Saturday, December 3, 2011

CBSE WORKSHEET FOR SA_II Ch03 Atoms and Molecules

1. Fill in the blanks
(a) In a chemical reaction, the sum of the masses of the reactants and products remains unchanged. This is called ————.
(b) A group of atoms carrying a fixed charge on them is called ————.
(c) The formula unit mass of Ca3 (PO4)2 is --------------------
(d) Formula of sodium carbonate is ———— and that of ammonium sulphate is ——

2. Compute the difference in masses of 103 moles each of magnesium atoms and magnesium ions.
(Mass of an electron = 9.1×10–31 kg)

3. Which has more number of atoms? 100g of N2 or 100 g of NH3

4. Compute the number of ions present in 5.85 g of sodium chloride.

5. A gold sample contains 90% of gold and the rest copper. How many atoms of gold are present in one gram of this sample of gold?

6. What are ionic and molecular compounds? Give examples.

7. Compute the difference in masses of one mole each of aluminum atoms and one mole of its ions. (Mass of an electron is (9.1×10–28 g). which one is heavier?

8. A silver ornament of mass ‘m’ gram is polished with gold equivalent to 1% of the mass of silver. Compute the ratio of the number of atoms of gold and silver in the ornament.

9. A sample of ethane (C2H6) gas has the same mass as 1.5 ×1020

10. What is the fraction of the mass of water due to neutrons?

11. Does the solubility of a substance change with temperature? Explain with the help of an example.

12. Calculate the number of moles of magnesium present in a magnesium ribbon weighing 12 g. Molar atomic mass of magnesium is 24g mol-1

13. Verify by calculating that
(a) 5 moles of CO2 and 5 moles of H2O do not have the same mass.
(b) 240 g of calcium and 240 g magnesium elements have a mole ratio of 3:5.

14. A sample of vitamin C is known to contain 2.58 ×1024 oxygen atoms. How many moles of oxygen atoms are present in the sample?

15.If bromine atom is available in the form of, say, two isotopes 7935Br (49.7%) and 8135Br (50.3%), calculate the average atomic mass of bromine atom.

Related post to 9th Atoms and Molecules
CBSE Test paper-1                                                        CBSE Test paper-2           CBSE Test paper-3
Numerical based on mole concept                                   Solved questions For FA-3
Self-evaluation on Mole concept                                     Question bank By CBSE Pathshala For CBSE


J Sunil said...

Question: When 4.2gram of sodium hydrogen carbonate is added to a solution of hydrochloric acid weighing 10g . it is observed that 2.2gram of carbon dioxide is released into the atmosphere .The residue left behind is found to weigh 12gram . Show that these observation are in agreement with a law of conservation of mass.
Solution: According to the law of conservation of mass " Mass can neither be created nor be destroyed "
which means that mass in a chemical reaction should remain conserved i.e. Total mass of reactant should be equal to the total mass of product.
The balanced equation for the reaction between sodium hydrogen carbonate and hydrochloric acid is as follows :-
NaHCO3 + HCl → CO2 + NaCl + H2O
Mass of NaHCO3 = 4.2 g
Mass of HCl = 10g
Hence the total mass of reactant is (4.2+ 10)g = 14.2 g
Mass of CO2 = 2.2g
Mass of residue = 12g
Hence the total mass of product is (2.2 + 12)g = 14.2g
since total mass of reactant = total mass of product therefore no mass is loss or no mass is created during the reaction which means the reaction is in agreement with law of conservation of mass.
Hence the observations are in agreement with law of conservation of mass.
Question: Differentiate between molar mass and molecular mass
Solution: The molecular mass of a substance is the sum of the atomic masses of all the atoms present in a molecule of that substance. It is expressed in atomic mass unit (u). Thus, to calculate the molecular mass, the mass of all the atoms present in it are added.
For example, Molecular mass of glucose C6H12O6 is = 6 (C) + 12 (H) + 6 (O) = 180 amu.
The molar mass, on the other hand is the mass of one mole (or 6.023 X 1023) particles of that substance. The molar mass of a substance is numerically equal to the atomic mass or the molecular mass of the substance in ‘u’ and is always measured in grams. For example, the molar mass or mass of 6.023 X 1023molecules of glucose is 180g. Similarly, mass of 6.023 X 1023 atoms of sodium or molar mass of sodium is 23g, but its atomic mass is 23u.
Question: what is the difference between 2N and N2
Solution: 2N means two molecules of Nitrogen atom.
N2 means two atoms of nitrogen in its one molecules.
The number written in subscript of the element symbol represents its number of atoms. The The number written in starting of the element symbol represents its number of molecules.
Question: Calculate the number of molecules present in a drop of chloroform (CHCl3) weighing 0.0239g.
Solution: molecular mass of CHCl3 = 12 + 1 +3 x 35.5 = 119.5g
119.5g contain = 6.022 x 1023 molecules
therefore, 0.0239g contain = 6.022 x 1023 x 0.0239 / 119.5 = 12.044 x 1019 molecules

J Sunil said...

Any one post answer for the benefit of student community in comment section

Asif Ahamed said...

Good 😃

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