Unit 4 ~ Learning Guide Name:bclearningnetwork.com/LOR/media/CH12/Learning_Guides/CH12_LG_… ·...

BCLN CHEMISTRY 11 - Rev. July/2014

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Unit 4 ~ Learning Guide Name: ______________________________

Instructions:

Using a pencil, complete the following notes as you work through the related lessons. Show ALL

work as is explained in the lessons. You are required to have this package completed BEFORE

you write your unit test. Do your best and ask questions if you don’t understand anything!

Please print out the Formula Sheet and found at the start of the course. You will need this

to do assignments and tests!

Acids and Bases:

1. What is the definition of a Bronsted-Lowry acid?

2. What are the two ways we write the formula for a proton?

3. What is the definition of a Bronsted-Lowry base?

4. What is the definition of an Arrhenius acid?

5. What is the definition of an Arrhenius base?

6. What is the definition of a salt?

7. What is the definition of an amphiprotic compound?


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8. Usually if you see OH you know you are seeing a base. What type of compound is the main

exception to this rule?

9. What are the four ways you can describe an acid or base to indicate that it is strong?

10. The hydroxides of which two groups on the periodic table form strong bases?

11. Complete and balance the following equations.

a) ___ HNO3(aq) + ___ Ba(s)

b) ___ H2SO4(aq) + ___ Sr(OH)2(s)

12. For each of the following state if the acid is monoprotic, diprotic or triprotic. Then state if the

acid is strong or weak.

Acid Protic Nature Weak/Strong

H2SO3

HNO3

H3PO4

HSO4-


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13. Fill in the table with the correct conjugate acid or base.

Acid Base

HCl

HSO4-

HSO4-

14. Why is pure water able to conduct electricity?

15. What is the value of Kw at 25 oC?

16. Is the dissociation of water an exothermic or endothermic process?

17. What happens to Kw as you LOWER the temperature of water?

18. What is the [OH-] in a 50.0 mL solution of 0.050 M HClO4?

19. What is the [H+] in a 150.0 mL solution of 1.5x10

-5 M Mg(OH)2?


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Strength of Acids and Bases:

1. The Relative Strengths of Acids and Bases Table will be used a lot in this unit. Which side of the

table will you find acids on?

2. When comparing two acids will you find the stronger acid higher or lower on the table?

3. When comparing two bases will you find the stronger base higher or lower on the table?

4. Which acid is stronger between HNO2 and HNO3?

5. What are the conjugate bases of the acids in question 4?

6. Which of the two bases in question 5 is stronger?

7. Fill in the boxes below each species with the following labels: SA (stronger acid), WA (weaker

acid), SB (stronger base), WB (weaker base)

H3PO4 + C2O4

2- H2PO4

- + HC2O4

-

8. Which is the favored side (reactants or products) in the equilibrium in question 7? Explain how

you know

9. What property would you actually measure in a lab to determine the strength of an acid?


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10. What is the Ka and Kb for HPO42-

?

11. What is the pOH of a 50.0 mL solution of 0.050 M HClO4? Hint: You already did some of the

work for this in question 18 on page 3. Be careful with significant figures!

12. What is the pH of the solution in question 11?

Calculations:

1. If the pH of a solution decreases by 1, by how much does the acidity of a solution increase?

2. If the pH of a solution increases by 3, by how much does the acidity of a solution decrease?

3. A 500. mL sample of HCl has a pH of 1.50, how much water needs to be added to the sample to

raise the pH to 2.20?


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4. The pH of a solution of Ca(OH)2 is 8.57. Find the [Ca(OH)2]. Be careful, the fact that this base

produces 2 OH- is important!

5. It is useful to assume that the percent ionization of an acid is quite small. This lets us simplify

many calculations. How small must the percent ionization be for this assumption to be valid?

6. Find the pH of a 0.75 M solution of HF.

[I]

[C]

[E]

7. Find the % ionization of a 0.75M solution of HF.


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8. Find the pH of a 1.85 M solution of HSO4-. Note that Ka is large enough here that you can NOT

assume x is much smaller than 1.85!

[I]

[C]

[E]

9. Find the % ionization of a 1.85M solution of HSO4-.


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10. A 0.045 M solution of hypobromous acid (HBrO) has a pH of 5.02. Calculate the Ka for

hypobromous acid.

[I]

[C]

[E]

11. A 750. mL sample of nitrous acid (HNO2) has a pH of 2.35. How many grams of HNO2 were

initially added to create the sample?

[I]

[C]

[E]


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12. What is the value of Kb for CN-?

13. Find the pH of a 0.75 M solution of NaF.

[I]

[C]

[E]


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14. A 2.0 M solution of a weak base B- has a pH of 10.673.

Determine the value of Kb for the base B-

[I]

[C]

[E]


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15. Identify the base B- from question 14.

16. The weak base ethylamine, C2H5NH2, has a Kb value of 5.6 x 10-4

. A particular solution of

ethylamine has a pH of 12.215. What was the initial [C2H5NH2]?

[I]

[C]

[E]


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17. What will happen to both the pH and the POH of pure water if you cool it below 25oC? Explain

why this occurs.

18. The [H+] of pure water at 30

oC is 1.4x10

-7.

a) What is the pH of the solution?

b) What is the [OH-]?

c) Is the solution acidic, basic or neutral. Explain.

d) Calculate pKw.

19. Which compound causes 70% of the acid in acid rain?

20. What substance is most commonly used to reverse the effect of acid rain?

21. Fill in the table below with the words acid and base.

Anhydride Acid/Base

Metal

Non-metal


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More about Acids and Bases:

1. Define buffer.

2. What type of acid and base can we NOT use to prepare a buffer?

3. If you wanted to created an equimolar buffer using 1.0 mol of NaHS in 1.0 L of water, what acid

would you need to add? How many moles of that acid do you need to add?

4. Write an equilibrium equation for the above buffer. Be sure the acid is on the left. Do not

include any spectator ions

5. What direction will the equilibrium shift if a small amount of acid is added and what will

happen to the pH of the solution?

6. What direction will the equilibrium shift if a small amount of base is added and what will

happen to the pH of the solution?

7. Does ammonia act as an acid or base in water? Write the formula for the compound

ammonia forms when placed in water


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8. What is the pOH and pH of a 0.250 M solution of NH4OH at 25°C?

[I]

[C]

[E]

9. What three letter symbol do we use as a short form for an indicator?


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10. What is the Ka for the second ionization of the indicator Thymol blue? Use the Acid-Base

Indicators page from your data booklet to help you get started.

11. What is the Kb for the indicator phenolphthalein? You will need to first determine the Ka!

Titrations:

1. Provide two definitions for the word titration

2. What is the point at which a titration will result in a color change called?

3. Complete and balance the following neutralization reaction:

___ H3PO4(aq) + ___ Sr(OH)2(aq)


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4. Write a balanced complete ionic equation for the reaction in question 3. Warning you may need

to write quite small to fit the entire equation on one line!

5. Write a balanced net ionic equation for the reaction in question 3 and 4.

6. If a strong acid is titrated with a strong base, what pH will the equivalence point be at?

7. If a weak acid is titrated with a strong base, will the pH of the equivalence point be above or

below your answer in question 6?

8. If a strong acid is titrated with a weak base, will the pH of the equivalence point be above or

below your answer in question 6?

9. A titration of two identical 20.00 mL samples of HBr was performed using 0.700 M KOH. The

following data was collected:

Burette Reading(mL) of KOH

Trial 1 Trial 2 Trial 3

Initial

1.07 1.02 2.12

Final

33.42 30.18 31.32


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What is the concentration of HBr?

10. If 159 mL of 0.0085 M HI is titrated with 125.0 mL of Al(OH)3, what is the concentration of

Al(OH)3?

11. If 300. mL of 0.758 M HBr is mixed with 650. mL of 0.362 M LiOH, what is the resulting pH?


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12. If 500. mL of 0.00673 M H2SO4 is mixed with 400 mL of 0.00487 M Al(OH)3, what is the

resulting pH and pOH?

13. Determine if each of the salts in the following table is acidic, basic or neutral.

Salt Acidic, Basic, Neutral

CaBr2

NH4Cl

KNO2

14. For each acidic or basic salt in question 13, write a hydrolysis reaction.


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15. Calculate the pH of a 0.0587 M solution of KHS.

[I]

[C]

[E]


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Answers:

Acids and Bases Hints:

18. and 19. You need to use this formula: Kw = [OH-][H

+]

Acids and Bases Answers:

18. 2.0x10-13

M 19. 3.3x10-10

M

Strengths of Acids and Bases Hints:

10. Ka and Kb are related using: Kw = [Ka][Kb(conjugate base)]

11. One way to calculate pOH is to use: pOH = -log[OH-]

12. pH and pOH are related using: pH + pOH = 14

Strengths of Acids and Bases Answers:

10. Kb = 1.6x10-7

M 11. pOH = 12.70 12. pH = 1.30

Calculations Hints:

3. You will need to convert pH into concentration and use the dilution formula.

4. The first step is to convert pH into pOH.

6. Your E boxes will have: 0.75 - x, nothing, x and x in them. These get plugged into a Ka.

8. Your E boxes will have 1.85-x, nothing, x and x in them. These get plugged into a Ka.

10. and 11. The first step is to convert pH into [H+]. No need for x's in your ICE box.

13. The first step is to calculate Kb. Your E boxes will have 0.75-x, nothing, x and x in them.

14. The first step is to calculate pOH. No need for x's in your ICE box.

16. The first step is to calculate pOH. Your E boxes will have: x-0.0164, blank, 0.0164 and

0.0164


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Calculations Answers:

3. 2000 mL 4. 1.9 x 10-6

M 6. pH = 1.80

7. 2.1% 8. pH = 0.85 9. 7.6%

10. Ka = 2.0x10-9

11. 1.7 g 12. Kb =2.0x10-5

13. pH = 8.68 14. Kb =1.1x10-7

16. 0.497 M

18. a) 6.85 d) 13.70

More about Acids and Bases Hints:

8. The first step is to calculate Kb. Your E boxes will have: 0.250, x and x. You can assume

that x is much much smaller than 0.250.

10. and 11. Determine the pH at transition by finding the middle of the range that the transition

occurs at

More about Acids and Bases Answers:

8. pOH = 2.67 pH = 11.33 10. 1.6x10-9

11. 1.3x10-5

Titrations Hints:

15. The first step is to calculate Kb. Your E boxes will have 0.0587 - x, nothing, x and x

Titrations Answers:

9. 1.02 M 10. 0.00360 M 11. pH = 11.9

12. pH = 3.01 pOH = 10.99 15. pH = 9.91

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