Thursday, 11 June 2015

Science: Neutralisation reactions


 

Chemicals are made up of atoms, atoms contain ions – ions are electrically charged particles, they are formed when atoms loose or gain electrons.  Ions of alike repel and opposites attract, much like magnets!

Electrons are particles of negative change. 

In an atom, electrons form a negative charge that balances out the positive charge of the protons in the atomic nucleus.

Electrons are extremely small, they are about 1000 times smaller than a proton.

If you truly want to understand what is happening in this experiment you need to know which ions are produced by alkalis and which ones are produced by acids.  You will also need to know the ionic equation for neutralisation which I have included at the end.

One of the safest experiment you can perform which will give you the result you need is Citric acid and Bicarbonate of Soda and this is how to perform your experiment...

You will need:
  • Goggles
  • 2 test tubes –Test tube stoppers
  • 2 pipettes – if you don’t have pipettes you could use a teaspoon instead.
  • A petri dish
  • Citric Acid
  • Bicarbonate of Soda
  • pH paper
  • Water

STEP ONE

Put your goggles on then add half a test tube of water to two of your test tubes.

STEP TWO

Add 5ml of citric acid to one test tube.

STEP THREE

Add 5ml of bicarbonate of soda to the other test tube.

STEP FOUR

Put your stoppers on your test tubes and gentle swirl them a bit until all has been dissolved in the water. 

Now they are aqueous! Aqueous is a term used in science meaning a substance is dissolved in water.

STEP FIVE

Using your pH strips first test the citric acid and then the bicarbonate of soda.  Write down your results if you like.  I like to keep a science notebook for this.

STEP SIX

Using your pipettes and the petri dish (or, as I have said in the list above an old lid or small dish) Take a small amount, about 3ml of the citric acid and put it into the petri dish.

STEP SEVEN

Now using a different pipette extract some of the bicarbonate of soda from one test tube, try 1ml at a time and put it into the petri dish.

STEP EIGHT

What happens?  It fizzes.  Wait for that reaction to calm down then test the pH again.
 

 


STEP NINE

If it’s still an acid, add another 1ml of bicarbonate of soda and repeat STEP EIGHT.  Keep repeating these steps until the solution becomes neutral. 

Your science notebook, if you wish to use one should look something like this for this experiment...


STEP THREE in our science notebook did look alkali until someone touched the pH strip, but this gives you an idea.

Other options for this experiment:

If you don’t have any test tubes you can use glasses or plastic beakers instead.

Instead of the petri dish you could use a third test tube or an old lid from a jar.

Citric acid and Bicarbonate of soda

Citric acid is a tripotic acid – this means it’s an acid that has three ionisable hydrogen atoms in each molecule – therefore the ratio between citric and bicarbonate of soda is 1:3.

The equation will look something like this…

C6H8O7 + 3NaHCO3 = C6H5O7Na3 + 3 CO2 + 3 H2O

Citric acid + Bicarbonate of soda = sodium citrate + carbon dioxide + water

Another neutralisation you might want to try …

Hydrochloric Acid and Calcium hydroxide

Ca2(OH) + 2 HCl  = 2 Ca(Cl)2 + 2 (H)2O  

We use neutralisation in the real world to balance out the acidity in lakes and soils caused by acid rain.  To do this we use the alkali, Calcium hydroxide.

This method is also used by gardeners, acids are also added to the soils sometimes if an acidic soil is needed.  You might like to check out my experiment: Soil pH Test

 

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