Engineering Chemistry-I Unit I

1. Molecular mass

2. • Atom:
The smallest particle of an element and that is
chemically indivisible and can take part in
chemical reaction.
• Molecule: The smallest particle of element or
compound that can exist freely.
eg. H2, N2, H2O

3. Atomic mass an molecular mass
mass of an atom
• Atomic mass = ---------------------
1/12th mass of an atom of carbon12
Mass of a molecule
• Molecular mass = -------------------------------------
1/12th mass of an atom of carbon12

4. Molecular formula
• A symbolic representation of molecule with
the simplified ratio of the atoms present in it.
• Significances of a molecular formula
 H2SO4 it contains …………of atoms of……… atom of
……………and ………………atoms of ……………….
 It indicates the number of different atoms present in it.
 It represent the correct proportion of each atom present
in it.
 It helps to calculate the percentage of each element in it.
 It indicates the name.
 It helps to identify the raw materials required for its
manufacture.

5. Mole
• Mole: one gram molecular mass is called one
mole.
• Number of moles= mass/molecular mass
• Calculation of molecular mass:
• H2SO4
• Calculation of number of moles: how many moles are there in 36 g of water?
• Given data:
Mass of water=36
Molecular mass=18
no. of moles = 36/18
=2 moles
Calculate the mass of 1.5 moles of ammonia?

6. Avogadro's hypothesis
• "equal volumes of gases at the same
temperature and pressure contain the same
number of molecules regardless of their
chemical nature

7. Relationship between molecular mass
and vapour density
• Vapour Density:It is the ratio of the mass of a volume of a gas, to the mass of an equal volume of
hydrogen, measured under the same conditions of temperature and pressure.
mass of certain volume of a gas
• Vapour Density = ---------------------------------------
Mass of same volume of H2 at the same P&T
• According to Avogadro's law, equal volumes of all gases contain equal number of molecules.Thus, let the
number of molecules in one volume = n,
Therefore, Mass of ‘n’moleculesof a gas
Vapour Density = --------------------------------------
Mass of n molecule of H2
• ‘n’can have any value; let n=1;
• So, mass of a mlecule
Vapour Density =--------------------------
Mass of H2 molecule
• However, since hydrogen is diatomic., Mass of amolecule is nothing but Molecular mass ,Mass of H2
molecule is 2
• Molecular Mass = 2 x Vapour density
•

8. Avogadros number

12. Acids and bases
• Which of the following are acids an bases
identify them?
• HCl, H2SO4, NaOH, Na2CO3, BF3, AlCl3, NH3, H2C2O4,
• CH3COOH

15. Arrheneous Theory
Arrhenius theory, introduced in 1887 by the
Swedish scientist SvanteArrhenius, that acids
are substances that dissociate in water to yield
electrically charged atoms or molecules, called
ions, one of which is a hydrogen ion (H +), and
that bases ionize in water to yield hydroxide
ions (OH −)

16. • The Bronsted-Lowry Theory of acids
and bases. The theory. An acid is a proton
(hydrogen ion) donor. A base is a proton
(hydrogen ion) acceptor.
• acid + base -> conjugate base + conjugate acid

17. In 1923 G. N. Lewis suggested
• Lewis acid is anelectron-pair acceptor. A Lewis base is an electron-
pair donor.
• The Lewis acid-base theroy explains why BF3 reacts with ammonia.
BF3 is a trigonal-planar molecule because electrons can be found in
only three places in the valence shell of the boron atom. As a result,
the boron atom is sp2 hybridized, which leaves an empty 2pzorbital
on the boron atom. BF3 can therefore act as an electron-pair
acceptor, or Lewis acid. It can use the empty 2pz orbital to pick up a
pair of nonbonding electrons from a Lewis base to form a covalent
bond. BF3 therefore reacts with Lewis bases such as NH3 to form
acid-base complexes in which all of the atoms have a filled shell of
valence electrons, as shown in the figure below.
•

19. PHand pOH

20. Buffer
• A buffer is a solution that can maintain a
nearly constant pH if it is diluted, or if
relatively small amounts of strong acids or
bases are added. Buffer solutions resist pH
changes. A buffer solution is typically made by
mixing a weak acid and one of its salts OR
mixing a weak base with one of its salts.

21. • Besides being toxic to cells, acidic blood also increases your risk of
cancer, because it decreases oxygen and nutrient levels in your
body; therefore, it can starve your cells of essential nutrients.
Studies have shown that people with acidosis have higher risk of
heart disease, cancer, osteoporosis, diabetes, arthritis and are more
susceptible to diseases.
• The human body works similar to an alkaline battery; thus, when its
blood pH is too acidic, it does not function properly. As a result, the
body’s energy decreases, cells cannot communicate properly,
fungus and bacteria starts to grow out of control, and the body’s
natural healing and defense system break down. The normal pH of
human blood is slightly higher than 7.0. To be more specific, most
experts agree that the normal pH of blood is between 7.35-7.45. If
your blood pH is lower than 7.3, it is considered somewhat acidic.

22. Applicatios of PH