Q. 1. A student performs a titration with different burettes and finds titre values of 25.2 mL, 25.25 mL, and 25.0 mL. The number of significant figures in the average titre value is (2010)
Ans. Sol. The least significant figure in titre values is 3.
Average titre value = = 25.1
The number of significant figures in average titre value will also be 3.
Q. 2. Silver (atomic weight = 108 g mol–1) has a density of 10.5 g cm–3. The number of silver atoms on a surface of area 10–12 m2 can be expressed in scientific notation as y × 10x. The value of x is : (2010)
Ans. Sol. d =
⇒ 10.5 g/cc means in 1 cc ⇒ 10.5 g of Ag is present.
Number of atoms of Ag in 1 cc ⇒ 1
In 1 cm, number of atoms of Ag =
In 1 cm2, number of atoms of Ag =
In 10–12 m2 or 10–8 cm2, number of atoms of Ag
= 1. 5 × 107
Hence x = 7
Q. 3. The difference in the oxidation numbers of the two types of sulphur atoms in Na2S4O6 is (2011)
Ans. Sol.
Difference in oxidation number = 5 – 0 = 5
Q. 4. If the value of Avogadro number is 6.023 × 1023 mol–1 and the value of Boltzmann constant is 1.380 × 10–23 J K–1, then the number of significant digits in the calculated value of the universal gas constant is (JEE Adv. 2014)
Ans. Sol. R = NA × k = 6.023 × 1023 × 1.380 × 10–23
= 8.312 which has 4 significant figures
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1. What are some basic concepts of chemistry? |
2. What is the importance of understanding basic chemistry concepts for JEE Advanced exam? |
3. What is stoichiometry in chemistry? |
4. How does atomic structure relate to chemistry? |
5. What is the periodic table and why is it important in chemistry? |
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