Acids and Bases
Science 10
Acid
In 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
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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
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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
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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
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Bleach
baking soda
Soap
Windex
tonic water
Acid or Base?
1) H2CO3
H+ + CO32-
2) Ca(OH)2 Ca2+ + OH3) NH3 + H2O
4) KOH
NH4+ + OH-
K+ + OH-
pH scale
pH: 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