Chemistry Reference
In-Depth Information
4.
[A. NaOH]—Work shown here:
# of moles of sodium =
57.5 g
A.
23.0 g/mole
= 2.50 moles
# of moles of oxygen =
40.0 g
16.0 g/mole
= 2.50 moles
# of moles of hydrogen =
2.5 g
1.01 g/mole
= 2.5 moles
2.50 moles
2.50 moles
B.
subscript for sodium =
= 1
2.50 moles
2.50 moles
subscript for oxygen =
= 1
2.5 moles
2.50 moles
subscript for hydrogen =
= 1
Empirical Formula = NaOH
5.
[B. CaCO
3
]—Work shown here:
A.
# of moles of calcium =
40.0 g
40.1 g/mole
= 0.998 moles
# of moles of carbon =
12.0 g
12.0 g/mole
= 1.00 moles
# of moles of oxygen =
48.0 g
16.0 g/mole
= 3.00 moles
subscript for calcium =
0.998 moles
0.998 moles
B.
= 1
1.00 moles
0.998 moles
subscript for carbon =
= 1
3.00 moles
0.998 moles
subscript for oxygen =
= 3
Empirical Formula = CaCO
3
6.
[A. CH
4
]—The empirical formula
is CH
4
, which has a total mass of 16.0
u (12.0 u + 4.0 u = 16.0 u). The molecular mass is also 16.0 u, so the
empirical and molecular formula must be the same.
7.
[C. C
2
H
6
]—The empirical formula is CH
3
, which has a total mass of 15.0 u
(12.0 u + 3.0 u = 15.0 u). The molecular mass is 30.0 u, which, when divided
by 15.0 u, gives us 2 (30.0 u / 15.0 u = 2). We multiply each subscript in the
empirical formula by 2 to get the molecular formula 2(CH
3
) = C
2
H
6
. To
check your answer, find the mass of your molecular formula, and you will
find that it is 30.0 u.
