Class VII CBSE Science -
Acids, Bases and Salts
CBSE Guess - CBSE Guide - Solved CBSE Questions
For answers of textbook exercises click - Acids,Bases and Salts - Class 7 Science Chapter 5, NCERT Solutions and Notes
Question: How would you prepare
(i) crystals of copper sulphate from metallic copper ?
(i) crystals of copper sulphate from metallic copper ?
(ii) Calcium chloride
from Marble (calcium carbonate) ?
Answer: (i) Take a solution of sulphuric acid and put some copper turnings to it. The solution
becomes blue due to the formation of copper sulphate, by the crystallisation of this solution and
crystals of copper sulphate can be obtained:
Cu + H2SO4
-------> CuSO4 + H2
(ii) Calcium chloride
can be obtained by treating marble (Calcium Carbonate) with hydrochloric acid.
CaCO3 + 2 HCL ------->
CaCl2 + H2 + CO2
Question: What is an oxide?
Answer: An oxide is the compound of
an element with oxygen. For example - water is an oxide of hydrogen, Rust is an
oxide of iron.
Question: Name there types of oxides
with their properties.
Answer: Three types of oxides are -
(a) Acidic Oxides:
The oxides which on treatment with
water form am acids are called acidic oxides. For example,
CO2 + H2 ------>
H2CO3 (carbonic acid)
Non-metals burn in oxygen and form
acidic oxides. Such oxides turn blue litmus red like - Carbon dioxide (CO2),
Sulphur dioxide (SO2).
(b) Basic or Metallic Oxides:
The oxides which on treatment with
water form alkalines are known as basic oxides. Metallic oxides are mostly
basic oxides which turn red litmus blue. For example - Na2O, MgO
etc.
Na2O + H2O ---->
2NaOH
(c) Amphoteric Oxides:
The oxides which show the properties of both acidic and basic oxides are
known as amphoteric oxides for example, Al2O3, SO2 etc.
Question: What is acid ? (Write
definition of acids with their examples) How acids are produced?
Answer: Acids are the chemicals
which contain hydrogen atom and are sour in taste.
Acids are produced when oxides of
non-metals react with water. Examples of some common acids are - HCl (Hydrochloric
Acid), H2SO4 (Sulphuric Acid), HNO3 (Nitric
Acid).
Question: Why are mineral acids
dangerous?
Answer: Mineral Acids are very
strong acids and are mostly used in industries other than laboratories. Being strong acids they are corrosive in
nature. Such acids need to be handled very carefully as they can easily corrode
skin, human body, metals, clothes and all coming in contact. Hence, mineral
acids are dangerous. Some examples of mineral acids are - hydrochloric acid,
sulphuric acid, nitric acid, etc.
Question: What are organic acids ? Name
some organic acids, which are used as food ingredients.
Answer: Acids which contain -COOH
functional groups are termed as organic acids. Organic acids are weak acids and
are present in animal and plant materials.
Examples of organic acids used as
food ingredients - acetic acid, citric acid (C6H8O7),
tartaric acid.
Question: What are the differences
between Dilute and Concentrated acids ?
Answer: Dilute acid - A
dilute acid solution is one which contains only small amount of solute or its
solution diluted to a definite strength is called dilute acid.
Concentrated Acid - A concentrated acid is one which
contains a high proportion of solute.
Question: Answer to these questions -
(a) Name the acid present in vinegar
used in kitchen
(b) Name the acid present in lemon
(c) Which is called "the king
of chemicals"
(d) Name the property due to which salts
absorb water from atmosphere
Answer: (a) acetic acid. (b) citric
acid. (c) sulphuric acid. (d) deliquescence.
Question: What are bases ? Give the characteristics
of bases.
Answer: Bases are the hydroxide of
metals, which give up hydroxide ion after dissociation in aqueous solution.
Characteristics of Bases -
- Bitter in taste.
- Turn red litmus to blue.
- React with acid to form salt and water.
- Bases are soluble in water and known as alkalies.
Question: What are Acids ? Give some
characteristics of acids.
Answer: For definition of acids please
refer to our post
Characteristics of Acids -
- Sour in taste.
- Turn blue litmus to red.
- Dilution of acid in water is an exothermic reaction (heat evolves).
- React with metals to evolve hydrogen gas.
2HCl + 2Na -------> 2NaCl + H2
H2SO4 + Zn ------->
ZnSO4 + H2
- React with bases to form salt and water. The process called, neutralisation.
HCl + NaOH ------> NaCl + H2O
H2SO4 + Ca(OH)2
------> CaSO4 + 2H2O
- React with basic oxides to form salt and water.
CaO + 2HCl -----> CaCl2
+ H2O
Na2O + H2SO4
-----> Na2SO4 + H2O
- React with carbonates to form salt, water and carbon dioxide.
CaCO3 + 2 HCl ----->
CaCl2 + H2O + CO2
MgCO3 + H2SO4
-----> MgSO4 + H2O + CO2
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solved questions, important "Fill in the blanks" and more from
Chapter 5 Acids, Bases and Salts
NCERT Solution, CBSE Notes on Acids, Bases and
Salts - further study
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