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Limewater (Ca (OH)2 )
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Nitric acid (HNO3 )
- Indicator (methyl orange)
- Deionised water
Diagram
Background information
Nitric acid
Nitric acid is a chemical compound, HNO3; it is colourless, highly corrosive. It is a very strong acid. It ionises readily in solution. It reacts with metals, oxides, and hydroxides forming nitrate salts.
Calcium Hydroxide
Calcium hydroxide (Ca (OH) 2), is a colourless crystal or white powder. It is prepared by reacting calcium oxide (lime) with water; a process called slaking, and is also known as slaked lime. A solution of calcium hydroxide, called lime water, is a strong base that reacts violently with acids and attacks many metals in presence of water. Limewater is a clear, saturated water solution of calcium hydroxide
Indicators
Methyl orange
Methyl orange is one of the indicators that is most commonly used in titrations. Its structure is simple enough to be able to see what is happening as it loses and gains hydrogen ions. Methyl Orange is a PH indicator frequently used in titrations. It is also toxic. It is often chosen to be used in titrations because of its clear colour change. Because it changes colour as a mid-strength acid, it is usually used in titrations between strong acids and weak bases.
Phenolphthalein Phenolphthalein is another commonly used indicator for titrations, and is another weak acid.
In this case, the weak acid is colourless and its ion is bright pink. Adding extra hydrogen ions shifts the position of equilibrium to the left, and turns the indicator colourless. Adding hydroxide ions removes the hydrogen ions from the equilibrium, which tips to the right to replace them - turning the indicator pink.
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I will use methyl orange indicator in place of phenolphthalein because methyl orange is more suitable because the reaction between Nitric acid and Calcium Hydroxide is that of a strong acid and a weak base. Methyl orange reaches its end point at the PH between 8-5 and so is good for the titration that I will be performing unlike phenolphthalein which reaches its end point before the reaction ends.
Method for diluting the Nitric acid * Firstly I will dilute the Nitric acid to reduce the concentration of the acid. I will do this by adding 3.0 cm³ of Nitric acid, measured by the graduated pipette (that I would have already rinsed by the Nitric acid) from the container containing the acid to the volumetric flask of the size of 250 ml.
* I will then add the deionised water which will be provided to the volumetric flask until it reaches the marked line on the volumetric flask. I will then shake the flask additionally in order to make sure that the Nitric acid has been diluted with the deionise water.
* Next I will measure some Calcium Hydroxide which will already have been prepared to the right concentration, by the volumetric pipette (25.0 cm³) after rinsing the volumetric pipette with Calcium hydroxide and add it to the conical flask.
* I will then add the diluted Nitric acid to the burette after I have rinsed the burette with the dilute Nitric acid. I will do this by putting a funnel at the top of the burette and pouring the Nitric acid from the volumetric flask. I will come at length of the burette and see if I have accurately filled the burette up until the desired value (meniscus). I will fill the burette to the 0.0 cm³ mark so that the burette is full just in case I may need more then I said I will, so the burette will have a volume of 45.0 cm³.
* I will then remove the small funnel and start the actual titration.
Method for the titration of Nitric acid with Calcium Hydroxide
* I will take the measured 25.0 cm³ of Calcium Hydroxide by the pipette and add it to the conical flask. In addition to this I will add a couple of drops of methyl orange indicator which is my chosen indicator as I have said above with valid reason. I will note the colour of the solution in the conical flask which will be yellow.
* I will finally add the Nitric acid with the Calcium Hydroxide in the conical flask and swirl continuously. I will not stir because if I use a glass rod when I take out the glass rod some solution may leave and this will affect my final result.
* Once there is a definite colour change which should be from a yellow colour to an orange colour, I will close the tap on the burette and record the titre value.
* I will follow the method that I have listed above for the rough titre first and then I will repeat the titration four times.
* I will make sure that the next time I do my titration again I let the acid down through the burette very slowly and after a couple of drops, I will close the tap on the burette and swirl the conical flask. If there is no colour change then I will allow some more Nitric acid to pass through the burette and I will swirl the conical flask to see if there is any colour change.
* I will get the average titre by adding the four real titre values and not the value of the rough titre and dividing the answer by four.
* I will present my results in a table, showing all the titre values that I have received and the calculated average titre.
