Question:
What is meant by a chemical formula ? Write the formulae of one element and one compound.
Answer:
A chemical formula represents the composition of a molecule of the substance in terms of the symbols of the elements present in the molecule.the formula of element is H
Atoms and Molecules
Q 1.
Write the full form of IUPAC.
Q 2.
Name the following compounds. Also write the symbols/formulae of the ions present in them :
(a) CuSO
Q 3.
How many moles are there in 34.5 g of sodium ? (Atomic mass of Na = 23 u)
Q 4.
Calculate the mass in grams of 0.17 mole of hydrogen sulphide, H
Q 5.
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 6.
Calculate the number of molecules of phosphorus (P
4) present in 31 gram of phosphorus.
Q 7.
What are the building blocks of matter ?
Q 8.
What is meant by atomicity ? Explain with two
Q 9.
Calculate the molecular masses of the following compounds :
(a) Methane, CH
Q 10.
Calculate the molecular mass of ethanoic acid, CH
Q 11.
State whether the following statements are true or false :
(a)A sodium ion has positive charge because it has more protons than a neutral atom
(b)A chloride ion has negative charge because it has more electrons than a neutral atom.
Q 12.
Fill in the following blanks with suitable words :
(a)The particle which is formed by the gain of electrons by an atom is called...........
(b)The particle which is formed by the loss of electrons by an atom is called............
(c)The particle which is formed by the loss or gain of electrons by an atom is called..........
(d)A potassium ion has positive charge because it contains less...........than...........
(e) A sulphide ion has negative charge because it contains less...........than..........
Q 13.
What is an ion ? How is an ion formed ? Explain with the help of two examples of different ions.
Q 14.
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 15.
What is the mass of 0.2 mole of oxygen atoms ?
Q 16.
Find the mass of 2 moles of nitrogen atoms.
Q 17.
If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.
Q 18.
(a) What is meant by 'a mole of carbon atoms' ?
(b)(b) Which has more atoms, 50 g of aluminium or 50 g of iron ? Illustrate your answer with the help of calculations.
(Atomic masses : A1 = 27 u ; Fe = 56 u)
Q 19.
What are the laws of chemical combinations?
Q 20.
Who established the two important laws of chemical combinations?
Q 21.
State Law of constant proportions. Explain with an example.
Q 22.
Fill in the blanks:
_________ are building block of all matter.
Q 23.
Name the element having following Latin names
(i) Stibium
(ii) Cuprum
(iii) Argentum
(iv) Natrium
(v) Stannum
(vi) Wolfram
(vii) plumbum
(viii) Kalium
Q 24.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 25.
(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 26.
What is the molecular mass of a substance?
Q 27.
What is molar mass?
Q 28.
Who introduced the term 'mole' in chemistry?
Q 29.
Fill in the following blanks with suitable words :
(a) In water, the proportion of oxygen and hydrogen is............by mass.
(b) In a chemical reaction, the sum of the masses of the reactants and the products remains
Q 30.
Calculate the molecular mass of nitric acid,HNO
Q 31.
Calculate the molecular masses of the following compounds :
(a) Hydrogen sulphide, H2S
(b) Carbon disulphide, CS
Q 32.
Name the elements water is made of. What are the valencies of these elements ? Work out the chemical formula for water.
Q 33.
How many atoms are present in one gram atomic mass of a substance ?
Q 34.
Calculate the mass m grams of 0.17 mole of hydrogen sulphide, H,S.(Atomic masses : H = 1 U/ S = 32 u)
Q 35.
(a) Define gram molecular mass of a substance. How much is the gram molecular mass of oxygen ?
(b) If sulphur exists as S8 molecules, calculate the number of moles in 100 g of sulphur.. (S = 32 u)
Q 36.
Is there any exception to law of conservation of mass?
Q 37.
What are the postulates of Dalton's atomic theory?
Q 38.
Fill in the blanks:
The mass of 5 moles of ammonia (NH
3) is __________.
Q 39.
Fill in the blanks:
Mass of 2 Hydrogen atoms is __________.
Q 40.
Can atoms of an element exist independently? Give examples of elements which exist in atomic form. Give examples of elements that do not exist in atomic form.
Q 41.
Which element has the smallest atom in size?
Q 42.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 43.
Give three examples of monoatomic molecules.
Q 44.
Give examples of triatomic molecules.
Q 45.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Q 46.
Calculate the molecular masses of H
2, O
2, Cl
2, CO
2, CH
4, C
2H
6, C
2H
4, NH
3, CH
3OH.
Q 47.
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 48.
What are ionic compounds?
Q 49.
Name one element each which forms diatomic and tetra atomic molecule.
Q 50.
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)?
