Question:
Calculate the formula unit masses of ZnO, Na2O, K2CO3, given atomic masses of Zn = 65 u, Na = 23 u, K = 39 u, C = 12 u, and O = 16 u.
Answer:
(i) Formula unit mass of ZnO = 1 × Atomic mass of Zn + 1 × Atomic mass of O = 1 × 65u + 1 ×16 u
= 65u + 16u = 81u
(ii) Formula unit mass of Na2O = 2 × Atomic mass of Na + 1 × Atomic mass of O
= 2 × 23u + 1 × 16u = 46u + 16u = 62u
(iii) Formula unit mass of K2CO3= 2 × Atomic mass of K + 1 × Atomic mass of C + 3 × Atomic mass of O
= 2 × 39u + 1 × 12u + 3 × 16u = 78u + 12u + 48u = 138u
Atoms and Molecules
Q 1.
How many atoms are present in one gram atomic mass of a substance ?
Q 2.
Fill in the following blanks :
(a)1 mole Contains...........atoms- molecules or ions of a substance
(b)A mole represents an..........number of Particles of a substance.
(c)60 g of carbon element are...........moles of carbon atoms.
(d) 0.5 mole of calcium element has a mass of..........
(e) 64 g of oxygen gas contains..........moles of oxygen atoms.
Q 3.
Fill in the blanks:
An element has only one type of __________.
Q 5.
State whether the following statement is true or false :The symbol of element cobalt is CO.
Q 6.
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 7.
Calculate the molecular mass of hydrogen bromide (HBr).
(Atomic masses: H=1; Br= 80 U)
Q 8.
Calculate the molecular masses of the following compounds :
(a) Hydrogen sulphide, H2S
(b) Carbon disulphide, CS
Q 9.
What do we call those particles which have more or less electrons than the normal atoms ?
Q 10.
Name the element having following Latin names
(i) Stibium
(ii) Cuprum
(iii) Argentum
(iv) Natrium
(v) Stannum
(vi) Wolfram
(vii) plumbum
(viii) Kalium
Q 11.
Which element has the smallest atom in size?
Q 12.
Based on type of substance, how molecules are classified?
Q 13.
How many atoms are there in 0.25 mole of hydrogen ?
Q 14.
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
Q 15.
What is the chemical symbol for iron?
Q 16.
Fill in the blanks:
The atomicity of sulphur S
8 is ________.
Q 18.
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 19.
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 20.
Define 'formula mass' of a compound.
Q 21.
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 22.
Give three examples of monoatomic molecules.
Q 23.
Write the cations and anions present, if any, in the following :(a) CH
Q 24.
What name is given to the amount of substance containing 6.022 x 10
23particles (atoms, molecules or ions) ofa substance?
Q 25.
Who established the two important laws of chemical combinations?
Q 26.
In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium ethanoate. Show that these observations are in agreement with the law of conservation of mass.
sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water
Q 27.
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
Q 28.
Fill in the blanks:
The _______________ of a compound is a symbolic representation of its composition.
Q 29.
Fill in the blanks:
The mass of 1 mole of a substance is called its _____________.
Q 30.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 31.
Based on atomicity, how molecules are categorized?
Q 32.
What is the molecular mass of a substance?
Q 33.
How do we know the presence of atoms if they do not exist independently for most of the elements?
Q 34.
What is gram-atomic mass of an element?
Q 35.
If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?
Q 36.
Calculate the molecular masses of the following :
(a) Hydrogen, H
2 (b) Oxygen O2 © Chlorine Cl2 (d) Ammonia NH3 (e) Carbon dioxide, CO2
(Atomic masses : H=1 U;O=16 U; Cl=35.5 U;N=14 U;C=12 U)
Q 37.
An element X has a valency of 4 whereas another element Y has a valency of 1. What will be the formula of the compound formed between X and Y ?
Q 38.
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 39.
Convert 12 g of oxygen gas into moles.
Q 40.
Find the mass of 2 moles of nitrogen atoms.
Q 41.
How many moles of calcium carbonate (CaCO
3) are are present in 10 g of the substance ? (Ca = 40 u • C= 12 u-O = 16 u)
Q 42.
What is the mass of 5 moles of sodium carbonate (Na
3CO3) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
Q 43.
State Law of constant proportions. Explain with an example.
Q 44.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Q 45.
Name one element each which forms diatomic and tetra atomic molecule.
Q 46.
What is gram-molecular mass of a substance?
Q 47.
What is the mass of:
(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?
Q 48.
Calculate the number of molecules of phosphorus (P
4) present in 31 gram of phosphorus.
Q 49.
Calculate the molecular masses of the following compounds :
(a) Methane, CH
4
(b) Ethane, C2H6 © Eathen C2H4 (d) Ethyne C2H2
(Atomic masses : C=12 U;H=1 U)
Q 50.
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.