Class 11 Ch. 1 Some Basic Concept of Chemistry Part 2

3. In this part we are going to learn about

4. In the last presentation we learnt about Nature of matter
and started about significant figures. A small clip on
Significant figures (SF) in the next slide will make you
understand the term in more detail about;
Addition, Subtraction
Multiplication and Division of SF

5. Uncertaintyin Measurements

7. Rounding off SF along with Addition and
Subtraction of Significant figures

8.  Question 1
Round off up to 3 significant figure the
below numbers
(a) 4.135
(b) 5.125
Answer
By following the rounding rules ,we get
(a) 4.14
(b) 5.12
Question 2
Express the following in the scientific notation
with 2 significant figures-
(a) 0.0023
(b) 586,00
(c) 100.0
Answer
(a) 2.3 × 10-3
(b) 5.9 × 10-4
(c) 1.0 × 102
Question 3
Round 451.45 to four, three, and two significant
digits
Answer
(a) 451.4
(b) 451
(c) 450

10. Laws of Chemical Combination is divided mainly into

14. Some more Ex

17.  In chemistry, the law of multiple proportions states that if two
elements form more than one compound between them, then the
ratios of the masses of the second element which combine with a
fixed mass of the first element will always be ratios of small whole
numbers. This law is sometimes called Dalton's Law, named after
John Dalton, the chemist who first expressed it.
 For example, Dalton knew that the element carbon forms two
oxides by combining with oxygen in different proportions. A fixed
mass of carbon, say 100 grams, may react with 133 grams of oxygen
to produce one oxide, or with 266 grams of oxygen to produce the
other. The ratio of the masses of oxygen that can react with
100 grams of carbon is 266:133 = 2:1, a ratio of small whole
numbers.

18. Find out the ratio for ?
 SO2 and SO3
 H2O and H2O2

20.  The law of multiple proportions is best demonstrated using
simple compounds. For example, if one tried to demonstrate it
using the hydrocarbons decane (chemical formula C10H22) and
undecane (C11H24), one would find that 100 grams of carbon
could react with 18.46 grams of hydrogen to produce decane or
with 18.31 grams of hydrogen to produce undecane, for a ratio
of hydrogen masses of 121:120, which is hardly a ratio of "small"
whole numbers.
 The law fails with non-stoichiometric compounds and also
doesn't work well with polymers and oligomers.

21. Brief Descriptionof Laws

23. Gay Lussac’s discovery of integer ratio in volume
relationship is actually the law of definite proportions by
volume. The law of definite proportions, stated earlier,
was with respect to mass. The Gay Lussac’s law was
explained properly by the work of Avogadro in 1811.

24. Avogadro's law (sometimes referred to as Avogadro's hypothesis or Avogadro's principle)
is an experimental gas law relating the volume of a gas to the amount of substance
of gas present.
The law is a specific case of the ideal gas law. A modern statement is:
Avogadro's law states that "equal volumes of all gases, at the same
temperature and pressure, have the same number of molecules."
Note that in the Fig. given each box contains equal number of molecules. In fact,
Avogadro could explain the above result by considering the molecules to be polyatomic.
If hydrogen and oxygen were considered as diatomic as recognized now, then the above
results are easily understandable.

25. Avogadro’s proposal was published in the French Journal de Physique.
In spite of being correct, it did not gain much support.

26. In the next part we will lookabout Dalton’s atomictheory