Solutions Review Pt 2
Electrolytes vs Non-electrolytes
Electrolytes vs Non-Electrolytes
Electrolyte
When dissolved in water,
allows for electron flow
Produces ions when dissolved
in water
Non-Electrolyte
When dissolved in water, does
not allow for electron flow
Does not produce ions when
dissolved in water
Substances which were formed Substances which were form by
by ionic bonds
covalent bonds
Acids, bases and salts
Note: for a substance to conduct electricity, it must be
dissolved in water
What’s ionic and covalent again?
Ionic bond→ bond between a metal and a nonmetal
– The metal looses electron to get a positive charge
– The non-metal gains electron to get a negative
charge
Covalent bond → bond between non-metal
sharing electrons to get stable octet
Electrolyte dissociation
• Def: electrolytes are dissolved in water,
dissociating from one another to their
respective positive and negatively charged
ions, allowing for conduction of electricity
• Key thing → get the production of ions during
dissociation!
– No ions, no electrical conductivity
Examples of electrolyte dissociation
Salts
NaCl(s)→Na+(aq) + Cl-(aq)
CaCl2(s)→Ca2+(aq) + 2Cl-(aq)
Acids
H2SO4(s)→2H+(aq) + SO42-(aq)
HCl(s)→H+(aq) + Cl-(aq)
Bases
KOH(s)→K+(aq) + OH-(aq)
NaOH(s)→Na+(aq) + OH-(aq)
Acids!
• An acid is a substance that releases H+ ions in
an aqueous solution
– How can you tell an acid from molecular formula?
• Usually an acid starts with H atom and is then followed
by a non-metal
• Exception! Acetic acid CH3COOH dissociates to H+
andCH COO3
• Acids rnx with blue litmus paper and turns it
red
Bases!
• A base is a substance that releases OH- ions in
an aqueous solution
– How can you tell an acid from molecular formula?
• Usually a base starts with a metal and is ends with OH
• Exception! Ammonia NH3 is actually a base even
though it doesn’t have an OH- group!
– When it reacts with water, the following reaction occurs
NH3 + H2O → NH4+ + OH-
• Bases rnx with red litmus paper and turns it
blue
Salts!
• A salt is a substance that is produced by
chemical bonding of a metal and a non-metal
other than H+ or OH– It is an ionic bond!
• NaCl: Sodium chloride dissociates to Na+ and Cl• KBr: Potassium bromide dissociates to K+ and Br• BeS: Beryllium sulfide dissociates to Be2+ and S2-
• Litmus paper has no effect on salts
Types of Electrolytes
Acids
Bases
Salts
Definition
Sub. that when
Sub that when
When dissociate
dissociate
dissociate release have metal and
release H+ in sol. OH- in sol.
non-metal
Litmus Paper
Test
Turns blue paper Turns red paper
red
blue
Does not rnx
Uses/Found
in
Neutralizes base, Neutralizes acid,
found in fruits
found in blood,
cleaning prods
Found in
fertilizers,
soaps,
How to
recognize
Usually starts
Usually ends with 1st = metal
with H, has H+ gr OH, has OH- gr
2nd= non-metal
Examples
HCl, HF, HNO3
NaOH, Ca(OH)2
Exceptions to
“H” rule
Water, Acetic
Acid (CH3COOH)
CH3OH, C2H50H ->
alcohols!; Not
bases, NH9 is a base
NaCl, AgNO3
pH Scale
• Used to determine whether or not a
substance in solution is an acid, a base, or
neutral
• Goes from 0 to 14
– 0-6.9 → acids
• Strong acids closer to 0
• Weak acids near 6.9
– 7.1-14 → bases
• Strong bases closer to 14
• Weak bases near 7.1
pH Scale
• The scale goes up by a 10-fold factor
– Meaning if you are comparing an acid with a pH 2
and pH of 3, the acid which has a pH 2 is 10 times
stronger
– If you are comparing an acid with pH 2 and pH 6,
the acid which has pH 2 is 104 times stronger
How to i.d if you have an acid, base or
neutral substance
1. Litmus Paper Test
•
Tells you if your substance is an acid, base or
neutral
2. Buffer Solution + Indicators
•
A buffer solution is a solution composed of a
weak acid and it’s associated base.
•
•
Key: it’s pH changes very little when strong acid/base
added to it, meaning it has specific pH levels!
An indicator is a chemical which undergoes a
colour change at specific pHs
Litmus Paper Test
• Blue paper
– Turns red when introduced to an acid
– Stays blue when introduced to a base or a neutral
solution
• Red paper
– Turns blue when introduce to a base
– Stays red when introduce to an acid or a neutral
solution
Buffer Solution + Indicator
• This procedure plays on the specificity of
buffer solutions
• The first step you do is introduce your solution
to the indicator and record that colour
• Then you introduce your indicator to buffer
solutions ranging from pH 1 to pH 14 and
match the colour
– You may have to use more than one indicator, for
their ranges overlap, thus allowing to get a more
precise pH value!
pH indicator example
pH
Thymol
Blue
Bromo.
Blue
Methyl
Red
Phenol
Red
Cresol
Red
Pheno.
Thymol.
1
2
3
4
5
Red
6
7
8
9
10
11
Yellow
Yellow
12
13
Blue
Purple
Red
Yellow
Yellow
Red
Yellow
Reddish-Purple
Colourless
Colourless
Fuchsia
Blue
pH indicator example
1. Which indicator(s) would you use to find a
strong acid? Strong base? Neutral substance?
2. My solution turned red using Methyl Red and
purple using Bromophenol Blue. What’s the
pH of my solution (range)?
3. My solution turned blue using Thymol Blue
and fuchsia using Phenolphthalein. What’s
the pH of my solution (range)?
Mnemonic to remember for acids and
bases
Acids are red, bases are blue, water is neutral,
what about you?
Acid → turn blue litmus paper red
Bases → turn red litmus paper blue
Water → as a neutral substance, does not rnx
with litmus paper (same as salts)