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# 3:Uncertainty in measurement Class 11 Notes | EduRev

## Class 11 : 3:Uncertainty in measurement Class 11 Notes | EduRev

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CBSE TEST PAPER-03
CLASS - XI CHEMISTRY (Basic Concepts of Chemistry)
Topic: - Uncertainty in measurement
Marks: 20
1. What is the difference between precision and accuracy? 
2. What do you understand by significant figures? 
3. How many significant figures are present in 
(a) 4.01 × 10
2
(b) 8.256
(c) 100
4. State law of definite proportions. 
5. Explain law of multiple proportions with an example. 
7. Write Postulates of Dalton’s atomic theory. 
8. Define one atomic mass unit (amu). 
9. Calculate molecular mass of – 
C 2H 6, C 12H 22O 11, H 2SO 4, H 3PO 4
10. What is formula mass? 
7
Page 2

CBSE TEST PAPER-03
CLASS - XI CHEMISTRY (Basic Concepts of Chemistry)
Topic: - Uncertainty in measurement
Marks: 20
1. What is the difference between precision and accuracy? 
2. What do you understand by significant figures? 
3. How many significant figures are present in 
(a) 4.01 × 10
2
(b) 8.256
(c) 100
4. State law of definite proportions. 
5. Explain law of multiple proportions with an example. 
7. Write Postulates of Dalton’s atomic theory. 
8. Define one atomic mass unit (amu). 
9. Calculate molecular mass of – 
C 2H 6, C 12H 22O 11, H 2SO 4, H 3PO 4
10. What is formula mass? 
7
CBSE TEST PAPER-03
Topic: - Uncertainty in measurement
Ans1: Precision means the closeness of various measurements for the same quantity.
Accuracy is the agreement of a particular value to the true value of the result.
Ans2: Significant figures are meaningful digits which are known with certainty. The
uncertainty in experimental or the calculated value is indicated by mentioning the
number of significant figures.
Ans3: (a) 4.01 × 10
2
– Three
(b) 8.256 – Four
(c) 100 – One
Ans4: Law of definite proportions states that a given compound always contains exactly
the same proportion of elements by weight.
Ans5: The law of multiple proportions rays that if two elements can
combine to form more than one compound, the masses of one
element that combine with a fixed mass of other element are
in a ratio of small whole numbers. e.g. hydrogen and oxygen
can combine to form water as well as hydrogen peroxide.
Here, the masses of oxygen (16g & 32g) which combine with a fixed mass of
hydrogen (2g) bear a simple ratio i.e., 16:32 = 1:2.
Ans6: According to Avogadro’s law, equal volumes of gases at the same temperature and
pressure should contain equal number of molecules.
Ans7  Postulates of Dalton’s atomic theory –
8
Page 3

CBSE TEST PAPER-03
CLASS - XI CHEMISTRY (Basic Concepts of Chemistry)
Topic: - Uncertainty in measurement
Marks: 20
1. What is the difference between precision and accuracy? 
2. What do you understand by significant figures? 
3. How many significant figures are present in 
(a) 4.01 × 10
2
(b) 8.256
(c) 100
4. State law of definite proportions. 
5. Explain law of multiple proportions with an example. 
7. Write Postulates of Dalton’s atomic theory. 
8. Define one atomic mass unit (amu). 
9. Calculate molecular mass of – 
C 2H 6, C 12H 22O 11, H 2SO 4, H 3PO 4
10. What is formula mass? 
7
CBSE TEST PAPER-03
Topic: - Uncertainty in measurement
Ans1: Precision means the closeness of various measurements for the same quantity.
Accuracy is the agreement of a particular value to the true value of the result.
Ans2: Significant figures are meaningful digits which are known with certainty. The
uncertainty in experimental or the calculated value is indicated by mentioning the
number of significant figures.
Ans3: (a) 4.01 × 10
2
– Three
(b) 8.256 – Four
(c) 100 – One
Ans4: Law of definite proportions states that a given compound always contains exactly
the same proportion of elements by weight.
Ans5: The law of multiple proportions rays that if two elements can
combine to form more than one compound, the masses of one
element that combine with a fixed mass of other element are
in a ratio of small whole numbers. e.g. hydrogen and oxygen
can combine to form water as well as hydrogen peroxide.
Here, the masses of oxygen (16g & 32g) which combine with a fixed mass of
hydrogen (2g) bear a simple ratio i.e., 16:32 = 1:2.
Ans6: According to Avogadro’s law, equal volumes of gases at the same temperature and
pressure should contain equal number of molecules.
Ans7  Postulates of Dalton’s atomic theory –
8
1. Matter consists of indivisible atoms.
2. All the atoms of a given element have identical properties including atomic mass.
Atoms of different element differ in mass.
3. Compounds are formed when atoms of different elements combine in a fixed ratio.
4. Chemical reaction involves reorganization of atoms. These are neither created nor
destroyed
Ans8: One atomic mass unit (amu) is defined as a mass exactly equal to one – twelfth the
mass of one carbon – 12 atom.
Ans9:
2 6
(2 12) (6 1) 30 C H = × + × =
12 22 11
2 4
3 4
(12 12) (22 1) (11 16) 342
(2 1) 32 (4 16) 98
(1 3) 31 (4 16) 98
C H O
H SO
H PO
= × + × + × =
= × + + × =
= × + + × =
Ans10:  When a substance does not contain discrete molecules as their constituent units and
have a three dimensional structure, formula mass is used to calculate molecular
mass which is sum of all the atomic masses of atom present in the formula.
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