Chapter 5: Acids and Bases

ACIDS Most acids are recognized because their formulas begin with H. Eg. H 2 SO 4 (sulphuric acid), HCl (aq) (hydrochloric acid). Acids are sour tasting, water soluble and good conductors of electricity. Many are in foods: vinegar, citrus fruits, tomatoes When dissolved in water, acids produce hydrogen ions (H + ). Example Hydrochloric acid  hydrogen ions + chloride ions HCl(aq)  H + (aq) + Cl - (aq)

Binary Acids When a hydrogen atom is combined with a halogen atom and they are dissolved in water, they form an acid. These acids are named by putting the name “hydro” before the non-metal and changing the ending to “ic” and adding “acid”. The four binary acids are: Hydrochloric acid, HCl(aq) Hydrofluoric acid, HF(aq) Hydroiodic acid, HI(aq) Hydrobromic acid, HBr(aq)

Oxyacids Oxyacids are compounds formed when hydrogen combines with polyatomic ions that contain oxygen. The hydrogen atom has an ionic charge of 1+. Common oxyacids:

BASES Most bases are recognized because they contain a hydroxide ion in their formulas. Bicarbonates are also bases. Bases are water soluble, bitter tasting and good conductors of electricity. Many are in cleaning products: soap, detergent, drain cleaner. The term “alkaline” may also be used to refer to a base When dissolved in water bases produce hydroxide ions (OH - ) Example: Sodium hydroxide  sodium ions + hydroxide ions NaOH (aq)  Na + (aq) + OH - (aq)

pH scale (page 196) A pH value is a measure of how acidic or basic (alkaline) a substance is. The pH scale ranges from 0 to 14, where a pH below 7 is acidic, a pH above 7 is basic and a pH of 7 is neutral. pH stands for “power of hydrogen” This scale is not linear, it is exponential, based on powers of 10 A difference of one pH unit means a difference of 10 times in acidity or basicity.

For Example A substance with a pH value of 1 is 10 times more acidic than something with a pH value of 2 and 100 times more acidic than something with a pH of 3. pH=1 vs. pH=2  = 10 1 = 10 times different pH=1 vs. pH=3  = 10 2 = 100 times different pH units are powers of 10

Question Coffee has a pH of 5 and bleach has a pH of 13. Which is more basic? How much more basic is it?

Bleach is more basic than coffee because it has the higher pH value. pH=5 vs. pH=13  = 10 8 = 100 million times more basic!

Indicators A pH indicator is a substance that changes colour in the presence of an acid or base. An indicator can be a natural substance such as red cabbage juice, tea, or litmus or it can be a chemical such as phenolphthalein or bromothymol blue.

Indicators Litmus – blue in base – red in acid Phenolphthalein –colourless if pH < 8.2 –Magenta if pH > 8.2 Bromothymol blue –Blue in base –Yellow in acid

Litmus hemistry/pc/learningsteps/ANALC/launch. htmlhttp://lgfl.skoool.co.uk/content/keystage3/c hemistry/pc/learningsteps/ANALC/launch. html

Universal pH Indicator Page od=cResource.dspView&ResourceID=432http:// od=cResource.dspView&ResourceID=432

Some Common Acids & Bases (Sulfuric)

Corrosive BOTH strong acids (pH 12) are corrosive Stomach acid is HCl, pH of 2 Drain cleaner is a base, pH of 14

Neutralization A neutralization reaction is a special case of double displacement reaction between an acid and a base. The products of a neutralization reaction are always water and a salt (an ionic compound). Examples: HCl (aq) + NaOH(aq)  HOH + NaCl Hydrochloric acid + sodium hydroxide  water + sodium choride H 2 SO 4 (aq) + 2KOH  2H 2 O + K 2 SO 4 Sulfuric acid + potassium hydroxide  water + potassium sulfate

Acid-Base Chemistry in Everyday Life Biology –“Heartburn” –Wasp & Bee Stings Environment –Acid rain –Ocean acidification

ACID REFLUX “Heartburn” It’s NOT your heart, its your esophagus!

ANTACIDS Acid reflux can be relieved by ingesting antacids These are bases that neutralize the stomach acid Mild antacids are usually carbonate and bicarbonate salts –Eg. Alkaseltzer, Tums, Rolaids, et. Strong antacids are hydroxides –Eg. “Milk of magnesia” is magnesium hydroxide

Treating Wasp & Bee Stings Wasp venom is basic and can be neutralized with a weak acid like vinegar (acetic acid) Bee venom is acidic and can be neutralized with a weak base like baking soda (sodium bicarbonate) hemistry/pc/learningsteps/ENRLC/launch. htmlhttp://lgfl.skoool.co.uk/content/keystage3/c hemistry/pc/learningsteps/ENRLC/launch. html

ACID PRECIPITATION

Effects of Acid Rain Aquatic – kills fish populations Forests – drains nutrients from the soil, leads to decreased growth and death of trees (especially in boreal) Visibility – Dry acidic particles in the air lessen visibility. Materials – corrosion of brickwork and statues Human Health –High concentrations of fine-particulate sulfate and nitrate can enter the cardiovascular and respiratory systems, resulting in disease or even death. –Heavy metals, such as mercury and cadmium, from soil deposits in lakes, streams, and reservoirs can accumulate in the tissues of fish, making them toxic to humans. –Metals also can be leached from the soil into reservoirs, or from old lead and copper pipes directly into home water supplies, causing serious illness.

Liming: adding a base to neutralize acidified soils & water

OCEAN ACIDIFICATION Over 70% of the earth’s surface is covered by oceans, making them the largest carbon sink on the planet Carbon dioxide reacts with seawater to make carbonic acid, increasing the acidity of the oceans CO 2 + H 2 O  H 2 CO 3(aq) Most life can only exist in a very narrow pH range Shell-bearing organisms are particularly at risk, because the acid reacts with the calcium carbonate in the shell, causing it to thin out. Without protection, these organisms die more easily. present-danger/ present-danger/

HOMEWORK Page 197 # 1 to 5 Page 200 # 1 & 2 Page 201 # 1 & 2 Page 203 # 1 to 4 UNIT TEST NEXT FRIDAY!