Chemistry

Emperical Formula - Explanation and Worked Examples of Emperical Formula

len Alfred Ajibola - Sat, 16th March, 2019 @ 11:00: AM

Topics in Chemistry

Le Chatelier's Principle: Changes in Concentration and Pressure explained in Dynamic Equilibrium Chemical Equilibrium: Dynamic Equilibrium in Chemistry Static and Dynamic Equilibrium explained with their Differences Chemistry Scheme of Work, SS1, First Term Chemistry Scheme of Work, SS1, Second Term Chemistry Scheme of Work, SS1, Third Term Compounds in Chemistry: Characteristics of Compounds Types of Mixture: Homogenous and Heterogeneous Mixtures Mixtures: Characteristics of Mixtures Physical Properties of Matter explained with Examples Chemical Properties of Matter explained with Examples Differences between Physical and Chemical Change Ionic Theory and Electrolysis Physical and Chemical Properties of Acids States of Matter: Characteristics of Solids Liquid State of Matter: Characteristics of Liquids Gaseous State of Matter: Characteristics of Gases Molar Mass, Worked Examples and Differences with Molecular Mass Elements: Characteristics of Elements Salts and Types of Salt in Chemistry


Academic Questions in Chemistry

Please check out our Test Your Knowledge page to see all Questions and Answers

Which of the following statement is false concerning hydrocarbons?

  • A. Hydrocarbons can be aromatic

  • B. Hydrocarbons are made up of carbon and hydrogen only

  • C. Alkynes are aliphatic hydrocarbons

  • D. Alkenes have a carbon-carbon double bond in their structure

  • E. Benzene ring has a carbon-carbon triple bond in its structure

  • F. Hydrocarbons are the main constituents of petroleum and natural gas

The ability of carbon to form long chain of itself is called _____.

  • A. Carbon chain reaction

  • B. Catenation

  • C. Carbontion

  • D. Carbontion

  • E. Organic chemistry

  • F. Carbon moleculation

Calculate the relative molecular mass of methane. (Carbon = 12.001, H = 1.00794).

  • A. 13.00894 amu

  • B. 11.00206 amu

  • C. 12.00794 amu

  • D. 14.001 amu

  • E. 15.001 amu

  • F. 16.033 amu

Which of he following is not a fact concerning gold?

  • A. 24 karat gold is the purest gold element

  • B. It is the 50th rarest metal amongst all elements found beneath the earth crust

  • C. It is the most malleable and ductile pure metal ever known

  • D. It is the only metal with a golden color

  • E. Gold is non toxic and can be eaten with food

  • F. It's present inside the earth crust in all seven continents

Which of the following is not an example of a chemical change?

  • A. The burning of wood
  • B. The melting of candle wax
  • C. The decomposition of food
  • D. The rotting of leaves
  • E. The lightening of a match stick
  • F. None of the above

Which of the following is not a fraction of crude oil?

  • A. Gasoline
  • B. Naphtha
  • C. Benzene
  • D. Wax
  • E. Paraffin
  • F. Lubrication Oil

The Separating Funnel is a technique used in the separation of mixtures. Another name for Separating Funnel is the _____ Funnel.

  • A. Partition
  • B. Separatory
  • C. Division
  • D. Liquid
  • E. Half
  • F. Dividing

2NH4+(aq) + Ag+(aq) -> 2H4AgN

The equation above represents _____ acid.

  • A. Svante Arrhenius'

  • B. Brønsted–Lowry's

  • C. Gilbert Lewis'

  • D. Avogadro's

  • E. Sir Isaac Newton's

  • F. Albert Einstein's

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Empirical Formula:

Let's begin by considering two atoms, say Hydrogen (H) and oxygen (O). If these atoms are combined to form a compound, let's say (HO) for instance, we will not be able to tell the ideal formula of the compound if this was an experimental sample; as it also could be H2O, H2O2 or something else.

With regards to the uncertainty of the compound formed in the above instance, the empirical formula comes into play. It is the simplest formula of a compound because it is derived from experimental data or analysis.

It is the empirical formula that tells us the relative ratios the of different atoms in a compound.

Please read on Matter, Mass and Weight here.

The empirical formula of a compound may be defined as the formula that shows only the relative number of atoms of each element present in the compound.

 

Now let's consider water molecule (H2O) as a reference:

H2O = 2 atoms of hydrogen (H) and 1 atom of oxygen (O).

H2O = 1 mole of hydrogen molecule and 1 mole of oxygen.

Please read on Molecular Mass and Molar Mass here.

Note: Always remember that when a number isn't written in front of a compound, then it means that the number "1" is actually in front of that compound. So, the H2O in our above example is actually 1H2O (1 mole of water).

The 1 (in front of the compound) is referred to as the Mole Ratio.

Therefore, if we know the amounts of mole of each element in a compound, then the emperical formula can be determined.

Note: Whenever we are working with the percentages of each element contained within a compound, we will need to convert the percentages into the mole ratio of the elements in order to get the empirical formula of the compound.

Please read on Graham's Law of Diffusion here.

 

Worked Example of Emperical Formula:

A compound composed of iron (Fe) and oxygen (O) was analyzed and found to contain 69.94% iron and 30.06% oxygen. Find the empirical formula of the compound. ( Molar mass of Fe=55.85, O=16)

Solution

Step 1: Identify the given parameter from the question.

Fe = 69.94%,   O = 30.06%.

Empirical formula = Fe?O?

 

Step 2: Convert the percentages to gram. (just attribute grams to the %).

69.94% = 69.94g while 30.06% = 30.06g

 

Step 3: To get the mole ratio of each element, convert the gram to moles using the formula (mole = mass/molarmass). Please merorize this formula because we always work with moles in Emperical Formula.

Mole of Fe: 69.94/55.85 = 1.252mol

Mole of O: 30.06/16 = 1.879mol

 

Step 4: Divide both sides by the smallest mole ratio.

Iron has the smallest mole ratio in our case, therefore: 1.252/1.252 = 1,    1.879/1.252 = 1.5

We now have the formula = Fe1O1.5

 

Step 5: Multiply each of the moles by the smallest whole number that will convert each into a whole number. (In our case, the number "2" is the smallest whole number that will make "1.5" and "1" whole numbers when multiplied by it.

For iron (Fe), we will have 1 x 2 = 2

For oxygen (O), we will have 1.5 x 2 = 3

 

Step 6: Write the empirical formula.

The empirical formula= Fe2O3

Iron(III)tetraoxosulphate(VI)

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Alfred Ajibola is a Medical Biochemist, a passionate Academician with over 7 years of experience, a Versatile Writer, a Web Developer, a Cisco Certified Network Associate and a Cisco CyberOps Associate.


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Amazing facts in Chemistry

The only letters that failed to appear on the periodic table are letters:

J     &     Q

Gold and copper are the only two non-silvery colored metals.

Please read some interesting facts about gold here

Copper is the only metal that is naturally antibacterial. This is why you would see some children utilize 'copper' water bottles in schools

Water actually freezes faster when it’s warm than when it’s cold

Most element in their pure state exists physically in different forms. For instance, pure carbon can exist as both diamond and graphite. This phenomenon is called allotropy.

Please read on modification of Dalton's atomic theory here.

If you pour a handful of salt into a full glass of water, the water level will go down rather than overflowing the glass.

Similarly, if you mix half liter of water and half litre of alcohol, the total volume of the liquid will be les than one litre


NOTABLE POINTS IN Chemistry

A major challenge encountered when calculating molecular mass is that it becomes difficult or impossible to calculate especially when the relative molecular mass of large molecules, polymers and macromolecules are involved.

Examples of large molecules (with indefinite molecular masses) include carbohydrates, cellulose and complex sugars.

The large molecules (above) have no specific chemical formula throughout their volume.

Please read more on Carbohydrates and Sugars here

Understand that Relative Molecular Mass prove to be useful only when we calculate substances with small and definite molecular sizes. This was proven through the Modifications of Dalton's Atomic Theory.

Please read on Dalton's Atomic Theory and its Modifications here.

Calculate the Relative Molecular Mass of Methane (CH4). (Carbon=12.001 and H=1.00794)

  • Molecular Mass = Atomic mass of carbon + Atomic mass of Hydrogen
  • Methane is composed of one atom of Carbon and 4 atoms of Hydrogen.
  • 12.001 + (1.00794 x 4)

Molecular Mass of Methane = 16.033 amu

Please read more on molecular mass here


Calculate the Relative Molecular Mass of Water (H2O). (Oxygen=15.9994 and Hydrogen=1.00794)

  • Molecular Mass = Atomic mass of Hydrogen + Atomic mass of Oxygen
  • Water contains 2 atoms of Hydrogen and 1 atom of oxygen.
  • (1.00794 x 2) + 15.9994

Molecular Mass of Water = 18.015 Da

Please read on Emperical Formula and its Calculations here

Gold ; Len Academy

Below are some facts about gold

  • It is the only metal that has a gold (golden) color.

  • Gold is present inside the earth crust in all the seven continents.

  • Pure gold is soft and very stretchable (It can even be stretched into threads).

  • The Latin name of Gold is aurum which means 'shining dawn'. For this reason, its chemical symbol is 'Au'.

  • Gold is a very good conductor of electricity. This is why it’s sometimes used in making USB and audio cables.

  • Gold is non toxic and can be eaten with food. It is sometimes added to desserts in some expensive restaurants.

  • The term Gold originated from an ancient English word 'geolu' which means yellow.

  • 24karat gold is the purest gold element.

Please read more interesting facts about gold here

An acid is a substance that produces Hydrogen ions (H+) when dissolved in water (or when in the form of an aqueous solution).

Svante Arrhenius definition of Acid

 

An acid is a substance that donates a proton in a chemical reaction.

Brønsted Thomas Martin Lowry definition of Acid

 

An acid is a substance that accept an electron pair in a chemical reaction.

Gilbert Newton Lewis definition of Acid

 

Finally, Acids can also be also defined as substances that gives out hydronium ion (H3O+) when dissolved in water.

 

In summary, all acids will always contain the positive H+ (cation) and an anionic group in their formula. For instance, the acid HCl (Hydrogen Chloride) contains H+ as cation and Cl- as its anion.

Please read the explanations of the above definitions of acid here