Preparing a standard solution
Having calculated the weight I can use (0.092g), I must weigh out the solute using an accurate electronic balance that goes to three decimal places. I must make sure I clean the balance with a fine brush assuming that it may not have been cleaned after the last time it was used and set the balance back to 0.00. I must also make sure I careful when using the spatula to add the white crystalline solid unknown acid. I then need to clean a 250cm3 beaker with distilled water and then add 50cm3 of distilled water to it; I will then carefully transfer the bulk of solute into the beaker stirring until all the solute has dissolved. This shouldn’t take long as the sample of unknown acid is very soluble in water. To make sure I have all the acid I will wash the weighing bottle with distilled water and add it to the beaker, I will do this three times just to be certain I have all the acid. I will carry on stirring with a glass rod (which will have also been washed in distilled water before use) and adding more distilled water if necessary until all the solute has dissolved. On completing that I will wash a 250cm3 volumetric flask out with distilled water. Then I need to transfer all the solution into the volumetric flask. I will do this using the aid of a funnel (which will have also been washed in distilled water). After all the solution has been transferred, I will wash the beaker with distilled water and transfer all the washings to the volumetric flask, I will carry out this three times, and then wash the funnel through, again repeating this several times. I will at that time add more distilled water to the volumetric flask until the water level is 1cm from the 250cm3 mark on the neck. After that I will place the stopper over the top and turn the flask upside down and shake the contents, returning it upright. I will do repeat this ten times to again to be certain all the solute has dissolved. Next using a dropping pipette (which will have also been cleaned with distilled water) I will add distilled water slowly to bring the meniscus up to the mark on the neck of the flask. I will be at eye level with the flask at this point to make sure it is as accurate as I can get it. I will then again place the stopper on the flask and turn it upside down and shake the contents, returning it upright, again repeating this ten times.
Thermometric titration
Before I start my titration I am going to leave my two solutions out in the room for a couple of hours, so they can adapt to the room temperature, and also so they are the same temperature. I must also make sure all my equipment is rinsed properly with distilled water. To clean the burette I will run distilled water through it, I will do this by setting the burette up with the use of a stand. I will close the tap at the bottom of the burette and fill the burette up to the top, I will then place a beaker under the burette and open the tap, letting the distilled water run out. When all the distilled water has run out of the burette I will close the tap and refill it with the solution of unknown acid, shaking the solution of the unknown acid before adding it. I will add the unknown acid using a funnel (which will have been rinsed with distilled water). I must always remember to remove the funnel as it can affect the results. Before I run the unknown acid through the burette I must make sure I shake the flask, to be sure it is all dissolved. I will again place the beaker under the burette and let the unknown acid run through the burette. I will then again fill the burette with unknown acid, making sure it goes above the zero mark. This time I will only run out the unknown acid until the meniscus of it is touching zero. This will also ensure that the jet space of the burette is full of unknown acid as it counts towards the measurement. I will then remove the drop remaining on the tip of the burette as this may affect results. Next I need to clean out a polystyrene cup; I do this by again rinsing with distilled water. I will also need to swill out a 50cm3 pipette, again using distilled water. After this is completed I have to shake the volumetric flask of sodium hydroxide, I do this by turning it upside down and shaking the contents, returning it upright, repeating this ten times. After that I will use the 50cm3 pipette with a pipette filler to suck up some sodium hydroxide. I will fill it up over the 50cm3 mark and then drain it out under gravity into a beaker, making sure the tip does not touch the liquid as it will not run out as good. Next I need to again shake the sodium hydroxide. I will then fill the pipette up again to the 50.0cm3 mark, making sure the meniscus of the sodium hydroxide touches the 50.0cm3 mark. I will then transfer this to the polystyrene cup. I will then need to wash a thermometer in distilled water. The thermometer I use should read to 0.1˚C. When all this equipment is set up I should start releasing the unknown acid from the burette slowly, adding 5cm3 at a time and then recording the temperature, should keep adding 5cm3 at a time and recording the result until I have used up all of the 50cm3 of unknown acid. One hand should be turning the tap and checking the flow while the other hand should hold the thermometer in the polystyrene cup. The thermometer should not touch the side or the bottom so it is only in contact with the solutions. I must always touch the side of the polystyrene with the tip of the burette to make sure the last drop lands in the polystyrene cup, as this could affect the results. The thermometer should always be read horizontal and at eye level, to make result as accurate as possible. Heat loss is inevitable but to minimise heat loss I used a polystyrene cup instead of a conical flask because polystyrene is a better insulator than glass.
Hazards and safety precautions
I must be careful throughout preparing the solution and the thermometric titration because the acid is unknown and could be very dangerous and the alkali is corrosive and toxic, and can be especially damaging to eyes. Any spillages must be cleaned up immediately; water can be used for this. To be careful, I must wear my lab coat and goggles at all times, gloves may also be helpful as most times.
Below is a table of my hypothetical results:
On the next page is a graph I have drawn using these hypothetical results. It shows that the temperature rise is 13.0°C
So from using the temperature rise of 13.0°C and the mass of 0.092g of the solid unknown acid, I worked out that the acid is a weak acid, and is CH3COOH.
