Chemistry For Class IX (New Book ) - Chapter No. 1- Fundamentals of Chemistry - Short Questions And Answers

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Chapter No.1 - Fundamentals of Chemistry
Short Questions And Answers
Text Book Exercise

SECTION- B: SHORT QUESTIONS:

Q.1: Differentiate between the physical and analytical chemistry?
Ans: Difference Between the Physical And Analytical Chemistry

S.NO.	Physical Chemistry	Analytical Chemistry
1.	Physical chemistry is the branch of chemistry which deals with relationship between composition and physical properties of matter with the changes in them.	Analytical chemistry is the branch of chemistry which deals with separation and analysis of kind, quality and quantity of various components in given substance.
2.	It deals with the laws and principles governing the combination of atoms and molecules in chemical reactions.	It used in chromatography, electrophoresis and spectroscopy.

Q.2: Define Molecules and Write down the classification of molecule?
Ans: Molecules:
A molecule is the smallest particle in a chemical element or Compound that has the chemical properties of that element or Compound. Molecules are made up of atoms that are held together by chemical bonds. These bonds form as a result of the Sharing or exchange of electrons among atoms.

In other words:

• Molecule is chemical combination of atoms.
• Molecule is smallest unit of a substance.
• Molecule shows properties of substance.
• Molecule can exist independently.

Classification Or Types Of Molecules:
Molecules are classifies as:

• On basis of number of atoms
• On basis of types of atoms

A) On Basis Of Number Of Atoms
1) Mono atomic Molecule:
Molecule consist of one atom is called mono atomic molecule.
e.g. Helium (He), Neon(Ne), Argon(Ar), Krypton(Kr), Xenon (Xe), Radon (Rn)

(2) Di atomic Molecule:
Molecule consist of two atoms is called di atomic molecule.
e.g. Hydrogen (H₂), Oxygen (O₂), Chlorine (Cl₂), Nitrogen (₂), Bromine (Br₂), Iodine (I₂)

(3) Tri atomic Molecule:
Molecule consist of three atoms is called tri atomic molecule.
e.g. H₂O, CO₂

(4) Poly atomic Molecule:
Molecule consist of many atoms is called poly atomic molecule.
e.g. CH₄, H₂SO₄, C₆H₁₂O₆, Ozone (O₃), Phosphorus₄, Sulphur₈

On Basis Of Types Of Atoms:
(5) Homo atomic Molecule:
Molecule consist of same type of atoms is called homo atomic molecule.
e.g. H₂, O₃, P₄, S₈

(6) Hetero Molecule:
Molecule consist of different type of atoms is called hetero atomic molecule.
e.g. CO₂, H₂O, NH₃

Q.3: Identify the differences among the following:
(a) Atom and Ion
(b) Molecule and Molecular ion
(c) Compound and Mixture
Ans: Difference between Atom and Ions

S.NO.	ATOM	ION
1.	Atom is the smallest particle of an element.	Ion is the smallest unit of ionic compound.
2.	Atom can or can not exist independently and take part in chemical reaction.	Ion can not exist independently and surrounded by oppositely charged ions.
3.	Atom is electrically neutral.	Ion has negative or positive charge.

Difference between Molecule and Molecular ion

S.NO.	MOLECULE	MOLECULAR ION
1.	Molecule is the smallest particle in a chemical element or compound that has chemical properties of that element or compound.	Molecular ion formed by gain and lose of electrons by a molecule.
2.	Molecule is always neutral.	Molecular ion have positive or negative charge.
3.	Molecule is stable unit.	Molecular ion is reactive species.
4.	Molecule is formed by the combination of toms.	Molecular ion formed by the ionization of a molecule.

Difference Between Compound And Mixture

S.NO.	COMPOUND	MIXTURE
1.	Compound is formed by a chemical combination of atoms of the elements.	Mixture formed by the simple mixing of the substances.
2.	Constituent of compound lose their identity and form a new substance with new properties.	Constituents of mixture retain their properties in mixture.
3.	Compounds have fixed composition by mass.	Mixtures have no fixed composition by mass.
4.	Components can not be separated by physical means.	The components can be separated by physical means.
5.	Every compound represented by chemical formula.	It consists of two or more components and does not show any chemical formula.
6.	Compounds have homogenous composition	Mixtures have homogenous as well as heterogeneous composition.
7.	Compounds have sharp and fixed melting points.	Mixtures do not have sharp and fixed melting points.

Q.4: Define the following terms:
(a) Gram atomic mass
(b) Gram molecular mass
(c) Gram formula mass
Ans: Gram Atomic Mass:
The atomic mass of an element expressed in gram is called gram atomic mass. It is also called 1 mole.
Example:

• 1 gram atom of oxygen = 16.00 g = 1 mole of oxygen atom
• 1 gram atom of carbon = 12.00 g = 1 mole of carbon atom
• 1 gram atom of nitrogen = 14.00 g = 1 mole of nitrogen atom

Its means 1 gram atom of different elements has different masses.

Gram Molecular Mass:
The molecular mass of an element or a compound expressed in gram is called gram molecular mass. It is also called 1 mole.
Example:

• 1 gram molecule of oxygen (O₂) = 32.00 g = 1 mole of oxygen molecule
• 1 gram molecule of water (H₂0) = 18.00 g = 1 mole of water
• 1 gram molecule of ethanol C₂H₅OH = 46.00 g = 1 mole of ethanol

Gram Formula Mass:
The formula mass of an ionic compound expressed in grams is called gram formula mass. It is also called 1 mole.
Example:

• 1 gram formula of NaCl = 58.5 g = 1 mole of sodium chloride
• 1 gram formula mass of CaCO₃ = 100 g = 1 mole of calcium carbonate

Q.5: Write down the chemical, empirical and molecular formula of the following?
Sulphuric acid, Carbon dioxide, Glucose, Benzene, Hydrogen peroxide, Acetic Acid
Ans: Compounds With Their Empirical And Molecular Formula:

Compounds	Empirical Formula	Molecular Formula
Sulphuric acid	H2SO4	H2SO4
Carbon dioxide	CO2	CO2
Glucose	CH2O	C6H12O6
Benzene	CH	C6H6
Hydrogen peroxide	HO	H2O2
Acetic Acid	CH2O	CH3COOH

Q.6: What is Free Radical?
Ans: FREE RADICALS:
Free radicals are atoms and group of atoms having number of unpaired electrons. It is represented by putting a dot over the symbol of an element.
For example: H^° , Cl^° ,H₃^°, C^°
Formation Of Free Radicals:
Free radicals are formed when homolytic breakage of bond between two atoms takes place by the absorption of heat or light energy. Free radical is very reactive chemical species.

Q.7: Describe relationship between empirical and molecular formula? Explain with examples.
Ans: Relationship Between Empirical and Molecular formula:
The empirical formula of a compound gives the simplest ratio of the number of different atoms present, whereas the molecular formula gives the actual number of each different atom present in a molecule. If the formula is simplified then it is an empirical formula. The molecular formula is commonly used and is an integral multiple (1,2,3 etc.) of the empirical formula.

The general statement relating molecular formula and the empirical formula is:

Molecular Formula = (Empirical Formula)n

OR

Molecular Formula = n x Empirical Formula

where n=1,2,3,etc

Example No.1: Benzene has molecular formula C₆H₆. Which has simplest ratio of hydrogen and carbon as follows:

C₆H₆

6:6

1:1

CH

So the empirical formula of benzene is CH and have simple ratio is 1:1 of atoms in molecule of benzene.

Example No.2: Glucose has molecular formula C₆H₁₂O₆ . It shows the ratio as follows:

C₆H₁₂O₆

6:12:6

1: 2: 1

C:H₂:O

So the empirical formula of glucose is CHO and have simple ratio 1:2:1 of atoms in molecule of glucose.

Q.8: Explain why hydrogen and oxygen are considered as element whereas water is compound?
Ans: Reason:
Hydrogen and oxygen are made up of same kind of atom hence these are considered as elements whereas water is made by the combination of different kinds of atoms such as hydrogen and oxygen, hence it is called as a compound and not an element.

BASIC DEFINITIONS

Q.9: Define:

1. Science
2. Chemistry
3. Matter , States Of Matters and Classification Of Matter
4. Atom
5. Substance
6. Valency
7. Compounds

Ans: 1. SCIENCE:
Word science comes from latin word “Scientia” which means “ knowledge, This knowledge is based on hypothesis observation and experiments of universal science.

2. CHEMISTRY:
Chemistry is the branch of science which deals with the properties, composition and structure of matter. Chemistry also deals with the changes involved in the matter.

3. MATTER:
Matter is all around us. Matter is simply defined as anything that has mass and occupies space.

States of Matter:
It is found in three common states:

1. Solid
2. Liquid
3. Gas
4. The plasma is also considered as fourth state of matter.

The different states of matter are due to difference of energy in increasing order.

Classification Of Matter:

4. ATOM:

• Matter is made up of smallest particles which are known as atom.
• Atoms are basic units of matter and definite structure of elements.
• Atoms are made up of three particles: proton, neutrons and electrons. Which are composed of even small particles.
• Neutron and proton are situated in nucleus and electrons are revolving around the nucleus.

5. SUBSTANCE:

• A piece of matter in pure form is termed as a substance.
• Every substance has a fixed or definite composition and specific properties.
• They are homogeneous in nature.
• Substances are elements and compounds.
• Example:
  Element: Tin, iron, sulphur, diamond or carbon, hydrogen, oxygen, silver)
  Compound: water, iron (II) sulfide, methane, Aluminum silicate. pure sugar (sucrose). table salt (sodium chloride). They are Chemically separable into their elements.

6. VALENCY:

• The Combining power of an element with other element is called valency.
• The valency depends upon the number of electrons in the outermost shell.
• Valency is the number of electron of an atom of an element can gain, lose or share.
• Example:
  (i) Hydrogen (H) has +1 valency.
  (ii) Oxygen (O ) has -2 valency.
  (iii) Aluminium (Al) has +3 valency.
  (iv) Carbon (C) has +4 and +2 valency etc.

7. Compounds:
The Compound is a substance formed when two or more elements are chemically bonded together in a fixed ratio by mass, As a result a new entirely different properties possessing substance formed.
The type of bonds holding elements may be:

• ionic bonds or
• covalent bonds

For Example:

• Ionic compounds:
  (i) Sodium Chloride (NaCl)
  (ii) Copper sulphate (CuSO₄)
  (iii) Potassium bromide (KBr) etc.
  
  
• Covalent compounds:
  (i) Water (H₂O)
  (ii) Methane (CH₄)
  (iii) Sulphuric acid (H₄SO₄) etc.

Q.10: Define element and its types?
Ans: Element:

• An Element is a substance made up of same type of atoms.
• Having same atomic number.
• It cannot be decomposed into Simple substances by ordinary chemical reaction.
• Elements occur in nature in free or combined form in solid, Liquid and gases states.
• Now 118 elements have been discovered.
• Example: Majority of elements are solids as copper, gold, zinc etc. Very few elements are liquid as mercury and bromine. Few elements are gases as hydrogen, oxygen and nitrogen.

Types Of Elements:
Elements are divided into metals, nonmetals and metalloids on the basis of their properties.

Metal:

• Metals are solid material.
• They are typically hard, shiny, malleable, fusible, and ductile.
• They have good electrical and thermal conductivity.
• e.g. iron, gold, silver, and aluminium, and alloys such as steel.

Non metals:

• Non metal is an element that doesn't have the characteristics of metal.
• They do not have ability to conduct heat or electricity.
• They do not have luster, or flexibility.
• e.g. An example of a nonmetal element is carbon.

Metalloids:

• Metalloid is an element whose properties are intermediate between those of metals and solid non-metals.
• They are semi conductors.
• e.g. arsenic, antimony, or tin.

Q.11: What are symbols Or How to write Symbol?
Ans: Symbol:
Symbol is an abbreviation to represent the name of elements. A symbol is taken from the name that elements from English , Latin, Greek and German.

• Symbols are usually one or two letter long.
• Every symbol starts with capital letter
  E.g. as carbon with C or sulphur as S.
• If symbol has second letter then start with capital and second will be in small letter
  E.g. as He for helium, Na for sodium, Cr for chromium.

Q.12: What is Chemical formula?
Ans: CHEMICAL FORMULA:
The compounds are represented by Chemical Formula as elements are represented by symbols with respect to valencies.

OR

The chemical formula represent the symbol of elements and ratios of elements to one another in a compound.

OR

Chemical formula tells us number of atoms of each element in a compound with symbols.
For Example:

1. Chemical formula of water is H₂O which indicates that 2 atoms of hydrogen combines with 1 atom of oxygen.
2. Chemical formula of ammonia NH₃ shows that one nitrogen atom combines with 3 atoms of hydrogen.

Q.13: Define mixture and its types?
Ans: MIXTURE:
When two or more elements or compounds physically combines without any fixed ratio is known as Mixture. The component substances retain their chemical properties. Mixtures can be separated again by physical methods, such as Filtration, Evaporation, Distillation and Crystallization. Mixture has variable composition.

Types of Mixture
There are two main types of mixtures, which are:

1. Homogeneous mixture and
2. Heterogeneous mixture.

Homogeneous mixture:
In a homogenous mixture all the substances are evenly distributed throughout the mixture, or It is uniform throughout, also called a solution.
Example: air, tap water, gold alloy, Salt water, blood etc.

Heterogeneous mixture:
In a heterogeneous mixture the substances are not evenly distributed or It has nonuniform distinct phases.
Example: chocolate chip cookies, pizza, rocks, soup, concrete, granite etc.

Test Yourself

Q.1: In which branch of chemistry analysis of quality and quantity of compounds studied:
Ans: Analytical Chemistry:
Analytical chemistry is the branch of chemistry which deals with separation and analysis of kind, quality and quantity of various components in given substance. It used in chromatography, electrophoresis and spectroscopy.

Q.2: What happens due to deficiency of bimolecules?
Ans: Deficiency or disorder of bimolecules cause diseases in living organisms (plants and animals).

Q.3: List some uses of salts in society?
Ans: Uses Of Different Salts:
1. Sodium Chloride (NaCl) is used in food flavouring. It is also used in the preparation of different chemicals in chemical industries.
2. Sodium nitrite (NaNO₂), Sodium sulphite (Na₂SO₃) and Sodium citrate (Na₃C₆H₅O₇) use as Food preservatives.
3. Silver Salts use in photography.
4. Ammonium sulphate [(NH₄)₂SO₄], Ammonium nitrate (NH₄NO₃) are used as Fertilizers in agriculture.
5. Plaster of Paris” (Calcium sulphate CaSO₄) uses in medical.

Q.4: Identify and list down examples of green chemistry in our environment?
Ans: Pesticides, Safer chemical (polyphenylsulfon), less hazardous chemical (poly carbons) and safer solvents are examples of green chemistry in our environment.