Wednesday, 10 July 2013

Science: Cleaning silver - Metal Displacement reaction

My father-in-law was asking me last Sunday about the best way to clean silver.  I thought is had something to do with baking powder but couldn't remember what so this week we found out how and why it  works.
 
So, have you got any silver in the house that needs cleaning?  Well this is a very easy way to clean it and of course there is science involved too!

As silver oxidises it will tarnish, this tarnish is called silver sulphide. This layer of oxidation can be removed without polishing and scrubbing by simply dipping your silver in this non-toxic electrochemical dip. The dip is also better than a scrub as it can reach places a polishing cloth cannot.


An electrochemical cell is a device capable of either deriving electrical energy from chemical reactions, or facilitating chemical reactions through the introduction of electrical energy.

So how do we do clean our silver then?
First we will need...




  • Sink bucket or glass pan
  • Hot water
  • Baking soda
  • Salt
  • Aluminum foil
  • Tarnished silver

  • Now you need to start the experiment...
    1. First line the bottom of the sink, a bucket or a glass baking dish with a sheet of aluminium foil.
    2. Fill the foil-lined container with steaming hot water - it is really important that it is steaming hot, probably better to boil your water on the stove you may like to use a thermometer to ensure your water is at boiling point.
    3. Add 2 teaspoons of salt (sodium chloride) and 2 teaspoons of baking soda (sodium bicarbonate) to the water.
    4. Carefully (remember the water is really hot) place the silver items into the container so that they are touching each other and resting on the foil. You will be able to watch the tarnish disappear. 
    5. Leave heavily tarnished items in the solution for as long as 5 minutes. Otherwise, remove the silver when it appears clean.
    6. Rinse the silver with water and gently buff it dry with a soft towel.
    7. Ideally, you should store your silver in a low-humidity environment. You can place a container of activated charcoal or a piece of chalk in the storage area to minimize future tarnish.

    Tips:

    1. Do be careful when polishing or dipping silver plated items. It is easy to wear away the thin layer of silver and cause more harm than good through over-cleaning.
    2. Minimize exposing your silver to substances which contain sulphur.  Things like mayonnaise, eggs, mustard, onions, latex and wool contain sulphur and  sulphur will cause corrosion.
    3. Using your silver items or wearing your silver jewellery helps to reduce the oxidisation process which causes your silver to tarnish.
    More about the science of this experiment...
     
    You will notice the silver that touches the foil cleans quicker this is because metal conducts electricity therefore this is where most of the reaction takes place. 
     
    Why Aluminium?  Well it much higher up in the activity series for metals - here is a list that shows us that the higher up the metal the more active the metal is...
     
     
    The reactivity series is metal is an arrangement of the metals in order of their reactivity starting with the most reactive metal at the top and ending with the least reactive metal at the bottom.
     
    The reactivity of a metal is determined by its ability to form a positive ion. For example, potassium is extremely reactive because it has only one valence electron, so it is very easy to lose it forming a positive ion.
     
    One the other hand, copper is a weakly reactive metal because it has more valence electrons so it is harder for it to become a positive ion.
     
    So What exactly is happening?
    This is a bit like the cleaning copper coins and copper plating nails.  Which ever metal is most active the sulphate will be most attracted to.  With the copper experiment you had this reaction...
     
    iron + copper sulphatecopper + iron Sulphate
     
    Fe + CuSO4 Cu(s) + FeSo4
     
    With the silver and Aluminium you have
     
    Aluminium + Silver sulphide → Silver + Aluminium sulphide.
     
     
    So if you want to have fun with some science go and offer to clean your grannies silver!
     

    No comments:

    Post a Comment