Download 7.2: Properties, Names, and Formulas page 268 •Acids and bases

7.2: Properties, Names, and Formulas
page 268
Acids and bases are two classes of chemicals that play an
important role in many consumer products and environmental
problems.
Acids and bases can be classified by their properties.
An acid is a compound that dissolves in water to give a solution
that does all of the following:





conducts electricity (release H+ ions)
tastes sour
changes the colour of litmus from blue to red
reacts with active metals such as zinc, releasing hydrogen gas
reacts with carbonates, releasing carbon dioxide gas
In general, when acids and metals react,
For example,
2 HCl(aq) + Mg(s)  H2(g) + MgCl2(aq)
In general, when acids and carbonates react,
For example,
2 HCl(aq) + CaCO3(s)  CO2(g) + H2O(l) + CaCl2(aq
Table 1: Common Binary Acids
Table 2: Common Oxyacids and Their Related Polyatomic Ions
A base is a compound that dissolves in water to give a solution that
does all of the following:





conducts electricity (releases OH- ions)
tastes bitter
changes the colour of litmus from red to blue
feels slippery on the skin
reacts with an acid to destroy its properties
acid + base → salt + water
In general, in neutralization reactions,
acid + base  ionic compound + water
For example,
HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
Table 4: Common Bases and Their Uses
Formulas for Acids and Bases
Common acids are easily recognizable because of their formulas
begin with hydrogen.
Sulfuric acid
Carbonic acid
H2SO4
H2CO3
To determine if a substance is basic from its formula is a little
more difficult. Most bases are compounds that contain the
hydroxide ion (OH-).
Sodium hydroxide
NaOH
Others may not contain the hydroxide ion.
Hydrogen carbonate HCO3Sodium bicarbonate NaHCO3
But when they react with water, they form OH- ions.
Check Your Learning: questions 1 – 8, page 271
Colour with Acid-Base Indicators
page 270
Acids and bases are common chemical compounds that can be
grouped according to their physical and chemical properties.
Acid-Base Indicators – a substance that turns a different colour in
acids and bases.
Litmus – is an indicator that determines whether a substance is an
acid or base.
RED litmus paper turns blue in the presence of n base, but stays
red in the presence of an acid.
BLUE litmus paper turns red in the presence of an acid, but stays
blue in the presence of a base.
Other indicators can be prepared from many sources including
plants. Flowers, fruits, roots, leaves, and other parts of plants
include teal leaves, black currants, beet roots, rose pedals, red
cabbage, tumeric, and blackberries.
Synthetic indicators are often used in chemistry laboratories rather
than plant extracts. This is because most natural indicators lose
their colours and sensitivities when stored for long periods of time.
Synthetic indicators can be prepared in large quantities as powders,
and stored, without losing their properties.
Table 3: Colours of common Synthetic Acid-Base Indicators
7.3: The pH Scale
page 272
Chemist use a pH Scale to represent how acidic or basic a solution
is. Most acids and bases can be ranked on this scale. The pH scale
has a range of 0 – 14.
pH Scale – a numerical scale ranging from 0 to 14 that is used to
compare the acidity of a solution.
pH – a measure of how acidic or basic a solution is
Neutral – neither acidic nor basic, with a pH of 7
The range from 0 – 6.9 represents acids, a pH of 1 is more acidic
then a pH of 5. Low value, the more acidic.
The range form 7.1 – 14 represents bases, a pH of 8 is less basic
then a pH of 12. High value, the more basic (Alkaline).
Figure 2 the pH scale is used to compare the hydrogen ion concentration of a broad range
of substances. Consumer products that are on opposite ends of the scale are corrosive ad
have Household Hazardous Product symbols indicating this on their labels.
pH: A Logarithmic Scale
A logarithmic scale means that every change of one unit on the
scale represents a tenfold effect on the concentration of the
solution. (10, 102, 103, etc.)
As the pH decreases, solutions become more acidic, a pH of 3 is
10x more acidic then a pH of 4.
As the pH increases, solutions become more basic, a pH of 13 is
10x more basic then pH of 12.
The pH is defined according to the following formula:
pH = -log10 [H+]
Check Your Learning: questions 1 – 10, page 275
7.5: Neutralization Reactions
page 278
Neutralization reactions are a special case of double displacement
reactions.
→
AB + CD
Acid + Base →
AD + CB
Water + Ionic Compound
The reaction between hydrochloric acid and sodium hydroxide
involves an exchange of ions.
HCl (aq) + NaOH
(aq)
→ H2O (l) + NaCl (aq)
Sulfuric acid and potassium hydroxide yields….
H2SO4(aq) + 2KOH(aq) → 2H2O(l) + K2SO4(aq)
During the neutralization reaction, the hydrogen ion from the acid
reacts with the hydroxide ion from the base to form water.
H+ + OH- → H2O
Applications of neutralization reactions include:
a) treating chemical spills
b) using antacids to provide relief of heartburn by
neutralizing stomach acid
c) restoring lakes affected by acid precipitation
Check Your Learning: questions 1 – 10, page 281
7.8: Acid Precipitation
page 285
Acid precipitation (rain, snow, fog) forms when certain
pollutants combine with water in the atmosphere before falling to
Earth.
Figure 1: Emissions of sulfur dioxide and nitrogen oxides combine with water in the
atmosphere to form acids that fall back to Earth as acid precipitation (rain, snow, and
sleet). Acid-forming pollutants can also fall to Earth directly as dry deposition (particles
or gases).
Two pollutants of special concern are sulfur dioxide (SO2) and
nitrogen oxides (NOx).
SO2 produces sulfuric acid through the following series of
reactions:
S(s) + O2(g) SO2(g)
2 SO2(g) + O2(g) 2 SO3(g)
SO3(g) + H2O(l) H2SO4(aq)
NOx produces nitric acid through the following reactions:
2 NO(g) + O2(g) 2 NO2(g)
3 NO2(g) + H2O(l) 2 HNO3(aq) + NO(g)
These pollutants are produced in Canada from the following
sources:
Acid precipitation has serious effects on
aquatic ecosystems
soil
forests
These effects result in
poor growing conditions for lumber and crops
a reduction in fish stocks
damage to steel structures, limestone buildings and stone
monuments
Possible remedies for acid precipitation include
switching to low-sulfur fossil fuels to generate electricity
scrubbers to remove sulfur from gas emissions
improved pollution control on vehicles
stricter vehicle emissions standards
Check Your Learning: questions 1 – 14, page 290
Chapter 7 Review: questions 1 – 22, page 294 – 295