpaste mildly basic?
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It neutralises the acid produced by bacteria in the mouth.
23. Why is shampoo often slightly acidic?
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To match the natural pH of hair and scalp.
24. What colour is red cabbage water in an acid, a base, and a neutral substance?
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Pink in acid, blue-green in base, purple when neutral.
25. Does 'neutral' mean a substance cannot react?
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No — it means acid and base properties are balanced, not that the substance is inert.
26. How much does acidity change for each step of 1 on the pH scale?
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A ten-fold change in hydrogen ion concentration.
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