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Dear students, prepare for chemistry class 9th chapter 1 long questions. These important long questions are carefully added to get you best preparation for your 9th class chemistry ch. 1 exams.
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Question: 1
Define Compund. How is it Classified?
Answer: 1
Compound: " Compound is a substance made up of two or more elements chemically combined together in a fixed ratio by mass." As a result of this combination elements lose their own properties and produce new substance that have entirely different properties. Compounds can't be broken down into its constituent elements by simple physical methods. 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. Classification of Compound: Compounds can be classified as ionic or covalent. Ionic compounds do not exist in independent molecular form they form a three dimensional crystal lattice , in which each ion is surrounded by oppositely charge ions. These oppositely charged ions attract each other very strongly , as a result ionic compounds have high melting and boiling points .These compounds are represented by formula mass units e.g NaCL, KBr, C^4SO^4 The covalent compounds, mostly exiting in molecular from A molecule is a true representative of the covalent compound and its formula is called molecular formula e.g. H^2O, HCL H^SO4 etc
Question: 2
Calculate the number of moles, number of molecules and the number of atoms present in 6 grams of water
Answer: 2
The known mass of water= 6g Molar mass of H^2O = 18g Number of moles =mass of substance/molar mass of the substance = 6/18 =0.33 mol Number of molecules = No.of moles x Avogadro's no =0.33x6.02x10^23 =1.98x10^23 molecules The number of molecules contained in 6 grams of water are 1.98 X 10^23 As we know 1 molecule of water consists of 3 atoms, therefore: Number of atoms = 3x1.98 x 10^23 =5.94x10^23
Question: 3
What is relative atomic mass and atomic unit. Relative Atomic Mass:
Answer: 3
Relative Atomic Mass : The relative atomic mass of an element is the average mass of the atoms of that element as compared to 1/12th the mass of an atom of carbon car-12 isotope Explanation: As we know that the mass of an atom is too small to be determined pratically However, certain instruments enable us to determine the ratio of the atomic masses of the element. Based on Carbon-12 standard, the mass of an atom of carbon is 12 units and 1/12th of it comes to be 1 unit. When we compare atomic masses of other elements with atomic mass of carbon-12 atom, they are expressed as relative atomic masses of those elements. Atomic Mass Unit: The unit for relative atomic masses is called atomic mass unit with symbol `amu'. One atomic mass unit is 1/12 the mass of one atom of carbon -12th. When this atomic mass unit is expressed in grams, it is: 1 amu =1.66 x 10^-24 g Example : Mass of a proton = 1.0073amu or 1.672 x10^-24g Mass of neutron = 1.0087 amu or 1.674 x 10^-24 Mass of electron = 5.486 x 10^-4 amu or 9.106x 10^-28 g
Question: 4
What is Avogadro's Number ? Give examples
Answer: 4
Avogadro's Number: Avogadro's number is a collection of 6.02 x 10^23 particle. It is represented by symbol `NA'. Hence the 6.02x10^23 number of atoms, molecule or formula units is called Avogafro's number that is equivalent to one `mole' of respective substance. In simple words 6.02x10^23 particles are equal to one mole as twelve eggs are equal to one dozen. Thus, 6.02 x 10^23 atoms of elements or 6.02 x 10^23 molecules of molecular substance or 6.02 x 10^23 formula units of ionic compounds are equivalent to 1 mole. Examples : 1- One mole of water is made up of 2 atoms of hydrogen and 1 atom of oxygen and be nce 2x6.02x10^23 atoms of hydrogen and 6.02 x 10^23 atoms of oxygen constitute one mole of water. 2- One formula unit of sodium Chloride consists of one sodium ion and one chloride ion. So there are 6.02 x10^23 Cl ions in one mole of sodium chloride. Thus, the total number of ions in 1 mole of NACL is 12.04 x 10^23 or 1.204 x10^24
Question: 5
What do you know about Atomic Number and Mass Number ? Explain them with examples.
Answer: 5
Atomic Number : The atomic number of an element is equal to the number of protons present in the nucleus of its atoms. It is represented by symbol `z'. As all atoms of an element have the same number of protons in their nuclei , they have the same atomic number . Hence, each element has a specific atomic number termed as its identification number. Examples: 1- All hydrogen atoms have 1 proton , their atomic number is z=1. All atoms in carbon have 6 protons , their atomic number is z=6. 2- In oxygen all atoms have 8 protons having atomic number z=8 Mass Number : 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'. It is calculated as A= z=n , where n is the number of neutrons. Each proton and neutron has 1 amu mass. Examples: 1- Hydrogen atom has one proton and no neutron in its nucleus, its mass number A= 1+0=1 2- Carbon atom has 6 protons and 6 neutrons, hence its mass number A= 12. ELEMENT NO.OF NO. OF ATOMIC MASS PROTONS NEUTRONS NUMBER NUMBER Z A Hydrogen 1 0 1 1 Carbon 6 6 6 12 Nitrogen 7 7 7 14 Oxygen 8 8 8 16 Fluorine 9 10 9 19 Sodium 11 12 11 23 Some Elements along with their Atomic and Mass Numbers
Question: 6
Calculate the gram molecule(number of moles) in 40 g of Phosphoric acid H^3PO^4.
Answer: 6
Solution: Given mass of H^3PO^$= 40g Molecular mass of H^3PO^4 = 98gmol^-1 putting these values in equation Number of = mass of a substance/molar mass of the substance (mole) = 40/98 = 0.408 Thus, 4o grams will contain 0.408 gram molecule (mol) of H^3PO^4
Question: 7
What is science and chemistry and what are its significance in daily life?
Answer: 7
Science: the knowledge that provides understanding of this world and how it works is called science.
Chemistry: the branch of science which deals with the composition, structure , properties and reactions of matter is called chemistry.
Significance of chemistry:
  • Chemistry facilitates us in petrochemical products
  • Chemistry helps in medicines and drugs
  • Soaps and detergents are minerals of chemistry
  • Chemistry helps in production of plastic, paints , pigments, medicines, pesticides and insecticides.

Question: 8
Discuss the branches of chemistry and also its use
Answer: 8
Physical chemistry:
Definition: the branch of chemistry that deals with the relationship between the composition and physical properties of matter along with the changes in them is called physical chemistry
Uses: the properties such as structures of atoms or formation of molecules, behavior of gases, liquids and solids and the study of the effect of temperature of radiation on matter , all are studied under this branch.
Question: 9
Define matter and substance.
Answer: 9
Matter: matter is defined as " anything that has mas and occupies space".
Example: our bodies , benches ,walls , houses ,boards etc are examples of matter .
Question: 10
What is mixture? give its types.
Answer: 10
Mixture; mixture is defined as
"impure matter is called mixture".
Types of mixtures:
a mixture is of two types
  1. Homogeneous mixture
  2. Heterogeneous mixture

Question: 11
What are elements? explain with examples.
Answer: 11
Definition: "it is a substance made up of same type of atoms having same atomic number and it cannot be decomposed into simplest substance by ordinary chemical means".
Question: 12
How to write the symbol?
Answer: 12
Representation: elements are represented by symbols.
Question: 13
What is valency? explain it with example
Answer: 13
Valency: " it is combining capacity an element with other element."
it depends upon the number of electrons in the outer most shell
Question: 14
Define compound . Give the types of compounds
Answer: 14
Definition: " compound is a substance made up of two or more elements chemically combined together in a fixed ration by mass."
Example: carbon dioxide(CO2) is formed by combining carbon and oxygen chemically in a fixed ratio 12:32 or 3:8 by mass. Similarly, water is a compound formed by a chemical combination between hydrogen and oxygen in a fixed ration of 1:8 by mass
Question: 15
Define molecular formula and givve some examples?
Answer: 15
Definition: " a molecule is a true representative of the covalent compound and its formula called molecular formlua".

Question: 16
Differentiate between compound and mixture
Answer: 16
Formation: it is formed by a decimal combination of atoms of the elements.
Identity of constituent: the constituent lose their identify and form a new substance having different properties from them.
Composition ratio: compound always have fixed ratio of composition by mass.
Separation: the components of compounds cant be separated by physical means.
Representation: every compound is represented by chemical formula.
Composition: compounds have homogenous composition.
Melting point: compound have sharp and fixed melting points.
Question: 17
Write a note on atomic number and atomic mass
Answer: 17
Atomic number : " the atomic number of an element is equal to the number of protons present in the nucleus of its atoms".
Representation: it is represented by Z
Note: each element have specific atomic number termed as its identification number.
Example: Hydrogen Z=1, Oxygen Z=8, Carbon Z=6, Sulphur Z= 16
Question: 18
Explain in details, how to write chemical formula?
Answer: 18
Introduction: compounds are represented by chemical formulae as elements are represented by symbols.
Question: 19
Define relative atomic mass? explain
Answer: 19
Expression in grams:
Example: Mass of proton= 1.0073amu or 1.672*10-24g
Mass of neutrons= 1.0087amu or 1.674*10-24g
Mass of electron= 5.486*10-4amu or 9.106*10-28g
Question: 20
What are empirical formula, formula unit and molecular formula? explain with example
Answer: 20
Empirical formula:
Definition: "it is the simplest whole number ratio of atoms present in a compound."
Example: the covalent compound silica(sand) has simplest ration of 1: 2 of silicon and oxygen respectively. Therefore, its empirical formula is SiO2 . Similarly, glucose has 2 simplest ration 1:2:1 of carbon , hydrogen and oxygen, respectively. Hence , its empirical formula is CH2O
Question: 21
Explain molecular mass and formula mass.
Answer: 21
Molecular mass:
Definition: " the sum of atomic masses of all the atoms present in one molecule of a molecular substance is its molecular mass".
Example: molecular mass Cl2=2(35.5)=71.0amu
molecular mass H2O= 2(1)+16=18.0amu
molecular mass of CO2=12+2(16)=44amu
Question: 22
What are ions, give the types of ions.
Answer: 22
Definition: " ions is an atom or group of atoms having charge on it".
Types of ions:
Ions are of two types
  1. Anions
  2. cations
Question: 23
What are molecules? describe their types.
Answer: 23
Definition of molecules: a molecule is formed by chemical combination of atoms.: it is simplest unit of a substances which shows all the properties of the substance and can exist independently".
Types of molecules: there are different types of molecules depending upon the number and types of atoms combining. Few types are discussed here.

Question: 24
Define and explain gram atomic mass, gram molecular mass and gram formula mass.
Answer: 24
As we know that all substances are made up of atoms, molecules or formula units. Their masses are referred to as atomic mass, molecular mass and formula mass respectively and are expressed in amu. but these masses can also be expressed in other units as well. When masses are expressed in grams , they are termed as following
  1. Gram atomic mass
  2. Gram molecular mass
  3. Gram formula mass
Question: 25
What are Avogadro's number? explain it with example and define mole.
Answer: 25
Avogadro's number :Definition:' the 6.02*1023 number of particles (atom, molecules or ions of substance formula unit is called Avogadro's number".The counting of these particles is not possible for the chemists. The concept of Avogadro's number facilitated the counting of particles mass of a substance.Symbol: Avogadro's number is represented by "NA".Value: 6.02*1023