Determination of the solubility of calcium hydroxide.

Volume of acid-

I will be measuring out a certain amount of acid and the adding the alkali from the burette until I reach my end point.

10cm  or 25cm  pipette

% error on 10cm      =        (0.04/10) X 100

                        0.4 %

% error on 25cm      =        (0.06/25) X 100

                        0.24 %

I have chosen to use the 25cm  as this measurement has the lowest percentage error.

Titre-

In 25cm  of acid        =         0.03dm X 25    =     0.00075 mols        =  0.000375 mols

                                  1000                          2

Average titre of alkali =         0.000375 X 1000        = 25cm

                                   0.015

As I am using a titre of 25cm I will be using a 50cm  burette (percentage error of 0.1 for one reading but will be 0.1 X 2 = 0.2 as two readings are needed for one measurement) If the titre was any larger or the burette any smaller then there is a greater risk of not having enough alkali to neutralise the acid and then having to refill the burette which would increase the percentage error immensely.

 

Indicator-

I am reacting a strong acid and a strong alkali, the information sheet about indicators suggests to use methyl orange, bromothymol blue or phenolphthalein. I have chosen to use methyl orange, as it is easy to see the end point, which would be a colour change to orange. I have to add enough of the indicator to see a slight colour change, normally about three drops.

Summary of apparatus-

25cm  pipette

Pipette filler

50cm  burette

White tile

100cm  conical flaks

100cm  beaker

250cm  volumetric flask

Waste beaker

Calcium hydroxide (approx. 0.015 mol dm  )

Hydrochloric acid ( 0.300 dm  )

Methyl orange indicator

Distilled water

Method-

1. Make up 250cm  of 0.03mol dm  of HCl in a volumetric flask using instructions on previous page.
2. Wash out pipette with HCl and then empty it in to the waste beaker (hold pipette at top when connecting the pipette filler).
3. Fill the pipette with 25cm  HCl again but this time add to the conical flask (which has also been washed out with HCL)
4. Add a few drops of methyl orange indicator.
5. Wash out burette with Ca(OH)  and the let it run out in to waste beaker. Re-fill with Ca(OH)  ensuring tap is closed. Make sure there are no air bubbles in the tap.
6. Run out the Ca(OH)  until it is at eye level as it is easier to read the volume. Read to volume that is at the bottom of the meniscus and record it.
7. While swirling the conical flask add the Ca(OH)  .
8.  Look for the end point (a slight colour change) and add drop by drop to ensure you do not go over the end point.
9. When the end point is reached record the volume and subtract this from the initial reading. This is the titre. The first attempt is a rough titration and is likely to be a larger volume then needed. You do however have an idea of what you expect the titre to be.
10. Repeat the experiment several times from point 3 until you have three reading that agree with to 0.1cm  to obtain an average reading.

My plan is likely to provide precise and reliable results as I have taken in to account all the things that may influence the results I obtain and tried to eliminate them. Below is a list of the things I will do to achieve this-

• I am washing out all the apparatus that I use with the solution that it will contain in the experiment to ensure that no other solutions will be present in the experiment. The solutions that I will wash the apparatus with will go in to a waste beaker.
• I will mark all the beakers I will be using clearly to ensure I do not confuse them
• When using the pipette I will touch the side of the beaker/flask it will be emptied in to ensure that it is all run out. (There is always one last drop left in the pipette which is accounted for by the manufacturers when the pipette is made)
• I am using a white tile so that it will be easier to see the colour change at the end point.
• When using the burette I will ensure that no air bubbles are left in the bottom below the tap, as this would make my titre incorrect.
• Each time I use the HCl I will tip the volumetric flask upside down to ensure the solution is mixed.

I have included detailed explanations of how to make up the diluted HCl and a method of how to carry out the experiment. In my method I have stated how to read apparatus correctly and things to do to ensure that it is a controlled experiment.

Risk Assessment-

Hydrochloric Acid-

Corrosive and irritant. Wear eye protection and a lab coat. If substance gets in to eyes, mouth or on skin wash with water and seek medical attention.

Calcium Hydroxide-

Corrosive and irritating to eyes. Wear eye protection and lad coat. If hands are contaminated and the substance gets in to eyes or mouth flood with plenty of water and always seek medical attention.

Calcium Chloride-

Irritant to eyes, skin and respiratory system. Is dangerous with water as it is an anhydrous salt and can cause water to boil. Wear eye protection and lab coat. Use in a well ventilated area. If substance gets in to eyes, mouth or on skin then wash with water and seek medical attention.

Sources I have used-

Information on the use of indicators in acid-alkali titration sheet

Hazard cards

Salters chemistry notes