2
Acids, Bases and Salts
CHAPTER
Tips and Tricks
Acids are sour in taste and bases are bitter in
taste.
Indicators are chemical substances which give
different colours in acidic and basic solutions. If a
substance gives change in odour in acidic or basic
medium, then it is olfactory indicator.
Indicator
Acid
solution
Basic
solution
Litmus
Red
Blue
Methyl Orange
Pink
Yellow
Phenolphthalein
Colourless
Pink
Yellow
Blue
[H+] × [OH–] = 10–14
pH scale is the scale for measuring hydrogen ion
concentration in a solution. Its value varies from
0 to 14 for solutions very acidic to very basic.
Neutral solution has pH equal to 7.
pH is defined as negative logarithm of hydrogen
ion concentration. The value of pH is very
important in our daily life. A pH range of 6–8 is
good for living organisms and plants.
Strong acids give H+ ions readily in aqueous
solutions, e.g., hydrochloric acid, sulphuric acid,
nitric acid etc.
Weak acids do not give all the hydrogen atoms
contained as H+ ions in water solution, e.g., acetic
acid, carbonic acid etc.
Strong bases give OH– ions readily, e.g., NaOH,
KOH etc.
Weak bases are ammonium hydroxide, calcium
hydroxide etc.
(iv) Acids and bases react to give salt and water.
This is neutralization reaction.
Salts are formed by combination of acids and
bases.
(v) Bases are the hydroxides of metals, which
give hydroxide ion (OH–) in aqueous solutions.
Acidic salts are formed by reaction of weak base
with a strong acid, e.g., ammonium chloride,
aluminium chloride. Their aqueous solution has
pH less than seven.
Basic salts are from strong base and weak acid,
e.g., sodium acetate, sodium carbonate. Their
aqueous solutions give pH greater than seven.
Neutral salts are formed from combination of
strong acids and strong bases, e.g., NaCl, Na2SO4,
NaNO3 etc. These give neutral aqueous solution
with pH nearly equal to seven.
Bromothymol blue
solution is fixed. If H+ ion cocentration is known,
that of OH– ions is determined.
Chemical properties of acids and bases
(i) Acids contain hydrogen atom and give
hydrogen ions (H+) in water.
(ii) Acids react with metals to give salt and
hydrogen gas.
(iii) Acids react with metal oxide to give salt and
water. In addition carbon dioxide is evolved if
metal carbonate is taken.
(vi) Bases react with only some metals to give
salt and hydrogen, e.g., zinc.
(vii) Bases which are soluble in water are known
as alkalies.
(viii) Acids and Bases in water conduct electricity
due to the presence of ions.
pH: All water solutions contain H+ and OH– ions.
Total of H+ and OH– ion concentration in aqueous
A-24
ACIDS, BASES AND SALTS
A-25
Hydrated salts: Some salts crystallize with a
fixed number of water molecules attached to one
formula unit of salt, e.g., Blue copper sulphate
(CuSO4.5H2O), washing soda (Na2CO3.10H2O),
Gypsum (CaSO4.2H2O).
Gypsum on controlled heating loses water
molecules partially and give calcium sulphate
hemihydrate,
CaSO4 · H2O or plaster of paris.
Calculation of pH values: If H+ ion concentration
in aqueous solution is 10−3 M,
pH = – log10 10–3 = 3
If OH– ion concentration in aqueous solution is
10–3 M,
H+ ion concentration =
Ō
Ō
∴
pH = – log10 10–11 = 11
Common salt is sodium chloride (NaCl)
commercial used variety is rock salt.
NaCl(aq)
+ H2O
+ CO2
+ NH3
Electrolysis
Cathode Anode
(Na)
(Cl2)
+
+
H2O
Ca(OH)2
↓
↓
NaOH
CaOCl2
Sodium
hydroxide
NH4Cl
+ NaHCO3
Ammonium
chloride
Sodium
hydrogen
carbonate
(Baking soda)
Bleaching
powder
heat
Na2CO3 + H2O + CO2
Sodium carbonate
(washing soda)
= 10–11
Formative Assessment
ORAL QUESTIONS (Conversation Type)
1. (a) Acids are sour in taste. Is it a way to find
whether a substance is an acid or a base?
(b) What is other physical test?
(c) Any test with solid acid?
(d) Can you check the evolution of CO 2
chemically?
2. (a) What are acids?
(b) Can presence of H+ in water be estimated?
How?
5. (a) What is washing soda?
(b) Name the process by which sodium
carbonate is manufactured.
(c) What are the raw materials used in the
preparation of washing soda?
(d) Sodium carbonate is obtained from another
carbonate on heating. Name it.
(e) What is the commercial name of sodium
bicarbonate.
6. (a) Name the substance used for bleaching
cotton and wood pulp in textiles.
(c) How is pH related to H+ ion concentration?
(b) What is its chemical name?
(d) How is pH related to strength of an acid?
(c) How is it manufactured?
(e) Name one strong acid and one weak acid.
(d) What is slaked lime?
3. (a) What are salts?
(b) How many types of salts are formed?
(c) What are neutral salts?
(d) What do you mean by acidic salts?
(e) Why does bleaching powder smell of
chlorine ?
ORAL QUESTIONS
(e) Define basic salts.
(f) Give the corresponding acid and base from
which sodium carbonate is formed.
4. (a) What is common salt?
(b) Why does common salt become moist in
rainy season?
1. Name the acid present in lemon juice.
2. Name an antacid.
3. What name is given to an indicator which gives
different odour in acidic and basic solution?
(c) How is it used as a freezing mixture?
4. What is the chemical difference between
washing soda and baking powder?
(d) Name two important laboratory chemicals
prepared from common salt on large scale.
5. How will you obtain sodium carbonate from
sodium bicarbonate?
A-26
NEW AGE CCE SCIENCE—X
6. Name the acid present in ant sting.
11. Metal oxides and bases are similar in their
reaction with acids.
7. Which of the two, curd or soap solution, give
blue colour with litmus paper?
12. Dry hydrochloric acid does not conduct
electricity but dissolves in water.
8. What happens when nitric acid is poured over
egg shells?
13. Water of crystallization of a salt depends on
the moisture content of air.
9. What is the ideal pH of the soil for the healthy
growth of a plant?
10. At what pH the mouth teeth start decaying?
14. Bleaching powder is obtained when brine is
passed over calcium hydroxide solution.
11. Name the base used to reduce acidity in
stomach.
15. Plaster of Paris is obtained by strongly heating
gypsum.
12. How is pH of an acid solution affected when it
is diluted?
QUIZ—WHO AM I
13. Give one example of an acidic salt and one of a
basic salt.
1. I can roughly measure pH value from 0 to 14.
14. Give one example each of basic oxide and acidic
oxide.
2. I am called antichlor and is used to remove
excess chlorine from clothes when treated with
bleaching powder.
15. Name the gas responsible for extinguishing fire
in a soda-acid fire extinguisher.
3. I am a product of gypsum and is used in making
chalks and fire proof materials.
16. What contributes to the basic character of a
base?
4. I am a compound of calcium and can be used
for disinfecting drinking water as well as for
decolourisation.
17. Out of glucose and acetic acid which one will
conduct electricity in water?
5. I give different smell in acid and base solutions
18. Name the scale which is used to measure H+
ion concentration in a solution.
6. I am an oxide capable of showing properties of
both acids and bases.
19. What is the pH of blood?
7. I am a covalent compound and conducts
electricity in aqueous medium.
20. What is the chemical name of the compound
which has the property of hardening when
mixed with water?
8. I am a salt of potassium hydroxide and nitric
acid.
9. I am the term used when a solid becomes liquid
when exposed to moist air.
TRUE OR FLASE
1. Ethyl alcohol (C2H5OH) produces H+ ions in a
solution.
10. I am derived from tomato and turn blue litmus
into red.
2. Dilute hydrochloric acid in stomach helps in
digestion.
PUZZLES
3. Sodium sulphate is a neutral salt.
4. Brine is an aqueous solution of sodium chloride.
5. Sodium acetate is an acidic salt.
6. The electrolysis of aqueous sodium chloride
gives hydrogen gas at cathode.
4
C
2
3
L
1
C
C
C
7. Carbonated soft drink gives blue colour with
litmus paper.
8. All metals react with bases to give salt and
hydrogen gas.
9. Phenolphthalein is an acid-base indicator.
10. Non-metallic oxides give amphoteric solution.
C
C
ACIDS, BASES AND SALTS
A-27
I. ⇒ Across
⇓ Down
1. Known as vinegar (6).
4. A mineral acid (12).
⇓ Down
2. Acid obtained from milk (6)
2. A gas obtained in the electrolysis of sodium
chloride (8).
4. A substance that gives relief from acidity
(7).
3. An acid obtained from lemon (6).
SUGGESTED PROJECTS/ACTIVITIES
II. ⇒ Across
1. A stone used for manufacture of sodium
carbonate (9)
3. A substance that changes colour in acidbase solution (9).
1. Prepare extract of natural materials like red
cabbage leaves, flower petals, tea petals etc.
and test with acid-base solutions to find which
can act as indicator.
2. Different students may check pH of their urine,
blood, cough etc and compare with their diet on
that day and summarise what diet suits human
body best.
2
C
3. Prepare extracts of different masala at home
and check their pH with pH paper and draw a
conclusion.
4
1
I
T
3
N
A
4. Compare the reaction of different acids with
carbonate/bicarbonate and suggest which
combination is best to construct a fire
extinguisher.
A-28
NEW AGE CCE SCIENCE—X
Assignments
CLASS ASSIGNMENT 1
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1. Give one example each of natural indicator and
synthetic indicator.
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2. Give an example each of acidic salt and neutral
salt as well basic salt. Explain.
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4. What name is given to an indicator which gives
different colour in different medium. Give
examples.
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5. How is phenolphthalein used as an indicator?
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3. What are the salts of nitric acid called? Give
one example of such a salt.
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ACIDS, BASES AND SALTS
A-29
6. What is that reaction called when acids and
bases react? What is the common product of all
such reactions?
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9. A student prepared two solutions (1) dil. HCl
and (ii) distilled water in separate test tubes.
She forgot to label the tubes. Both solutions are
colourless. Solutions of litmus, phenolphthalein
and lime water are available to her. How will
she distinguish between the two solutions?
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7. Name the salt formed when nitric acid reacts
with ammonium hydroxide. Is it an acidic salt
or a basic salt?
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10. What are strong acids and weak acids? Do both
behave similarly with litmus solution.
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8. Show that sodium acetate is a basic salt.
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