CHM101
FOUNDATION
CHEMISTRY
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Stoichiometry
 Stoichiometry
is a quantitative study of amount of
substances in a chemical species or in chemical
reactions.
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UNITS
 You
are expected to use SI units. SI means “Systeme
Internationale” and refers to a set of agreements between
scientists to arrive at a system of commonly used units.
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UNITS
 All
other SI units are derived from these units.
Quantity
Name of the Symbol Equivalent form
base unit
Volume
force
Pressure
Energy, work
Electric charge
power
Cubic metre
newton
Pascal
Joule
Coulomb
watt
m3
N
Pa
J
C
W
kg m-1 s-1
N m-2 / kg m-1 s-2
N m/ Kg m2 s-2
C
J s-1 , kg m2 s-3
temperature
Degree
Celsius
oC
K-273.15
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UNITS
 Some
non-SI units in common use
Physical
quantity
Volume
Pressure
Energy
Temperature
Concentration
Symbol
Units
Physical quantity
V
Litre
P
atmosphere
bar
Torr
mmHg
E
Electron volt
T
Degree centigrade
c
Molarity
Symbol of
Units
L
atm
Bar
torr
mmHg
eV
°C
M = mol L-1
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UNITS
 There
are seven base units.
Quantity Physical
quantity
Mass
Length
Time
Temperature
Amount of substance
Electric current
Luminious intensity
Symbol of
Physical
Quantity
m
l
t
T
n
I
Iv
Name of the
base unit
kilogram
Metre
Second
Kelvin
Mole
Ampere
Candela
Symbol
of base
Unit
Kg
m
S
K
Mol
A
cd
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MEASUREMENTS
 [Physical
quantity] = [significant digits] [prefix] [Units]
V
= 25.00 mL
 Significant figures (digits) in a measurement are number of
digits that are known with some degree of confidence
 Example


m = 2.2g
m= 2.2159g
-lab balance
[2 sig. fig.]
-analytical balance [5 sig. fig.]
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MEASUREMENTS
 In
calculations of a physical quantity, the final answer must
contain the correct number of sig. fig.
Rules of significant figures
Rule 1:
 Digits 1-9 are always significant
 Zero to the right of the significant digit after a decimal place are
significant, e.g. m = 2.00g -3 sig. fig.
 Zero to the right of significant digit are not significant, e.g. m =
2500g
-2sig. fig
 Zero used merely for placing a decimal place are not
significant, e.g. m = 0.00250g - 3 sig. fig.
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MEASUREMENTS
Rule 2: Adding or subtracting numbers
 Answer must have the least number of decimal point.
 Example:
3.2 + 4.62 = 7.82 = 7.8
Rule 3: Multiplying or dividing numbers
 Answer must have the least number of significant digits.
 Example:
n = 0.033 mol/L x 0.02500L
= 0.00082500
= 0.00083 mol
-2sig. fig.
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MEASUREMENTS
 Rule
4: conversion factors, molar mass, physical constants
 Not considered in establishing sig. fig in the answer
 Example: n = 0.2512g/1.01/ mol
= 0.2487129 mol
= 0.2487 mol
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MEASUREMENTS
Rule 5: Rounding of Rule
 If the digit next to the significant digit is 5 or greater than 5,
increase the significant digit by one.
PREFIX
 A prefix is a letter or symbol that is fixed before the unit
Prefix
name
Symbol
Value
Pico
Nano
Micro
milli
Kilo
Mega
Giga
p
10-12
n
10-9

10-6
m
10-3
k
103
M
106
G
109
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MEASUREMENTS
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LECTURE 2
13
Atoms, molecules and ions
 Elementary
idea of atoms, molecules, and ion
 All substances are made of atom, molecules, and ions
 Atomic Structure
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ISOTOPES OF ELEMENTS
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ATOMIC MASS
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Mass spectrum
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 Atomic
masses of elements are tabulated in a Periodic table of
element
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Molar mass
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Lecture 3
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The Mole
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PERCENT COMPOSITION
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EMPIRICAL, MOLECULAR FORMULA
 Chemical
formula: empirical, molecular and structural
formulae

Empirical formula shows the simplest ratios of atoms in a
chemical formula.

Molecular formula shows the actual number of atoms in a
chemical formula.

Structural formula shows special, geometric and bonding of
atoms in a chemical formula.
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 Example:

A compound contains 47.08% C, 6.59% H and 46.33% CI by
mass; the molar of the compound is 153g/mol. What is the
empirical and molecular formula of the compound?
 Solution
 Assume 100g sample
C
H
Cl
Mass in 100g Sample
47.08g
6.59g
46.33g
Mole n=m/M
3.920
6.525
1.307
Ratio of moles
2.999
4.992
1
3
5
1
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The mole concept
 Mole
concept provides a simple mole-mole relationship in:
 1. Species in a molecular formula
 2. Species in a balanced chemical reaction
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1. Mole concept in molecular formula
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2. Mole concept in chemical reaction
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LIMITING REAGENT AND EXCESS REAGENT



A limiting reagent is a reactant that will be exhausted in a
chemical reaction and the reaction will stop.
The limiting reagent determines the part of the excess reagent
that will be used up and how much of the products are to be
formed
An excess reagent is a reactant that will remain in excess after
the reaction has stopped,
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SOLUTION
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PERCENT YIELD
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Nature of Aqueous Solutions



Solute – substance being dissolved.
Solvent – liquid water.
Electrolyte – substance that when dissolved in water
produces a solution that can conduct electricity.
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Electrolytes

Strong Electrolytes – conduct current very efficiently
(bulb shines brightly). Completely ionized in water.

Weak Electrolytes – conduct only a small current (bulb
glows dimly). A small degree of ionization in water.

Nonelectrolytes – no current flows (bulb remains unlit).
Dissolves but does not produce any ions.
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Chemical Reactions of Solutions

We must know:


The nature of the reaction.
The amounts of chemicals present in the solutions.
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Molarity

Molarity (M) = moles of solute per volume of solution in
liters:
moles of solute
M = Molarity =
liters of solution
3 M HCl =
6 moles of HCl
2 liters of solution
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Concentration of Ions

For a 0.25 M CaCl2 solution:
CaCl2 → Ca2+ + 2Cl–

Ca2+: 1 × 0.25 M = 0.25 M Ca2+

Cl–: 2 × 0.25 M = 0.50 M Cl–.
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Notice

The solution with the greatest number of ions is not
necessarily the one in which:


the volume of the solution is the largest.
the formula unit has the greatest number of ions.
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Dilution



The process of adding water to a concentrated or stock
solution to achieve the molarity desired for a particular
solution.
Dilution with water does not alter the numbers of moles
of solute present.
Moles of solute before dilution = moles of solute after
dilution
M1V1 = M2V2
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EXERCISE!
What is the minimum volume of a 2.00 M NaOH
solution needed to make 150.0 mL of a 0.800 M NaOH
solution?
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Types of Reactions



Precipitation Reactions
Acid–Base Reactions
Oxidation–Reduction Reactions
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Precipitation Reaction

A double displacement reaction in which a solid forms
and separates from the solution.


When ionic compounds dissolve in water, the resulting solution contains the
separated ions.
Precipitate – the solid that forms.
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The Reaction of K2CrO4(aq) and Ba(NO3)2(aq)

Ba2+(aq) + CrO42–(aq) → BaCrO4(s)
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