Transcript Acids, bases and salts
Acids, bases and salts
Acids
by definition are any substance that releases H 3 O +
(Hydronium ions)
when added to water. Acids are hydrogen donors -- they give away a hydrogen to a H 2 O molecule to produce H 3 O + ions. Acids have several many chemical and physical
properties
including: 1) Taste sour 2) Are
Electrolytes
– fall apart into ions when added to water 3) Conduct electricity 4) are
Corrosive
– rust, oxidize or destroy metals 5) have the element hydrogen in their formula
BASES
Bases-
by definition are anything that releases
Hydroxide ions
(OH ) when added to water. Bases are hydrogen removers – they remove a hydrogen from H 2 O to produce the OH ion. Bases have many chemical and physical
properties
including: 1) Taste bitter 2) are electrolytes 3) conduct electricity 4) are corrosive 5) usually have (OH) in their formula 6) feel slippery
Common bases and their uses 1) Ammonia-
(NH 3 ) used as household cleaners and to make fertilizers NH 3 + H 2 O NH 4 + + OH -
2) Lime
– Calcium Hydroxide -Ca(OH) 2 Used to make concrete and mortar
3) Lye –
Sodium Hydroxide – NaOH used to make soap and as a drain cleaner
The Arrhenius Theory of acids and bases
• Acids are substances which produce hydrogen ions in solution.
• Bases are substances which produce hydroxide ions in solution.
• Neutralization happens because hydrogen ions and hydroxide ions react to produce water.
• H + + OH H 2 O
The Bronsted-Lowry Theory of acids and bases
• An acid is a proton (hydrogen ion) donor.
• A base is a proton (hydrogen ion) acceptor.
• The Bronsted-Lowry theory doesn't go against the Arrhenius theory in any way - it just adds to it.
Equilibrium
• HCl + H 2 O H 3 O + Cl • The reaction works in both directions intil the amount of product produced from left to right equals the amount of product produced from right to left. This is the point of equilibrium • HCl is a strong acid so not so much true for this equation but gets point across.
Conjugate Pairs
• HA + H 2 O H 3 O + • Thinking about the
forward reaction:
+ A • The HA is an acid because it is donating a proton (hydrogen ion) to the water.
• The water is a base because it is accepting a proton from the HA.
• But there is also a
back reaction
hydroxonium ion and the A ion: between the • The H 3 O + is an acid because it is donating a proton (hydrogen ion) to the A ion.
• The A ion is a base because it is accepting a proton from the H 3 O + .
Conjugate Pairs Continued
• HA + H 2 O H 3 O + + A • The reversible reaction contains and
two two
acids bases. We think of them in pairs, called
conjugate pairs
.
Common acids and their uses
Acid names
end in the suffix
–ic
to tell chemists the compound is an acid.
Pickling -
a method of cleaning, oil, paint, grease, rust and other oxides from metal surfaces.
Dehydrating agent –
removes water from substances in industrial application and in skin cells to cause acid burns
1) Sulfuric acid
(H 2 SO 4 ) –used to treat metals, make fertilizers, found in batteries. This is the most common 2) 3) chemical made in the world
Phosphoric acid
– (H 3 PO 4 ) used to make fertilizers and soft drinks
Nitric acid
(HNO 3 ) –used to make dynamite and other explosives, fertilizers and to treat metals 4)
Hydrochloric acid-
(HCl) common name is Muriatic acid or stomach acid, used to clean metal surfaces, bricks and other masonry surfaces
Strengths of acids and bases The strength of an acid or base is determined by how much it ionizes or falls apart into ions.
Strong acids Weak acids Strong base-
only partly ionizes CH 3 COOH + H 2 O ionizes completely NaOH + H 2 O Na + H 3 O + + OH + CH +H 2 O 3 COO -
Weak base-
ionizes or falls apart completely HCl + H 2 O H 3 O + + Cl partly ionizes NH 3 + H 2 O NH 4 + + OH -
The pH Scale The pH scale measures how strong or weak an acid or base solution is by measuring the number of ions present in the solution. The number of H + ions for the acid or the number of OH ions for the base. The scale only goes from 0 to 14 but the numbers increase by powers of ten so one acid can be as much as a million times stronger than another acid. One base can be as much as a million times stronger than another base.
Because the pH numbers increase in powers of ten a ph of 1 is ten times greater than a ph of 0 and a ph of 2 is 100 times greater than a pH of 0 and a pH of 3 is 1000 times greater than a pH of 0 and pH of 4 is ten thousand times greater than a pH of 0
Concentrations of acids and bases • Remember Molarity • Mol of Solute per Liter Solvent • We use the term Molar to describe concentrations of Acids or Bases.
• Ex: Two Molar is more Concentrated than 1 Molar • I wonder if there will be math associated with this……YES!!!
• Grams to moles • mL to L • Comparisons etc…. GOOD STUFF
Neutralization reactions A
neutralization reaction
occurs when an acid is combined with a base. The low pH of the acid is counteracted by the high pH of the base and the solution moves toward a pH of 7 which is neutral. The reaction is a double displacement reaction and always produces a
salt and water
. The salt comes from the positive ion in the base and the negative ion in the acid. Look at the following neutralization reaction.
HCL + NaOH Acid + base NaCl + H 2 0 salt + water A salt can also be produced when a acid reacts with a metal and hydrogen is produced instead of water. Example below.
H 2 SO 4 + Zn (Battery + metal Zn(SO 4 ) + H 2 salt + hydrogen Acid)
Titration A type of neutralization reaction between and acid and a base and uses the concentration of a known solution (or
standard solution
) to determine the concentration of an unknown solution
Buffers-
are chemicals that react with acids or bases to slow down ionization or the formation of H + and OH ions to reduce or eliminate the acid or base properties.
Indicators-
are substances that change color when they come in contact with an acid or base.
Litmus paper-
is the most well known indicator and turns red in an acid and blue in a base.
Standard solution-
In a titration it is the solution with the known concentration.
End Point-
in a titration the indicator will change colors as the unknown solution changes from an acid to a base or from a base to an acid and the titration is complete. At the end point the quantity of the known solution is measured and with this value the concentration of the unknown solution can be determined.
Esters-
are chemicals that have strong aromas. Most of them are artificial and have been made in a laboratory by mixing an organic acid (COOH) with an alcohol. Each ester has a distinct odor or fragrance such as peppermint or wintergreen or strawberries. The perfume and cologne industries use many kinds of esters.
Acid rain
Acid Rain-
is any rainfall below 5.6 on the pH scale. Normal rain is naturally acidic and can register as low as 5.6 on the pH scale. Any rainfall with a
pH below 5.6
is caused by man and is considered acid rain.
Effects of acid rain
1) Kills Plankton –
microscopic plants and animals found in rivers lakes and oceans. Plankton is the bottom of the food chain. Destroying plankton adversely affects all organisms in the food chain.
2) Dissolves minerals and nutrients in soil-
allowing them to be washed away with the rain runoff. Plants need the nutrients that were washed away
3) Destroys statues and buildings-
acid dissolves buildings and statues made of marble and limestone.
Sources of acid rain
1) Burning coal-
to produce electricity or to make steel releases (SO 3 ) Sulfur Trioxide which combines with rain water to make sulfuric acid and acid rain.
H 2 O + SO 3 .
H 2 SO 4 (Sulfuric acid) 2) Burning gasoline-
releases (NO 2 ) nitrous dioxide which combines with rain water to produce Nitric acid and acid rain.
NO 2 + H 2 O HNO 3 (nitric acid)
Naming Bases
• Most common bases are formed when a metal (especially Groups 1A and 2A) bonds with a hydroxide. naming bases once you've identified them is easy!
1. Name the metal CATION first; it keeps its name as listed in the Periodic Table.
2. The polyatomic ion "hydroxide" (-OH) also keeps its name.
• Examples: • LiOH is "lithium hydroxide" • Ca(OH)2 is "calcium hydroxide" • NH4OH is "ammonium hydroxide"
Naming Acids
• There are two basic types of acids: 1) Binary acids (made up of two elements, one of which is hydrogen) and Oxo acids (which form when hydrogen bonds with a polyatomic ion).
• Binary or "Hydro" acids 1. Start with the word "hydro" (for our friend hydrogen) 2. Change the second element's name so it ends with " ic" 3. End with the word "acid" • Examples: • HCl is "hydrochloric acid" • HF is "hydrofluoric acid" • HBr is "hydrobromic acid"
"Oxo" acids
• DO NOT start with "hydro!" ("Hydro" is reserved for binary acids) 1. Start with the full name of the polyatomic ion (nitrate, sulfate) and CHANGE the ending as follows: • If the polyatomic anion ends with "-ate" change it to "-ic" • If the polyatomic anion ends with "-ite" change it to "-ous" • End with the word "acid" • Examples: • HNO3 is "nitric acid" (nitrate was the polyatomic ion) • H2SO4 is "sufuric acid" (sulfate was the polyatomic ion) • HNO2 is "nitrous acid" (nitrite was the polyatomic ion)