Chemistry

Molar Mass, Worked Examples and Differences with Molecular Mass

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

Topics in Chemistry

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 Mixtures and Separation of Mixtures Mixtures and Separation of Mixtures - part 2 Mixtures and Separation of Mixtures - part 3


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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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

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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.

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