Large pipette- measures 25cm3 accurately
Small pipette- measures very accurately up to 5cm3
(0.025 cm3 error).
Indicator- methyl orange- to show end point of titration
Hydrochloric acid- 2 molar, will need to be diluted
Goggles- to protect eyes
Large beaker
Small beaker
Funnel
Stand
Glass tile
METHOD
Once all the equipment is set up. The first thing I will have to do is dilute the 2.0 molar HCl. From my calculations I know that I will need 2.5cm3 of acid and 247.5cm3 of distilled water. I will first use a small pipette to transfer 2.5cm3 of 2 mol acid from a small beaker into the volumetric flask. I will then add 247.5cm3 of distilled water into the volumetric flask using a funnel. This will make a 250cm3 solution of diluted acid. I will then mix the solution evenly by turning the flask up and down. I will then pipette 25cm3 of limewater from a small beaker into a conical flask. I will then pour the distilled hydrochloric acid from the volumetric flask into the burette using a funnel. I will make sure the acid is level at 0cm3 by running off the excess into a small beaker. I will then add three drops of methyl orange into a conical flask, I will give the flask a swirl and then place it on the glass tile under the burette. Now all the equipment is ready for the titration. This part of the experiment has to done precisely as even one drop can cause a change. I will start by doing 1cm3 at a time and then swirling. After that I will drip a few drops at a time while swirling at the same time, this way I will be aware of any change in colour while it happens. Once the colour changes I will swirl the conical flask for a while to make sure the colour change is permanent. I will then fill the burette back to the top and start the experiment again. However I will try and use a new conical flask if there is one available if not I will wash it out thoroughly and then start again. I will try to do as many titrations as possible or until I get three concordant results.
AIM
The aim of this investigation is to find the concentration of a sample of limewater solution in gdm.
Limewater is also known as Ca(OH) . It is produced by the following reactions-
- strong heating of calcium carbonate produces calcium oxide and carbon dioxide.
This type of reaction, where a compound is broken down by heat is known as thermal decomposition
- calcium oxide reacts vigorously with water to produce calcium hydroxide (slaked lime)
- further addition of water to calcium hydroxide produces a saturated aqueous solution
Calcium hydroxide (limewater) is only slightly soluble in water. These compounds are often called ‘sparingly soluble’. As the concentration of calcium hydroxide in limewater is low, the solution has a low concentration of hydroxide ions, OH . The ph of limewater is about 9-10.
USES AND PRODUCTS OF LIMEWATER
Limewater can be used to identify carbon dioxide gas. When a sample of CO is bubbled through limewater, a cloudy white precipitate forms. The precipitate is solid calcium carbonate..
This precipitate of CaCO will dissolve in excess CO to form calcium hydrogencarbonate. It is this reaction which is responsible for the formation of hard water.
FAIR TEST
To make the experiment fair I will take many precautions.
- Firstly I will make sure that when using the burette, pipette and volumetric flask, the meniscus is level with the line. I will do this by looking at it from eye level. This is very important as any extra solution added can effect my final results.
- Once pouring the diluted HCl from the volumetric flask into the burette I will wait for a few minutes and then check the meniscus is level, this is because there may have been a few drops on the sides of the top of the burette which got left behind and therefore moved down later, this again can effect my results as I will not know the exact volume of acid used for the reaction.
- I will remove the funnel after I finish pouring the acid into the burette as there may be a few drops left which could fall into the burette during the titration, which again could mean I wouldn’t know the exact volume of acid used.
- When dropping the indicator into the conical flask, I will put the drops straight into the solution, if the indicator runs down the side I will rinse the flask out and start again. This is because the amount of indicator will differ for each one so the experiment wouldn’t be fair.
- I will rinse out the equipment before use, this is in case of contamination. For example before using the burette I will pour some of the diluted acid in and pour it out. This is just to make sure that the solution used before is washed away. For example the burette may have been used with 2 mol acid before therefore this would have effected my results if it wasn’t washed away. I will also wash the volumetric flask and pipette out with distilled water.
SAFETY
It is important to wear eye protection when working with chemicals, especially acid, which is corrosive and may cause burns. Also it is important not to inhale the indicator when opening the bottles as these can irritate the eyes and the respiratory system. Limewater is also an irritant to eyes. I will also keep all the equipment in the middle of the table as most equipment is glass so I will be careful not to break anything.
ANALYSIS
From my results I can see that my prediction was not absolutely correct, however I feel that it was very close. I did have an anomalous result which was my first titration. In my first titration I used 16.7cm3 of acid for the colour change. However this did not tie in with my 3 other titrations which were all concordant with each other. I believe that an average of 14.3cm3 is not as accurate as it should be, as I predicted that I would roughly use around 10cm3, because of the fact that we were using 10cm3 of limewater. My final result of 1.06 gdm was a good result as it was very near 1.0. I am happy with this result as it was very close. However I feel the reason my titrations weren’t closer to 10cm3 is due to the percentage errors (0.05cm3 on burette and 0.025cm3 on pipette). I feel that the first experiment was not very accurate I was not sure when to go slowly with the titration therefore I may have added I bit to much, but after I knew where about to start adding a few drops at a time.
