Class 9 Science CBSE Problems for Atoms and Molecules

Short Answer Questions

Question 1
Convert into mole:
12 g of oxygen gas
22 g of carbon dioxide
Question 2
What is molecular weight? Explain with example.
Question 3
(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) Aluminium sulphide
(b) Strontium fluoride
(c) Titanium (IV) oxide
(d) Calcium bromide
Question 4
How many moles of AI atoms are needed to combine with 1.58 moles of O atoms to make aluminum oxide, AI₂O₃?
Question 5
What is the volume of 32 g of sulphur dioxide measured at STP?
Question 6
How many grams of sodium will have the same number of atoms as 6 grams of magnesium? (Na = 23, Mg = 24).
Question 7
How many grams of Chromium
(molar mass Cr = 52 g/mol) are there in 85 g of C₂S₃?
Question 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)
Question 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?
Question 10
How many moles of nitrogen atoms are combined with 8.60 mol of oxygen atoms in dinitrogen pentoxide, N₂O₅
Question 11
Calculate the volume occupied by 2.8 g of N₂ at TP.
Question 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)
Question 13
What is the mass of 0.5 mole of water (H₂O). (Atomic masses: H = 1u, O = 16u)
Question 14
How many moles of sulphur atoms ad oxygen atoms are present in one mole each of H₂SO₄, H₂O₃ and SO₂?
Question 15
What is the percentage composition of the elements in ammonia, NH3? (at. Mass: H = 1, = 14)
Question 16
Calculate the theoretical percentage composition of N₂O₃.
Question 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.
Question 18
In which of the following, the number of hydrogen atoms is more:
(a) 3 moles of H₂O
(b)10 moles of HCI
Question 19
If we decompose 50g of water by passing electricity through it, how many grams of oxygen and hydrogen we obtain?
Question 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?
Question 21
Calculate the number of molecules in 32 grams of oxygen gas and 14 grams of nitrogen.
Question 22
Calculate the mass of a sample of iron metal that would contain 0.250 moles of iron atoms.
Question 23
Calculate the number of atoms in a 0.123-gram sample of aluminium foil.

Long Answer Questions

Question 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
Question 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
Question 3
Calculate the number of aluminium ions present in 0.051 g of aluminium oxide (AI₂O₃).
(Atomic mass: AI = 27 u, O = 16 u)
Question 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,
(d) HCIO
(e) HIO₃
Question 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.
Question 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.
Question 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
Question 8
(i) Distinguish between an atom and a molecule.
(ii) Differentiate between atom and ion.

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