9th Class Chemistry Chapter 1 Fundamentals of Chemistry Short Questions Answer
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The branch of chemistry that deals with the manufacturing of chemical compounds on commercial scale is called industrial chemistry. It deals with the preparation of basic chemicals such as oxygen, chlorine, ammonia, caustic soda, nitric acid and sulphuric acid etc.
Analytical Chemistry is the branch of chemistry that deals with the separation and analysis of a sample to identify its components. This separation is carried out before qualitative and quantitative analysis.
Organic Chemistry is the branch of chemistry that deals with the study of structure and properties of natural and synthetic organic compounds. Organic compounds are hydrocarbons (compounds of carbon and hydrogen) and their derivatives e.g. Benzene, methane, chloroform etc.
Inorganic Chemistry is the branch of chemistry that deals with the all elements and compounds except hydrocarbons and their derivatives e.g. ammonia, silica and metals etc.
The scope of biochemistry lies in many fields such as medicine, food science and agriculture etc.
A mixture which has uniform composition throughout is called homogeneous mixture.
Homogeneous mixtures include air, gasoline and ice-cream etc.
A mixture which does not have uniform composition throughout is called heterogeneous mixture.
Heterogeneous mixtures include soil, rock and wood etc.
Relative Atomic Mass:
Relative atomic mass of an element is the average mass of an atom of that element as compared with 1/12th the mass of an atom of carbon – 12 isotope. Relative atomic mass of an element is related to grams as follows:
1amu = 1.66 x 10⁻²⁴ g
The type of formula which shows the simplest whole number ratio of atoms or ions present in one molecule or formula unit of a substance is called its empirical formula.
The empirical formula of glucose is CH₂O because it has the simplest ration of 1:2:1 of carbon, hydrogen and oxygen atoms respectively.
(i). Water is a compound because it is formed by the chemical combination of hydrogen and oxygen whereas air is a mixture because it is formed by the simple mixing of different gases such as nitrogen, oxygen and argon etc.
(ii). Air as a whole does not have any chemical formula whereas water has chemical formula H₂O.
(iii). In air different gases retain their physical and chemical properties but in case of water hydrogen and oxygen which are the two components of water lose their identity and water has entirely different properties from its constituents, hydrogen and oxygen.
Hydrogen and oxygen are considered elements because in these substances same types of atoms with same atomic number are present whereas water is a compound because it is formed by the chemical combination hydrogen and oxygen. Moreover, hydrogen and oxygen are elements because they cannot be broken down into simpler substances by simple physical or chemical methods and water is a compound because it can be broken down into its components hydrogen and oxygen by electrolysis.
A symbol is used to refer an element or its atom or its mole in general.
Symbols for the elements are the alphabets of the language of chemistry.
Use of symbols saves our time because instead of writing the full names of elements we use their abbreviated forms (short names).
With the use of symbols it becomes easy to write chemical formulae and hence chemical equations and reactions can be described very easily and efficiently.
(i). Soft drink is a mixture because it is formed by the simple mixing of different substances such as water, sugar, carbon dioxide etc. whereas water is a compound because it is formed by the chemical combination of hydrogen and oxygen.
(ii). Soft drink as a whole does not have any chemical formula whereas water has chemical formula H₂O.
(iii). In Soft drink different components retain their identities but in case of water hydrogen and oxygen which are the two components of water lose their identity and water has entirely different properties from hydrogen and oxygen.
(iv). The components of soft drinks can be separated by simple physical methods which shows that it is a mixture. But the components of water cannot be separated by simple physical methods which proves that water is compound.
He and H₂
Ans: He and H₂ both are elements.
CO and C
Ans: CO is a compound known as carbon monoxide while Co is an element known as cobalt.
Water and Milk
Ans: Water is compound made up of two elements hydrogen and oxygen having formula H₂O while milk is a mixture of water, sugar, fats, proteins, mineral salts and vitamins.
Gold and Brass
Ans: Gold is an element while brass is a mixture of two metals copper and zinc.
Iron and Steel
Ans: Iron is an element while steel is a mixture made up iron, carbon and some other metals such as chromium, nickel and manganese, etc.
Atomic mass unit:
The unit which is used to express the relative atomic mass of an element is called atomic mass unit. It is represented by amu. One atomic mass unit is equal to 1/12th the mass of one atom of C-12. It is represented by ‘amu’.
The mass of atoms are too small to be determined practically. Therefore, to determine the atomic masses of different elements relative atomic mass unit is required.
Zinc + Copper
Ans: When Zn and Cu are mixed together it forms a mixture. If both are combined together and heated then they form an alloy (mixture of two or more than two metals) known as brass.
Water + Sugar
Ans: When water and sugar are mixed together a homogenous mixture is formed which is known as sugar solution or syrup.
Aluminum + Sulphur
Ans: When aluminum and Sulphur are mixed together and heated, they form a compound known as aluminum sulphide as follows:
Iron + Chromium + Nickel
Ans: When iron, chromium and nickel are mixed together in a specific proportion and heated together then a mixture (alloy) is formed known as Nichrome. Nichrome is a type of steel.
H₂O, NaCl, Kl, H₂SO₄?
The sum of the atomic masses of all the atoms present in one molecule of a covalent/molecular compound is called its molecular mass. The term molecular mass is used for covalent compounds because they exist as molecules. Its unit is amu.
Molecular mass of H₂O:
= 1 x 2 + 1 x 16 = 2 + 16 = 18 amu
Molecular mass of CO₂:
=1 x 12 + 3 x 16 = 12 + 32 = 44 amu
The sum of the atomic mass of all the atoms present in one formula unit of an ionic compound is called its formula mass. The term formula mass is used for the ionic compounds because they exist as formula units. Its unit is amu.
Formula mass of NaCl:
= 1 x 23 + 1 x 35.5 = 58.5 amu
Formula mass of KCI:
= 1 x 39 + 1 x 35.5 = 74.5 amu
Note; Smaller the number of moles, small will be number of particles.
Given mass of Al = 10g
No. of moles Al = 10/27 = 0.37
No. of atoms of Al = number of moles x 6.02 x 10²³
= 0.37 x 6.02 x 10²³ = 2.23 x 10²³ atoms
Given mass of iron = 10
No. of moles of iron = 10/56 = 0.178
No. of atoms of Fe = 0.178 x 6.02 x 10²³ = 1.07 x 10²³ atoms
Thus aluminium has greater number of atoms.
Known mass of water = 9g
No. of moles of water = 9/18 = 0.5
No. of molecules of water = 0.5 x 6.02 x 10²³ = 3.01 x 10²³
Known mass of sugar (C₁₂H₂₂O₁₁) = 9 g
No. of moles of sugar = known mass of sugar/molar mass of sugar = 9/342 = 0.26
No. of molecules of sugar = 0.26 x 6.01 x 10²³ = 1.58 x 10²² molecules
Known mass of NaCI = 1g
No. of moles of NaCI = 1/58.5 = 0.017
No. of formula units of NaCI = 0.017 x 6.02 x 10²³ = 1.02 x 10²²
Known mass of KCI = 1 g
No. of moles of KCI = 1/39 + 35.5 = 0.013
No. of formula units of KCI = 0.013 x 6.02 x 10²² = 8.01 x 10²¹
Thus NaCI have greater number of formula units.
The molecules which are made up of only one type of atoms are called homoatomic molecules.
H₂, N₂, O₂, F₂ etc.
The molecules which are made up of two or more than two types of atoms are called heteroatomic molecules.
H₂O, CO₂, C₆H₁₂O₆ and C₆H₆ etc.
No. of moles of hydrogen in 1 mole of HCI = 1 mole
No. of moles of hydrogen in 2 mole of HCI = 2 mole
No. of hydrogen atoms in 2 mole of HCI = 2 x 6.02 x 10²³ = 1.204×10²⁴ atoms
No. of moles of hydrogen in 1 mole of NH₃ = 3 moles
No. of hydrogen atoms in 1 mole of NH₃ = 3 x 6.02 x 10²³ = 1.804 x 10²⁴ atoms
Hence 1 mole of NH₃ contains more hydrogen atoms than 2 moles of HCI