Download What is an acid or a base

CHEM 10
Brakke
T07D01 – Acid Base Intro (Def’s, Props) Notes
ECA - Topic 07
There are a few ways to define acids and bases. All are accurate descriptions of acids and bases, but are each used to describe
properties in certain settings. The three definitions are the Arrhenius, Lowry-Brønsted, and Lewis. Each is briefly described below.
Arrhenius: Following original ideas of the Swedish scientist, Svante Arrhenius, the Arrhenius definitions state:
•
An Arrhenius acid is a material that can donate _________ or ______________. Just like a salt, hydrogen chloride (HCl) in
+
water solutions ionizes and becomes hydrogen ions (H ) and chloride ions (Cl ).
+
o HCl  H (aq) + Cl (aq)
•
A Arrhenius base, or alkali, is a material that can donate________________ . Sodium hydroxide in water solutions becomes
+
sodium ions (Na ) and hydroxide ions (OH ).
+
o NaOH  Na (aq) + OH (aq)
Brønsted-Lowry: Another definition by two chemists Thomas Lowry and J.N. Brønsted working independently from England and
Denmark respectively was proposed in 1923. The Lowry-Brønsted definitions state:
•
A Brønsted-Lowry acid is a material that _______________.
•
A Brønsted-Lowry base is a material that __________________.
Lewis: The Arrhenius definition is very similar to the Lowry-Brønsted definition of acids and bases. Another chemist, G.N. Lewis
(1923), proposed a model of acids and bases that was much more broad. The Lewis definitions are:
•
Lewis Acids ________________________.
•
Lewis Bases________________________.
Properties of Acids
Acids release a ___________________ into water (aqueous) solution.
Acids neutralize bases in a ____________ reaction. An acid and a base combine to make a salt and water. A salt is any ionic
compound that could be made with the anion of an acid and the cation of a base. The hydrogen ion of the acid and the hydroxide
ion of the base unite to form water.
Acids ___________________________. Even gold, the least active metal, is attacked by an acid, a mixture of acids called 'aqua
regia,' or 'royal liquid.' When an acid reacts with a metal, it produces a compound with the cation of the metal and the anion of the
acid and hydrogen gas.
Acids turn __________________. Litmus is one of a large number of organic compounds that change colors when a solution changes
acidity at a particular point. Litmus is the oldest known pH indicator. It is red in acid and blue in base. The phrase, 'litmus test,'
indicates that litmus has been around a long time in the English language. Litmus does not change color exactly at the neutral point
between acid and base, but very close to it. Litmus is often put onto paper to make 'litmus paper.'
Acids taste ________. TASTING LAB ACIDS IS NOT PERMITTED!! The word 'sauer' in German means acid and is pronounced almost
exactly the same way as 'sour' in English. (Sauerkraut is sour cabbage, cabbage preserved in its own fermented lactic acid. Stomach
acid is hydrochloric acid. Although tasting stomach acid is not pleasant, it has the sour taste of acid. Acetic acid is the acid ingredient
in vinegar. Citrus fruits such as lemons, grapefruit, oranges, and limes have citric acid in the juice. Sour milk, sour cream, yogurt, and
cottage cheese have lactic acid from the fermentation of the sugar lactose.
CHEM 10
Brakke
Properties of Bases
ECA - Topic 07
Bases release a _____________________________. (Or, in the Lowry- Brønsted model, cause a hydroxide ion to be released into
water solution by accepting a hydrogen ion in water.)
Bases neutralize acids in a __________________ reaction. Acid plus base makes water plus a salt. Symbolically, where 'Y' is the anion
of acid 'HY,' and 'X' is the cation of base 'XOH,' and 'XY' is the salt in the product, the reaction is:
HY + XOH  HOH + XY
HCl + NaOH  HOH + NaCl
Bases ____________________. To denature a protein means to render parts of it useless most likely by unfolding it. This accounts
for the "slippery" feeling on hands when exposed to base. Strong bases that dissolve in water well, such as sodium or potassium lye
are very dangerous because a great amount of the structural material of human beings is made of protein. Serious damage to flesh
can be avoided by careful used of strong bases.
Bases turn ________________________. This is not to say that litmus is the only acid- base indicator, but that it is likely the oldest
one.
Bases taste ___________. There are very few food materials that are alkaline, but those that are taste bitter. It is even more
important that care be taken in tasting bases. Again, TASTING OF LAB CHEMICALS IS STRICTLY PROHIBITED. Tasting of bases is more
dangerous than tasting acids due to the property of stronger bases to denature essential proteins in the body.
Write an equation for each when dissolved in water:
+
+
(Note that the formation of H3O (hydronium ion) in water is H and acidic)
Common Acids:
HCl – Hydrochloric (strong)
H2SO4 – Sulfuric Acid (strong)
HNO3 – Nitric Acid (strong)
CH3COOH – Acetic (ethanoic) acid (weak)
H3PO4 – Phosphoric Acid (weak)
Common Bases:
NaOH – Sodium Hydroxide (strong)
KOH – Potassium hydroxide (strong)
Ba(OH)2 – Barium Hydroxide (strong)
NH3 – Ammonia (weak)
Fe(OH)2 – Iron (II) hydroxide (weak)