Class 9 Science CBSE Problems for Atoms and Molecules

Given below are the Class 9 Science CBSE Problems for Atoms and Molecules
a) Short questions
b) Long answer type questions
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Short Answer Questions:

1) Convert into mole:
12 g of oxygen gas
22 g of carbon dioxide
2) What is molecular weight? Explain with example.
i) Write formulas for ionic compounds formed from:
a) Na and F,
b) Na and O,
c) Mg and F
d)   AI and C
ii)  Write formulas for:
a) Aluminum sulfide
b) Strontium fluoride
c) Titanium (IV) oxide
d) Calcium bromide
4) How many moles of AI atoms are needed to combine with 1.58 moles of O atoms to make aluminum oxide, AI2O3?
5) What is the volume of 32 g of sulphur dioxide measured at STP?
6) How many grams of sodium will have the same number of atoms as 6 grams of magnesium? (Na = 23, Mg = 24).
7) How many grams of Chromium
(molar mass Cr = 52 g/mol) are there in 85 g of C2S3?
8) Which has more number of atoms: 100 grams of sodium or 100 grams of iron (Given atomic mass of a = 23 u and F = 56 u)
9) A compound of nitrogen and oxygen has the formula NO. In this compound, there are 1.143 g of oxygen for each 1.000g of nitrogen. A different compound of nitrogen and oxygen has the formula NO2. How many grams of oxygen would be combined with each 1.000g of nitrogen in NO2?
10) How many moles of nitrogen atoms are combined with 8.60 mol of oxygen atoms in dinitrogen pentoxide, N2O5
11) Calculate the volume occupied by 2.8 g of N2 at TP.
12) How much weight of carbon dioxide is present in same volume which is occupied by 4.0 grams of oxygen? Volumes are measured at normal temperature and pressure. (NTP)
13) What is the mass of 0.5 mole of water (H2O). (Atomic masses: H = 1u, O = 16u)
14) How many moles of sulphur atoms ad oxygen atoms are present in one mole each of H2SO4, H2O3 and SO2?
15) What is the percentage composition of the elements in ammonia, NH3? (at. Mass: H = 1,  = 14)
16) Calculate the theoretical percentage composition of N2O3.
17) 10 gram of CaCO3 on heating gave 4.4g of CO2 and 5.6 of CaO. Show that these observations are in agreement with the law of conservation.
18) In which of the following, the number of hydrogen atoms is more:
a) 3 moles of H2O
b)10 moles of HCI
19) If we decompose 50g of water by passing electricity through it, how many grams of oxygen and hydrogen we obtain?
20) Hydrogen and oxygen combine I the ratio of 1: 8 by mass to form water. What mass of oxygen gas would be required to react completely with 3g of hydrogen gas?
21) Calculate the number of molecules in 32 grams of oxygen gas and 14 grams of nitrogen.
22) Calculate the mass of a sample of iron metal that would contain 0.250 moles of iron atoms.
23) Calculate the number of atoms in a 0.123-gram sample of aluminum foil.

Long Answer Questions:

1) Calculate the formula mass of each of the following and round your answer to the nearest 0.1 u.
a) NaHCO3
b) K2Cr2O7
c) (NH4)2CO3
d) AI2 (SO4)3
e) CuSO4.5H2O
2) Calculate the molar mass of the following substances.
Ethyne, C2H2
Sulphur molecule, S8
Phosphorus molecule, P4 (atomic mass of phosphorus = 31)
Hydrochloric acid, HCI
Nitric acid, HNO3
3) Calculate the number of aluminum ions present in 0.051 g of aluminum oxide (AI2O3).
(Atomic mass: AI = 27 u, O = 16 u)
4) (I) Write the chemical formulas for the following compounds:
a) Copper (I) oxide,
b) Potassium peroxide
c) Mercury (I) bromide,
d) Iron (III) carbonate,
e) Sodium hydrobromite.
(II) Give the name for each of the following acids:
a) HBrO3,
b) HBr,
c) H3PO4,
e) HIO3
5) (I) Calculate both the average mass of a single molecule of carbon dioxide and glucose and the molecular weight of these compounds.
(II) Determine the number of carbon atoms in 0.500 grams of carbon dioxide, CO2.
6) (I) 1.375g of cupric oxide was reduced by heating in a current of hydrogen and the weight of copper that remained was 1.098g. in another experiment 1.179g of copper was dissolved in nitric acid and resulting copper nitrate converted into cupric oxide by ignition. The weight of cupric oxide formed was 1.476g. Show that these results illustrate the law of constant proportion.
(II) in an experiment, 1.288 g of copper oxide was obtained from 1.03 g of copper. In another experiment, 3.672 g of copper oxide gave, on reduction, 2.938 g of copper. Show that these figures verify the law of constant proportions.
7) Calculate the following quantities:
Mass, in grams 1.73 mol CaH2
Moles of Mg (NO3)2 in 3.25 g of this substance
Number of molecules in 0.245 mol CH3OH
Number of H atoms in 0.585 mol C4H10.
Number of moles of AI are in 2.16 mol of AI2O3
8) (i) Distinguish between an atom and a molecule.
(ii) Differentiate between atom and ion.


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