Download File - cpprashanths Chemistry

ACIDS ,BASES AND SALTS
Q1.What are acids?
Give name and chemical formula of some common acids. Give any three physical
properties of acidic solutions.
A=Acids are substances which release one or more H+ ions in aqueous solutions.
a) Hydrochloric acid=HCl
b) Sulphuric acid = H2SO4
c) Nitric acid = HNO3
d) Acetic acid = CH3COOH
e) Phosphoric acid = H3PO4
Physical properties:- Acidic solutions are
a)Sour to taste
b)Change the colour of litmus from blue to red
c)Conducts electricity
Q2.What are bases?
Give name and chemical formula of some common bases Give any three physical
properties of basic solutions.
A=Bases are substances which are capable of releasing one or more OH—ions in
aqueous solutions.
a) Sodium Hydroxide = NaOH
b) Potassium Hydroxide = KOH
c) Ammonium Hydroxide = NH4OH
d) Calcium Hydroxide = Ca(OH)2
e) Barium Hydroxide = Ba(OH)2
Physical properties:- Basic solutions
a) Tastes bitter
b) Feels slippery
c) Change the colour of litmus from red to blue
d) Conducts electricity
Q3.Give the name and formula of some common salts. give any three physical
properties of salts.
A=
a) Sodium chloride = NaCl
b) Sodium carbonate = Na2CO3
c) Potassium chloride = KCl
d) Ammonium nitrate = NH4NO3
e) Potassium sulphate = K2SO4
Physical properties :a) Tastes salty
b) Conducts electricity
Q4.What are indicators. Explain with examples.
Indicators are substances which indicate the nature of a particular solution whether acidic
basic or neutral.
Common acid base indicators
Indicator
colour in
Neutral soln.
colour in
acidic soln
colour in
basic soln soln
Litmus
purple
red
blue
Phenolphthalein
colourless
colourless
pink
Methyl orange
yellow
red
orange
Red cabbage juice
purple
red
green
Turmeric juice
yellow
yellow
reddish or
deep brown
Q5.What are olfactory indicators
A=The substances whose odour changes in acidic or basic media are called olfactory
indicators
Eg:- onion, vanilla essence, clove oil.
Q6.How do acids react with metals?
A=Metals displace hydrogen from acids to form salt and hydrogen.
Zn(s) + H2SO4(aq)  ZnSO4(aq) + H2(g)
Mg(s)+ H2SO4 (aq) MgSO4(aq) + H2(g)
Q6.How do bases react with metals.
A=Metals like Zn,Sn,and Al react with strong alkalies to liberate H2
Zn(s) + 2 NaOH (aq)  Na2ZnO2 (aq) + H2(g)
Sn(s) + 2NaOH (aq)  Na2SnO2(aq) + H2(g)
2Al + 2NaOH + 2H2O  2NaAlO2 (aq) + 3H2(g)
Q7.How do metal carbonates react with acids? Give examples.
A=Metal carbonates react with acids to evolve CO2 gas and form salts.
Eg:- CaCO3 + 2HCl  CaCl2 + H2O + CO2
Na2CO3 + 2HCl  2NaCl + H2O + CO2
Q8.How do metal bicarbonates react with acids? Give examples.
A=Metal bicarbonates react with acids to evolve CO2 gas and form salts.
Eg:- NaHCO3 + HCl  NaCl + H2O + CO2
KHCO3 + HCl  KCl + H2O + CO2
Q9.What will happen if CO2 is passed through lilme water first in small amount and
then in excess?
A=Lime water truns milky first due the the formation of insoluble calcium carbonate.
Ca(OH)2 + CO2  CaCO3 + H2O
The milkiness disappears when CO2 is passed in excess due to the formation of soluble
calcium bi carbonate.
CaCO3 + H2O + CO2  Ca(HCO3)2
Q10.What is meant by the neutralization ?
A=The reaction between an acid and a base to give a salt and water is known as
neutralization reaction.
NaOH + HCl  NaCl + H2O
Base + Acid  salt + water
We can view neutralization reaction as
H+ + OH--  H2O
Q11.How do metal oxides react with acids? Give examples.
A=Metal oxides react with acids to form salt and water
CaO + 2HCL  CaCl2
FeO + 2HCl  FeCl2 + H2O
MgO + H2SO4  MgSO4 + H2O
Q12.Metallic oxides are said to be basic oxides whereas non metallic oxides are
called acidic oxides. Explain with examples.
A=Metallic oxides react with acids to form salt and water .ie metallic oxides are called
basic oxides.
CaO + 2HCl  CaCl2 + H2O
(basic oxide)
(Metallic oxide)
Non metallic oxides react with bases to form salt and water .ie Non metallic oxides are
called acidic oxides..
SO2 + Ca(OH)2  CaSO3 + H2O
CO2 + Ca(OH)2  CaCO3 + H2O
(acidic oxide)
(Non metallic oxide) note:- non metallic oxides dissolve in water to form acids ,metallic
oxides form bases / alkali.
Q13.Alcohols and glucose also contain Hydrogen,but are not referred to as
acids.Explain.
A=Compounds like alcohols and glucose do not undergo dissociation in water to form
H+ ions.hence they do not exhibit the characheristic properties of acids.
The aq solution of alcohols and glucose do not conduct electricity which shows that their
aq solution do no contain ions.
Q14.What happens to acids and bases in water solution?
A= Acids dissociate in water to form H+ ions which exist as H3O+ ions.
HCl + H2O  H3O+ + Cl—
(H+ + H2O  H3O+)
bases dissolve in water to give OH—ions.
NaOH (H2O)  Na+ + OH—
Q15.What is an alkali?
A=An alkali is a base that dissolve in water.
Q16.Why does distilled water not conducts electricity where as rainwater does?
A= Distilled water contains only negligible concentration of ions due to slight ionization
of water.Therefore it does not conduct electricity.
Rain water contains many impurities which are formed by dissolution of gases present in
the atmosphere.
SO2 + H2O  H2SO3
CO2 + H2O  H2CO3.
These acids dissociate in rainwater to furnish appreciable conc. of ions. Due to the
presence of these ions rainwater conducts electricity.
Q17.What care must be taken while mixing conc. HNO3 / H2SO4 with water?
A=The acid must be always added slowly to water with constant stirring.
If water is added to conc. acids the heat generated may cause the mixture to splash out
and cause burns.
The glass container may break due to excessive heat.
Q18.What is universal indicator?
A=Universal indicator is a mixture of several indicators.
This shows different colours at different concentrations of hydrogen ions in a solution.
Q19.What is pH scale?
A=A scale for measuring hydrogen ion concentration in a solution is called pH scale.
PH is a number ( from 0 to 14 ) which indicates the acidic or basic nature of a solution.
Higher the hydronium ion concentration lower is the pH value.
.pH of neutral solution =7
.pH of acidic solution =less than 7
.pH of basic solution =more than 7
(pH + pOH of a solution =14.,
[H+] in neutral solution =10-7moles/litre [OH--] in neutral soln= 10-7moles/litre.,
[H+] in acidic solution > 10-7moles/litre [OH--] in acidic soln < 10-7moles/litre.
[H+] in basic solution < 10-7moles/litre [OH--] in basic soln > 10-7moles/litre.
[H+][OH--] = 10-14 , pH + pOH of a solution =14
Q20.Differentiate between strong acid and week acids?
A=Acids with high degree of dissociation to give more H+ ions are said to be strong
acids. Eg HCl
Acids with low degree of dissociation to give less H+ ions are called weak acids.
Eg:-CH3COOH
HW Q21.Brirfly explain the importance of pH in everyday life.
Q22.What will be the value of pH of
a) salt of strong acid and strong base?
b) Salt of strong acid and weak base?
c) Salt of weak acid and strong base?
A=
a) Salt of strong acid and strong base are neutral with pH value of 7.
Eg:-Na2SO4
b)Salt of strong acid and weak base are acidic with pH value less than 7
Eg:-CaSO4
c)Salt of weak acid and strong base are basic with pH value mare than 7
Eg:-CH3COONa , Na2CO3
Q23.How is NaOH prepared from NaCl?
A= When electricity is passed through aq.solution of NaCl it decomposed to form NaOH
2NaCl (aq.) + 2H2O (l)  2NaOH (aq) + Cl2 + H2(g)
Chlorine is liberated at anode H2 is liberated at cathode.
This process is called Chlor-Alkali process.
Q24.Explain the method of preparation of bleaching powder.
A=Bleaching powder is produced by the action of chlorine on dry slaked lime.
{ Ca(OH)2 }
Ca(OH)2 + Cl2  CaOCl2 + H2O.
Q25.Give any three uses of bleaching powder.
A=
a)For bleaching cotton and in linen in textile industry, wood pulp in paper
industry.
b)As oxidizing agent in many chemical industries.
c)For disinfecting drinking water.
Q26.How is NaHCO3 prepared?
A= It is prepared by passing NH3 and CO2 through NaCl solution.
NaCl + H2O + CO2 + NH3  NH4Cl + NaHCO3
Q27.Why is NaHCO3 used in baking powder?
A= Baking powder is a mixture of baking soda NaHCO3 and a mild edible acid such as
tartaric acid.
When baking powder is heated or mixed with water NaHCO3 reacts with acid to form
CO2.
NaHCO3 + H+  CO2 + H2O + Sodium salt of acid.
CO2 produced causes the bread or cake to rise making them soft and spongy.
Q28.How is washing soda prepared?
A=By heating baking soda NaHCO3, Na2CO3 can be obtained.
2NaHCO3  Na2CO3 + H2O + CO2
Recrystallisation of Na2CO3 from water gives Na2CO3.10H2O (washing soda)
Na2CO3 + 10H2O  Na2CO3.10H2O
Q29.Give any three uses of NaHCO3?
A=
a)For making baking powder
b)For preparing antacids.
c)In soda acid fire extinguishers.
Q30.Give any three uses of washing soda?
A=
a)In glass ,soap and paper industries
b)In the manufacture of borax
c)As cleaning agent for domestic purposes, removal of permanent hardness of
water.
Q31.Define water of crystallization. Give examples.
A= The fixed number of water molecules present in one formula unit of sat is known os
water crystallization.
Eg:- CuSO4.5H2O ,Na2CO3.10H2O , CaSO4.2H2O
Q32.Explain the method of preparation of Plaster of Paris.
A=Plaster of Paris is prepared by heating gypsum at 373k.
CaSO4.2H2O  CaSO4 ½ H2O + 1 ½ H2O
Q33.When Plaster of Paris is mixed with water , it changes to a hard mass.Explain.
A= On mixing with water plaster of Paris changes back to gypsum.
CaSO4 ½ H2O + 1 ½ H2O  CaSO4.2H2O
Q34.What will happen if copper sulphate crystals are heated?
A= When CuSO4.5H2O is heated it turns to white due to the removal of water of
crystallization.
CuSO4.5H2O  CuSO4
Blue
white
If the crystals are mixed with water again blue colour of the crystals will reappear.
…………………………………………………………………………………………..