Chemistry

Molar Mass, Worked Examples and Differences with Molecular Mass

len Alfred Ajibola - Sat, 14th December, 2019 @ 12:16: PM

Topics in Chemistry

Le Chatelier's Principle: Changes in concentration and pressure 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 isn't an element of the periodic table.

  • A. J

  • B. Y

  • C. W

  • D. B

  • E. U

  • F. K

According to the periodic table, elements in the same group have got the same number of shells.

  • A. True

  • B. False

The periodic table of elements is also called the Mendeleev's table.

  • A. True

  • B. False

The simplest formula of a compound is termed _____.

  • A. Emperical formula

  • B. Molecular formula

  • C. Avogadro's number

  • D. Mass formula

  • E. Molar mass formula

  • F. Mole ratio

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)

  • A. FeO

  • B. Fe2O3

  • C. Fe3O4

  • D. FeO2

  • E. Fe3O6

  • F. Fe2O4

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

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What is Molar Mass?

Molar mass is the Mass of one mole of a substance expressed in grams per mole (g/mol).

For instance, since one mole of oxygen atom (O) has a mass of 15.9994 gram, its molar mass would therefore be 15.9994g/mol.

Please read more on the Periodic Table of Elements here.

The formulas below will prove useful in chemical calculations involving mole, mass and molar mass respectively.

Mole = Mass/Molar Mass

Mass = Mole x Molar Mass

Molar Mass = Mass/Mole

Please read on Matter, Mass and Weight here.


Worked Examples on Molar Mass

Example 1

  • Calculate the molar mass of 2 moles of Ethanol (2C2H5OH). (Carbon = 12, Oxygen = 16 and Hydrogen = 1)

Notice the 2 in front of ethanol's chemical formula. It stands for the number of moles; (that is; 2 moles in this case). If no value is present, then then it's regarded as 1 mole.

Two moles of Ethanol are composed of 4 atoms of carbon; 10 atoms of hydrogen and 2 atoms of oxygen. (We got the values by multiplying the atoms of each element by the “2” in front of the compound).

(12 x 4) + (1 x 10) + (16 x 2)

48 + 10 + 32

Molar Mass of 2 moles of Ethanol = 90g/mol

Please read on Graham's Law of Diffusion with Worked Examples here.

 

Example 2

  • Calculate the molar mass of Sodiumtrioxocarbonate(IV). (Na2CO3) (Sodium=23, Carbon=12, Oxygen=16)

Na2CO3 is composed of 2 atoms of sodium, 1 atom of carbon and 3 atoms of oxygen.

(23 x 2) + 12 + (3 x 16)

46 + 12 + 48

Answer is 106g/mol

Please read on Emperical Formula with Worked Examples here.

 

Example 3

  • Calculate the molar mass of Ca3(PO4)2. (Calcium=40.078 , Phosphorus=30.973762 and Oxygen=15.999)

Ca3(PO4)2 is composed of 3 atoms of calcium, 2 atoms of phosphorus and 8 atoms of oxygen

Note: The subscript 2 applies to only (PO4). We therefore multiplied potassium (P) by 2 and the O4 by 2.

(40.078 x 3) + (30.973762 x 2) + (15.999 x 3)

120.234 + 61.947524 + 47.997

Answer is 230.2g/mol

You can Attempt LEN ACADEMY Questions and Answers on various Subjects here.

 

Differences between Molecular Mass and Molar Mass

Please read on Molecular Mass here.

Molecular Mass refers to mass of a molecule in relation to carbon-12.

Molar Mass refers to the mass of one mole of a substance.

Molecular Mass is measured in Atomic Mass Unit (AMU) or Dalton (Da).

Molar Mass is measured in grams per mole (g/mol).

The Molecular Mass of a molecule is derived by calculating the sum of the atomic mass of each atom present in the molecule.

The Molar Mass is derived by dividing the mass of the substance by the number of moles in that substance.

Note: The values of molecular mass and molar mass are always the same, except that they have different Standard International Units S.I Units.

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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.

Copper is the only metal that is naturally antibacterial. For this reason, some children utilize 'copper water bottles' in schools

Water 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

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

In chemistry, hydrocarbons can be classified as either aliphatic or aromatic. Recently, both classifications of hydrocarbon were based on their structure rather than their origin.

Aliphatic hydrocarbons are put into three main groups according to the types of bonds they possess. These are:

  1. Alkanes

  2. Alkenes

  3. Alkynes

They are shown in the image below:

Alkanes, Alkenes and Alkynes - Len Academy

It's important to note the followings:

  • Alkanes have single bonds (only) in their structures.

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

  • Alkynes always have a carbon-carbon triple bond present in their structure.

 

Aromatic hydrocarbons are classified into:

  • Arenes: They contain benzene ring as a structural unit. Below is the structure of a benzene ring.

Benzene Ring - Len Academy

 

  • Nonbenzenoid aromatic hydrocarbons: They possess special stability but lack a benzene ring as a structural unit.

Organic chemistry is the study of carbon and it's compounds.

Carbon is the focus of organic chemistry because it has a wide chemical diversity in the sense that it can combine with other carbon atoms to form a long chain of carbon molecule. This ability and process whereby carbon can form a long chain of itself is called catenation.

Please read the introduction to organic chemistry here

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