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Chemistry Notes Chapter 2 for Class 9

This is a discussion on Chemistry Notes Chapter 2 for Class 9 within the 9th forums, part of the Classes category; Q - 1) Sate the following laws: Law of conservation of Mass: “It states that in any chemical reaction the ...

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    Chemistry Notes Chapter 2 for Class 9

    Q - 1) Sate the following laws:

    Law of conservation of Mass: “It states that in any chemical reaction the initial weight of reacting substances is equal to the final weight of the products.”

    Law of Definite proportions: “It states that the different samples of the same compound always contain the same elements combined together in the same proportions by mass.”

    Law of Multiple proportions: “It states that if two elements combine to form more than one compound. The masses of one element that combine with a fixed mass of the other element are in the ratio of small whole numbers or simple multiple ratios.”

    Law of Reciprocal proportions: “It states that the two different elements separately combine with the fixed mass of third element, the proportions shall be either in the same ratio or simple multiple of it.”

    Q -2) State law of conservation of mass with Landolt’s experiments :

    Law of conservation of Mass: “It states that in any chemical reaction the initial weight of reacting substances is equal to the final weight of the products.”
    Landolt experiment: German Chemist H. Landolt tested different chemicals to verify Law of conservation of mass.
    1) He took H – shaped tube that has two limbs.
    2) He filled limbs A and B with Silver Nitrate (AgNO3) & Hydrochloric acid (HCl) respectively.
    3) The tube was sealed and weighted initially.
    4) The reactants were mixed by inverting and shaking the tube.
    5) After mixing the tube weigted again and he observed that weight remain same.
    Chemical Reaction: AgNO3 + HCl → AgCl + HNO3

    Q -3) State the law of Constant|Defenite proportion with example?

    Law of Definite proportions: “It states that the different samples of the same compound always contain the same elements combined togather in the same proportions by mass.”
    Example:Every sample of pure water, through prepared in loboratory or obtained from rain, river, or water pump cantains one part of Hydrogen (H) and eighgt parts of Oxygen (O). Like H2O = 2 : 16 or 1 : 8

    Q -4) State the law of Multiple proportion with example?

    Law of Multiple proportions: “It states that if two elemnts combine to form more than one compounds. The masses of one element that combine with a fixed mass of the other element are in the ratio of small whole numbers or simple multiple ratio.”
    Example: Carbon (C) form two stable compounds with Oxygen (O) namely carbon monooxide (CO) and carbon dioxide CO2.
    Compound Mass of Carbon (C) Mass of Oxygen(0) Ratio of Oxygen (0)
    CO 12 16 1
    CO2 12 32 2
    Q -5) State the law of Reciprocal proportion with example?

    Law of Reciprocal proportions: “It states that the two different elements separately combine with the fixed mass of third element, the proportions shall be either in the same ratio or simple multiple of it.”

    Example:
    When two elements Carbon (C) and Oxygen (O) sepratlely combine with fixed mass of Hydrogen (H) to form methane CH4 and water H4O.
    Ratio of H is 1 in CH4 & H2O
    Ratio of C is 3 in CH4 & CO2
    Ratio of O is 8 in H2O & CO2
    H
    CH4 H2O
    12 : 4 2 : 16
    3 : 1 CO2 1 : 8
    C O
    12 : 32
    3 : 8
    Q -6) What is Einstein theory? & Write reatiaon B/W mass & energy:
    Einstein Theory: The famous physicist and mathematicain Albert Einstien proposed the relation between mass and energy. i.e. “There is no detectable gain or loss of mass in a chemical reaction”.
    Mathematically E = mc2 where “E” is energy, “m” is mass and “c” is speed of light.

    Q -7) What is chemical reaction? Define and give example each of the following:

    Chemical Reaction: It is a change in which the compostion of substances is changed and new substances formed. It has five types as follows.

    (1) Decompostion Reaction: It is the reaction in which a compound or chemical substances break down to form two or more substances.
    Heat
    CaCO3 ======> CaO + CO3
    (2) Addition Reaction: It is the reaction in which two or more substances combine togather to form new substances.
    Example: CaO + CO3 ======> CaCO3
    Example: Na + Cl2 ======> 2NaCl

    (3) Single Displacement Reaction: It is the reaction in which one atom or a group of atoms of a compound replaced by another atom or group of atoms.

    Example: 2Na + 2H2O ======> 2NaOH + H2
    Example: Zn + 2HCl ======> ZnCl2 + H2
    (4) Double Displacement Reaction: It is the reaction in which two compounds exchange their partners to form new compounds.
    Example: NaCl + AgNO3 NaNO3 + AgCl
    Example: CaCl2 + Na2CO3 2NaCl + CaCO3
    (5) Combustion Reaction: It is the reaction in which substances react with either free oxygen or oxygen of air, with rapid release of heat and flame.
    Example: CH4 + O2 ======> CO2 + 2H2 + ∆H (Heat)
    Example: C + O2 ======> CO2 + ∆H (Heat)
    What is chemical reaction? Define & give one example each:
    (1) Addition reaction (2) Double Displacment reaction
    Chemical Reaction: It is a change in which the compostion of substances changes to forms new substances.
    (1) Addition Reaction: It is the reaction in which two or more substances combine togather to form new substances.
    Example: CaO + CO3 ======> CaCO3
    (2) Double Displacement Reaction: It is the reaction in which two compounds exchange their partners to form new compounds.
    Example: NaCl + AgNO3 ======> NaNO3 + AgCl
    Q - 8) What is chemical reaction? Define & give one example of each:
    (1) Combustion reaction (2) Single Displacment reaction
    Chemical Reaction: It is a change in which the compostion of substances is changed and new substances formed.
    (1) Combustion Reaction: It is the reaction in which substances react with either free oxygen or oxygen of air, with rapid release of heat and flame.
    Example: CH4 + O2 ======> CO2 + 2H2 + ∆H (Heat)
    (2) Single Displacement Reaction: It is the reaction in which one atom or a group of atoms of a compound replaced by another atom or group of atoms.
    Example: 2Na + 2H2O ======> 2NaOH + H2
    Q - 9) What is Empirical formula? Give an example:
    Empirical Formula: (E.F) The formula that describes the smallest or least ratio of the combining atoms of different elements presents in a molecule.
    Example: The empirical formula of Benzene is CH Mathmatically
    Example: The empirical formula of Glucose is CH2O E.F=(M.F.)/n
    Q - 10) What is Molecular formula? Give an example:

    Molecular Formula: (M.F) The formula that describes actual number and type of the combining atoms of all elements presents in a molecule.

    Example: The molecular formula of Benzene is C6H6 Mathmatically
    Example: The molecular formula of Glucose is C6H12O6 M.F=(E.F)_n
    Q - Define the following:
    Atomic mass Mole MolarMass Avogadro’s Number

    Atomic mass: It is the average mass of naturally occurring isotopes which is compared to the mass of one atom of carnob – 12 a.m.u.

    Mole: It is the amount of substances that contains as many elementary particales such as ( atoms, ions, molecules etc). It is denoted by n.
    Formula "n =" "m" /"M"

    Molar mass: It is the mass in grams of one mole of a substances. Such as (molecular mass, formula mas, atomic mass) etc.

    Avogadro’s Number: It is the constant number that is equal to "6.02 × " 〖"10" 〗^"23" of one mole of any substances. It is denoted by NA.
    Q - 11) Can one substances have the same empirical formula and molecular formula? Explain with examples:

    Ans: Yes, one substances can have the same empirical formula and molecular
    formula because they have the simplest and least whole number and have no difference between their molecular and empirical formulas.
    Example:
    Name Empirical Formula Molecular Formula
    Sodium Hydroxude NaOH NaOH
    Sugar C12H22O11 C12H22O11
    Methane CH4 CH4
    Potassium Nitrate KNO3 KNO3
    Q -12) What is chemical equation? What is a co-efficient and expression? Give and example of balance equaction:

    Chemical Equation: It is short hand method of describing the chemical reaction, in terms of symbols and formulae of the substances involved in a chemical reaction.

    Co – efficient: The number, in front of the formulas in a chemical equation is called a Co – efficient. It is present before molecule or atoms.

    Expression: the latters, (g), (l) and (s) are placed as subscript indicates the states of products and reactants.

    Balanced Equation:
    Example: MnO2
    2KClO3 (S) ======> 2KCl(s) + 3O2(g)
    Q -13) The value of carbon in periodic table is 12.011 a.m.u rather than 12.00 a.m.u. Explain it:
    Ans: The value of carbon in periodic table is 12.011 a.m.u rather than 12.00 a.m.u because naturally Corbon has two isotopes C – 12 with 98.889% and C- 13 with 1.111. Thus the atomic mass of Carbon (C) atoms becomes 12.011 a.m.u.
    "Avrage/Sum of Carbon isotopes "="12×98.889+13×1.111" /"100" "= 12.011a.m.u."
    Q -14) Differentiate Empirical formula and molecular formula:
    Empirical formula Molecular formula
    It describes smallest or least ratio of the elements in compound. It describes actual number and type of elements in compound
    Some compound may have same empirical formula.No, any two compounds may have the same molecular formula.
    Example: Empirical formula of Acetic acid and glucose is same as CH2O Example: Molecular formula of Acetic acid is CH3COOH and Glucose is C6H12O6
    Deffirences B/T:

    Molecular mass:

    1) The term molecular mass cannot be used with ionic compounds because there are no discrete molecule in ionic compounds.
    2) It is the sum of atomic masses of all atoms in a molecular formula of a substances.
    3) Molecular mass of CO2 is 44 a.m.u.

    Formula mass:

    1) The term formular mass can be used with either molecular compounds or ionic compounds.
    2) It is the sum of atomic masses of all atoms in a formula unit of a substances.
    3) Formula mass of NaCl is 58.5 a.m.u.

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