CHAPTER 1- INTRODUCTION TO CHEMISTRY

by • 14/07/2011 • 9th class ChemistryComments (6)1301

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.

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 and their compounds except those of carbon-hydrogen compounds and their derivatives.

3: Physical chemistry: Physical chemistry is the branch of chemistry which deals with the 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 unit volume 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 as one mole.

Q14: Define atomic mass?
Ans: Atomic mass:-The atomic mass of an element is the average relative mass of the isotopes of that element referred to the atomic mass of carbon which is taken as 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 gram atomic 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 Avogadro number.

 

 

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 found that the lead sulphide had the same fixed percentage of lead and sulphur.

Q20: Define heterogeneous mixture?
Ans: Heterogeneous mixture: the mixture which 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:

Compound Mixture

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 components by 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 of each compound. 5:the melting point and boiling point of a mixture are not sharp.
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