Acids and Bases

Science 10

AcidIn an aqueous solution, acids

produce hydrogen H+ ions

Example: hydrochloric acid, HCl, which is found in our stomachs. In water the acid will produce H+ and

Cl- ions.HCl (aq) H+

(aq) + Cl- (aq)

Characteristics of Acids• Sour taste• Can burn the skin• Conducts electricity• Reacts with metals to produce

hydrogen gas (H2)• Neutralizes a base• Reacts with carbonate and

bicarbonate to produce carbon dioxide gas (CO2)

Examples of Acids

• Lemons• stomach acid• acid rain• battery acid• vinegar

Bases• In an aqueous solution a base

produces hydroxide OH- ions

• Example: sodium hydroxide (NaOH). In water this base produces Na+ and OH- ions.

NaOH(aq) OH- (aq) + Na+(aq)

Characteristics of Bases

• Bitter taste• Slippery texture• Can burn skin• Conducts electricity• Neutralizes acids• Reacts with certain metals (like Al)

to produce hydrogen gas (H2)• Does not react with carbonates

Examples of Bases

• Bleach• baking soda• Soap• Windex• tonic water

Acid or Base?

1) H2CO3 H+ + CO32-

2) Ca(OH)2 Ca2+ + OH-

3) NH3 + H2O NH4+ + OH-

4) KOH K+ + OH-

pH scalepH: the measure of the acidity of a

solution.

• The scale ranges from 0 to 14.• 0 – 6 = acid • 7 = neutral (distilled water) • 8 – 14 = base

• Most acids and bases are clear and colorless. You need an indicator to tell them apart.

• Indicator: a chemical that changes color as the concentration of H+ or OH- changes.

• There are many different indicators such as Litmus, phenolphthalein and even cabbage juice!

Litmus Test

• Red and blue litmus paper– Acids turn blue litmus paper red. – Bases turn red litmus paper blue– Neutral substances will not change

the colour of red OR blue litmus paper.

A good tip = BRA (blue to red in an acid)

Source: http://cahm.nbed.nb.ca/Science/science61d.htm

pH Paper

• You compare the colour with a given chart

• Instead of telling you whether something is an acid or a base it gives you the exact pH.

Source: http://escalade.nbed.nb.ca/images/ex15.jpg

Other Indicators

• Phenolphthalein– Turns bright pink in bases, at pH of 8.2 or

higher– Will be clear in acids

• Cabbage Juice– A homemade indicator– Turns a rainbow of colors based on

various pH levels

Neutralization Reactions• An acid and a base react

together to form a new compound.

• The general equation is:Acid + Base → Salt + Water

• Example: HCl + NaOH → NaCl + H2O