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Atoms and Molecules Test - 44

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Atoms and Molecules Test - 44
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  • Question 1
    1 / -0

    A 78.0 g sample of an unknown compound contains 12.4 g of hydrogen.  What is the percent by mass of hydrogen in the compound?

    Solution

    % of HH==12.478×100\dfrac{12.4}{78}\times100=16=16%

  • Question 2
    1 / -0

    Law of conservation of mass is also known as :

    Solution
    Law of Conservation of mass is also known as Law of indestructibility because the mass is conserved and it proves that matter is always conserved and can never be destroyed.
  • Question 3
    1 / -0

    16.8 g of metal carbonate on thermal decomposition gave 8 g of metallic oxide and 8.8 g of carbon dioxide. They follow:

    Solution
    Metal carbonate (16.8 g) Metallic oxide (8 g)+Carbon dioxide (8.8 g)Metal\ carbonate\ (16.8\ g) \rightarrow  Metallic\ oxide\ (8\ g) + Carbon\ dioxide\ (8.8\ g)

    The total mass of reactants (metal carbonate) is 16.8 g. 
    The total mass of products (metallic oxide + carbon dioxide) is 8 + 8.8 = 16 g.

    Since the total mass of reactants and products remains the same, this reaction follows the law of conservation of mass.
  • Question 4
    1 / -0
    During any chemical change, the total mass of the products is equal to the total mass of reactants. This is a statement according to:
    Solution
    According to the law of conservation of mass, the mass of products in a reaction must be equal to the mass of reactants, which can be stated as "mass is neither created nor destroyed during a chemical reaction".
  • Question 5
    1 / -0
    AgNO3+NaClAgCl+NaNO3AgNO_3+NaCl\rightarrow AgCl+NaNO_3. In this reaction, mass of AgNO3AgNO_3 and NaClNaCl is equal to the mass of AgClAgCl and NaNO3NaNO_3. Then this chemical reaction satisfies:
    Solution
    Law of conservation of mass states that "In a chemical reaction,  mass of the products will always be equal to the mass of the reactants".
  • Question 6
    1 / -0
    The percentage of copper and oxygen in samples of CuO obtained by different methods were found to be the same. This illustrates the law of:
  • Question 7
    1 / -0
    When magnesium is burnt in air, the weight of magnesium :
    Solution
    When magnesium is burnt in air, the weight of magnesium increases due to the formation of MgOMgO.

    2Mg+O22MgO2Mg+O_2\rightarrow 2MgO
  • Question 8
    1 / -0
    2Pb(NO3)22PbO+X+O22Pb(NO_3)_2\rightarrow 2PbO+X+O_2

    What is X'X' in the given balanced chemical equation?
    Solution
    Chemical equation is given by:

    2Pb(NO3)2(s)Δ 2PbO(s)+4NO2(g)+O2(g)2Pb(NO_3)_2 (s) \xrightarrow{\Delta} 2PbO (s) + 4NO_2 (g) + O_2 (g) 

    When heated, lead(II) nitrate crystals decompose to lead(II) oxide, oxygen and we can see brown fumes of nitrogen dioxide.
  • Question 9
    1 / -0
    Magnesium + Oxygen \longrightarrow     Magnesium Oxide + Oxygen
     48.6 g        +     50.0 g \longrightarrow     80.6 g                   +      ? 

    Predict the mass of oxygen that will be left over after the reaction of 48.6 grams of magnesium with 50.0 grams of oxygen. 
    Solution
    According to law of conservation of mass, the total mass of reactants must equal the total mass of products 
    If we assume the mass of oxygen as XX g then,

    Total mass of reactants = Total mass of products 

    48.6+50=80.6+X48.6+50=80.6+X

    X=18 gX = 18\ g
  • Question 10
    1 / -0
    The chemical equation is balanced to satisfy one of the following laws in chemical reactions. This law is known as the:
    Solution
    Basically, the chemical equations are the symbolic representations of chemical reactions in which the reactants and products are expressed in terms of their respective chemical formulae. These equations satisfy the law that matter can be changed from one form into another but the total amount of mass remains constant. According to the law of conservation of mass, the mass of products in a reaction must be equal to the mass of reactants so the balancing of equations is done to obey this law.
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