Aim: To Determine The Concentration Of a Limewater Solution

First I would need to find what would be an optimal concentration for the HCl. (molar mass of Ca(OH)2= 74.1)

Converting the g dm-3 to mol dm-3 of the limewater.

Concentration (g dm-3) / Molar Mass = Concentration (mol dm-3)

/ 74.1 = 0.0135

0.01 mol dm-3 limewater concentration (3 s.f)

Therefore as the equation above states for every 1 mol of Ca(OH)2, you would require 2 moles of HCl to neutralize it, I will require my HCl to be of concentration:

0.01 x 2= 0.02 mol dm-3

Therefore I will need to standardize my HCL, to ensure that it is of concentration 0.02 mol dm-3.

Creating the HCL Concentration

I will be using a 250cm3 volumetric flask and a 25cm3 pipette. Hence I will have to prepare a 0.2mol dm-3 concentrate then down into a 0.02mol dm-3. To calculate the required volume of 2.00 mol dm-3 HCL I will use the calculation below.

Initial molarity (Mi) x initial volume (Vi) = final molarity (Mf) x final volume (Vf). (Jim Clark AS calculations).

2.00 x Vi = 0.2 x 0.25 (litres)

Vi= 0.2 x 0.25/2.00

Vi= 0.025 (litres) Vi= 0.025 x 1000 = 25cm3

Standardisation Method Therefore, I will, fill up a 25cm3 pipette with HCL and empty into a 250cm3 volumetric flask. I will then top up the flask to the line with distilled water, ensuring the bottom of the meniscus is touching the line. This will give me acid of 0.2mol dm-3, so I will take 25 cm3 of this diluted acid and repeat the method above, consequently giving me 250cm3 of HCL at concentration, 0.02 mol dm-3 . N.B to ensure the diluted acid is thoroughly mixed I will invert the solution several times.

Indicator Choice

Through research on the internet (wikipedia), I was able to find out that methyl orange would be the best indicator for my experiment. This indicator usually turns from yellow to a bronze/ deep orange.

The limewater is a relatively weak base therefore I feel the using methyl orange would be appropriate, as it has an end point on the pH scale between 5-8. Alternatively I could have used phenolphthalein however I felt that using this would detect the end point prematurely.

Method

. Create the HCl solution mentioned above.

2. Set up the titration apparatus. Place the burette in the wooden clamp with the white tile and conical flask on sitting on the stand. First rinse the burette with the 0.02mol dm-3 HCL, once rinsed fill the burette with the 0.02mol dm-3 HCL, below eye level, using a funnel ensuring the bottom of the meniscus is touching the 0 mark. You also have to make sure that there are no air bubbles inside.

3. Now rinse the 25cm3 pipette, using pipette filler and the limewater provided. Once the pipette is sufficiently rinsed, fill the pipette carefully to the line and add the limewater to a conical flask. Finally add four drops of methyl orange to the flask.

4. The first run of the titration will be used as a 'range finder', so add the HCL from the burette until there is a distinct colour change. 5. Once this change in colour has occurred take the reading of the burette and minus this away from the initial volume to give you the volume used in the neutralisation reaction. The first reading can be used as a range finder.

6. Repeat the experiment; this time release the acid drip by drip closer to the end point, ensuring the exact end point is recorded. Do this until your results are reliable and you have at least two concordant results.

7. All your results should be recorded in a table for later use in the analysis where you can calculate these.

Safety

Due to the chemicals used (HCl) lab coats, and safety specs have to be worn at all times.

Apparatus

Wooden Clamp and Stand

Burette 50cm3

Pipette 25 cm3 and pipette filler

Distilled Water

Volumetric Flask 250cm3

Conical Flask 250cm3

White Tile

Funnel

Beaker

Methyl Orange Indicator

250 cm3 of Limewater

2.00mol dm-3 Hydrochloric Acid