Acids GapFill

Acids can react with metals to form  an alkalia salta metal acida halogen and hydrogen, with metal hydroxides and metal oxides to form a salt and  watera baseoxygenmethane, and with metal carbonates to form a salt, water and  hydrogen carbonatea metalcarboncarbon dioxide. The salts which are formed in these reactions depend on the metal and the acid used.

To make a pure, dry sample of a soluble salt, heat  a salt solutionan acidwatera halogen and then add a solid, insoluble metal, alkali or base until no more reacts. The mixture should be filtered and the solution heated to  evaporatecondensemeltfreeze the water away until  bluesoftpurecolourless, dry salt crystals appear.

Acids release  Cl⁻K⁺Na⁺H⁺ ions in solution, and alkali solutions contain OH⁻ ions. The  pHweighingacidosisdensity scale uses the numbers 0 to 14 to describe the acidity or  alkalinityconcentrationdensityreactivity of a solution, which can be determined using  a barometeruniversal indicatora thermometera buffer.

In a titration, acid is placed in a  beakerconical flaskburettepipette and dripped slowly into a beaker containing a  metalbasesolidgas and a suitable indicator, which changes colour when the reaction is complete. Strong acids completely  evaporateprecipitateionisereact in solution, compared to weak acids, which do not.

When a gas is produced in a reaction, there are many tests which can be used to find out what the gas is. For example:

• a lit splint gives a squeaky pop with hydrogen
• carbon dioxide turns  the airwaterlime watermetals cloudy