SC8 Acids and Alkalis

SC8 Acids and Alkalis

1. Acids, Alkalis and Indicators

   • The acidity or alkalinity of a solution is measured on the pH scale
     • Acidic = pH 1-6
       • Alkalic = pH 8-14
     • Indicators can be used to measure this
   • Acids have excess hydrogen ions H+
     • Alkalis have excess hydroxide ions OH-
       • The higher the concentration of these ions, the more acidic/alkane the solution is

2. Looking at Acids

   • As you go down in pH, hydrogen ions multiply by 10x
     • The more concentrated a solution of acid is, the lower the pH will be
       • A dilute solution is opposite to a concentrated solution
   • Concentration = g/dm
     • Grams dissolved/volume of solution

3. Bases and Salts

   • Bases are substances that NEUTRALISE acids to form salt + water
     • The hydrogen ions combine with oxide ions to form water, this removes the H+ so pH increases
   • Preparing Soluble Salts

4. Alkalis and Balancing Equations

   • A base that can dissolve in water, a soluble base, is called an alkali
     • Acid + Alkali -> Salt + Water
   • Balancing Equations, make sure everything is equal on both sides

5. Alkalis and Neutralisation

   • During neutralisation, the H+ ions and OH- ions join to form water
     • The other ions from the acid and alkali stay in the solution as ions of the dissolved salt
   • Soluble salts can be made via crystallisation but you need a NEUTRAL solution
     • This can be done using TITRATION
       • Acid is added from a burette to a fixed volume of alkali in a flask
         • A pipette is used to measure out the alkali, this provides more accurate measurements
           • Indicator is added to record the end-point when the solution changes colour due to there being enough acid to neutralise

6. Reactions of Acids with Metals + Carbonates

   • Metal + Acid -> Salt + Hydrogen
     • The first name of the salt comes from the metal and the second name comes from the acid
     • Half equations can show us what happens to the electrons
   • Metal Carbonate + Acid -> Salt + Water + Carbon Dioxide

7. Solubility

   • A PRECIPITATION reaction is one in which soluble substances in solutions cause an insoluble precipitate
   • We can predict whether a precipitate will form by checking the solubilites of the products
     • If both are soluble, no precipitate will form
   • Preparation of insoluble salts
     • A pure sample of an insoluble salt can be prepared from two soluble salts
       • Mix the two solutions, then filter the mixture
         • Rinse the beaker with distilled water and pour through funnel
           • Remove filter paper containing the precipitate and dry in oven

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