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

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

According to Brønsted Thomas Martin Lowry, an acid is defined as _____.

  • A. Any substance that produces hydrogen ion (H+) when dissolved in water

  • B. A substance that accepts electron pair in a chemical reaction

  • C. A substance that gives out hydronium ion (H3O+) when dissolved in water

  • D. A substance that donates a proton in a chemical reaction

  • E. A substance that reacts with a base to form salt and water

  • F. A substance whose hydrogen ions  (H+) are displaced after a reaction with metals higher in the activity, reactivity or electrochemical series

Which of the following is NOT a characteristic of chemical change?

  • A. A new thing is formed
  • B. It cannot be easily separated into it's constituents elements
  • C. A new chemical formula accompanies whatever is formed
  • D. The burning of candle is an example of a chemical change
  • E. Blood is an example of a chemical change
  • F. Iron rust is an example of a chemical change

Which of the following statement is FALSE concerning a physical change _____.

  • A. Substances formed in a physical change have a unique chemical formula and IUPAC name
  • B. It's a change that is easily reversible
  • C. It's a change that can be separated via an appropriate separation technique
  • D. No new substance is formed
  • E. A mixture of salt and water is a physical change
  • F. Physical change can result to a change in color and shapes of substances

The following substances will sublime EXCEPT _____.

  • A. Sodium Cryolite
  • B. Solid Carbon(IV)oxide
  • C. Arsenic
  • D. Sulphur
  • E. Iodine Crystals
  • F. Naphthalene

Which of the following is a state of matter?

  • A. Ions
  • B. Plasma
  • C. Compounds
  • D. Molecules
  • E. Atoms
  • F. None of the above

The ideal way of separating a mixture of blood is through _____.

  • A. Chromatography
  • B. Fractional Distillation
  • C. Centrifugation
  • D. Filtration
  • E. Separating Funnel
  • F. Fractional Crystallization

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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

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