Transcript ACID - TeacherWeb

Title: Acids, Bases, and Salts
• Acid and base are terms used by chemists to classify chemicals
according to their pH.
• ACID - A class of compounds whose water solutions taste sour,
turn blue litmus to red, and react with bases to form salts.
Acids generally give up a hydrogen ion (H+) in solution.
• BASE - A class of compounds that taste bitter, feel slippery in
water solution, turn red litmus to blue, and react with acids to form
salts.
Bases generally create hydroxide ion (OH-) in solution.
• NEUTRAL - These are items that are neither acids or bases.
• There are 4 main ways to determine if a substance is an acid or a
base. They are: Red litmus paper, Blue litmus paper, a pH meter,
and Red Cabbage Juice.
• Acids and bases neutralize each other. This reaction called
neutralization produces water and a salt.
Acids and Bases
• Acid and base are terms used by chemists
to classify chemicals according to their pH.
• The pH is the negative logarithm of the
hydronium ions (H3O+) ion concentration of an
aqueous solution; used to express acidity.
• Low pH has high a concentration of H3O+
and high pH means low concentration of
H3O+.
the negative logarithm of the hydronium ions (H3O+) ion
concentration of an aqueous solution; used to express acidity.
Low pH has high a concentration of H3O+ and high pH means low
concentration of H3O+.
• pH is the measure of the acidity or basicity of a solution.
• The pH scale ranges from 0 to 14.
• 0 through 6 being acidic.
• 7 is considered neutral .
• 8 through 14 being basic.
A class of compounds whose water
solutions taste sour, turn blue litmus to
red, and react with bases to form salts,
generally give up a hydrogen ion (H+) in
solution.
.
Acids produce solutions that:
• Taste sour
• Turn blue litmus paper red
• Conduct electricity
• react with metals to liberate a hydrogen gas
• are corrosive (to corrode means to wear away, corrosion, acid
rain)
• lose the above properties when reacted with a base.
Examples of acids:
• Vinegar
• Lemon Juice
• Soft Drink
• Battery Acid
• Stomach Acid
• Apple Juice
• Black Tea
• Strong Acids – any acid that dissociates completely in aqueous solution.
• Weak Acids – any acid that dissociates only partially in aqueous solution.
Strong Acids
Weak Acids
1. chloric acid, HClO3
1. acetic acid, Ch3COOH
2. hydorbromic acid, HBr
2. boric acid, H3BO3
3. hydorchloric acid, HCl
3. hydorfluoric acid, HF
4. sulfuric acid, H2SO4
4. phosphoric acid, H3PO4
5. nitric acid, HNO3
5. sufurous acid, H2So3
A class of compounds that taste
bitter, feel slippery in water solution,
turn red litmus to blue, and react with
acids to form salts, generally create
hydroxide ion (OH-) in solution.
Bases produce solutions that:
• taste bitter
• turn red litmus blue
• conduct electricity
• feel slippery
• are corrosive (basic solution in glass container)
• lose the above properties when reacted with an acid.
Examples of bases:
• Detergent
• Baking Soda
• Drain Cleaner
• Ammonia
• Soaps (hand, dish)
• Antacid
• Strong Bases – any base that dissociates completely.
• Weak Bases – any base that dissociates only partially in aqueous solution.
Strong Bases
Weak Bases
1. barium hydroxide, Ba(OH)2
1. ammonia, NH3
2. calcium hydroxide, Ca(OH) 2
2. aniline, C6H5NH 2
3. potassium hydroxide, KOH
3. potassium carbonate,K 2 CO3
4. sodium hydroxide, NaOH
4. sodium carbonate, Na 2 CO3
5. trisodium phosphate, Na3PO4
5. trimethylamine, (CH3) 3N
• These are items that are neither acids or
bases.
• Neutral items will turn blue and red litmus
paper green.
• The main example of a neutral item is:
Pure Water, and Salts
Physical Properties
of Acids & Bases
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ACIDS
Acids taste sour (e.g. vinegar, lemon juice).
Acids are harmful to living cells.
Aqueous solutions of all acids contain hydrogen ions.
Acid turns blue litmus red.
Strong acids are corrosive.
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BASES
Alkalis are taste bitter
Strong alkalis are corrosive.
Aqueous solutions of all alkalis contain hydroxide ion.
Alkalis turns red litmus blue.
Soapy touch.
Chemical Properties of Acids
With metals
• Metals above copper in the reactivity series will react
with acids, giving off hydrogen gas, forming a salt.
Mg(s) + H2SO4(aq)  MgSO4(aq) + H2(g)
With bases (metal oxides and hydroxides)
• The base dissolves in the acid and neutralizes it. A
salt is formed.
H2SO4(aq) + CuO(s)  CuSO4(aq) + H2O(l)
With metal carbonates
• With metal carbonates, effervescence occurs, salt,
water and carbon dioxide gas is produced.
2HCl(aq) + CaCO3(s)  CaCl2(s) + H2O(l) + CO2(g)
USES OF ACIDS
• HCl in stomach
• H2SO4 in car batteries, as drying agent’
• HNO3 in manufacturing of fertilizers
• Ethanoic acid in food industry
• Fatty acids in soap making
• Ascorbic acid in medicine
Chemical Properties of Bases
• Neutralization.
• Ammonium salts are decomposed when mixed with a
base e.g. sodium hydroxide. The ammonia is readily
detected by its pungent odor (strong smell) and by turning
damp red litmus blue.
NaOH + NH4Cl ==> NaCl + H2O + NH3
Ionically: NH4+ + OH- ==> H2O + NH3
– This reaction can be used to prepare ammonia gas and
as a test for an ammonium salt.
• Red litmus paper
• Blue litmus paper
• pH
• Red Cabbage Juice
•Robert Boyle discovered litmus paper
•certain plant extracts, such as litmus, can be used to
distinguish acids from bases.
• blue and red litmus paper turn red when dipped in an
acid
• red and blue litmus paper turn blue when exposed to a
base
the negative logarithm of the hydronium ions (H3O+) ion
concentration of an aqueous solution; used to express acidity.
Low pH has high a concentration of H3O+ and high pH means low
concentration of H3O+.
• pH is the measure of the acidity or basicity of a solution.
• The pH scale ranges from 0 to 14.
• 0 through 6 being acidic.
• 7 is considered neutral .
• 8 through 14 being basic.
• red cabbage can be used as an acid/base indicator
• after boiling the red cabbage, pour a small amount of the
juice into a small sample of a substance your checking
• the juice will turn blue if the substance is a base
• the juice will turn red if the substance is an acid
What happens when you mix an acid and a base?
• When an acid and a base are mixed, they react to
neutralize each other, this is called neutralization.
• This results in the formation of water and a salt.
• A salt is any ionic compound that results from a
neutralization reaction.
• Since salts are made of ions, they share the same
properties of ionic compounds, including crystal
shape, high melting points and boiling points, and
electric conductivity.
What happens when you mix an acid and a base?
USES OF SALTS
S. No.
SALT
USE
1
Ammonium Chloride
In torch batteries
2
Ammonium Nitrate
In fertilizers
3
Calcium Chloride
As drying agent
4
Iron Sulphate
In Iron tablets
5
Magnesium Sulphate
In medicine
6
Potassium Nitrate
In gunpowder etc.
7
Silver Bromide
In photography
8
Sodium Chloride
Making NaOH
9
Sodium Stearate
In making soap.
There are three common acid-base theories:
• the Arrhenius theory
• the Bronsted-Lowry theory
• the Lewis theory
• Svante Arrhenius was a Swedish chemist.
• In 1887, he published a paper concerning acids and bases.
• He concluded that solutions with acids and bases in them released
particles when dissolved.
• He concluded that acids were substance which separated (ionized) in
water solution to produce hydrogen ions (H+, or free protons).
• He also believed that bases were substance which ionized to produce
hydroxide ions (OH-) in water solution.
• HCl
• NaOH
H+ + ClNa+ + OH-
• T. M. Lowry was an English scientist, while J. N. Bronsted
was a Danish scientist.
• In 1923, they independently proposed a new definition of
the terms acid and base.
• They stated that in a chemical reaction, any substance
which donates a proton is an acid and any substance which
accepts a proton is a base.
• When hydrogen chloride gas is dissolved in water, ions are
formed:
• HCl + H2O
acid
H3O+ + Cl-
base
Lowry
Bronsted
• Gilbert Newton Lewis was and American chemist.
• In 1923, proposed an even broader definition of acids and
bases.
• Lewis focused on electron transfer instead of proton transfer.
• He defined and acid as an electron-pair acceptor, and a base as
an electron-pair donor.
• This definition applies to solutions and reactions which do not
even involve hydrogen or hydrogen ions.
THEORY
ACID DEFINITION
Arrhenius
Theory
Any substance which
releases H+ ion in
water solution.
Any substance which
releases OH- ions in
water solution.
Any substance which
donates a proton.
Any substance which
accepts a proton.
Bronsted-Lowry
Theory
Lewis
Theory
Any substance which can
accept an electron pair.
BASE DEFINITION
Any substance which
can donate an
electron pair.
• Proteins
in your hair, nails, cell membranes,
and other parts of you body consist of amino
acids.
• Enzymes that catalyze reactions in your body
are composed of amino acids.
• Hydrochloric acid is in your stomach to aid in
the digestion of food.
• Organic bases are major components of DNA
and products of the digestion of proteins.
• DNA contains thousands of sites where H+ ion transfer
can take place
• Therefore DNA fits the definition of a Bronsted acid.
• DNA is a weak acid, but it is stronger than phosphoric
acid.
• ACID - A class of compounds whose water solutions taste
sour, turn blue litmus to red, and react with bases to form
salts.
• BASE - A class of compounds that taste bitter, feel slippery
in water solution, turn red litmus to blue, and react with acids
to form salts.
• NEUTRAL - These are items that are neither acids or bases.
There are 4 main ways to determine if a substance is and
acid or a base. They are: Red litmus paper, Blue litmus paper,
pH, and Red Cabbage Juice.
• Background information on acids and bases.
<http://educ.queensu.ca/~science/main/concept/chem/c10/C10CDMJ1.htm>
• Acids and Bases. <http://www.bookrags.com/research/acids-and-bases-woc/>
• Acids and bases Lab. <http://www. Scribd.com/doc/2977162/Acids-and-Bases-Lab/>
• Smoot, Robert C.; Price, Jack S.; Smith, Richard G. Chemistry A Modern Course.
Chapter 24, Acids, Bases, and Salts.
• Holt, Rinehart, and Winston, Inc. Chemistry Visualizing Matter. Chapter 13, Acids and
Bases.