To determine the concentration of a limewater solution

Calcium = 40

Oxygen = 16

Hydrogen =1

          =            1                         =          1

             40+(16×2)+(1×2)                      74

     

        = 0.0135 moles of calcium hydroxide

The formula which the calcium hydroxide will react with the hydrochloric acid is:

Ca(OH)2(aq)  +  HCL                                             CaCl2(aq)  +  H2O(l)

When balanced=

Ca(OH)2(aq)  +  2HCL                                             CaCl2(aq)  +  2H2O(l)

The ratio in which the calcium hydroxide reacts with hydrochloric acid is 1:2.

Therefore, to work out the mole of hydrochloric acid needed for this investigation is shown below:

                            Ca(OH)2  +  2HCL

Ratio =                      1         :           2

Moles =            0.0135        : (0.0135×2) = 0.0270

Since the ratio is 1:2 then it should be twice as much therefore it will be 0.02

Moles                   0.01        :   0.02

Since the concentration of 2.00 mol dmֿ³ hydrochloric acid is to high , I will therefore need to dilute it.

The dilution formula is:

M1V1 = M2V2

                                    

Calculation:

M1 = 2.00 mol dmֿ³                                 V1 = ?

M2 = 0.02                                                  V2 = 250cm³

2 × V1 =0.02 × 250

Therefore:

V1 = 0.02 × 250                  

               2

= 2.5cm³

Apparatus:

• Volumetric flask(250cm³)
• Pipette(5cm³)
• Pipette filler
• 100cm³ beaker
• Limewater(1gdmֿ³ Solution)
• Distilled water
• 2M hydrochloric acid
• Burette
• 25cm³ pipette
• Indicator
• 250cm³ conical flask
• White tile
• Butterfly clamp
• Stand
• Wash bottle
• White tile
• Indicator(phenolphthalein)

Risk Assessment:

Method:

I have to find the concentration of limewater by titration. Its concentration is too high for this purpose, so it needs to be diluted before hand.

Dilution:

1. Rinse all the equipment such as the volumetric flask etc as it can be contaminated.
2. Fill the burette with the hydrochloric acid of concentration 2.00 mol dmֿ³.
3. Then run exactly 2.5cm³ of this into a 250cm³ volumetric flasks.
4. Next add distilled water and make up ‘to the mark’.
5. Then turn it up and down several times to ensure thorough mixing.
6. This dilution 2.5cm³ into the volumetric flask will give me an acid which had a new concentration.
7. Now that this is done we can now empty our burette and rinse it and refill it with the diluted acid that I have just prepared.
8. The 0.02 mol dmֿ³ of hydrochloric acid has now been produced. Rinse all the equipment which was used to use for the titration procedure.

Titration:

1. Rinse all the equipment such as the burette, pipette etc because it can be contaminated.
2. Fill the 25cm³ pipette with limewater or calcium hydroxide and then put it into the conical flask using a pipette and pipette pump.
3. Fill the burette with the diluted hydrochloric acid.
4. Use the stand and clamp to position the burette accurately.
5. Place the conical flask underneath the burette stand.
6.  The solution of calcium hydroxide will need to have 2-3 drops of phenolphthalein.
7. This will make it turn from red to colourless. Then we will need to release the burette and let the product in there mix with the limewater or calcium hydroxide.
8. Consequently the outcome will be is the solution will turn orange/brown colour and when this occurs I will need to take the reading on the burette.
9. Empty out the equipment and wash them thoroughly and repeat the titration method 3 times to get accurate readings.

Actions to ensure accuracy:

1. Repeat experiment at least 3 times to ensure results are very accurate
2. Rinse pipettes and burette with appropriate solutions
3. Make sure there are no air bubbles in the burette

Bibliography:

Books/Notes/Websites

1. AS- Level Chemistry-CGP-Revision Guide-page 18- information on indicators
2. Classroom notes for chemistry-05/02/07-equipment and diagram
3.  - information on method