Please answer this Question!Q: Give the reactions of Atomic hydrogen with the following.
1)Phosphorus
2)Cuproc Oxide
Answers
Explanation:
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 of 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
SOLUTION:
Total mass of reactants = mass of sodium
carbonate + mass of ethanoic acid
= 5.3 g + 6 g = 11.3 g
Total mass of products = mass of sodium ethanoate + mass of carbon dioxide + mass
of water
= 8.2 g + 2.2 g + 0.9 g = 11.3 g
Thus, the mass of reactants is equal to the mass of products, therefore the observations are in agreement with the law of conservation of mass.
Q 2.
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?
SOLUTION:
1 g of hydrogen reacts with = 8 g of oxygen
∴ 3 g of hydrogen reacts with = 8 × 3 = 24 g of oxygen
Thus, 24 g of oxygen gas would be required to react completely with 3 g of hydrogen gas.
SOLUTION:
The postulate that “atoms can neither be created nor destroyed in a chemical reaction” is the result of the law of conservation of mass.
Q 4.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
SOLUTION:
The postulate that “A chemical compound always consists of the same elements combined together in the same proportion by mass” is the law of definite proportions.
Q 5.
Define the atomic mass unit.
SOLUTION:
Atomic mass unit is defined as the mass unit equal to exactly one-twelfth (1/12th) of the mass of one atom of carbon-12. It is denoted by u (unified mass).
i.e. 1 u = 1.66 × 10–24 g
Q 6.
Why is it not possible to see an atom with naked eyes?
SOLUTION:
It is not possible to see an atom with naked eye because of its extremely small size (atomic radius is of the order of 10–10 m).
Q 7.
Write down the formulae of
(I) sodium oxide,
(ii) aluminium chloride,
(iii) sodium sulphide,
(iv) magnesium hydroxide
SOLUTION:
(I) Sodium oxide
(ii) Aluminium chloride
(iii) Sodium sulphide
(iv) Magnesium hydroxide
Q 8.
Write down the names of compounds represented by the following formulae :
(I) Al2(SO4)3
(ii) CaCl2
(iii) K2SO4
(iv) KNO3
(v) CaCO3
SOLUTION:
(I) Aluminium sulphate
(ii) Calcium chloride
(iii) Potassium sulphate
(iv) Potassium nitrate
(v) Calcium carbonate
Q 9.
What is meant by the term chemical formulae?
SOLUTION:
The chemical formula of a compound is a symbolic representation of its composition. e.g., formula of calcium oxide.
Thus, chemical formula of calcium oxide is CaO.
Q 10.
How many atoms are present in a
(I) H2S molecule and
(ii) PO43– ion?
SOLUTION:
(I) 3 atoms because H2S molecule has two atoms of hydrogen and one atom of sulphur.
(ii) 5 atoms because ion has one atom of phosphorus and four atoms of oxygen.
Q 11.
Calculate the molecular masses of H2, O2, Cl2, CO2, CH4, C2H6, C2H4, NH3, CH3OH
SOLUTION:
Molecular mass of H2 = 2 × atomic mass of H
= 2 × 1 u = 2 u
Molecular mass of O2 = 2 × atomic mass of O
= 2 × 16 u = 32 u
Molecular mass of Cl2 = 2 × atomic mass of Cl
= 2 × 35.5 u = 71 u
Molecular mass of CO2 = atomic mass of C
+ 2 × atomic mass of O
= 12 + (2 × 16) = (12 + 32) u = 44 u
Molecular mass of CH4 = atomic mass of C
+ 4 × atomic mass of H
= 12 + (4 × 1) u = (12 + 4) u = 16 u
Molecular mass of C2H6 = 2 × atomic mass
of C + 6 × atomic mass of H
= (2 × 12 + 6 × 1) u = (24 + 6) u = 30 u
Molecular mass of C2H4 = 2 × atomic mass
of C + 4 × atomic mass of H
= (2 × 12 + 4 × 1) u = (24 + 4) u = 28 u
Molecular mass of NH3 = atomic mass of N
+ 3 × atomic mass of H
= (14 + 3 × 1) u = (14 + 3) u = 17 u
Molecular mass of CH3OH = atomic mass of C
+ 3 × atomic mass of H + atomic mass
of O + atomic mass of H
= (12 + 3 × 1 + 16 + 1) u = (12 + 3 + 17) u = 32 u
Q 12.
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
SOLUTION:
Formula unit mass of ZnO = atomic mass of Zn
+ atomic mass of O
= (65 + 16) u = 81 u
Formula unit mass of Na2O = 2 × atomic mass
of Na + atomic mass of O
= (2 × 23 + 16) u = 62 u
Formula unit mass of K2CO3
= 2 × atomic mass of K + atomic mass of C
+ 3 × atomic mass of O
= (2 × 39 + 12 + 3 × 16) u = (78 + 12 + 48) u
= 138 u
Q 13.
If one mole of carbon atoms weighs
12 gram, what is the mass (in gram) of
1 atom of carbon?
SOLUTION:
Molecular mass of carbon = 12 g
∵ 6.022 × 1023 atoms of carbon have mass
= 12 g
∴ 1 atom of carbon has mass
Q 14.
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)?
SOLUTION:
100 g of sodium :
Number of sodium atoms
Thus, 100 g of sodium has t are sodium, hydrogen, carbon and oxygen.
(D) Potassium sulphate is K2SO4. Elements present are potassium,
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