C.B.S.E class 10

2.  117 different chemical elements are
known to us. These elements combine to
form a large number of compounds.
 On the basis of their properties all the
compounds can be classified into- Acids,
bases and Salts.

3.  An indicator is a dye that changes color
when it is put into an acid or a base.
 Common indicators- Litmus, Methyl
orange and Phenolphthalein.

4.  An acid turns blue litmus to red.
 A base turns red litmus to blue.
 Methyl orange indicator gives red color in
acid solution.
 Methyl orange indicator gives yellow color
in basic solution.
 Phenolphthalein is colorless in acid solution.
 Phenolphthalein gives pink color in basic
solution.

5.  Litmus is a natural indicator. It is a purple
dye extracted from a type of plant
called Lichen.
 It is neither acidic nor basic.

6.  Turmeric- contains a yellow dye which
turns red in basic solution.
 The red cabbage extract which is
neutral in nature remains red in acidic
solution but turns green on adding to
basic solution.

7.  Onion has a characteristic smell . When
basic solution is added to a strip treated
with onions then the smell can’t be
detected. Acids don’t have any effect.
 Vanilla extract has a characteristic
pleasant smell. In basic solution the smell
can’t be detected whereas acids do not
destroy the smell.

8.  Acids are sour in taste and turn blue
litmus red.
 The acids present in plant materials and
animals are called organic acids.
 Citric acid.
 Tartaric acid.
 Oxalic acid.
 Methanoic acid.
 Organic acids are weak acids

9.  The acids prepared from the minerals of
the earth are called mineral acids.
 Hydrochloric acid
 Sulphuric acid
 Nitric acid
 The mineral acids are strong acids.

10.  Acids have a sour taste.
 Acids turn blue litmus red.
 Acid solutions conduct electricity.

11.  Acids react with metals to form
hydrogen gas.
 Metal + Acid → Salt + Hydrogen gas
 Eg. Zn(s) +H₂SO₄(aq)→ ZnSO₄ +H₂(g)

12.  Acids react with metal carbonates to
from carbon dioxide gas.
 Metal carbonate +Acid → Salt + carbon dioxide +Water.
 Na₂CO₃(s) + 2HCl(aq) → 2NaCl (aq) +CO₂(g) +H₂O(l)

13.  Acids react with bases to form salt and
water. This is called neutralization
reaction.
 Acid + Base → Salt + Water
 NaOH (aq) + HCl (aq) → NaCl (aq) + H₂O (l)

14.  Acids react with metal oxides to form salt
and water.
 Metal oxide + Acid → Salt + Water
 CuO (s) + 2HCl (aq) → CuCl₂ (aq) + H₂O (l)

15.  Acids have corrosive nature.
 The mineral acids cause severe burns on
the skin and attack and eat up meterials
like cloth, wood, metal and stone work.

16.  An acid is a substance that releases H+
ions in an aqueous solution
› Aqueous means water
 Example: when hydrochloric acid is
dissolved in water, the compound
separates into chlorine ions (Cl-) and
hydrogen ions (H+)

17.  A strong acid breaks down completely in
water and gives off many H+ ions
 HCl
 H₂SO₄
 HNO₃

18.  A weak acid only partially breaks down.
It gives off much less H+ than a strong
acid
 CH₃COOH
 H₂CO₃
 H₂SO₃

19.  Sulphuric acid is used in manufacture of
fertilizers (like ammonium sulphate ),
paints ,dyes ,chemicals, plastics,
synthetic fibres, detergents, explosives
and car batteries.
 Nitric acid is used for making fertilizers ,
explosives, dyes and plastics.
 Hydrochloric acid is used for removing
oxide film before galvanizing.

20.  A base is a substance that releases
hydroxide (OH-) ions in an aqueous
solution
 Example: When sodium hydroxide
(NaOH) is dissolved in water, the
compound separates into sodium ions
(Na+) and hydroxide ions (OH-)

21.  The solution of substances like caustic soda,
lime(chuna) and washing soda are bitter in
taste and soapy to touch.
 Bases are those chemical substances which
have a bitter taste
 Most of the bases do not dissolve in water
those bases which dissolve in water without
any chemical reaction have a special
name .They are called alkali.
 Example- NaOH, KOH, Ca(OH)₂, NH₂OH.

22.  Bases usually taste bitter
 Bases feel slippery
 Bases contain hydroxide ions (OH-)
 Bases are the chemicals opposites of acids.
 A base is a chemical substance which can
neutralize an acid.
 All the metal oxides and metal hydroxides
are base.
 For example- Sodium oxide(Na₂O) is a metal
oxide so it is a base and Sodium
hydroxide(NaOH) is a metal hydroxide , so it
is a base.

23.  A base is a substance which dissolves in
water to produce Hydroxide ions(OH⁻
ions)
 NaOH(s) → Na⁺ (aq) + OH⁻ (aq)
 KOH(s) → K⁺ (aq) + OH⁻ (aq)
 A common property of all the bases is that they
produce hydroxide ion when dissolved in water.
Water
Base/Alkali Sodium ions Hydroxide ions
Base/Alkali Pottasium ions Hydroxide ions
Water