chapter 5: acids and bases

Chapter 5: Acids and Bases

ACIDSMost acids are recognized because their formulas begin with H. Eg. H2SO4 (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:

phosphoric acidH3PO 4(aq)3-PO 43-Phosphate

sulfuric acidH2SO 4(aq)2-SO 42-sulfate

carbonic acidH2CO 3(aq)2-CO 32-carbonate

chloric acidHClO 3(aq)1-ClO3-chlorate

nitric acidHNO 3(aq)1-NO 3-nitrate

Oxyacid NameOxyacid FormulaIonic ChargeIon FormulaIon Name

2

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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.

• A difference of one pH unit means a difference of 10 times in acidity or basicity. So, pH value of 1 is 10 times more acidic than a pH of 2 and 100 times more acidic than a pH of 3.

Question

• Coffee has a pH of 5 and bleach has a pH of 13.

• Which is more basic?

• How much more basic is it?

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

• http://lgfl.skoool.co.uk/content/keystage3/chemistry/pc/learningsteps/ANALC/launch.html

Universal pH Indicator

• Page 202• http://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=432

Some Common Acids & Bases

(Sulfuric)

Corrosive• BOTH strong acids (pH < 2) and strong

bases (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

H2SO4(aq) + 2KOH 2H2O + K2SO4

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)

• http://lgfl.skoool.co.uk/content/keystage3/chemistry/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

CO2 + H2O H2CO3(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.

HOMEWORK

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