More Chemistry
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Yeah!

A mole is simply a number (like a dozen)

Moles
Used in conversion formulas

1 mole is equal to Avogadro’s Number –
6.022x1023 particles

Moles
So, 1 mole = 6.022x1023 particles

1 mole is also equal to the number of
daltons in 1 gram of a substance
Moles

You find the number of daltons (or amu)
in 1 gram of a substance by calculating
the molecular/formula mass

So, 1 mole = molecular/formula mass in
grams

To find the molecular/formula mass:


Sum all of the atomic masses of all atoms in
the chemical formula of the substance
Examples:
H2O – 1+1+16 = 18 g
 C6H12O6 – (12x6) + (1x12) + (16x6) = 180 g

Moles

In a nutshell:
Moles

Particles × 6.022x10^23 Moles × formula mass Grams

Grams ÷formula mass Moles ÷ 6.022x10^23 Particles

Molarity is equal to the number of moles
of solute in one liter of solution

1M would stand for a 1 molar solution

To make up a 1M solution, you would calculate the
number of grams in one mole of the substance
(=formula mass) and then add the solute to total 1
liter
Molarity
Because water is a polar molecule, each
molecule has partial positive and partial
negative charges
 This allows water molecules to form
weak hydrogen bonds with other water
molecules

Acids and Bases

At times, because of the high
electronegativity of oxygen, one water
molecule can completely strip a single
hydrogen atom from another water
molecule

This leaves:


One oxygen atom with three hydrogen atoms
attached (H3O+, hydronium) and a positive charge
And, one oxygen with only one hydrogen attached
(OH-, hydroxide) and a negative charge
Acids and Bases

The formation of hydronium and
hydroxide ions is very rare – 1 in
10,000,000 (or 1x107) in pure water at 25
degrees Celsius

At this temperature, the concentrations of
H3O+ (or H+) and OH- is equal
Acids and Bases
pH is a is a measure of the concentration
of hydrogen (or hydronium) ions in a
solution
 To calculate pH:


-log [H+] (or –log [H3O+]

So, for pure water at 25 degrees Celsius:


pH = -log [1 in 10,000,000]
Or, -log [1x107] = 7
Acids and Bases

So, which is an acid and which is a base?
In a neutral solution, the concentration of
OH- and H3O+ is equal (pH of 7)
+
 In an acid, the concentration of H3O is
greater than that of OH- (pH below 7)
 In a base, the concentration of OH- is greater
than that of H3O+ (pH above 7)

Acids and Bases

When an acid is added to water:


It breaks down (dissociates) which adds H+ to
the solution
When a base is added to water:
It breaks down (dissociates) which adds OHto the solution
 These OH- ions bond with the H+ ions
already present in the water, which decreases
the H+ ions in the solution


However, the product of the molar
concentrations of the OH- and H+
remains constant at 10-14
Acids and Bases

Buffers are solutions that prevent large
changes in pH
Most often made of a weak acid and its
conjugate weak base
 These weak acids and bases very rarely react
with water but are very likely to react with
strong acid or a strong base

Buffers

When a strong base is added to the
solution:
OH- ions are added
 The weak acid from the buffer gives up
(donates) its H+ which reacts with the OHand forms water and the conjugate base


Buffers
This prevents any large changes in pH

When a strong acid is added to the
solution:
H+ ions increase
 The weak base in the buffer reacts with the
H+ ions to form the corresponding weak acid
and the pH does not change very much

Buffers