Look at some examples, and see if you can figure out what an acid is… HCl (Hydrochloric acid) HNO 3 (Nitric acid) H 2 SO 4 (Sulfuric acid) H 3 PO 4 (Phosphoric acid)

Official definition: (or one of the definitions, anyway) Acids are substances that give away hydrogen ions. Example: HCl gives away hydrogen to water: HCl (aq) + H 2 O  H 3 O+ (aq) + Cl- (aq) Draw the hydrogen ion. What does it consist of?

A hydrogen ion is simply a proton. Acids are also called “proton donors.”

Tell-tale signs of an acid:  sour taste (orange juice and lemonade contain citric acid)  turns litmus paper red (by reacting with a chemical in (by reacting with a chemical in the litmus paper) the litmus paper)  reacts with metals to produce hydrogen gas

Examples of acids: Vinegar Lemon Juice Soft Drink Battery Acid Stomach Acid Apple Juice Black Tea

Chemists write the formulas for acids with the H at the front, so they’re easy to identify as acids: HCl (Hydrochloric acid) HNO 3 (Nitric acid) H 2 SO 4 (Sulfuric acid) H 3 PO 4 (Phosphoric acid)

An acid is a proton donor A base is a proton acceptor acidbase

Acids and Bases: An acid is a compound that donates H+ ions: HCl + H 2 O  H 3 O + + Cl- HCl + H 2 O  H 3 O + + Cl-  A base is a compound that accepts H+ ions. In the equation above, water is acting as a base.  btw: H 3 O + is called the hydronium ion

Looking at the last two reactions, notice that water acted as an acid in one, and as a base in the other. Substances that can act as an acid or a base are called amphoteric.

Tell-tale signs of a base:  bitter taste  slippery feel  turns litmus paper blue (Conveniently, base, bitter, and blue all start with B!)

Examples of bases: Detergent Baking Soda Drain Cleaner Ammonia Soaps (hand, dish) Antacid

Conjugate acids and bases: Acids and bases are identified based on whether they donate or accept H +. Remember, though, most reactions are reversible. Look at the reverse reaction. Can you identify an acid and base in the reverse reaction? + ClH H H O + H H HO + acidbase

Conjugate acids and bases: Acids and bases are identified based on whether they donate or accept H +. “Conjugate” acids and bases are found on the products side of the equation. A conjugate base is the same as the starting acid minus H +. + ClH H H O + H H HO + acidbase conjugate acidconjugate base conjugate acid-base pairs

Conjugate Acids and Bases:  The Bronsted-Lowry definitions: HCl + H 2 O  H 3 O + + Cl - HCl + H 2 O  H 3 O + + Cl - The forward reaction is a reaction between an acid (HCl) and a base. The reverse reaction is also a reaction between an acid (H 3 O+) and a base.

Acids and Bases: HCl + H 2 O  H 3 O + + Cl- HCl + H 2 O  H 3 O + + Cl- After the acid HCl donates its proton, it becomes a base (Cl-). A conjugate base is the substance that results after an acid donates a hydrogen ion to a base. It’s a base, because it could take the H + back again. And what do we call something that can take H + ?

Acids and Bases: HCl + H 2 O  H 3 O + + Cl- HCl + H 2 O  H 3 O + + Cl- After the water accepts the H+ ion from HCl, it becomes H 3 O+, the conjugate acid that can donate a proton. Every acid-base interaction involves conjugate acid-base pairs.

Think of it like playing catch, with the H+ ion as the baseball. When you have it, you’re the acid, after you throw it, you’re the conjugate base. Who is the acid, and who is the base?

Acids and Bases: Summary  Acid – H + donor  base – H + acceptor  acid-base reaction  acid + base  conjugate base + conjugate acid  conjugate acid – what base becomes after it accepts H +  conjugate base – what acid becomes after it donates H +

Practice problems 1 and 2: Identify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs: acidbase conjugate acidconjugate base HC 2 H 3 O 2 (aq) + H 2 O (l)  C 2 H 3 O 2 – (aq) + H 3 O + (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base OH – (aq) + HCO 3 – (aq)  CO 3 2– (aq) + H 2 O (l) conjugate acid-base pairs

Practice: Identify the conjugate acid-base pairs in these reactions: 3. NH OH -  NH 3 + H 2 O 4. HSO H 2 O  H 3 O + + SO 4 2-

acidbase conjugate acidconjugate base HF (aq) + SO 3 2– (aq)  F – (aq) + HSO 3 – (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base CO 3 2– (aq) + HC 2 H 3 O 2 (aq)  C 2 H 3 O 2 – (aq) + HCO 3 – (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base H 3 PO 4 (aq) + OCl – (aq)  H 2 PO 4 – (aq) + HOCl (aq) conjugate acid-base pairs (5) (6) (7)

Neutralization reactions: If you combine an acid with a base… Predict the products: HCl + NaOH  ? Hint: It’s a special kind of double replacement reaction!

If you combine an acid with a base… HCl + NaOH  H 2 O + NaCl This is called a neutralization reaction because the acid and base neutralize each other.

If you combine an acid with a base… HCl + NaOH  H 2 O + NaCl The products of any neutralization reaction are water and a salt.

Acid/Base reactions: Produce water and a salt (and sometimes carbon dioxide). Hint: concentrate on the water first. Remember, water has the formula HOH. Complete and balance the following: HCl + KOH  HCl + Ca(OH) 2  HOH + KCl 2 Require equal numbers 2HOH + CaCl 2

1. Ba(OH) 2 + H 3 PO 4  2. HC 2 H 3 O 2 + NaOH  3. H 2 SO 4 + KOH  4. H 2 CO 3 + NaOH 

Everyday application: The stomach secretes acids to help digest foods. These acids, which include hydrochloric acid, have a molarity of about 0.1M. Antacids, like Tums, Maalox, Mylanta and Alka-seltzer are simple bases that neutralize stomach acids.

Naming acids Look at the names of these acids – can you come up with the rule? H 2 SO 4 : sulfuric acid HNO 3 : nitric acid H 3 PO 4 : phosphoric acid

Naming acids Rule #1: If the acid comes from a polyatomic ion that ends in “ate,” the acid is named ____-ic. H 2 SO 4 : sulfuric acid (from sulfate) HNO 3 : nitric acid (from nitrate) H 3 PO 4 : phosphoric acid (from phosphate)

Naming acids Rule #1: If the acid comes from a polyatomic ion that ends in “ate,” the acid is named ____-ic. Practice: What is – HC 2 H 3 O 2 ? HClO 3 ? H 2 CO 3 ?

Naming acids Rule #2: If the acid does not have oxygen in it, then name it… hydro + second element + ic Example: HCl is hydrochloric acid. What would HBr be? H 2 S?

Acids and Bases: Strength  What makes an acid a strong acid? It ionizes completely in water!  These are strong acids (in order of increasing strength): 1.HNO 3 (nitric acid) 2.HCl (hydrochloric acid) 3.HBr (hydrobromic acid) 4.HI (hydroiodic acid) 5.H 2 SO 4 (sulfuric acid) 6.HClO 4 (perchloric acid) (the strongest)

Strong acids:  HCl + H 2 O  H 3 O + + Cl- Remember, strong acids ionize completely in water. The reaction goes all the way to the right. A single arrow is used. There are virtually no HCl molecules left intact.

Strong acids:  HCl + H 2 O  H 3 O + + Cl- Remember, strong acids ionize completely in water. The reaction goes all the way to the right. A single arrow is used. There are virtually no HCl molecules left intact.

Strong acids:  HCl + H 2 O  H 3 O + + Cl- Looking at the equation above, with the single arrow, is Cl - a strong base or a weak base?

General rule: The conjugate base of a strong acid is a weak base. Similarly, the conjugate acid of a strong base is a weak acid.

One more reminder: “Weak” does not mean the same thing as “diluted.” HCl, for example is always a strong acid. If you add 1000 liters of water to it, it will be diluted, but still strong because what little there is will be completely dissociated.

Electrolytes: Acids and bases are both examples of electrolytes. Electrolytes are compounds that form ions when dissolved in water. They’re called electrolytes because they can conduct electricity through water.

More on electrolytes: If two wires connected to a light bulb and to a power source are placed in a beaker of water, the light bulb will not glow. If an electrolyte, such as sodium chloride, is dissolved in the water, the light bulb will glow because the solution can now conduct electricity. The amount of electric current that can be carried by an electrolyte solution is proportional to the number of ions dissolved. Thus, the bulb will glow more brightly if the amount of sodium chloride in the solution is increased. light bulbbeakerglowchloridelight bulbbeakerglowchloride

Practice Questions

Which of these could be used to determine whether a substance is a base? A Thermometer B Litmus paper C Balance D Bunsen burner

An element common to all acids is – a. chlorine b. hydrogen c. oxygen d. sodium