UHA Chemistry Notes 9th Class
Chapter-1
Important short Question:
1.What is chemistry?
Ans:
The branch of science which deals with the composition, structure, properties and reactions of matter is called chemistry.
2.What
role is played by chemistry in our daily life ?
Ans:
The development of science and technology has provide
us a lot of facilities in daily life . Imagine the role and
importance of petrochemical products , medicines and drugs , soap ,
detergent , soap , plastic , paint , pigments , insecticides , pesticides
, which all are fruit of the efforts of chemists.
3.What is physical chemistry also give two
example about physical chemistry?
Ans:
Physical Chemistry is defined as the branch of chemistry that deals with the relationship between the composition and properties of matter along with the changes in them. For example the properties such as structure of atoms or formation of molecule, behavior of gases, liquids and solids.
4. What is matter?
Ans:
Matter is simply defined as anything that has mass and occupies space.
5. Define substance?
Ans:
A piece of matter in pure form is termed as a substance. Every substance has a fixed composition and specific properties or characteristics.
6. What do you know about mixture?
Ans:
Impure matter is called mixture; which can be homogeneous or heterogenous in its composition.
7. What is physical properties?
Ans:
The properties those are associated with the physical state of the substance are called physical properties; like color smell, taste, hardness, shape of crystal, solubility, melting and boiling points etc.
8.What is chemical properties ?
Ans:
The chemical properties depend upon the composition of the substance. When a substance undergoes a chemical change, its composition changes and a new substance are formed. For example, decomposition of water is a chemical change as it produce hydrogen and oxygen gases.
9.Give modern definition of element?
Ans:
Modern definition of element is a that it is substance made up of same type of atoms, having same atomic number and cannot be decomposed into simple substance by ordinary chemical means.
10.What is symbol and derived from which language?
Ans:
Elements are represented by symbols. which are abbreviations for the name of elements. H for Hydrogen, N for Nitrogen, and C for Carbon etc.
11.What is meant by valency? how it is work.
Ans:
The unique property of an element is valency. It is combining capacity of an element with other elements. It depends upon the number of electrons in the outermost shell.
12. What is compound ? describe with example.
Ans:
Compound is a substance made up of two or more elements chemically combined together in a fixed ratio by mass. For example, carbon dioxide is formed when elements of carbon and oxygen combine chemically in a fixed ratio of 12:32 or 3:8 by mass. similarly water is a compound formed by chemical combination between hydrogen and oxygen in a fixed ratio of 1:8 by mass.
13. What is molecular formula?
Ans:
Molecules are formed by the combination of atoms. These molecules are represented by molecular formulae that show actual number of atoms of each element present in a molecule of that compound. Molecular formula is derived from empirical formula by the following relationship:
Molecular formula =( Empirical formula) n
14.What is mixture ? also give its important example.
Ans:
When two or more elements or compounds mix up physically without any fixed ratio, they form a mixture.
15.What is homogenous mixture ? give its example?
Ans:
Mixtures that have uniform composition throughout are called homogeneous mixture. For example air, gasoline, ice cream.
16.What is heterogenous mixture ? also give example.
Ans:
Those mixture in which composition is not uniform are called heterogeneous mixtures. For example soil, rock and wood.
17.Difference between a compound and a mixture give
reason?
Ans:
18:What is atomic number also give its symbol?
Ans:
The atomic number of an elements is equal to the number of protons present in the nucleus of its atoms. It is represented by symbol 'Z'.
19.What is mass number how it is represent?
Ans:
The mass number is the sum of number of protons and neutrons present in the nucleus of an atom. It is represented by symbol 'A'.
20.What
is relative atomic mass of an element?
Ans:
The relative atomic mass of an element is the average mass of the atoms of that element as compared to 1/12th(one-twelfth) the mass of an atom of carbon-12 isotope( an element having different mass number but same atomic number.
21.What is chemical formula?
Ans:
Compounds are represented by chemical formulae as elements are represented by symbols.
22.Define empirical formula?
Ans:
The simplest type of formula is empirical formula. It is the simplest whole number ratio of atoms present in a compound.
23.What is formula unit?
Ans:
It is defined as the simplest whole number ratio of ions, as present in the ionic compound. For example, formula unit of common salt consist of one Na+ and one Cl- and its empirical formula is NaCl.
24.What is molecular formula?
Ans:
Molecules are formed by the combination of atom. These molecule are represented by molecular formulae that show actual number of atoms of each element present in a molecule of that compound.
Molecular formula = ( Empirical formula)n
25.What is molecular mass also give its example?
Ans:
The sum of atomic masses of all the atoms present in one molecule of a molecular substances, is its molecular mass. For example, molecular mass of chlorine(Cl2) is 71amu, of water (H2O) IS 18amu and that of carbon dioxide ( CO2) is 44amu.
26.What is ion?
Ans:
Ion is an atom or group of atoms having a charge a charge on it. The charge may be positive or negative.
27.Difference between anion and cation?
Ans:
Cation:
An atom or group of atoms having positive charge on it is called cation. For example Na+
Anion:
An atom or a group of atoms that has a negative charge on it, is called anion.
For example Cl−
28.Define molecular ion with example?
Ans:
When a molecule loses or gains an electron, it forms a molecular ion. Molecular ion have both charges positive and negative. It is formed by the ionization of a molecule.
29.What is free radical?
Ans
Free radical are atoms or group of atoms possessing odd number of electrons. It is represented by putting a dot over the symbol of an element e.g. HO•
30.Define gram atomic mass?
Ans:
The atomic mass of an element expressed in grams is called gram atomic mass or gram atom. It is also called a mole.
1 gram atom of hydrogen = 1.008 g = 1mol of hydrogen atoms
31.Define gram molecular mass?
Ans:
The molecular mass of an element or a compound expressed in grams is called gram molecular mass or gram molecule. It is also called a mole.
1 gram molecule of H2O = 18.0 g = 1mol of water
32.Define gram formula mass?
Ans:
The formula mass of an ionic compound expressed in grams is called gram formula mass or gram formula. This is also called a mole. For
1 gram formula of NaCl = 58.5 g = 1mol of sodium chloride
33.What is Avogadro's number?
Ans:
Avogadro's Number is a collection of 6.02 × 1023 particles. It is represented by symbol 'NA'. Hence, the 6.02 × 1023 number of atoms, molecules or formula units is called Avogadro's number.
34.What is mole?
Ans:
A mole is defined as the amount(mass) of a substance that contains6.02 × 1023 number of particles ( atoms, molecules or formula units).
Number of moles = known mass of a substance/ molar mass of the substance
35.What is chemical calculation write its formula?
Ans:
Calculating the number of moles and number of particles from known mass of a substance. Calculate the number of moles from given mass by using equation
Number of moles = known mass of a substance/ molar mass of the substance.
Sir kindly add the mcqs in the file lots of thanks
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