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an unknown substance was found to have the percent composition of 36.90% nitrogen and 63.10% oxygen. how much nitrogen and oxygen would be in 100.0 g of the unknown substance

Sagot :

The empirical formula is KCO2

Explanation:

As with all these problems, we assume a

100

g

mass of unknown compound, and then we work out the molar quantity:

Moles of potassium

=

47.0

g

39.10

g

m

o

l

1

=

1.20

m

o

l

Moles of carbon

=

14.5

g

12.011

g

m

o

l

1

=

1.21

m

o

l

Moles of oxygen

=

38.5

g

16.0

g

m

o

l

1

=

2.41

m

o

l

We divide thru by the smallest molar quantity to give the empirical formula:

K

C

O

2

.

Now the molecular formula is always a whole number of the empirical formula:

i.e.

molecular formula

=

n

×

empirical formula

And thus with the molecular mass, we can solve for

n

.

166.2

g

m

o

l

1

=

n

×

(

39.1

+

12.011

+

2

×

16.00

)

g

m

o

l

1

166.2

g

m

o

l

1

=

n

×

(

83.1

)

g

m

o

l

1

Clearly,

n

=

2

, and the

molecular formula

=

K

2

C

2

O

4

The compound is LIKELY the potassium salt of oxalic acid,

K

+

O

(

O

=

)

C

C

(

=

O

)

O

K

+

, i.e.

potassium oxalate.

Answer linkExplanation:

As with all these problems, we assume a

100

g

mass of unknown compound, and then we work out the molar quantity:

Moles of potassium

=

47.0

g

39.10

g

m

o

l

1

=

1.20

m

o

l

Moles of carbon

=

14.5

g

12.011

g

m

o

l

1

=

1.21

m

o

l

Moles of oxygen

=

38.5

g

16.0

g

m

o

l

1

=

2.41

m

o

l

We divide thru by the smallest molar quantity to give the empirical formula:

K

C

O

2

.

Now the molecular formula is always a whole number of the empirical formula:

i.e.

molecular formula

=

n

×

empirical formula

And thus with the molecular mass, we can solve for

n

.

166.2

g

m

o

l

1

=

n

×

(

39.1

+

12.011

+

2

×

16.00

)

g

m

o

l

1

166.2

g

m

o

l

1

=

n

×

(

83.1

)

g

m

o

l

1

Clearly,

n

=

2

, and the

molecular formula

=

K

2

C

2

O

4

The compound is LIKELY the potassium salt of oxalic acid,

K

+

O

(

O

=

)

C

C

(

=

O

)

O

K

+

, i.e.

potassium oxalate.