District 7 - Acids and Bases

Welcome to your training for how to take down District 7 when you are in the arena. We all know the deadliness of acids and bases and it is important to remember this as you prepare to do battle with this District. The key is that you don't want to turn your back on this District for too long, otherwise they will likely kill you and then dispose of the body without leaving any evidence of the grotesque murder behind. They are advised by past champions Arrhenius and Bronsted-Lowry.

Past District 7 Champions

  • Arrhenius
  • Lowry
  • Bronsted

Properties of Acids and Bases

We can categorize a number of compounds as either acids or bases. Acids react with bases to produce a salt in a neutralization reaction

We say things can conduct electricity or not conduct electricity. Recall that metals are good conductors When you dissolve an ionic compound in a solution it breaks apart into its ions. This positive and negative charge allows for the solution to now conduct electricity. You need charges to conduct electricity. Therefore, in order to conduct electricity you need ions. IONIC compounds conduct electricity and COVALENT compounds do not!

There are many common properties that help to identify acids. The common properties of acids are:

  • Taste sour
  • Conduct electricity
  • React with a base to form a salt
  • Often contains hydrogen

There are many common properties that help to identify bases. The common properties of bases are:

  • Taste bitter
  • Dilute bases feel slippery
  • React with an acid to form a salt
  • Conduct an electrical current
  • Often contain OH

These are solid guidelines to stick to, but you should never taste a substance to check for acidity/basicity!

Water conducts electricity only when it self-ionizes or has ions dissolved in it.

Many common household cleaners are bases.

Identifying Acids and Bases

Arrhenius Acids and Bases

There are two main theories of acids and bases. The first theory is the Arrhenius acid/base theory. An Arrhenius acid gives a H+ to a solution in an acid/base reaction. An Arrhenius acid will have a H in its chemical compound (e.g. HCl, HNO3, H2SO4, etc.). An Arrhenius base gives an OH- to a solution in an acid/base reaction. An Arrhenius base will have an OH in its chemical compound (e.g. NaOH, KOH, Ca(OH)2, etc.).

Bronsted-Lowry Acids and Bases

The second theory of acids/bases is the Bronsted-Lowry theory. Bronsted-Lowry refined Arrhenius’ theory of acids/bases. Bronsted-Lowry acids donate (give) a H+ to solution. Bronsted-Lowry bases accept (take) a H+ from solution. All Arrhenius acids/bases are Bronsted-Lowry acids/bases, but not all Bronsted-Lowry acids/bases are Arrhenius acids/bases.

Acids and Bases in Chemical Reactions

When looking at chemical reactions, identifying acids and bases is a relativly straightforward process. The most important thing to remember is that acids and bases will always be listed as reactants if you are studying an acid/base reaction.

Acids are usually identified by the presence of a hydrogen ion. For example, HCl, HNO3, and H2SO4 all contain a hydrogen ion that can be donated to solution. Therefore, if you are examining an acid/base reaction, the acid is usually the compound that contains a hydrogen ion.

Bases are slightly more difficult to identify, but the rules are relativly straightforward. Most bases contain an OH ion. Therefore, if a compound contains an OH, then it is a base. Often times, elements do not contain a base, but can be considered a base due to the fact that they can accept a hydrogen ion. For example, NH3 can accept a H in order to form NH4+. Becuase of this ability to accept hydrogen ions, NH3 is considered a base. Therefore, the presence of OH or the ability to accept a hydrogen is an indication that a compound is a base.

Strong vs. Weak Acids and Bases

Acids/Bases can be classified as strong or weak based on how much it disassociates. When we say something disassociate this means to break apart. Acids/Bases that completely dissociate are called strong acids/bases. Acids/Bases that only partially dissociate are called weak acids/bases. A solution of weak acid/base has some in the acid/base form and some in the broken apart form.

The seven strong acids are:

  1. HI
  2. HBr
  3. HCl
  4. HNO3
  5. HCl3
  6. HCl4
  7. H2SO3

The seven strong bases are:

  1. Ca(OH)2
  2. Sr(OH)2
  3. Ba(OH)2
  4. NaOH
  5. KOH
  6. RbOH
  7. CsOH

The pH Scale

The concentrations of acids and bases are often very low. We use the pH scale in order to more effectively convey the concentration of H+ in our solution. The pH scale is 0-14. An acid has a pH of 0-7 A base has a pH of 7-14 Neutral chemicals have a pH of 7.

p(anything) means -log(anything), so pH means -log(H+). We calculate the pH by:

pH=-log(H)

We calculate pOH by:

pOH=-log(OH)

A strong acid/base means that the compound completely dissociates. This means that if we have a 0.1 M solution of HCl, then [H+]=0.1 M

If we have a strong base, then that means that all of the compound dissociates. This means if we have a 0.1 M solution of NaOH, then we have [OH-]=0.1 M We can calculate the pOH if we have this. Once we have the pOH, we calculate the pH by:

pH=14-pOH

Practice!

In Need of a Sponsor!

It is well known that having sponsors in the arena can be the difference between a win and a loss. Kill District 7 with a little flair and you are bound to get sponsors lining up! SEE ASTOR FOR DISTRICT 7 ASSESSMENT!