Class 9th Chemistry Unit 1 Question And Answer
Class 9th Chemistry Unit 1 Question And Answer On Newsongoogle By Bilal Articles
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unit 1
Q1: Define Science.
Ans: The knowledge that provides understanding of this world and how it works, is called science.
Q2: Define industrial chemistry and analytical chemistry.
Ans: Industrial Chemistry: The branch of chemistry that deals with the manufacture of chemical compounds on commercial scale, is called industrial chemistry. It deals with the manufacturing of fertilizers, textile, soap, agricultural products paints and paper etc.
Analytical Chemistry: It is the branch of chemistry which deals with the separation and analysis of a sample to identify its components: The separation is carried out prior to qualitative and quantitative analysis. In this branch different techniques and instruments used for analysis are also studied.
Q3: How can you differentiate between organic and inorganic chemistry?
Ans: Organic Chemistry: Organic chemistry is the study of covalent compounds of carbon and hydrogen (hydrocarbons) and their derivatives
Inorganic Chemistry: Inorganic chemistry deals with the study of all elements and their compounds except those of compounds of carbon and hydrogen (hydrocarbons) and their derivatives.
Q4: Give the scope of bio chemistry.
Ans: vast. Its applications are in the fields of medicines, food, science The scope of biochemistry is very vast. Its and agriculture etc.
Q5: How does homogeneous mixture differ from heterogeneous mixture?
Ans: Homogeneous mixture: Mixture that has uniform composition throughout are called homogeneous mixtures e.g. air Heterogeneous mixture: Heterogeneous mixture is that in which composition is not uniform throughout e.g. soil
Q6: What is the relative atomic mass? How it is related to gram?
Ans: The relative atomic mass of an element is the average mass of atoms of that element as compared to 1/12th the mass of one atom of carbon-12 isotope. Its unit is called atomic mass unit with symbol “amu”. One atomic mass unit is 1/12th the mass of one atom of carbon-12, When this atomic mass unit is expressed in grams, it is as 1-amu = 1.66×10-24g.
Q7: Define empirical formula with example.
Ans: The simplest type of formula which shows the simplest whole number ratio of atoms present in a compound is called empirical formula. For example, glucose has simplest ratio 1:2:1 of carbon, hydrogen and oxygen respectively. Hence its empirical formula is CHâ‚‚O.
Q8: State three reasons why do you think air is a mixture and water a compound.
Ans: The three reasons are as:
(i) Water is a compound because it is formed by chemical combination of hydrogen and oxygen whereas air is formed by simple mixing of different gases.
(ii) Water has fixed ratio between masses of hydrogen and oxygen, whereas in air ratio between masses of component gases is not fixed.
(iii) Water has definite melting and boiling points whereas air does not have any fixed melting and boiling point.
Q9: Explain why Hydrogen and Oxygen are considered as elements. Whereas water a compound?
Ans: Hydrogen and oxygen are elements because:
(i) In these substances same type of atoms with same atomic number are present whereas water is made up of hydrogen and oxygen atoms having different atomic numbers.
(ii) Hydrogen and oxygen cannot be decomposed into simpler substances by chemical means whereas water can be decomposed into hydrogen and oxygen by electrolysis.
Q10: What is the significance of the symbol of an element?
Ans: Symbol is the international recognition of an element. With the help of symbols, scientists form the formula of different compounds. Symbol of clements also helps to write and understand chemical equation for different chemical reactions. The periodic table is based on symbols of different elements. We should say without symbols Chemistry would not be easy to understandable.
Q11: State the reasons, Soft drink is a mixture whereas water is a compound?
Ans: Cold drink is a true solution of sugar and water in which CO2 is dissolves through pressure. We can separate these components by physical methods. It does not have definite melting and boiling point. That’s why we can say cold drink is a mixture. Whereas, water is formed by chemical combination of hydrogen and oxygen.
Q12: Define atomic mass unit. Why is it needed?
Ans: The unit for relative atomic mass is called atomic mass unit. Its symbol is “amu”. One atomic mass unit is (1/12)th the mass of one atom of carbon-12″. The mass of an atom is too small to be determined practically. So, to determine the “atomic mass of various elements atomic mass unit is needed.
Q13: Differentiate between molecular mass and formula mass. Which of the following will be molecular formula?
Ans: The sum of atomic masses of all the atoms presents 3 in-one molecules of a molecular mass c.g. molecular mass of water is 18 amu. The sum of atomic masses of all atoms present in one formula unit of a substance is called formula mass e.g. formula mass of sodium chloride is 58,5 amu. Hâ‚‚O and H_{2}*S*O_{4} are molecular formula of molecular compounds water and Sulphuric acid respectively.
Q14: Differentiate between homoatomic and heteroatomic molecules with examples.
Ans: The difference between homoatomic and heteroatomic-molecules can described as:
Homoatomic molecules: A molecule containing same type of atoms is called homoatomic molecule. For example Hydrogen (H2), Oxygen (O2), Ozone (O3) and sulphur (Ss) are homoatomic molecules.
Heteroatomic molecules: A molecule consisting of different type of atoms is-called heteroatomic molecule. For example NH3, H2O and CO2 are heteroatomic molecules.
Q15: In which one of the following cases the number of hydrogen atoms is more?
Ans: No. of moles of hydrogen in 1 mole of HCl = 1 mole
No. of moles of hydrogen in 2 moles of HCI = 2 moles
Whereas;
No. of moles of hydrogen in 1 mole of NH3 = 3 moles
Hence 1 mole of NH3 contains 3 moles of hydrogen will have more hydrogen atoms than 2 moles of hydrogen present in 2 moles of HCl.
Q16: What is Chemistry?
Ans: The branch of science which deal with the composition, structure, properties and reactions of matter is called Chemistry.
Q17: Define Physical Chemistry.
Ans: The branch of f Chemistry that deals with the relationship between the composition and physical properties of matter along with the change in them is called Physical Chemistry between th
Q18: Define Bio Chemistry.
Ans: It is the branch of chemistry in which we study the of substances found in living organisms. ure, composition and chemical reactions
Q19: What is Nuclear Chemistry?
Ans: Nuclear Chemistry is the branch of fchemistry, which deals with the reactivity, nuclear process and fchemi properties. The main concern of this branch is with the energy of atom and its uses in daily life.
Q20: What is Environmental Chemistry?
Ans: The branch of Chemistry that deals with the components of the environment and the effects of the human activities on the environment.
Q21: What is matter? Show classification of matter.
Ans: Anything that has mass and occupies space is called matter. Matter can exist in any of the three physical states; solid, liquid or gas. Classification of Matter can be identify in following chart as:
Q22: What is valency?
Ans: The combining capacity of an element with other elements is called valency. For example valency of carbon is 4.
Q23: What is meant by variable valency?
Ans: Some elements show more than one combining power (valency) that is called variable valency. For example, in ferrous sulphate (FeS*O_{4}) the valency of iron is 2 whereas, in ferric sulphate Fe 2 (S*O_{4}) 3 the valency of iron is 3.
Q24: What is a radical?
Ans: An atom or a group of atoms that have some charge and keeps in contact during a chemical reaction is called a radical e.g. Hydronium H_{3} O^ + and carbonate.CO C * O_{3} ^ – 2 during a
Q25: What is Atomic Number and Mass Number?
Ans: The number of protons present in the nucleus of an atom of an element is called its atomic number.
It is represented by symbol “Z”. For Example carbon atom has 6 protons, so its atomic number (Z) is 6. The sum of protons and neutrons present in the nucleus of an atom of an element is called mass number or nucleon number. It is represented by symbol “A”. For Example carbon atom has 6 protons and 6 neutrons, so its mass number (A) is 12.
Q26: What is molecular formula? How molecular formula is derived from empirical formula?
Ans: The formula of molecular substances that shows actual number of atoms of each element present
in a molecule of that substance is called molecular formula e.g. molecular formula of benzene is C6H6. Molecular formula is derived from empirical formula by the following relationship: Molecular formula = (Empirical formula)n Where n is 1, 2, 3 and so on, e.g. molecular formula of benzene C_{6}*H_{6} is derived from the empirical formula CH where the value of n is 6.
Q27: What is ion? What are its types?
Ans: An atom or group of atoms having a charge on it is called ion. There are two types of ions i.e. cation and anion.
i. Cation: An atom or group of atoms having positive charge on it is called cation. Cation are formed when an atom loses electrons from its outermost shell. Following equations show the formation of cations from atoms:
ii. Anion: An atom or group of elements that has negative charge on it, is called anion. Anion is formed by the gain or addition of electrons to an atom. The following examples show the formation of an anion
Q28: Define free radicals? How they are generated?
Ans: Free radicals are atoms are group of atoms possessing an odd (unpaired) electron. It is represented by putting a dot over the symbols of an element. For example, H, CL, H3C. Free radicals are generated by the hemolytic (equal) breakage of the bond between two atoms when they absorb heat or light energy.
Q29: What is Avogadro number?
Ans: Avogadro number is a collection of 6.02 x 1023 particles. It is represented by symbol NA. Hence, the 6.02×1023 number of atoms, molecules or formula units are called Avogadro number that is equivalent to one “Mole” of respective substance.
Q30: Define a mole.
Ans: A mole is defined as the amount (mass) of a substance that contains 6. 02×1023 number of particles (atoms) molecules or formula units. It is abbreviated as “mol”. For Example, 6.02×1023 carbon
atoms 1 mole of carbon. It can be defined as the atomic mass, molecular mass or formula mass of a substance expressed in grams is called mole. e.g., Atomic mass of carbon expressed as 12g = 1 mole of carbon.
Q31: Write the composition of following mixtures.
i) Air
ii) Soil
iii) Milk
iv) Brass
Ans: Air is a mixture of nitrogen, oxygen, carbon dioxide, noble gases and moisture.
Soil: Soil is a mixture of sand, clay, mineral salts, water and air.
Milk: Milk is a mixture of eat, water, sugar, fat, proteins, mineral salts and Vitamins.
Brass: Brass is a mixture of copper and zinc metals.
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