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Water pulls itself apart! = H + + OH - H 3 O + + OH - OR Bond breaking.

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Presentation on theme: "Water pulls itself apart! = H + + OH - H 3 O + + OH - OR Bond breaking."— Presentation transcript:

1 Water pulls itself apart! = H + + OH - H 3 O + + OH - OR Bond breaking

2 Since water pulls itself apart…. HOH (l) H +1 + OH -1 HOH (l) H +1 + OH -1 We can write a K sp or K w = [H + ][OH - ] We can write a K sp or K w = [H + ][OH - ] [H 2 O] [H 2 O] Only one out of ten million water molecules dissolve, so…. Only one out of ten million water molecules dissolve, so…. This equals [1 x M][1 x M] [1] [1]

3 Water has a K w = 1 x M Once again, this means only one out of every ten million water molecules breaks apart! Once again, this means only one out of every ten million water molecules breaks apart! Most of water is just that…. Undissociated, unbroken, whole, not dissolved water! Most of water is just that…. Undissociated, unbroken, whole, not dissolved water! This natural balance in a glass of water can be upset by dissolving substances in a glass of water that have either H + or OH - in them - this will increase the H + or OH - to an amount more than 1 x M…. This natural balance in a glass of water can be upset by dissolving substances in a glass of water that have either H + or OH - in them - this will increase the H + or OH - to an amount more than 1 x M…. These substances are known as………… These substances are known as…………

4 ACIDS AND BASES!!!!!!! Acids are ionic substances that have H + acting as the metal! Acids are ionic substances that have H + acting as the metal! Examples: HCl, H(NO 3 ), H 2 (SO 4 ) Bases are ionic substances that have OH - acting as the non-metal! Bases are ionic substances that have OH - acting as the non-metal! Examples: Na(OH), Ca(OH) 2, K(OH) What happens when these substances dissolve in water?

5 Acids, Like HCl, break apart in water! HCl > H + + Cl - HCl + HOH > H 3 O + + Cl -

6 This causes the balance to be upset! No longer is there an equal amount of H + and OH - (1 x M of each). Now there is more H +, or H 3 O +, and this means you have an ACID!!! No longer is there an equal amount of H + and OH - (1 x M of each). Now there is more H +, or H 3 O +, and this means you have an ACID!!!

7 Bases, like NaOH, break apart in water! NaOH > Na + + OH -

8 This causes the balance to be upset! No longer is there an equal amount of H + and OH - (1 x M of each). Now there is more OH -, and this means you have a BASE!!! No longer is there an equal amount of H + and OH - (1 x M of each). Now there is more OH -, and this means you have a BASE!!!

9 How do we determine if we have an acid or a base??? If the H + concentration is higher in a solution than the OH - concentration, we have an ACID. If the H + concentration is higher in a solution than the OH - concentration, we have an ACID. If the OH - concentration is higher in a solution than the H + concentration, we have a BASE. If the OH - concentration is higher in a solution than the H + concentration, we have a BASE.

10 What is the pH scale? The pH scale is an easy way to measure whether you have an acid or a base……. The pH scale is an easy way to measure whether you have an acid or a base……. It ranges from 1 to 14: It ranges from 1 to 14: Anything with a pH of 1 to 6 is an acid, anything with a pH of 8 to 14 is a base, and pH 7 is neutral, or water! Anything with a pH of 1 to 6 is an acid, anything with a pH of 8 to 14 is a base, and pH 7 is neutral, or water!

11

12 H +1 concentration pH = -log H +1

13 acidicbasic

14 pH is a measure of…… The amount of H + or acid that is present in solution…… The amount of H + or acid that is present in solution…… We find pH by taking the - log of [H + ] concentration: We find pH by taking the - log of [H + ] concentration: pH = -log [H + ]

15 How does that translate into pH???? If a solution has a concentration of [H+] ions that = 1 x M, that is extremely high and the pH = 2 - this is an acid!!! If a solution has a concentration of [H+] ions that = 1 x M, that is extremely high and the pH = 2 - this is an acid!!! If a solution has a concentration of [H + ] ions that = 1 x M, that is extremely low and the pH = 11- this is a base! If a solution has a concentration of [H + ] ions that = 1 x M, that is extremely low and the pH = 11- this is a base!

16 Let’s go back and look at the K w for water…. [H + ][OH - ] = 1 x M…… [H + ][OH - ] = 1 x M…… [H 2 O] [H 2 O] Why is this….? Why is this….? This is a natural balance in the universe…. This is a natural balance in the universe…. Water always balances itself…. Water always balances itself…. If there is too much H +1, then the H +1 will react with any OH -1 in the water to reform HOH If there is too much H +1, then the H +1 will react with any OH -1 in the water to reform HOH This will dramatically decrease the amount of OH -1 in the water This will dramatically decrease the amount of OH -1 in the water The balance will always equal 1 x though! The balance will always equal 1 x though! So……. So……. HOH (l) H +1 + OH -1

17 If [H + ] is high, say at 1 x M, then the [OH - ] concentration is low, and would equal….. If [H + ] is high, say at 1 x M, then the [OH - ] concentration is low, and would equal….. [1 x M][ OH - ] = 1 x M [OH - ] = 1 x M The pH of this solution would be: The pH of this solution would be: - - log [1 x M] = 2 Why, again, would the [OH - ] be so low…? Why, again, would the [OH - ] be so low…? The reverse reaction is going to occur when you dump in so much [H + ] into the water… The reverse reaction is going to occur when you dump in so much [H + ] into the water… H +1 + OH -1 HOH (l) H +1 + OH -1 HOH (l) And more water is going to be made… And more water is going to be made… Your [OH - ] concentration is going to go way down, and get used up! Your [OH - ] concentration is going to go way down, and get used up! Because your [H + ] concentration is so extremely high, because you added so much extra, there is going to be tons of it left over, even though some of it got used up! Because your [H + ] concentration is so extremely high, because you added so much extra, there is going to be tons of it left over, even though some of it got used up! The two together will still equal 1 x though! The two together will still equal 1 x though! [H + ][OH - ] = [H + ][OH - ] = [H + ][OH - ] = 1 x M [H 2 O] [1] [H 2 O] [1] Why did the concentration of the water become 1?


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