1. NOTES 10 – Acids, Bases, & pH

2. Ion Review
An ion is an atom that gains or loses electrons giving it an overall positive or negative charge
Lose electrons = positively charged ion
Gain electrons = negatively charged ion
Sometimes a compound acts like an ion
Hydrogen atoms have 1 proton and 1 electron
Compounds that take hydrogen’s electron can become negative ions (more electrons than protons)
The leftover hydrogen proton becomes a positive hydrogen ion

3. Water Molecules Form Ions
Water molecules break apart into ions and then reform into molecules
Water forms two different ions
Hydrogen Ions = H+
Hydroxide Ions = OH-
H2O  H OH-
When water breaks into ions, it is called dissociation (Water dissociates into ions)
In pure water there are equal numbers of hydrogen and hydroxide ions

4. Dissociation of Water
In any sample of water, very few of the molecules are dissociated at any one time
About 1 in 550 million 
There is constant change
As one hydrogen ion reattaches to a hydroxide ion to form a water molecule, another water molecule dissociates to replace the hydrogen ion and the hydroxide ion in solution

5. What are acids?
Acid – a compound that increases the number of hydrogen ions (H+) when dissolved in water
In water, acids dissociate producing H+ ions
Acidic solutions (acid substance + water) have more hydrogen ions than hydroxide ions (More H+ than OH-)
Acids taste sour
Acids can cause burns
Acids can be good conductors of electricity
EX. acetic acid, citric acid, ascorbic acid

6. Strong Vs. Weak Acids Strong acids ionize completely
Every molecule of the acid produces H+ ions and negative acid ions
Strong acids have a pH in the range of 0 to 3
EX. Nitric acid in water
HNO3  H+ + NO3-
Weak acids do not ionize completely
Some molecules form ions, some do not
Weak acids have a pH above 3
EX. Acetic acid in water
CH3COOH  CH3COO- + H+

7. Acids Are Useful But Can Be Dangerous
Acids are used for cleaning, in batteries, making fertilizers, dyes, etc.
Foods contain acids (vinegar & citrus fruits)
Stomach acid helps digest your food
Acids in concentrated forms can cause severe skin damage
Acid vapors can damage the eyes, mouth, and lungs

8. What are bases?
Base – a compound that increases the number of hydroxide ions (OH-) when dissolved in water
In water, bases dissociate producing OH- ions
Basic solutions (base substance + water) have more hydroxide ions than hydronium ions (More OH- than H+)
Bases taste bitter
Bases feel slippery and may cause burns
EX. baking soda, bleach, ammonia

9. Strong Vs. Weak Bases
Strong bases are ionic compounds that contain hydroxide ions (OH-)
When dissolved in water, a strong base dissociates (separates) forming hydroxide ions
EX. Sodium hydroxide in water
NaOH  Na+ + OH-
Weak bases do not contain hydroxide ions, but form them when mixed with water
EX. Ammonia and water
NH3 + H2O  NH OH-

10. Bases Are Useful But Can Be Dangerous
Bases are used to make soaps, to clean drains, to make cement, fertilize soil, etc.
Bases attack living tissue very quickly
In concentrated form, bases can be very harmful
Even in diluted form, some bases can be fairly dangerous

11. Acids, Bases, & Electricity
Strong acids and strong bases are good conductors of electricity (electrolytes)
Electrolyte – a substance that dissolves in water forming a solution that conducts electricity
EX. A solution of sulfuric acid and water conducts electric current in car batteries

12. What is pH?
pH – a number used to indicate how acidic or basic a solution is
The pH scale goes from 0 to 14
Solutions with a pH below 7 are acids
Lower number = stronger acid
EX. A solution with a pH of 2 is a stronger acid than a solution with a pH of 5

13. What is pH? Solutions with a pH above 7 are bases
Higher number = stronger base
EX. A solution with a pH of 13 is a stronger base than a solution with a pH of 9
Pure water has a pH of 7 and is neither acid nor base

14. pH measures the relative amount of H+ ions in a solution

15. Neutralization To neutralize means to make the pH of a solution 7
Acids and bases can neutralize each other
If the amounts are equal:
strong base + strong acid = neutral solution
strong base + weak acid = weaker base solution
weak base + strong acid = weaker acid solution

16. Neutralization Reactions
Acids and bases react to form water and salt
Salt – an ionic compound that is a product of a neutralization reaction between an acid and a base
The base provides the OH- and the acid provides the H+
OH- + H+  H2O
The other ions from the acid and base form the salt
EX. sodium hydroxide + hydrochloric acid
NaOH + HCl  NaCl + H2O

17. What is acid rain? Normal rain is slightly acidic, with a pH over 5.7
Acid rain – rain with a pH below 5.5
Acid rain can harm plants
Acid rain can harm animals, particularly those that live in the water
Acid rain can damage buildings and other structures

18. How does acid rain form?
Burning fossil fuels releases sulfur and nitrogen compounds into the atmosphere
Sulfur dioxide reacts with moisture in clouds to produce sulfuric acid
Nitrogen oxides react with moisture producing nitric acid
The acids drop the pH of rainwater below 5.5
The largest natural cause of acid rain is the release of sulfur dioxide by volcanoes

19. Acids & Bases - Main Idea
Acids and bases react in water to form ions
Acid and base solutions contain large amounts of positive or negative ions
These solutions are highly reactive
When mixed, acid and base solutions can neutralize one another
pH scale measures the strength of an acid or base