EXERCI
Give three kinds of information conveyed by the formula
H.O.
Explain the terms, empirical formula and molecular
formula
3. Give the empirical formula of:
(2) CH.
(b) CH20
(c) C,H,
(d) CH,COOH.
1. Find the percentage of water of crystallisation i
CuSO -5H, O. (At. mass Cu = 64, H = 1, 0 = 16, S = 3
Answers
Answer:
C
2
H
4
O
2
Explanation:
Empirical formula
= CH
2
O
Empirical formula mass
= 12g/mol + 2 g/mol + 16 g/mol = 30 g/mol
Molecular formula mass
Empirical formula mass
=
60 g/mol
30 g/mol
=
2
Molecular formula
=
2
×
CH
2
O
=
C
2
H
4
O
2
(1).
Reaction: 2 H₂ + O₂ ⇒ 2 H₂ O
Information conveyed:
(i) This is the decomposition/electrolysis reaction.
(ii) There are 2 Hydrogen atoms and 1 atom of Oxygen.
(iii) There are 2 Volumes of Hydrogen atoms and 1 Volume of Oxygen.
(2)
Molecular Formula - Gives actual number of atoms of the element present in its molecule.
Ex: Molecular formula of glucose is C₆H₁₂O₆.
Empirical Formula - Defined as the ratio of different elements present in the compound. It does not show the exact number of elements present.
Ex: Empirical formula of glucose is CH₂O.
(3)
Relative molar mass of CUSO₄.5H₂O
= 63.5 + 32 + (4 * 16) + (5 * 18)
= 249.5
Percentage of water = (90/249.5) * 100
= 36.1%
∴ Percentage of mass of water of crystallization is 36.1%.
Hope it helps!