📘 Acids, Bases, and Salts — Solutions
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✅ Q1.
A solution turns red litmus blue — it is basic, so pH > 7.
Out of the options:
(a) 1 → strongly acidic
(b) 4 → acidic
(c) 5 → weakly acidic
(d) 10 → basic
🎯 Answer: (d) 10
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✅ Q2.
A solution reacts with crushed egg shells (calcium carbonate) to produce a gas that turns lime-water milky → this is CO₂ → acid reaction.
🎯 Answer: (b) HCl
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✅ Q3.
If 10 mL NaOH is neutralised by 8 mL HCl, then 20 mL NaOH needs double the amount:
🎯 Answer: (d) 16 mL
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✅ Q4.
Medicine for indigestion neutralises excess stomach acid → antacid.
🎯 Answer: (c) Antacid
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✅ Q5. Write word & balanced equations:
(a) Sulphuric acid + Zinc → Zinc sulphate + Hydrogen
Zn + H_2SO_4 → ZnSO_4 + H_2↑
(b) Hydrochloric acid + Magnesium → Magnesium chloride + Hydrogen
Mg + 2HCl → MgCl_2 + H_2↑
(c) Sulphuric acid + Aluminium → Aluminium sulphate + Hydrogen
2Al + 3H_2SO_4 → Al_2(SO_4)_3 + 3H_2↑
(d) Hydrochloric acid + Iron → Iron chloride + Hydrogen
Fe + 2HCl → FeCl_2 + H_2↑
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✅ Q6.
Why alcohol & glucose are not acids?
🎯 Activity:
• Take a beaker with alcohol/glucose & another with acid.
• Dip the wires of a bulb circuit into each.
• Bulb glows with acid (conducts electricity — due to H^+).
• Bulb does NOT glow with alcohol/glucose (no free H^+).
So, alcohol & glucose have hydrogen but do not release H^+.
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✅ Q7.
Why does distilled water not conduct electricity, but rainwater does?
🎯 Distilled water → pure → no ions → no conduction.
🎯 Rainwater → dissolved CO₂ & salts → ions → conducts.
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✅ Q8.
Why do acids need water to show acidic behaviour?
🎯 Because acids release H^+ only in aqueous solution → otherwise no H^+, so no acidity.
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✅ Q9.
Solutions with pH: 4,1,11,7,9.
• (a) Neutral → 7
• (b) Strongly alkaline → 11
• (c) Strongly acidic → 1
• (d) Weakly acidic → 4
• (e) Weakly alkaline → 9
Increasing order of [H^+]:
11 < 9 < 7 < 4 < 1
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✅ Q10.
Mg ribbon in HCl vs CH₃COOH — which fizzes more?
🎯 Fizzing (H₂ gas) is more in HCl, because HCl is a stronger acid than acetic acid → more H^+.
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✅ Q11.
Fresh milk pH 6 → curd pH?
🎯 Curd has lactic acid → more acidic → pH decreases.
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✅ Q12.
(a) Adding baking soda makes milk slightly alkaline → delays curdling.
(b) Alkaline milk resists acidification → takes longer to turn into curd.
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✅ Q13.
Why store plaster of Paris (POP) in moisture-proof container?
🎯 POP absorbs water & turns into gypsum → loses setting property:
CaSO_4·½H_2O + 1½H_2O → CaSO_4·2H_2O
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✅ Q14.
What is a neutralisation reaction?
🎯 When an acid & base react to form salt & water.
e.g.,
HCl + NaOH → NaCl + H_2O
H_2SO_4 + 2KOH → K_2SO_4 + 2H_2O
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✅ Q15.
Uses of washing soda & baking soda:
📄 Washing soda (Na₂CO₃·10H₂O):
• Softens hard water.
• Cleans clothes.
📄 Baking soda (NaHCO₃):
• Used in baking (makes dough fluffy).
• Used as an antacid & fire extinguisher.
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