No QOTD Today 5/16/14

Please have your HW out to be checked off (p. 71-72)

Please pick up the HW key and check your work. We will have time to ask questions after I finish checking off HW.

Remember that “chemistry in my life” posters are due Monday!

Learning Target

1. You should be able to describe the effect on pH when water is added to an acid, a base or salt water.

2. You should be able to describe the relationship between [H+], [OH-], pH and pOH and perform calculations to determine missing information.

QUIZ over acids, bases and pH on Tuesday!

Turn and Talk #1: diluting HCl

[ HCl ] pH1.0 M 00.1 M 10.01 M 20.001M 30.0001 M 40.00001 M 50.000001 M 60.0000001 M 70.00000001 M ?

1. How does diluting acid affect the acidity?

2. If you continue to dilute the solution, will you get a pH above 7? Why or why not?

3. What do you think will happen to the pH if you were to dilute the last solution even more?

Diluting HCl

[ HCl ] pH1.0 M 00.1 M 10.01 M 20.001M 30.0001 M 40.00001 M 50.000001 M 60.0000001 M 70.00000001 M ?

1. How does diluting acid affect the acidity?

Acidity decreases (lower H3O+ concentration)

2. If you continue to dilute the solution, will you get a pH above 7? Why or why not?

NO! It will still have some acid in it and acids are never above pH 7!

3. What do you think will happen to the pH if you were to dilute the last solution even more?

It will not change. It is already neutral!

Turn and Talk #2: diluting NaOH

[ NaOH ] pH1.0 M 140.1 M 130.01 M 120.001M 110.0001 M 100.00001 M 90.000001 M 80.0000001 M 70.00000001 M ?

1. How does diluting base affect the basicity?

2. If you continue to dilute the solution, will you get a pH above 7? Why or why not?

3. What do you think will happen to the pH if you were to dilute the last solution even more?

Turn and Talk #2: diluting NaOH

[ NaOH ] pH1.0 M 140.1 M 130.01 M 120.001M 110.0001 M 100.00001 M 90.000001 M 80.0000001 M 70.00000001 M ?

1. How does diluting base affect the basicity?

Basicity decreases (lowers OH- concentration)

2. If you continue to dilute the solution, will you get a pH above 7? Why or why not?

NO! Bases are always above pH 7

3. What do you think will happen to the pH if you were to dilute the last solution even more?The pH will stay at 7 (it is already neutral)

Turn and Talk #3: diluting NaCl

[ NaCl ] pH1.0 M 70.1 M 70.01 M 70.001M 70.0001 M 70.00001 M 70.000001 M 70.0000001 M 70.00000001 M ?

1. How does diluting NaCl affect the pH? Why?

There is no effect!

NaCl is neither an acid nor a base!

Therefore, you don’t change either [H3O+] or [OH-] when you add water.

Activity

Turn to page 68-69.

Fill in the tables and answer the questions.

We will debrief these in about 15 minutes.

If you finish early, ask me for the homework!

An

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68

Substance Acid? Base?

pH [H+] decimal [H+] scientific notation?

1 M HCl Acidic 0 1 M 1.0 x 100 0.1 M HCl Acidic 1 0.1 M 1.0 x 10-1 Clear soda Acidic 3 0.001 M 1.0 x 10-3 Rain water Acidic 6 0.000001 M 1.0 x 10-6 Distilled water

Neutral 7 0.0000001 M 1.0 x 10-7

Alcohol Neutral 7 0.0000001 M 1.0 x 10-7 Salt water neutral 7 0.0000001 M 1.0 x 10-7 Washing soda

Basic 8 0.00000001 M 1.0 x 10-8

Ammonia Basic 10 0.0000000001 M 1.0 x 10-10 0.1 M NaOH Basic 13 0.0000000000001 M 1.0 x 10-13

1 M NaOH basic 14 0.00000000000001 M 1.0 x 10-14

Answers p. 68

1. If you know [H+] in decimal form, how do you find the pH?pH = decimal place the 1 is in (0.1 has the digit in the 1st decimal place and has pH = 1)2. If you know [H+] in scientific notation, how do you find the pH? pH = the exponent number (without the – sign). But the only works if you have 1.0 as the coefficient! Ex: 1.0 x 10-4 would have pH = 43. As the value of pH increases, what happens to [H+] ?It decreases4. As the value of pH decreases, what happens to [H+] ?It increases

Answers p. 68

5. Solution A has a pH of 5. Solution B has a pH of 9.

a) What is [H+] for each solution?A = 1.0 x 10-5 M B = 1.0 x 10-9 Mb) Identify if they are acidic or basicA = acidic B = basic (hey, those match the letter numbers! c) How many times more acidic is the acid than the base?A is 104 times more acidic (10,000 times more!)

p. 69 table (HCl)

Well pH [H+] [OH-] pOHA 1 1.0 x 10-1 M 1.0 x 10-13 M 13B 2 1.0 x 10-2 M 1.0 x 10-12 M 12C 3 1.0 x 10-3 M 1.0 x 10-11 M 11D 4 1.0 x 10-4M 1.0 x 10-10 M 10E 5 1.0 x 10-5 M 1.0 x 10-9 M 9F 6 1.0 x 10-6 M 1.0 x 10-8 M 8G 7 1.0 x 10-7 M 1.0 x 10-7 M 7H 7 1.0 x 10-7 M 1.0 x 10-7 M 7I 7 1.0 x 10-7 M 1.0 x 10-7 M 7

p. 69 table (NaOH)

Well pH [H+] [OH-] pOHR 7 1.0 x 10-7 M 1.0 x 10-7 M 7Q 7 1.0 x 10-7 M 1.0 x 10-7 M 7P 7 1.0 x 10-7 M 1.0 x 10-7 M 7O 8 1.0 x 10-8 M 1.0 x 10-6 M 6N 9 1.0 x 10-9 M 1.0 x 10-5 M 5M 10 1.0 x 10-10 M 1.0 x 10-4 M 4L 11 1.0 x 10-11 M 1.0 x 10-3 M 3K 12 1.0 x 10-12 M 1.0 x 10-2 M 2J 13 1.0 x 10-13 M 1.0 x 10-1 M 1

p. 69 answers

1. What does [OH-] stand for?Molar concentration of hydroxide ions

2. What can you say about [OH-] in solutions with high acidity?[OH-] will be very low

3. How is the value of pH related ot the value of pOH for each concentration?

If pH is 1, then pOH is 13. THEY ALWAYS ADD UP TO 14!pH = pOH = 14

p. 69 answers

4. If you know the value of pH, how do you determine pOH?

Subtract pH from 14 to get pOH

5. If you know the value of pOH, how do you find pH?Subtract pOH from 14 to get pH

pH equations ( you’ll want these for the HW )

pH is an example of a “p function”: p(stuff) = - log(stuff)

pH = - log [H+] = - log [H3O+]

pOH = - log[OH]

pH + pOH = 14 So to find the pH of a base, find pOH and subtract from 14

Practice Problems (use calculator!) pH = -log[H+] pOH = - log[OH-]

pH + pOH = 14

1. What is the pH of a 0.25 M HCl solution?pH = - log(0.25) = 0.6

2. What is the pH of a 12 M HCl solution?pH = - log(12) = -1.08 (yes, it CAN be negative!)

3. What is the pH of a 0.5 M NaOH solution? (hint: find pOH first since this is a base)pOH = -log(0.5) = 0.3pH = 14-pOH = 14 – 0.3 = 13.7

Homework

Answer HW Qs 1-6 on p. 70