Question:
Which has more number of atoms, 100 grams of sodium or 100 grams of iron (given, atomic mass of Na = 23 u, Fe = 56 u)?
Answer:
We know that, 1 mol of atoms of an element has mass = gram atomic mass.
∴ mass of 1 mol of Na atoms = 23g
Or 23g of Na has = 1 mol of atoms
∴ 100g of Na = 100/23 = 4.35 moles
Similarly, 56g of Fe has = 1 mol of atoms
∴ 100g of Fe has = 100/56 = 2.17 moles
⇒ 100g of Na has more number of atoms than 100g of Fe.
Atoms and Molecules
Q 1.
What is the chemical symbol for iron?
Q 2.
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
Q 3.
Explain with example that law of conservation of mass is valid for chemical reactions.
Q 4.
Define 'formula mass' of a compound.
Q 5.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Q 6.
Name one element each which forms diatomic and tetra atomic molecule.
Q 7.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 8.
What is gram-atomic mass of an element?
Q 9.
Magnesium is two times heavier than C-12 atom, what shall be the mass of Mg atom in terms of atomic mass units? (Given mass of C-12 atom = 12u)
Q 10.
Define molecule. What are its important properties?
Q 11.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Q 12.
Convert 12 g of oxygen gas into moles.
Q 13.
What is valency of an element?
Q 14.
If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?
Q 15.
How many atoms are there in 0.25 mole of hydrogen ?
Q 16.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
Q 17.
Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
Q 18.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 19.
Write the chemical symbols of the following:
(i) Gold
(ii) Iron
(iii) Chlorine
(iv) Mercury
Q 20.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 21.
Fill in the blanks:
One mole of water contains ______________ molecules.
Q 22.
What is the molecular mass of a substance?
Q 23.
What are ionic compounds?
Q 24.
Which has more number of atoms, 100 grams of sodium or 100 grams of iron (given, atomic mass of Na = 23 u, Fe = 56 u)?
Q 25.
Find out number of atoms in 15 moles of He.
Q 26.
Calculate the number of aluminium ions present in 0.051 g of aluminium oxide.
(
Hint: The mass of an ion is the same as that of an atom of the same element. Atomic mass of Al = 27 u)
Q 27.
Fill in the blanks:
The mass of 5 moles of ammonia (NH
3) is __________.
Q 28.
Name the international organization who approves names of elements.
Q 29.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 31.
(i) What is the chemical formula of Water molecule?
(ii) What is its atomicity?
(iii) Calculate the ratio of masses of atoms of elements present in water molecule.
(iv) Calculate the ratio by number of atoms of elements present in water molecule.
Q 32.
Write the chemical formulae of the following. Also identify the ions present.
(a) Magnesium chloride
(b) Calcium oxide
(c) Copper nitrate
(d) Aluminium chloride
(e) Calcium carbonate.
Q 33.
What is gram-molecular mass of a substance?
Q 34.
How many moles are there in 4.6 gms of Sodium(Na)?
Q 35.
Convert into moles: (a) 12 g of oxygen gas (b) 20 g of water (c) 22 g of carbon dioxide
Q 36.
Calculate the number of molecules of phosphorus (P
4) present in 31 gram of phosphorus.
Q 37.
Give one major drawback of Dalton's atomic theory of matter.
Q 38.
Write the formulae of the following compounds. Also name the elements present in them.
(a) Water
(b) Ammonia
(c) Methane
(d) Sulphur dioxide
(f) Ethanol
Q 39.
Calculate the molecular masses of the following compounds :
(a) Methanol, CH
Q 40.
If one mole of nitrogen molecules weighs 28 g, calculate mass of one molecule of nitrogen in grams.
Q 41.
(a) What is meant by the 'molar mass'of a substance ? State the unit in which molar mass usually expressed.
(b) Calulate the molar masses of the following substances. Write the results with proper units
(1) Ozone molecule, O
Q 42.
What are the laws of chemical combinations?
Q 43.
Who established the two important laws of chemical combinations?
Q 44.
Fill in the blanks:
___________ is the combining capacity of an element.
Q 45.
Give four examples of diatomic molecules.
Q 46.
Give examples of triatomic molecules.
Q 47.
Calculate the mass percentage of Carbon(C) , Hydrogen (H) and Oxygen (O) in one molecule of glucouse (C
6H
12O
6).
(Atomic mass of C = 12u, H = 1u and O = 16u)
Q 48.
What is the difference between a cation and an anion ? Explain with examples. Using this information, write down the formulae of:
(i) Sodium sulphide
(ii) Copper nitrate
Q 49.
How many atoms are present in one gram atomic mass of a substance ?
Q 50.
Give an example to show Law of conservation of mass applies to physical change also.
