Question:
If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?
Answer:
1 mol of Carbon atoms = 12g
1 mol of atoms = No atoms = 6.023 × 1023 atoms⇒ 6.023 × 1023 carbon atoms = 12g
∴ mass of 1 carbon atom = 12g ÷ No = 12g / 6.023 × 1023 = 1.992 × 10-23 gram
Atoms and Molecules
Q 1.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Q 2.
What is gram-atomic mass of an element?
Q 3.
What is the chemical symbol for iron?
Q 4.
Define molecule. What are its important properties?
Q 5.
Define 'formula mass' of a compound.
Q 6.
Name the international organization who approves names of elements.
Q 7.
Write the chemical symbols of the following:
(i) Gold
(ii) Iron
(iii) Chlorine
(iv) Mercury
Q 8.
Name one element each which forms diatomic and tetra atomic molecule.
Q 9.
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 10.
Give four examples of diatomic molecules.
Q 11.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
Q 12.
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
Q 13.
Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas?
Q 14.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 16.
Write down the names of compounds represented by the following formulae:
(i) Al
2(SO
4)
3 (ii) CaCl
2 (iii) K
2SO
4 (iv) KNO
3 (v) CaCO
3
Q 17.
How many atoms are there in 0.25 mole of hydrogen ?
Q 18.
Which of the following statements is NOT true about an atom?
(a) Atoms are the building blocks from which molecules and ions are formed.
(b) Atoms cannot exist independently.
(c) Atoms are neutral in nature
(d) Atoms combine together to form matter that we can see, feel or touch.
Q 19.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 20.
What are polyatomic ions? Give examples?
Q 21.
Convert 12 g of oxygen gas into moles.
Q 22.
Who established the two important laws of chemical combinations?
Q 23.
Fill in the blanks:
The mass of 5 moles of ammonia (NH
3) is __________.
Q 24.
Name the element having following Latin names
(i) Stibium
(ii) Cuprum
(iii) Argentum
(iv) Natrium
(v) Stannum
(vi) Wolfram
(vii) plumbum
(viii) Kalium
Q 25.
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 26.
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 27.
What is the mass of
(a) 1 mole of nitrogen atoms?
(b) 4 moles of aluminium atoms (Atomic mass of aluminium = 27)?
(c) 10 moles of sodium sulphite (Na
2SO
3)?
Q 28.
State Law of constant proportions. Explain with an example.
Q 29.
Based on type of substance, how molecules are classified?
Q 30.
Calculate the formula unit masses of ZnO, Na
2O, K
2CO
3, given atomic masses of Zn = 65 u, Na = 23 u, K = 39 u, C = 12 u, and O = 16 u.
Q 31.
Magnesium and oxygen combine in the ratio of 3 : 2 by mass to form magnesium oxide. How much oxygen is required to react completely with 12 g of magnesium?
Q 32.
Fill in the blanks:
The mass of 1 mole of a substance is called its _____________.
Q 33.
Fill in the blanks:
_________ are building block of all matter.
Q 34.
How will you define chemical symbol?
Q 35.
Fill in the blanks:
An element has only one type of __________.
Q 36.
Fill in the blanks:
Hydrogen and oxygen combines to form H
2O and H
2O
2. These two compounds obey the law of ____________________.
Q 38.
(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 39.
Calculate the number of molecules of phosphorus (P
4) present in 31 gram of phosphorus.
Q 40.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 41.
What is the significance of a chemical symbol?
Q 42.
Which element has the smallest atom in size?
Q 43.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 44.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 45.
What is valency of an element?
Q 46.
Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium suphide
(iv) magnesium hydroxide
Q 47.
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 48.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Q 49.
What are ionic compounds?
Q 50.
Define mole. What is its significance?
