Using the atomic weights of selected elements given below, find the formula weig
ID: 912883 • Letter: U
Question
Using the atomic weights of selected elements given below, find the formula weights for the following compounds:
Atomic weights of selected elements
Ca = 40 g moL-1, C = 12 g moL-1, O = 16 g moL-1, H = 1 g moL-1, P = 31 g moL-1, K = 39 g moL-1 Si = 28 g moL-1, Al = 27 g moL-1, S = 32 g moL-1, N = 14 g moL-1
Example: (NH4)2SO4
Element
no. of moles
Atomic wt. (g moL-1)
no. moles x Atomic wt.
S
1
32
32
O
4
16
64
N
2
14
28
H
8
1
8
Formula wt.= (no. moles x Atomic wt.) =
132
Compound
Formula weight
(g moL-1)
(1pt) CaCO3
(1pt) Ca(OH)2
(1pt) CaO
(1pt) P2O5
(1pt) K2O
(1pt) SiO2 (quartz)
(2pt) KAl3Si3O10(OH)2 (muscovite)
(1pt) CO2
Element
no. of moles
Atomic wt. (g moL-1)
no. moles x Atomic wt.
S
1
32
32
O
4
16
64
N
2
14
28
H
8
1
8
Formula wt.= (no. moles x Atomic wt.) =
132
Explanation / Answer
Solution :-
Formula weight is the sum of the atomic weights of the elemetns in the formula
Lets calculate the formula weight of the each compound using the given formula weight
1). CaCO3 = (Ca*1)+(C*1)+(O*3)
= (40 *1) +(12*1)+(16*3)
= 100 g/mol
2) Ca(OH)2 = (Ca*1)+(O*2)+(H*2)
=(40*1)+(16*2)+(1*2)
= 74 g /mol
3) CaO = (Ca*1)+(O*1)
=(40*1)+(16*1)
= 56 g /mol
4) P2O5 = (P*2)+(O*5)
= (31*2) +(16*5)
= 142 g/mol
5)K2O = (K*2)+(O*1)
= (39*2)+(16*1)
= 94 g/mol
6) SiO2 = (Si*1)+(O*2)
= (28*1)+(16*2)
= 60 g /mol
7) KAl3Si3O10(OH)2 = (K*1)+(Al*3)+(Si*3)+(O*12)+(H*2)
= (39*1)+(27*3)+(28*3)+(16*12)+(2*1)
= 398 g/mol
8) CO2 = (C*1)+(O*2)
= (12*1)+(16*2)
= 44 g/mol
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