1. Lesson 3: Electrolytes, Ph, acids, bases and salts
Pure water does not conduct electricity!

2. What are Electrolytes?
Def: substances that, when dissolved in water (aqueous solution), conduct an electric current.
Therefore, an electrolytic solution allows electricity to flow.
The electrical conductivity of a solution is a measure of its ability to allow an electric current to flow through it.

3. Electrolytic Dissociation
When an electrolyte is dissolved in water, it separates into two ions of opposite charges (positive and negative).
This is a physical change.

4. Conditions for Current to Flow
3 conditions must be met in order for an electric current to flow:
Electric charges (ions) must be present
 ions are found in ionic compounds
These charges must be mobile
 when dissolved in water, the ions are pulled apart and are free to conduct electricity
The charges must move in a particular direction
 the electrodes on the electrical conductivity meter direct the charges

5. What type of compound is made of ions???
Ionic compounds!!!!
When an ionic compound is placed in water, the ions dissociate. This means that they separate. The solution will now be filled with ions.

6. Electrolytic solutions
Def: A solution that contains an electrolyte
(hence, that conduct electricity!)
Applications: batteries!

8. Electrolytic Dissociation

9. Electrolytic Dissociation (physical change!)
solid
aqueous
When NaCl dissolves in water, sodium and chlorine ions are produced.
A dissociation equation must be balanced (a subscript on the reactant side becomes a coefficient on the product side.)
The charges on the ions must be present. (This is determined by the periodic table)
Subscripts must be written showing the state of the compound or ion.

10. Nonelectrolytes! C12H22O11(s) C12H22O11(aq)
When dissolved in water, no ions are produced!
For example: when sugar is dissolved in water, the molecules remain intact, although they become detached!

11. electrolyte VS nonelectrolyte

12. When electricity present!
Positive ions negative electrode (cathode)
Negative ions positive electrode (anode)

13. Let’s Practice

14. Types of Electrolytes
Acids
Bases
Salts

15. Acids
The following are all acids:
HCl, H2SO4, HBr, H2S
What are some properties of these compounds?
Turn blue litmus paper red.
Conduct electricity (electrolytic!)
React with metals
Sour in taste (but never taste an unknown acid!!)

16. Electrolytic Dissociation
What ions are produced when these acids are dissolved in water?
HCl →H+1 + Cl-1
H2SO4 →2H+1 + SO4-2
HBr → H+1 + Br-1
H2S → 2H+1 + S-2
CH3COOH → H+1 + CH3COO-1
Acids produce hydrogen ions in solution.

17. Recognizing Acids Acids often start with an “H” in the formula.
They may also end with “COOH” (exception!)
Combinations of C’s and H’s only are not acids. They are hydrocarbons (CH4 and C3H8 ).
NH3 is also an exception: it is a base.

18. Bases NaOH, Mg(OH)2,KOH What are some properties of these compounds?
The following are all bases:
NaOH, Mg(OH)2,KOH
What are some properties of these compounds?
Turn red litmus paper blue.
Conduct electricity (electrolytic!)
Do not react with metals
Bitter
Slippery to the touch

19. Electrolytic Dissociation
What ions are produced when these bases are dissolved in water?
NaOH →Na+1 + OH-1
Mg(OH)2→Mg+2 + 2OH-1
KOH → K+1 + OH-1
NH3 + H20 → NH4+ + OH-1 (exception!)
Bases produce hydroxide ions in solution.
Bases contain “OH” in their formula.

20. Salts What are some properties of these compounds?
A substance produced by the chemical bonding of a metallic ion and nonmetallic ion (other than H+ and OH- )
Examples (NaCl, MgBr2 , CaSO4)
What are some properties of these compounds?
Do not affect litmus paper (neutral!)
Conduct electricity
Do not react with metals

21. Identify the following as A/B/S
NaOH
HClO4
CsOH HI
HBr
HNO3
MgCl2
Sr(OH)2
H2SO4
CH3COOH
Ba(OH) 2
CH4
MgSO4
Ca(OH)2
HNO2
K3P
HSO4-
KOH

22. pH Scale
The pH of a solution is actually an indication of the concentration of H+ ions in that solution.
pH means the “power of Hydrogen”

23. Acids Acids release hydrogen ions in solution (water).
The water already contains a mixture of hydrogen and hydroxide ions.
H2O →2H+1 + OH-
Therefore in an acidic solution there will be both hydrogen and hydroxide ions.
However there will be more hydrogen ions.
The pH of acids is less than 7.

24. Bases Bases release hydroxide ions in solution (water).
The water already contains a mixture of hydrogen and hydroxide ions.
H2O →2H+1 + OH-
Therefore in a basic solution there will be both hydrogen and hydroxide ions.
However there will be more hydroxide ions.
The pH of bases is greater than 7

25. Calculating pH pH = -log[H+]
[H+] is the concentration of hydrogen ions
On the pH scale, a difference of 1 unit is equivalent to 10 fold difference in acidity!
Ex: a solution with a pH of 3 is 10 times more
acidic than a solution with a pH of 4!

26. pH units Each unit on the scale represents a factor of 10.
A substance with a pH of 9 is 10x10x10x10 more basic than a substance with a pH of 5.
9 - 5 = = 10x10x10x10 =
A substance with a pH of 2 is 10x10x10x10x10 more acidic than a substance with a pH of 7.
7 - 2 = = 10x10x10x10x10 =
Makes sense?