acids & bases

• N is the number of moles (mol), which is a measurement of how many particles are in a substance.
• The pH scale represents the “power of hydrogen” and is a scale of the

  concertation of hydrogen ions present in the solution.

  The scale can run below 0 and above 14 but for ease, the scale of 0 to 14 is often used.
• The more acidic a solution is, the lower the pH

  The more alkaline a solution is, the higher the ph.
• hydrochloric acid - HCl - H+Cl−
• sulfuric acid - H2SO4 - 2H+(SO4)−2
• Nitric acid - HNO3 - H+NO3−
• sodium hydroxide - NaOH - Na+OH−
• calcium hydroxide - Ca(OH)2 - Ca^2+ 2OH^-
• magnesium hydroxide Mg(OH)2 - Mg^2+ 2OH^-
• ammonia NH3 - NH4+ OH-
• Acids have a pH of less than 7, neutral substances have a pH of 7 and alkalis have a pH of greater than 7.
• Water is a neutral substance that dissociates (breaks up) naturally into H2O(l) <-> H+(aq) + OH- (aq).
• H2O(l) is a water molecule.
• H+(aq) is a hydrogen ion.
• OH-(aq) is a hydroxide ion.
• Water is neutral due to the number of hydrogen ions is equal to the number of hydroxide ions, represented by the equation [H + ] = [OH - ].
• When a solution dissociates and the hydrogen ion concentration is greater than the hydroxide ion concentration, the solution is acidic, represented by the equation [H + ] > [OH - ].
• When a solution dissociates and the hydroxide ion concentration is greater than the hydrogen ion concentration, the solution is alkaline, represented by the equation [H + ] < [OH - ].
• Acidic solutions contain more [H + ] than [OH - ].
• Alkaline solutions contain more [OH - ] than [H + ].
• Neutral solutions contain equal concentrations of [H + ] and [OH - ].
• The pH balance explains what happens when an acid or alkali is diluted.

  Adding water to any aqueous solution will decrease the concentration of the solution.
• In acidic solutions diluting increasing the pH of the acid towards 7, as the solution is diluted the hydrogen ion concentration decreases. This causes the pH to increase towards 7.
• In alkaline solutions diluting decreasing the pH of the alkali towards 7, as the solution is diluted the hydroxide ion concentration decreases. This causes the pH to decrease towards 7.
• Acids can be formed by dissolving soluble non-metal oxides in water.

  Sulfur Dioxide + Water ->Sulfuric Acid

  Nitrogen Dioxide + Water -> Nitric Acid

  Carbon Dioxide + Water -> Carbonic Acid

  Hydrogen is the only non-metal that will not give an acidic solution.

  Dissolving hydrogen into water gives you water!
• Alkalis can be formed by dissolving soluble metal oxides in water.

  For example, sodium metal dissolves in water to make Sodium Hydroxide

  Na + H 2 O -> NaOH

  There is one exception; nitrogen, which is a non-metal, dissolves in water to form ammonia, NH 3 .

  Ammonia is a colourless gas and is lighter than air. It has a very distinct pungent smell!
• A base is a substance that can neutralise an acid to form water.

  There are three different types of bases:

  1. Metal Hydroxides (alkalis)

  2. Metal Oxides

  3. Metal Carbonates
• Neutralisation is when a known volume of acid and base react together to form a neutral substance.

  The hydrogen ion from the acid reacts with the hydroxide ion from the base to form water.

  ACID + BASE -> SALT + WATER
• A salt is formed when the metal ion from the base and the non-metal ion from the acid join together.

  Hydrochloric acid forms Chloride salts

  Sulfuric acid forms Sulfate salts

  Nitric acid forms Nitrate salts
• the name of the salt comes from the name of the alkali it is formed from

  the metal or ammonia (base) provides the first part of the name

  the acid provides the ending of the name
• if you are reacting a metal carbonate with and acid the reaction will produce a salt and water and carbon dioxide (CO2)
• the test for carbon dioxide is that it will turn lime water cloudy
• Titration is an analytical technique used to determine the accurate volumes involved in chemical reactions such as neutralisation.
• An indicator is normally used to show the endpoint of the reaction.

  Titrations can be used to determine the concentration of a solution.
• The most important pieces of apparatus require to carry out a titration include a burette, volumetric pipette and conical flask.
• titration

  The base is added to the burette, ensuring the burette is filled and a specific volume of acid is measured using the volumetric pipette and added to the conical flask.

  Universal indicator is added to the acid to make the end-point of the reaction clearer.

  To carry out the neutralisation and determine the exact volume of base required to neutralise the acid, the base is added drop wise to the acid.

  The end point of the reaction occurs when the indicator turns from red (acidic) to green (neutral) .
• Titrations are always repeated to ensure the reliability of the results. An average volume must be calculated.

  The results from the first titration (also known as rough titre) is never used.

  The average volume must be taken from concordant results. (when the volume is within 0.02cm 3 of each other).
• how to improve titration experiments

  place a white tile under the conical flask

  read the numbers from eye level
• the easiest way to make a soluble salt is to neutralise the relevant acid with a base-

  either react the acid with a soluble base ( alkali )

  or react the acid with an insoluble base
• reacting soluble base and acid

  1. add alkali to acid with indicator until PH7 is reached - note the volume used
  2. repeat the experiment without indicator
  3. evaporate the liquid to leave salt crystals