1. Goals Explain the differences between acids and bases
Identify substances as an acid or a base
Explain why water is special
Describe the pH scale

2. What is an acid?
An acid is an ionic compound that contains a hydrogen ion
Hydrogen ion = H+
Hydrogen ion is basically just a proton
H has no neutrons and 1 electron, but in an ion, the electron gets removed
An acid is a compound that donates (gives up) a proton (H+)

3. What is a base?
A base is an ionic compound that contains a hydroxide ion
Hydroxide ion = OH-
1 hydrogen bonded with 1 oxygen and they always stick together
As a whole, a hydroxide ion has a -1 charge
A base is a compound that accepts (takes on) a proton (H+)

4. What about water? Water is a special chemical for lots of reasons
Water can act as an acid AND a base

5. What about water? HCl + H2O --> Cl- + H3O+ water acts as a base
it accepts a proton to become H3O+
H3O+ is called a HYDRONIUM ion (created when water gets an extra proton)

6. What about water?
H2O NH > OH NH4+
Water acts as an acid
It loses a proton to become OH-
Water acts different depending on who it is combining with. Sort of like you act different around your friends and around your parents.
Water is really H(OH): a hydrogen ion bonded with a hydroxide ion.

7. How do we know if something is an acid or a base?
Look at the chemical formulas, look for H (acid) or OH (base)
Look at a chemical reaction, does the compound accept a proton (base) or lose one (acid)
Determine the pH of the substance

8. Acid or Base? NH3 + H2O  NH4+ + OH- Ca(OH)2 + H2CO3  CaCO3 + H2O
H2O + CH3COO-  CH3COOH + OH-

9. What is pH?
pH is a number that tells us how acidic or basic a substance is.
pH is determined based on the concentration of hydrogen ions or hydroxide ions in the solution.
More hydrogen ions = lower pH = acid
More hydroxide ions = higher pH = base

10. What is pH?
The pH scale starts at 0 and goes to 14

11. What is pH? If the pH is from 0-6.9, the substance is an acid
The closer to 0, the stronger the acid
the closer to 6.9, the weaker the acid
If the pH is from 7.1 – 14, the substance is a base
The closer to 14, the stronger the base
The closer to 7.1, the weaker the base.

12. What is pH?
A pH of 7 is a neutral substance (neither an acid nor a base): WATER, lots of everyday substances
We can measure pH using pH strips (special skinny pieces of paper)

13. There are other ways to determine if something is an acid or a base
Indicators
these are chemicals that change colors based on their environment
Phenolphthalein (Pth)
Clear in acids and neutral
Turns pink in bases

14. Litmus paper (red and blue)
Turns blue in bases
Stays red in acids and neutral substances
Blue
Turns Red in Acids
Stays blue in bases and neutral substances
Universal Indicator
methyl red, methyl yellow, thymol blue, and bromthymol blue

15. There are other ways to determine if something is an acid or a base
Acids feel clean to the touch and taste sour
Bases feel slippery and taste bitter

16. Rule of Thumb:
If you drop a compound into water and it forms hydrogen ions (aka hydronium ions), the compound is an acid. If you drop a compound into water and it forms hydroxide ions, the compound is a base.

17. Rule of Thumb
Ionic compounds will always break down when put into water, this is called IONIZATION (ex. NaCl will break up into Na+ and Cl- in water). Since acids and bases are ionic compounds, they break up in water too.

18. Agenda Items
Part 2 of HW Pkt
Part 3: Do NOT do number 3!