Acids and bases Packet (Chapters 16 & 17)
Unit objectives:
I. Understand the different theories of acids and bases
II. Understand how the strength of acids and bases are measured and what determines the strength of acids and bases.
III. Understand how to name and write formulas for Arrhenius acids and bases.
IV. Understand why Bronsted acids and bases are always found as pairs, how to identify conjugate acid-base pairs, and how to determine the direction of Bronsted acid- base reactions depending on the strength of the Bronsted acids and bases.
V. Understand what pH measures and how it is a log base measurement.
VI. Understanding titrations and how to use titrations to find the strength of an acid or base.
Below you will find notes on some of these topics. Please answer the assigned text book questions on notebook paper to be turned in and checked for correctness.
Part I. There are 3 theories of acids and bases. These are indicated below:
1) Arrhenius theory:
Acids - substances that ionize when dissolved in water to produce H+ or (H3O+, hydronium) ions.
Ex: HCl à H+ + Cl-
Ex. H2SO4 à 2H+ + SO4-2
Bases – substances that dissociate in water when dissolved to produce OH- (hydroxide) ions.
Ex: NaOH à Na+ + OH-
Ex: Mg(OH)2 à Mg+2 + 2OH-
2) Bronsted-Lowry theory:
Acids – substances that are donating a proton (H+ ion)
Bases – substance that are accepting a proton (H+ ion)
Note: You cannot have one without the other. If something is going to lose a proton, there must be something to take it!
Note: a conjugate base is a substance that is left remaining after an acid has lost its proton (H+ ion).
Note: a conjugate acid is the substance that is left after a base has gained a proton (H + ion.)
Note: The direction of a conjugate acid-base system is always from the stronger acid-base pair to the weaker acid-base pair. This should make sense as there are two possible acids, one on the left of the arrow, one on the right. Which one wants to lose its proton (H+ ion) more eagerly? This one is the stronger acid and the reaction will go in a direction from this acid to the weaker acid. See below:
Ex: HClO4 + NH3 àß ClO4- + NH4+
acid base conjugate base conjugate acid
Ex: HSO4- + H2O àß OH- + H2SO4
conjugate base conjugate acid base acid
3) Lewis theory:
Acids – substances that have an ability to accept an e- pair.
Bases – substances that have an ability to donate an e- pair.
Ex: BF3 PCl3
Part II. Understanding the strength of acids and bases.
A pH scale is used to measure the strength of acids and bases. The pH scale measures the concentration of H+ ions ion solution. H+ ions in aqueous solutions are actually hydronium ions (H3O+). The greater the number of hydronium ions in solution, the stronger the acid. The greater the number of hydroxide ions in solution, the stronger the base.
pH scale: 0 ------7------14
strong weak neutral weak strong
acid acid base base
[H+] > [OH-] [H+] = [OH-] [OH-] > [H+]
Note above: Just because a solution is neutral does not mean that the solution does not have hydrogen or hydroxide ions. It just means that the concentration of each ion is the same.
If the above statement is true, which it is, then why is AL(OH)3 and Mg(OH)2 weaker bases than NaOH and KOH? When they dissociate (shown below), aren’t more hydroxide ions produced from the aluminum and magnesium hydroxide?
Al(OH)3 à Al+3 + 3OH- NaOH à Na+ + OH-
Vs.
Mg(OH)2 à Mg+2 + 2OH- KOH à K+ + OH-
Note: In order to produce the ions shown above, the substance must be able to dissolve in water. Aluminum and magnesium hydroxide are NOT very soluble in water. Therefore, you really do not see the ions shown above produced by the dissociation of aluminum and magnesium hydroxide. Sodium and potassium hydroxide ARE very soluble and therefore produce lots of hydroxide ions and are therefore, strong bases.
Therefore, the strength of an Arrhenius base ultimately depends on the ability of the base to dissolve in water, its solubility.
Now, what about the strength of acids? Why is H3PO4 weaker than HCl, even though H3PO4 produces 3 H+ ions per molecule while HCl produces only 1 H+? The reason for this is not the solubility of the acid. The reason for this is due to the % ionization. HCl ionizes 100%. This means that for every 100,000 HCl molecules, you’ll make 100,000 H+ ions. (See below.)
HCl à H+ + Cl-
100,000 molecules 100,000 ions
H3PO4, however, ionizes to a much smaller amount, let’s say 0.0045 %. This means for every 100,000 H3PO4 molecules, only 0.0045 % of them, or 4.5, will break into ions. (See below.)
H3PO4 à 3H+ + PO4-3
100,000 molecules 4.5 ions/
molecule
Part III. Understanding how to name and write formulas for Arrhenius acids and bases.
Bases – to name and write formulas for bases is no different than what was already learned in class. Be aware of the fact that all Arrhenius bases contain the hydroxide anion.
Acids – to name and write formulas for acids is a little different than typical nomenclature done earlier in the year. You first must recognize if the acid is a binary acid (hydrogen and a nonmetal) or an oxyacid (hydrogen + nonmetal + oxygen).
Naming binary acids:
Write the prefix hydro + root word of the nonmetal + ic
Ex: HCl = hydrochloric acid
Ex: H2S = hydrosulfuric acid
Naming oxyacids:
Identify the polyatomic ion found in the formula for the acid. If the ion ends with “ate”, change the ending to “ic”. If the ion ends with “ite”, change the ending to “ous”.
Ex: H2SO4 - contains the “sulfate” ion – therefore, the acid is called sulfuric acid
Ex: H2SO3 - contains the “sulfite” ion – therefore the acid is called sulfurous acid
To write formulas, simply determine the charge of the anion and add the correct number of hydrogen ions to balance the charge.
Ex: nitric acid - ic ending indicates the use of the nitrate ion, which is -1. Therefore 1 hydrogen ion is needed to balance the charge. The formula is HNO3.
Answer the following questions on notebook paper, to be collected and graded for correctness.
1. Name the following binary acids:
a. HCl ______
b. HF ______
c. H2S ______
2. Name the following oxyacids:
a. H2SO4 ______
b. H3PO4 ______
c. HC2H3O2 ______
d. HNO3 ______
e. HSO3 ______
f. HNO2 ______
g. HClO4 ______
h. HClO ______
3. Write formulas for the following acids:
a. Perbromic acid ______
b. Chlorous acid ______
c. Phosphoric acid ______
d. Hypochlorous acid ______
4. What is the difference between monoprotic, diprotic, and triprotic acids and give 2 examples of each.
5. Write the equation showing the 2-step ionization of sulfuric acid in dilute aqueous solution.
Step 1)
Step 2)
6. Explain why HCl(aq) which is monoprotic is a stronger acid than H3PO4(aq), which is triprotic.
7. Below are listed some common industrial acids. For each, include the formula, 1 property of that acid, and some of it’s most common uses.
Sulfuric acid –
Nitric Acid –
Phosphoric Acid –
Hydrochloric Acid –
Acetic Acid –
8. Write the formula equation and net ionic equation fro the reaction between Ca(s) and HCl(aq).
9. Name the following bases:
a. NaOH ______
b. Ca(OH)2 ______
c. Li(OH) ______
d. Al(OH)3 ______
e. Mg(OH)2 ______
10. Explain why Mg(OH)2 is weaker that NaOH, even though it contains more hydroxide ions per molecule.
11. What general relationship can be made regarding the size of the cation and the positive charge of the cation with regards to the solubility of an Arrhenius base containing these ions in water.
12. Dilute HCl(aq) and KOH(aq) are mixed in chemically equivalent quantities. Write the following:
a. Formula equation for the reaction:
b. overall ionic equation:
c. net ionic equation:
13. What is a conjugate base?
14. What is a conjugate acid?
15. Determine the conjugate acid for each:
H2O / F-HCO3- / SO42-
OH- / PO43-
H2PO4- / Cl-
ClO4- / CH3COO-
SH- / CN-
HSO4- / NH3
16. Determine the conjugate base for each:
HCO3- / HSO4-
OH- / HPO42-
H3PO4 / HCl
HBrO2 / CH3COOH
H2S / HOCN
HSO4- / NH3
Use the table below to identify the proton donor (Bronsted-Lowry acid), identify the proton acceptor (Bronsted-Lowry base). Use arrows to show the conjugate acid-base pairs and circle the arrow showing the correct direction of the proton transfer reaction.
ACID / BASEStrength of Acid / Name / Formula / Formula / Name / Strength of Base
STRONG
ACIDS / perchloric acid / HClO4 / ClO4– / perchlorate ion / Neutral Anionsulfuric acid / H2SO4 / HSO4– / hydrogensulfate ion /
Moderately Strong Acid!
hydroiodic acid / HI / I– / iodide ion / NeutralAnions
hydrobromic acid / HBr / Br– / bromide ion
hydrochloric acid / HCl / Cl– / chloride ion
nitric acid / HNO3 / NO3– / nitrate ion
Strong Acid / hydronium ion / H3O+ / H2O / water / Neutral
Moderately Strong Acid / hydrogensulfate ion / HSO4– / SO42– / sulfate ion /
Neutral Anion!
WEAK ACIDS
Acid strength INCREASES as you go UP the column. / hydrofluoric acid / HF / F– / fluoride ion /WEAK BASES
Base strength INCREASES as you go DOWN the column.nitrous acid / HNO2 / NO2– / nitrite ion
acetic acid / HC2H3O2 / C2H3O2– / acetate ion
carbonic acid / H2CO3 / HCO3– / hydrogencarbonate ion
hydrosulfuric acid / H2S / HS– / hydrogensulfide ion
ammonium ion / NH4+ / NH3 / ammonia
hydrocyanic acid / HCN / CN– / cyanide ion
Basic Anion! / hydrogencarbonate ion / HCO3– / CO32– / carbonate ion
Weak Acid / methylammonium ion / CH3NH3+ / CH3NH2 / methylamine
Neutral / water / H2O / OH– / hydroxide ion / Strong Base
Neutral
Molecules / ammonia / NH3 / NH2– / amide ion / STRONG
BASES
hydrogen / H2 / H– / hydride ion
methane / CH4 / CH3– / methide ion
Strong Base!
/ hydroxide ion / OH– / O2– / oxide ion17 a) CH3COOH(aq) + H2O(l) àß H3O+(aq) + CH3COO-(aq)
b) HCl(aq) + NH3(g) àß NH4+(aq) + Cl-(aq)
c) NH3 + H2O àß NH2- + H3O+
d) HCO3- + H2O àß H2CO3 + OH-
17e) What is the term used to refer to any substance that can be an acid or a base? ______
What are two examples of such a substance?
1) ______2) ______
18. Complete the matching section below testing your general knowledge on acids & bases
______Has the Hydroxide ion (OH-) as its only anion
______Ionizes in water to produce hydronium ions.
______Does not contain a H+ or OH- ion. A = Acid
______Tastes sour (examples are vinegar and citrus fruits).
______Can change the color of indicators. B = Base
______Feels slippery (example being soaps).
______CaCO3 is an example (chalk). S = Salt
______Dissociates in water to produce hydroxide ions.
______Has a pH > (greater than) 7. A,B = Acids & Bases
______Has a pH < (less than) 7.
______Is a proton (H+) acceptor. B,S = Bases & Salts
______Is a proton (H+) donor.
______Is an electron pair acceptor. A,B,S = Acids, Bases & Salts
______Is an electron pair donor.
______Can be corrosive. A,S = Acids & Salts
19. What is the product of all Neutralization reaction between aqueous acids and bases? ______
20. What is the product of all acid anhdrides and basic anhydrides? ______
21. Show that carbon dioxide is an acid anhydride of carbonic acid.
22. Show that magnesium oxide is a basic anhydride of magnesium hydroxide.
23. Complete the following neutralization reactions, making certain the balance the end product.
a) HNO3 + Al(OH)3 à
b) H3PO4 + Mg(OH)2 à
c) CaO + HNO3 à
d) HCl + Ca(OH)2 à