Acids, Bases and Salts

JKBOSE/CBSE
Acids, Bases and Salts Class 10 Notes | pH Scale & Indicators
Notes - Acids Bases Salts - Class 10

Acids, Bases & Salts

Overview: Indicators, Chemical properties of Acids & Bases, pH Scale, and Chemicals from Common Salt.

1. Acids and Bases

  • Acids: Sour taste, turn Blue litmus Red, give H+ ions in solution. (HCl, H2SO4).
  • Bases: Bitter taste, turn Red litmus Blue, give OH- ions in solution. (NaOH, KOH).
  • Indicators: Litmus (Natural), Phenolphthalein (Synthetic - Pink in base), Methyl Orange (Red in acid, Yellow in base).

2. Chemical Properties

  • Acid + Metal → Salt + Hydrogen Gas (Pop sound).
  • Base + Metal → Salt + Hydrogen Gas (Zn + NaOH → Na2ZnO2 + H2).
  • Acid + Metal Carbonate → Salt + CO2 + Water.
  • Acid + Base → Salt + Water (Neutralization).
  • Metal Oxide + Acid → Salt + Water (Basic oxide).
  • Non-metal Oxide + Base → Salt + Water (Acidic oxide).

3. pH Scale

Measure of H+ concentration. Range 0-14.

  • pH < 7: Acidic
  • pH = 7: Neutral
  • pH > 7: Basic

4. Important Salts

  • Common Salt: NaCl.
  • Bleaching Powder: CaOCl2 (Action of Cl2 on Slaked Lime).
  • Baking Soda: NaHCO3 (Mild base, used in cooking).
  • Washing Soda: Na2CO3.10H2O (Glass, soap, paper industry).
  • Plaster of Paris: CaSO4.1/2H2O (From Gypsum).

NCERT In-Text Questions (Solved)

Page 18

Q1. You have 3 test tubes (Distilled water, Acid, Base). You only have Red Litmus. How to identify?
1. Dip Red Litmus in all 3. The one turning it Blue is Base.
2. Now use this Blue Litmus. Dip in remaining 2. The one turning it Red is Acid.
3. The remaining one is Distilled Water.

Page 22

Q1. Why should curd and sour substances not be kept in brass/copper vessels?
Curd contains acid. Acid reacts with copper/brass to form toxic salts which spoil the food and are harmful to health.
Q2. Which gas is usually liberated when an acid reacts with metal? Test for it.
Hydrogen gas. Test: Bring a burning candle near the gas bubbles. It burns with a pop sound.
Q3. Metal A reacts with dilute HCl to produce effervescence. Gas extinguishes candle. Reaction?
Gas is CO2 (Extinguishes fire). Metal compound A is Calcium Carbonate (CaCO3) as formed CaCl2.
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)

Page 25

Q1. Why do HCl, HNO3 show acidic character in aq solution but alcohol/glucose do not?
Acids dissociate to produce H+ ions in water, causing acidic character. Alcohol/Glucose contain Hydrogen but do not dissociate to give H+ ions.
Q2. Why does aq solution of acid conduct electricity?
Due to presence of charged particles called ions (H+) which carry current.
Q3. Why does dry HCl gas not change color of dry litmus paper?
Dissociation of H+ ions happens only in presence of water. Dry HCl has no H+ ions, so no acidic effect.
Q4. How to dilute acid?
Always add Acid to Water slowly with stirring. Not Water to Acid, because it is highly exothermic and may splash/break container.
Q5. How is H3O+ conc affected when acid is diluted?
Concentration of Hydronium ions (H3O+) per unit volume decreases.

Page 28

Q1. Solution A has pH 6, B has pH 8. Which has more H+? Acidic/Basic?
pH ∝ 1/[H+]. Lower pH means more H+. Solution A (pH 6) has more H+. A is acidic, B is basic.
Q2. Do basic solutions have H+ ions? If yes, why basic?
Yes, they have H+ ions but OH- ions are much more in concentration, making the solution basic.
Q3. Soil pH treatment?
If soil is too acidic, farmers treat it with Quick lime (CaO) or Slaked lime (Ca(OH)2) or Chalk (CaCO3).

Page 33

Q1. Common name of CaOCl2?
Bleaching Powder.
Q2. Name substance which yields chlorine with Cl2.
Dry Slaked Lime [Ca(OH)2].
Q3. Sodium compound for hard water softening?
Washing Soda (Sodium Carbonate Decahydrate).
Q4. Heating NaHCO3?
2NaHCO3 → Na2CO3 + H2O + CO2.
Q5. Reaction Eq for Plaster of Paris and Water.
CaSO4.1/2H2O + 1.5H2O → CaSO4.2H2O (Gypsum).
Exercise Solutions - Acids Bases Salts - Class 10

NCERT Exercise Questions

Complete solutions for Chapter 2 exercises.

Q1. A solution turns red litmus blue, its pH is likely to be:
(d) 10. (Base turns red litmus blue, pH > 7).
Q2. Solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains:
(b) HCl. Egg shells are CaCO3. Reacts with acid to give CO2.
Q3. 10 mL of NaOH requires 8 mL of HCl. If we take 20 mL NaOH, amount of HCl required?
(d) 16 mL. (Double the base, double the acid).
Q4. Which type of medicine is used for treating indigestion?
(c) Antacid (Neutralizes excess acid).
Q5. Write word equations and balanced equations:
(a) Zn + H2SO4 → ZnSO4 + H2
(b) Mg + 2HCl → MgCl2 + H2
(c) 2Al + 3H2SO4 → Al2(SO4)3 + 3H2
(d) Fe + 2HCl → FeCl2 + H2
Q6. Alcohol and glucose contain hydrogen but are not acids. Explain.
To be an acid, substances must dissociate in water to produce H+ ions. Alcohol and glucose do not ionize to give H+ ions, so they don't show acidic properties (don't conduct electricity).
Q7. Why does distilled water not conduct electricity, while rain water does?
Distilled water is pure and has no ions. Rain water dissolves CO2 and SO2 from air to form acids (Carbonic/Sulphurous acid) which dissociate into ions, conducting electricity.
Q8. Why do acids not show acidic behavior in absence of water?
Acidic behavior is due to H+ ions. Acids produce H+ ions ONLY in presence of water.
Q9. Five solutions A, B, C, D, E tested with Universal Indicator showing pH 4, 1, 11, 7, 9 respectively. Arrange in increasing H+ conc.
A(4), B(1), C(11), D(7), E(9).
Neutral: D (7).
Strong Alkaline: C (11).
Strong Acidic: B (1).
Weak Acidic: A (4).
Weak Alkaline: E (9).
Increasing H+ (Decreasing pH): C < E < D < A < B.
Q10. Mg ribbon in HCl vs Acetic Acid. Which fizzes more vigorously?
HCl test tube. HCl is a strong acid, dissociates completely producing more H+ ions, leading to faster reaction and vigorous evolution of H2 gas.
Q11. Fresh milk pH 6. Changes when turns to curd?
pH decreases. Lactose turns to Lactic Acid. Acidic means pH < 7.
Q12. Why add baking soda to fresh milk?
(a) To make it slightly alkaline so it doesn't get sour easily.
(b) It takes longer to set as curd because the lactic acid formed first has to neutralize the added alkali.
Q13. Plaster of Paris storage?
In moisture-proof container. Because it absorbs moisture to form hard solid Gypsum.
Q14. Neutralization reaction?
Reaction between acid and base to form salt and water. NaOH + HCl → NaCl + H2O.
Q15. Two uses of Washing Soda and Baking Soda.
Washing Soda: Glass/Soap industry, Removing permanent hardness of water.
Baking Soda: Antacid, Making baking powder (cakes).
Formulas & Facts - Acids Bases Salts - Class 10

Chemical Formulae & Facts

List of important chemical formulas of salts and key facts.

Important Chemical Formulas

Common Salt NaCl
Washing Soda Na2CO3.10H2O
Baking Soda NaHCO3
Bleaching Powder CaOCl2
Plaster of Paris CaSO4.1/2H2O
Gypsum CaSO4.2H2O
Limestone CaCO3
Sulphuric Acid H2SO4

50 Important Facts

1. Acids taste sour.
2. Bases taste bitter.
3. Acids turn blue litmus red.
4. Bases turn red litmus blue.
5. Litmus is a purple dye from Lichen.
6. Phenolphthalein is pink in base.
7. Methyl orange is yellow in base.
8. Olfactory indicators change smell in acid/base.
9. Turmeric turns reddish-brown in base.
10. Acids give H+ ions in water.
11. Bases give OH- ions in water.
12. Alkalis are bases soluble in water.
13. Metal + Acid gives Hydrogen gas.
14. Hydrogen gas burns with a pop sound.
15. Neutralization: Acid + Base = Salt + Water.
16. Metal oxide is basic in nature.
17. Non-metal oxide is acidic in nature.
18. Acids conduct electricity in water.
19. Dry HCl gas changes dry litmus color? No.
20. Diluting acid is exothermic.
21. Always add acid to water, not reverse.
22. pH scale measures H+ ion concentration.
23. pH 7 is neutral.
24. pH less than 7 is acidic.
25. pH more than 7 is basic.
26. Our stomach produces HCl.
27. Antacids neutralize excess stomach acid.
28. Milk of magnesia is an antacid.
29. Tooth decay starts below pH 5.5.
30. Nettle sting contains Methanoic acid.
31. Baking soda treats ant/bee sting.
32. Vinegar contains Acetic acid.
33. Orange/Lemon contains Citric acid.
34. Tamarind contains Tartaric acid.
35. Tomato contains Oxalic acid.
36. Sour milk (Curd) contains Lactic acid.
37. Brine is aqueous solution of NaCl.
38. Chlorine gas is used in water treatment.
39. Bleaching powder is Ca(OCl)Cl.
40. Baking soda releases CO2 on heating.
41. Tartaric acid makes cake bitter-free.
42. Washing soda removes permanent hardness.
43. Copper Sulphate crystals are blue.
44. Anhydrous Copper Sulphate is white.
45. Water of crystallization gives color to salts.
46. Plaster of Paris sets into hard mass with water.
47. Gypsum is CaSO4.2H2O.
48. PoP is used for making toys.
49. Common salt is hygroscopic (absorbs moisture).
50. Strong acid + Strong base = Neutral Salt.
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