**Emperical Formula Examples and Answer**

**Â ****Emperical Formula** of a compound is the simpliest possible formula giving the ratio of atoms in a molecule of the compound. Example CH, HO, NH_{3}, H_{2}O e.t.c.

**Molecular Formula **The molecular is the formula which shows the actual number of atoms of the different elements present in one molecules of the compound. Example ( CH)n, (H_{2}CO)n, (CH_{3})n e.t.c

**Some given solution to some test questions**

1. Determine the molecular formula of an alkane whose vapour density is 15 (H=1, C=12, R.M.M = 2, VD)

A. CH_{4} **Answer**

B. C_{3}H_{6}

C. C_{2}H_{4}

D. C_{2}H_{6}

**Solution **

emperical formular of alkane = (CH_{4})

(1 x 12 + 4 x 1)n = 2 x 15

16n = 30

Divide both sides by 16

16n/16 = 30/16

n = 1

**Â **2. A hydrocarbon X has a relative molar mass 56 and consists of 87.8% by mass of carbon and 12.2% hydrogen. Determine the empirical formula of X give its molecular formula

**Solution**

**CÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â H **

87.8Â Â Â Â Â Â Â Â Â Â 12.2

12Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 1

Divide

7.32Â Â Â Â Â Â Â Â Â Â 12.2

Divide by the smallest ratio which is 12.2

1Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 1Â Â therefore **Emperical formula of X is CH**

**Molecular formula**

(12 + 1)n = 56

13n = 56

Divide both sides by 13

13n/13 = 56/13

NÂ = 4Â Â Â Â therefore **Molecular formular of X is C _{4}H_{4}**

Do you know Emperical Formula Examples and Answer is among the simplest solving in chemistry?

**Â **3. A hydrocarbon containing 88.9% carbon has the empirical formula (H=1, C=12)

A. CH

B. CH_{2}

C. C_{2}H_{3}

D. C_{2}H_{5}

**Solution**

CÂ Â Â Â Â Â Â Â Â Â H

88.9Â Â Â Â Â Â Â Â Â Â Â Â 11.1

12Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 1

Divide

7.4 1Â Â Â Â Â Â Â Â Â Â Â Â Â Â 11.1

Divide by the smallest ratio

1Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 1Â Â Â Â Â Â Â therefore the **empirical formular is CH**

**Â **

**Try this and solve**

A compound contains 31.9% potassium, 28.93% chlorine and the rest oxygen. What is the chemical formular of the compound? ( K=39, CL=35.5, O=16)

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the number 1 answers provided is wrong . the answer is C2H6

empirical formula for alkanes is CnH2n+2

so CnH2n+2 = molar mass

molar mass = 2Ã— vapour density

molar mass= 30

CnH2n+2 = 30

12n + 2n + 2 = 30

14n + 2= 30

14n = 30 – 2

14n = 28

n = 28/14

n = 2

then plug in the value of n in the empirical formula (CnH2n+ 2)

C2H2(2)+2

C2H4+2

C2H6 is the final answer …

to check if the answer is correct

C2H6 = 30g/mol , which has a relative vapour density of 15