Planning of Titration
Aim: The aim of this experiment is to find the concentration of a sample of sulphuric acid using methyl orange as an indicator and a sodium carbonate solution as the base with known concentration.
In order to find the concentration of Sulphuric acid, I will have to perform a Titration and this will allow me to find out the concentration of Sulphuric acid. I will use the alkaline base which is Sodium Carbonate Solution to neutralise acid solution which is Sulphuric acid. An indicator present in the sulphuric acid solution will change colour after some time when the acid has been neutralised and that will be the end point. For this experiment I will be given anhydrous Sodium Carbonate of which I will make a solution of a concentration in the range between 0.05 and 0.15 mol dm-3. This is the only range of concentration of Na2CO3 I can make because the concentration of base lies between these two values. Another reason for this is that this is a one to one reaction. I will also be given Sulphuric acid and access to equipment for Titration in Laboratory.
Introduction to Titration: Titration is a laboratory technique by which we can determine the concentration of an unknown reagent using a standard concentration of another reagent that chemically reacts with the unknown. This standard solution is referred to as the "titrant". We have to have some way to determine when the reaction is complete that we are using. This is referred to as the "end point" or more technically the equivalence point. At that point all the unknown has been reacted with the standard titrant and some kind of chemical indicator must let us know when that point has been arrived at.
Introduction to Indicators: A chemical indicator is any substance used to assist in the classification of another substance. Indicators or are weak acids or bases that undergo dissociation in a known pH range. It is in this range that the acid (or base) is a different color from its conjugate base (or acid). There are many different kinds of chemical indicators. The classic example is litmus paper. I will use methyl orange for my experiment because it is the most suitable indicator for a weak alkali and strong acid. This indicator will change color from red (at pH 3.1) to orange-yellow (at pH 4.4) when acid is neutralised.
Equation of the Titration I will be doing:
Acid + Base Salt + Water
Sodium carbonate + sulphuric acid ===> sodium sulphate + water + carbon dioxide
Na2CO3(aq) + H2SO4(aq) ===> Na2SO4(aq) + H2O(l) + CO2(g)
mole + 1 mole 1 mole + 1 mole + 1 mole
Instructions to make a Standard Solution and to work out its molarity
* Wear Goggles and Coats
* Using the ± 0.001g balance, weigh approximately between 2.650g of sodium
carbonate into the weighing bottle.
* Using the ± 0.001g balance, weigh the weighing bottle and its contents accurately.
Record this mass.
* Transfer the contents of the bottle into a 250 cm3 beaker.
Weigh the weighing bottle again using the ± 0.001g balance.
Record this mass.
The difference between the two accurate masses is the mass of sodium carbonate in
your flask.
* Add distilled water cautiously down the side of the beaker containing anhydrous Na2CO3.
Use about 150cm3 of water, and swirl the beaker to mix the contents.
* Stir using a glass rod crush and to dissolve the solid completely.
* Transfer the solution into the volumetric flask using the funnel.
Remember: pour down the glass rod;
Remove the last drop of solution from the glass rod onto the funnel.
Wash the beaker, rod and funnel several times using distilled water from the wash
bottle, letting the washings go into the flask. But do not go over the volume of the
volumetric flask (Not over 250 cm3)
* Make up to the mark on the volumetric flask with de-ionised water.
Stopper firmly, and shake the flask thoroughly to mix the contents.
* Now a solution of Sodium Carbonate ...
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Remember: pour down the glass rod;
Remove the last drop of solution from the glass rod onto the funnel.
Wash the beaker, rod and funnel several times using distilled water from the wash
bottle, letting the washings go into the flask. But do not go over the volume of the
volumetric flask (Not over 250 cm3)
* Make up to the mark on the volumetric flask with de-ionised water.
Stopper firmly, and shake the flask thoroughly to mix the contents.
* Now a solution of Sodium Carbonate with a known concentration is made and can be used.
Apparatus to be used for making a Standard Solution
Goggles 250 cm3 beaker 250 cm3 volumetric flask Funnel
Glass Rod Pipette 10 cm3 Spatula Na2Co3(s) Distilled Water Weighing Bottle
Calculation of Sodium Carbonate
According to equation 1 mol of Na2CO3 = 1 mol of H2SO4
Mr of Na2CO3 = (23)2 + 12 + (16)3
= 106 g mol-1
dm3 = 1000 cm3
Below are the calculations of finding the mass of Na2CO3 required to make up a solution of 0.10 mol dm-3 of Na2CO3
* I will make a 0.10 mol dm-3 concentration solution of Sodium carbonate because this is the middle value. And because the concentration of base lies between 0.05 and 0.15 mol dm-3 .
* A Volumetric Flask holds 250 cm3 solution but when using the formula c = n/v then the volume is 0.250 dm3
* C = n/v therefore 0.10 = n/0.250 so n = 0.025 mol
* Now number of moles of Na2CO3 = mass/Mr so 0.025 mol = grams/Mr
* So 0.025 = g/106 so g = 2.650 This is the amount of Sodium Carbonate in grams needed to make a solution of concentration 0.10 mol dm-3 Na2CO3
n = 0.0250 mol v = 0.250 dm3 c = 0.10 mol dm-3
Instructions for carrying out Titration
* Write a balanced equation of the Reaction
* Wear Goggles and coat.
* First do all the steps below for a rough Titration to see when approximately the end point is so you do not put too much sodium carbonate solution into the acid, which won't give accurate results. Do the rough Titration carefully so you can compare the colour change with the real experiment. (This Titration will give you an idea of how to do the real experiment and any mistakes can be improved)
* First rinse the Burette with distilled water to remove any dirt or other chemicals stuck in the burette.
* Now rinse the burette with the acid to remove all the water in the burette. (Rinse 2 times to make sure only acid is present and nothing else in the burette to get accurate results). Also if water is left in the burette it will dilute the acid, which will give inaccurate results.
* To fill a burette, close the stopcock at the bottom and use a funnel. You may need to lift up on the funnel slightly, to allow the solution to flow in freely.
* Check the tip of the burette for an air bubble. To remove an air bubble, whack the side of the burette tip while solution is flowing down the burette. If an air bubble is present during a titration, volume readings may be in error.
* Rinse the tip of the burette with water from a wash bottle and dry it carefully. After a minute, check for solution on the tip to see if your burette is leaking. The tip should be clean and dry before you take an initial volume reading.
* When your burette is conditioned and filled, with no air bubbles or leaks, take an initial volume reading. A burette-reading card with a black rectangle can help you to take a more accurate reading. Read the bottom of the meniscus. Be sure your eye is at the level of meniscus, not above or below. Reading from an angle, rather than straight on, results in a parallax error.
* Deliver solution to the titration flask by turning the stopcock. The solution should be delivered quickly until a couple of ml from the endpoint.
* Prepare the solution to be analyzed by placing it in a clean or rinsed with distilled water conical flask. Add the indicator methyl orange to the sulphuric acid. Continuously move the flask in a circle under the burette to mix any acid in the whole volume flowing down the burette.
* Use the burette to deliver a stream of titrant to within a couple of ml of your expected endpoint. You will see the indicator change colour when the titrant hits the solution in the flask, but the colour change disappears upon stirring.
* Approach the endpoint more slowly and watch the colour of your flask carefully. Use a wash bottle to rinse the sides of the flask and the tip of the burette; to be sure all titrant is mixed in the flask.
* As you approach the endpoint, you may need to add a partial drop of titrant. You can do this with a rapid spin of a Teflon stopcock or by partially opening the stopcock and rinsing the partial drop into the flask with a wash bottle.
* Make sure you know what the endpoint should look like. For methyl orange, the endpoint is the first orangey yellow.
If you think you might have reached the endpoint, you can record the volume reading and add another partial drop. Sometimes it is easier to tell when you have gone past the endpoint.
* If the flask looks dark yellow (with methyl orange), you have gone too far!
* When you have reached the endpoint which is when the colour of solution has changed from pinkie red to orangey yellow, read the final volume in the burette and record it in your notebook.
* Do the whole procedure 4 or 5 more times to get accurate results.
* Subtract the initial volume to determine the amount of titrant delivered. Use this, the concentration of the titrant, and the stoichiometry of the titration reaction to calculate the number of moles of reactant in your analyte solution.
At the equivalence point (end point):
Number of equivalent weights of titrant = Number of equivalent weights of unknown
The apparatus to be used for Titration
> Burette 50 cm3
> Clamp Stand
> Conical Flask 250 ml
> Stirrer
> Funnel
> White Tile
Risk Assessment and Precautions
Always wear approved laboratory eye protection and coats for self protection.
A burette is necessary since the volume of the solution being run into the alkali must be measured. Other precautions are to have the burette vertical, to read the bottom of the meniscus, and to constantly swirl the conical flask during the titration. Also watch fairly constantly the solution as the colour changes very suddenly which is most important in this experiment.
Do not put dangerous chemicals in containers for food use (i.e.: cups, glasses, bottles) because they could be mistaken for beverages or foods. At the end of the experiments, empty the beakers and wash them. Place the containers of the remaining substances, which you want to preserve in suitable places.
Sulphuric acid is normally very corrosive and irritant when over 1.5 M but in this titration there is only a concentration between 0.05 and 0.15 mol dm-3 which is not as irritant and corrosive and harmful. In high concentrations this strong acid can burn skin and when swallowed can damage organs. We are using low concentration of it but still it can damage eyes when splashed in it so goggles should be worn and also coats.
Sodium Carbonate is a weak alkali but irritant to eyes, skin and respiratory system so if swallowed drink a lot of water and seek medical attention and it gets in eyes wash the eyes for at least 10 minutes under running water. If spilt on cloths or skin then wash skin with plenty of water and wear other clean cloths. However this is not as harmful as Sulphuric acid. If spilt in laboratory scoop as much solid as possible.
Methyl orange is thought to be toxic if swallowed or inhaled. Skin contact with the solution should be avoided. Wear safety glasses. If the solution comes into contact with your skin wash it off without delay. When it gets in eye immediately flush the eye with water.
If irritation persists, seek medical attention. If it comes into contact with the skin wash off with plenty of water and if swallowed, drink plenty of water and call for medical help.
If any glass equipment is broken care should be taken and the teacher should be informed who will clean away the glass panes straight a way and the students can carry on with the experiment.
Also bags and everything on the table should be put away except paper and pen for writing down the results before the experiment so no one falls over the bags. The working area should be clean and dry with no spillages before the experiment. Also the chairs should be tucked in and no food should be on anywhere in the laboratory except in bags.
Main thing is that do not hectic as this will increase the chances of any of the things listed above happening and also you wont be able to do the experiment properly which will affect the results so make sure that take time but work smoothly and accurately.
Titration
rough
2
3
4
5
Final Burette Reading (cm3)
Initial burette reading (cm3)
Titre (cm3)
Average Titre = cm3
Precise and reliable results (Justification)
* I will carry out the experiment at least 5 times to get accurate results and to avoid any anomalies.
* I have used pipettes rather than the normal measuring Cylinder so that I get accurate volume of solution.
* I will wash the beaker and glass rod 3 times to make sure that all the solution I will make goes in the Volumetric Flask.
* I will rinse the burette once with water to get rid of any other chemicals or dirt in the burette and then 2 times with Sodium Carbonate solution to get rid of the water which will only dilute the solution
* I will rinse the conical flask after the titration to make sure all the Sodium carbonate dissolves in the acid. I will do this to mix all of the base which is spitted on the wall of the flask
* I will use 4 decimal places for all my calculations except for the answer which will be in 3 decimal places. This will give me more accurate results.
* For all of my trials of experiment I will compare the colour change so that they are as similar as possible. This will give me accurate results.
* I will use bulb pipette and volumetric Flask and Burette to get measurements as accurate as possible.
* I will make a standard solution of Sodium Carbonate to use in titration and make sure the anhydrous sodium carbonate is completely dissolved in the distilled water.( any solid present in solution will not give accurate concentration)
* I will use an electric balance rather than weighing scale to increase the accuracy
* I will use only 2-3 drops of methyl orange and not more than that because of 2 reasons. First reason is that it will make the solution too dark so it will be difficult to identify the colour change. Second reason is that it itself is a weak alkali which will make the solution alkaline and this will give inaccurate results.
* I will put all of the solid Na2CO3 in beaker and all of solution in flask by rinsing the beaker.
* I will make sure the Volumetric Flask is clean and dry or only rinsed with distilled water to make as accurate as possible solution of 0.10 mol dm-3 concentration.
* I will make the solution in a Volumetric Flask because it is made for making solution and it is very accurate because of its shape. It makes exactly 250 cm3 of solution. It is far more accurate than a beaker an also more accurate than a conical flask. A Volumetric Flask is one of the most accurate apparatus in use for making such a large volume of solution.
* I used methyl orange for this experiment because it is the most suitable indicator for this experiment which has a weak alkali and strong acid. ( different combinations of alkali (strong or weak) and acids may need different indicators)
* I will use a bulb pipette for taking out an accurate volume of Sulphuric acid and put it into the conical flask. This is more accurate than a teat pipette.
* I will do a rough Titration to find out where approx. the end point is (approx. volume of acid needed to neutralise the base) and to make sure that I do not do any mistake for the real trial. Also I will compare the colour of the rough with the real experiment if it is correct.
* I will use a white Tile which will make easy to see the colour change in solution.
* I will use a Funnel to deliver the sodium carbonate solution into the burette so that no solution is wasted.
* I will use a pipette pump to suck in the Sulphuric acid into the bulb pipette.
* The Clamp Stand will hold the Burette
* The stirrer will be used to mix and crush the solid in distilled water when making standard solution.
* The teat pipette is only used in the case when bulb pipette is not available or you can't be bothered to use the bulb pipette.
* The weighing bottle is specifically made for weighing compounds and I will be weighing anhydrous Sodium carbonate in it.
* The Spatula is used to take small amount of Na2CO3 and weigh it.
* Finally the 100 cm3 beaker is used to dissolve the Sodium Carbonate into distilled water. It is small so it is easy to mix the solid in water with this beaker.
* I will make a suitable concentration of the alkali which is within the range of 0.05-0.15 mol dm-3 because this is the range of concentration of the acid. I will use this concentration for both solution because if they differ too much it wont give accurate results as this is a one to one reaction.
Source of information
* I used the activity sheet M 2.4. I used this especially for the method. (How to do follow everything step by step)
* I used the Book 'Advanced Chemistry 2000' (second edition. I used it especially for the formulas of finding concentrations etc.
* I also used the website 'www.creative-chemistry.org.uk'. This was especially useful for understanding how to make a standard solution.
* I used the Salter activity sheet El 2.1. I used this for the table of results and for the procedure.
Planning of Titration Sadiq Ahmed
Chemistry
