CHAPTER 1- INTRODUCTION TO CHEMISTRY
Chemistry
The branch of science which deals with the composition and properties
of matter, changes in matter and the laws or principles which govern
these changesis called Chemistry.
Q1: Define Chemistry also define the branches of chemistry?
Ans:Chemistry:-The branch of science which deals with the composition
and properties of matter, changes in matter and the laws or principles
which govern these changes is called Chemistry.
The five branches of chemistry are as follows:
1:Organic chemistry:-Organic chemistry is the study of carbon
containing substances and the synthesis of such material. many
consumer products are organic in nature.
2:Inorganic chemistry:Inorganic chemistry is the chemistry of element
andtheir compounds except those of carbon-hydrogen compounds and their
derivatives.
3:Physical chemistry:Physical chemistry isthe branch of chemistry
which deals withthe forces and principles involved in the combination
of atoms and molecules.
4:Analytical chemistry:Analytical chemistry is the study of method and
techniques used to determined the kind and quantity of various
component in a given substance.
5:Biochemistry:Biochemistry is the chemistry of living organisms such
as plants and animals.
Q2: Define mass?
Ans :Mass:-The quantity of matter contained in a body is called its mass.
its SI unit is "kilogram" and its symbol is "m".
Q3: Define volume?
Ans :Volume:-Space occupied by a body is known as volume.
its SI unit is "m3″ and its symbol is "v".
Q4: Define density?
Ans:Density:-It is define as ratio between mass and volume. mass per
unitvolume is known as density.
mathematically: d=m
v
Its SI unit is kg/m3. density of solid and liquid usually expressed in
g/cm3 and that of gases as g/dm3.
Q5: Define temperature?
Ans:Temperature:-Temperature is a measure of the intensity of heat. it
is thus a measure of the degree of hotness and coldness in a body.
Q6: Define specific gravity?
Ans:Specific gravity:-The specific gravity of a substance is the ratio
of its mass to the mass of an equal volume of water at a specified
temperature.
Specific gravity =mass of substance
mass of an equal volume of water
specific gravity of a substance ia a ratio between two same quantities
and then fore has no unit.
Q7: Define element?
Ans:Element:-An element is defined as a substance in which all the
atoms are chemically identical having same atomic number. for example:
iron: silver: gold: copper: oxygen: hydrogen: etc.
Q8: Define compound?
Ans:Compound:-A compound is pure substances which consist of two or
more element chemically combined in a fixed proportion by mass.
compound can be broken down by chemical method.
for example: water(H2O); salt(NaCl).
Q9: Define mixture?
Ans:Mixture:-A mixture contains two or more element which can easily
be separated by physical method. the component doesn't lose its
chemical properties.
for example: soil; rock; etc
Q10: Define valency?
Ans:Valency:-The chemical combining capacity of an atom or an element
with another element is called valency.
Q11: Define atom?
Ans:Atom:-It is the smallest particle of an element. it does not exist
freely into nature. it is the unit of an element involved in a
chemical reaction.
Q12: Define molecule?
Ans:Molecule:-It is the combination of two or more atom. it can exist
freely in the nature.
Q13: Define mole?
Ans:Mole:-The weight of an atom or a molecule expressed in grams is
known asone mole.
Q14: Define atomic mass?
Ans:Atomic mass:-The atomic mass of anelement is the average relative
mass of the isotopes of that element referred to the atomic mass of
carbon which is takenas 12.0000 amu.
Q15: Define molecular mass?
Ans:Molecular mass:-The molecular mass of an element when it exists in
the form of molecular or of a compound is the average mass of the
molecular as compound to one atom of 12C6.
Q16: Define gram atomic mass?
Ans:Gram atomic mass:-The weight of an atom expressed in gram is
called gramatomic mass. it is also called gram atom.
Q17: Define gram molecular mass?
Ans:Gram molecular mass:-The weight of molecule expressed in gram is
called gram molecular mass .it is also called gram molecule.
Q18: Define Avogadro's number (n)?
Ans:Avogadro's number:-The number of particles contained in a mole is
equal to 6.023*10 power 23 is known as Avogadronumber.
Q19: Define low of constant composition with examples?
Ans:Low of constant composition:-Proust formulate the low of constant
composition in 1799 as that every pure sample of a particular chemical
compound contain the same element combined in the same fixed
proportion. it is also called the low of definite proportions.
examples:
1, He obtained several samples of copper carbonate from different
sources and also prepared it through different methods in his
laboratory. he found whatever source of method of preparation was
used, it always had the same proportion of copper, carbon and oxygen
by mass.
2, He also mixed ten grams of lead with different amount of sulphur to
make the grey solid lead sulphide. he always foundthat the lead
sulphide had the same fixed percentage of lead and sulphur.
Q20: Define heterogeneous mixture?
Ans:Heterogeneous mixture:the mixturewhich do not have uniform
composition throughout their mass, are called heterogeneous mixture.
Q21: Define homogenous mixture?
Ans:Homogenous mixture:mixtures having uniform composition are called
homogenous mixture.
Q22: Differentiate between compound and mixture?
Ans:
CompoundMixture
1:it is a pure substance.1:it is an impure substance.
2:it cannot be separated by physical methods.2:it can be separated
into its componentsby simple physical methods.
3:element forming compound lose their original
properties-s.3:substance making up the mixture do not lose their
original properties.
4:its composition is fixed.4:its composition is not fixed.
5:the melting point and boiling point of compound are sharp and
characteristic ofeach compound.5:the melting point and boiling point
of a mixture are not sharp.
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