NCERT
Solution, MCQs, Study Notes, Q & A
Q1:
Name the international organization who approves names of elements.
Q2:
How do we know the presence of atoms if they do not exist independently for
most of the elements?
Answer: Atom join in different way to form matter(neutral molecules or
ion) that we are able to touch, feel and see.
Q3:
Give an example to show Law of conservation of mass applies to physical change
also.
Ans: When ice melts into water, is a physical change. Take a piece of ice in
small flask, cork it and weight it (say Wice gm). Heat the
flask gently and ice (solid) slowly melts into water (liquid). Weigh the flask
again (Wwater gm). It is found there is no change in the weight
i.e. Wice= Wwater.
Heat(Δ)
Ice
----------➜ Water
This shows law of conservation of mass holds true for physical changes.
Q4:
Explain with example that law of conservation of mass is valid for chemical
reactions.
Ans: According to this law, total mass of the products (chemicals produced)
is equal to the total mass of the reactants (chemicals take part in reaction).
e.g. Carbon combines with Sulphur to form Carbon disulphide. The mass of
reactants i.e. carbon and sulphur is same mass of products (carbon disulphide).
Carbon + Sulphur -----➜ Carbon DiSulphide
C +
S -----➜ C2S
1g +
5.34g = 6.34 g
LHS =
RHS
Q5:
Is there any exception to law of conservation of mass?
Ans: Later after atoms were discovered, it was found during nuclear
reactions this law does not hold good. In a nuclear reaction, some of the mass
gets converted into energy, as given by famous Einstein's mass-energy
relationship (E = mC2). The law was rechristened as Law of
conservation of mass and energy.
Q6.In
a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The
products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium
ethanoate. Show that these observations are in agreement with the law of
conservation of mass.
sodium
carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water
Ans: Mass of sodium carbonate (Na2CO3) =
5.3 g Mass of ethanoic acid (CH3COOH) = 6g
Mass of carbon dioxide (CO2) = 2.2g Mass of Water (H2O)
= 0.9 g
Mass of sodium ethanoate (CH3COONa) = 8.2 g
Total mass of reactants = 5.3g + 6g = 11.3g
Total mass of products = 2.2g + 0.9 g + 8.2g = 11.3g
Since, Total mass of reactants = Total mass of products, the observations
in this reaction are in agreement with the law of conservation of mass.
Q7 If
12 g of carbon is burnt in the presence of 32 g of oxygen, how much carbon
dioxide will be formed?
Ans: Given, the reaction is carbon + oxygen → carbon dioxide
Mass of carbon = 12g Mass of oxygen = 32g
Mass of carbon dioxide (CO2) = xg
Since the reaction is in agreement with law of conservation of mass, then
Total mass of reactants = Total mass of products
i.e. 12g + 32g = x i.e. x = 44g
∴ mass of carbon
dioxide (CO2) formed = 44g
Q.8.
A 0.24 g sample of compound of oxygen
and boron was found by analysis to contain 0.096 g of boron and 0.144 g of
oxygen. Calculate the percentage composition of the compound by weight.
Ans: Given, mass of boron = 0.096 g
mass of the oxygen = 0.144g
mass of the sample compound (boron+oxygen) = 0.24 g
According to Law of definite proportions, boron and oxygen are in fixed
ratio in the given compound.= 0.096 : 0.0144 = 2:3
% of boron = mass of boron × 100 / mass of compound = 0.096 ×
100/0.24 = 40%and % of oxygen = mass oxygen × 100 / mass of
compound = 0.144 × 100/0.24 = 60%
Q.9.
When 3.0 g of carbon is burnt in 8.00 g oxygen, 11.00 g of carbon dioxide is
produced. What mass of carbon dioxide will be formed when 3.00 g of carbon is
burnt in 50.00 g of oxygen? Which law of chemical combination will govern your
answer?
Answer: The given reaction is
Carbon + Oxygen ➜
Carbon Dioxide
3g +
8g = 11g
⇒ Total mass of
reactants = Total mass of products
∴ Law of conservation
of mass is obeyed.
It also shows that carbon dioxide (CO2) contains carbon and
oxygen in fixed ratio i.e. 3:8 which follows Law of Constant proportion.
⇒ 3g of carbon (C) will
react with 8g of oxygen (O) to give 11g of carbon dioxide (CO2).
⇒ Remaining oxygen (50
-8 = 42g) will not participate in the reaction.
Q10 :
Magnesium and oxygen combine in the ratio of 3 : 2 by mass to form magnesium
oxide. How much oxygen is required to react completely with 12 g of magnesium?
Answer: Magnesium (Mg) and Oxygen (O) combine in the ratio = 3:2 to form
compound magnesium oxide (MgO). It follows Law of Constant proportions.
⇒ 3g of Mg combines
with = 2g of O.
∴ 12g of Mg combines with = 2 × 12/3 = 8g of O.Q.11.Why are Dalton's symbol not used in chemistry?
Answer:Dalton was the first scientist to use the symbol for the name of the elements a specific sense but it was difficult to memorize and in uses so Dalton's symbol are not used in chemistry
Related post to IX(9th) Atoms and Molecules
2 comments:
It is so gooooood............but other notes is not here???
It is so gooooood............but other notes is not here???
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