Calibrating equipment
Calibrating a balance-
Equipment:
I will need a balance and 4 different weights (100g, 300g, 500g and 700g)
1. Get your chosen weight which tells you how much it weighs on the side of it
2. Set up your scales and zero them so it shows 0.0 g
3. Using pincers pick up the weight securely within the grip off the pincers
4. Gently place the weight on the scales without dropping it onto the scales with force
5. Wait a few seconds for the scales to weigh the weight sufficiently
6. Put this reading into a table of results of the actual weight of the object and the weight the scale reads
7. Repeat this three times for each weight to establish a mean
Your scales should be within 0.1g of the actual weight of the object, if not you will need to use a different set of scales as the ones you have are not accurate enough.
The results I collected when I was calibrating my balance were
Weight 1st attempt of weighing on scales 2nd attempt of weighing on scales 3rd attempt of weighing on scales
100g 100g 100g 99.9g
300g 299.9g 300g 300g
500g 499.9g 500g 500.1g
700g 700g 700.1 699.9g
These results showed me that on average my balance was 0.1g out of being the exact value. However some of my results were exactly the correct value. Due to the average result only being 0.1g out which was inside the catchment zone that would make the scales calibrated accurately.
Calibrating a pipette-
Equipment:
I will need a pipette, bottle of distilled water, beaker x 2 and a calibrated balance
1. You will need to rinse the pipette through with distilled water to make sure there’s no excess fluid in the pipette
2. You will need a beaker full of distilled water of which you will take 25ml out of using the pipette
3. You will then put an empty beaker onto the scales (that you have just calibrated) and zero it so it reads 0.0g
4. You will then need to empty the pipette out into the beaker onto the scales
5. Making sure it reads 25ml or within 0.05 g of the 25ml either side
If the pipette reads more than this I would recommend trying again to see if its human error before you change to a different pipette if it then still reads too far out of the catchment area then you will need to get another pipette and do it again you must also do this three times so your results are accurate.
The results I collected when calibrating my pipette were
Weight that should be shown on scales 1st 2nd 3rd
25g 24.98g 25.01g 24.99g
These results show that once I have poured all 25ml out of the pipette it was 0.01 g out of the exact value which means the pipette was inside the catchment value so it had been calibrated.
Calibrating a burette-
Equipment:
I will need a burette, a bottle of distilled water, beaker and scales
1. Take apart the stop cock at the bottom of the burette (carefully making sure you remember how it goes together)
2. Clean it out using a solution called alconox by rinsing each part of the stop cock separately
3. Rinse the burette with distilled water without the stopcock on and swirl the burette as the distilled water is going through it making sure there is no excess fluids inside
4. Reassemble the stop cock and put in back onto the end of the burette
5. Pour distilled water into the burette until the waters meniscus is on the zero (make sure this is done at eye level and its secured in a clap stand )
6. Put an empty beaker onto the scales and zero the scales so they read 0.0 g
7. Take the burette out of the clamp stand and release the stop cock allowing the distilled water to flow out of it.
8. Wait until all the water is out and see what the scales read in grams. It should be in-between 49.99-50.01 so you know that your scales are accurate.
If the scales do not say that the amount of water is in the catchment area you will need to try again in case of human error making sure you don’t pour too little or too much of distilled water into the burette if that still isn’t right try using a different burette until it works.
The results I got when I was calibrating the burette they were
Weight that should be shown on scales 1st 2nd 3rd
50g 50g 50g 50g
My results have shown me that once I had calibrated my burette the results that I got where accurate enough to use the burette during the experiment
Calibrating the colorimeter
Equipment:
I will need a colorimeter, 1 cuvet and a bottle of distilled water and the made up solutions of known absorbances
1. Prepare 5 solutions with known absorbances.
2. Fill a cuvette with each of the solutions and place in the colorimeter individually making sure that clear side is in the slot correctly so it is able to be tested correctly.
3. Record each of the readings then, you know what reading each absorbance shows.
4. Repeat each of the 5 solutions with the known absorbance three times to get an average
As you know what the absorbance of the solutions should be you are able to discover if the average is spot on which would make it calibrated or if it’s outside the catchment zone. If your average is 0.01 out you are able to use it as it is in the allowed catchment zone which would allow results to still be as accurate. However if the results in average are 0.05 out you should repeat it again using different solutions and if that doesn’t work use a different colorimeter.
Preparing standard solutions.
Equipment:
I will need a weighing boat, a balance (calibrated), 2.65g of sodium carbonate, bottle of distilled water, volumetric flask and a beaker
1. Take a weighing boat and place it on the balance. Tare the balance (set it to zero). Carefully weigh out the mass that you need to use (2.65g) of sodium carbonate
2. Transfer this amount of sodium carbonate into a beaker which contains 25ml of distilled water
3. Stir the sodium carbonate into the distilled water using a stirring rod making sure all the substance dissolves
4. Once it’s all dissolved take a volumetric flask and pour the standard solution that you have made into the volumetric flask
5. You need to make the standard solution up to 250ml of standard solution rather than 25ml on the volumetric flask there is a line which represents the 250ml quantity.
6. You will need to fill it up to that marker using distilled water making sure you get it as accurately as possible
7. Put the lid on the volumetric flask and swirl it around so the standard solution is all mixed together will the distilled water you have just added.
I worked out how much sodium carbonate I needed to make a 0.1 mol/dm3 solution. I did this by working out the molar mass of Na2CO3 which was 106g I then worked out that this was for a 1 molar solution. To make it into a 0.1 mol/dm3 I had to divide the 106g by 10 which gave me 10.6g I then had to divide it by 4 as I wasn’t using 1litre of distilled water and was using 250ml instead. This then gave me 2.65 which is the amount of sodium carbonate I would use to create my solution.
Safety- Make sure when you are always wearing goggles to make sure no substances get in your eyes and also so there is no temptation to scratch eyes when you have a product on your hand that is dangerous. Also when swirling the volumetric flask make sure you have your thumb on the lid so there is no possibility of the lid falling off and the solution spilling out. Finally when making the standard solution make sure you are wearing a lab coat to limit the possibility of any adhesive solutions spilling onto your clothes
Method of titration
This is the first titration this is done by titrating hydrochloric acid against Na2CO3 . This is important as it allows people to accurately determine the pH of Na2CO3. It would help to understand what pH help people for example doctors would understand what the correct pH would be to be used as medicine
1. Take two conical flasks. Take one of the conical flasks and fill it with exactly 50ml of sodium carbonate
2. Take the volumetric pipette and measure exactly 25cm3 of sodium carbonate (from the first conical flask)
3. Empty the pipette into the empty conical flask and add 2-3 drops of indicator(make sure readings are taken from the meniscus)
4. Put the conical flask containing the 25cm3 of sodium carbonate that you’ve added the indicator on a white tile
5. Record the start point on the burette (should be 0)
6. Open the tap on the burette opening it and letting it go down 1cm3 then closing it swirling the conical flask after closing it each time(hydrochloric acid should be in the burette)
7. Once the colour looks like it is about to change colour, swirl it around and make sure has changed colour
8. Record the end reading on the burette
Using the two readings you obtained (one from a trial run which gives you an idea of what the value should be and other from the experiment) calculate the amount of hydrochloric acid needed to neutralize sodium carbonate.
Na2CO3 +2HCl 2NaCl + H2O + CO2
1 : 2 ratio
Moles/vol Na2CO3 =moles/volume HCl
2 x (moles Na2CO3) = 0.1 x vol HCl/25(vol of Na2CO3)
8.8-2=6.8 I did this as it enabled me to find out the gap between the 8.8 and 2
Find 5.45 on graph and find the vol used it was 25ml on my graph after working it out which gave me a concentration of 0.2 moles in 1000ml of hydrochloric acid. To then work out the concentration you have to do c=n/v so it would be number of moles=0.2/1000 x 25 which gave me the number of moles to be 0.005 I then worked out the concentration by doing c=n/v so it was c=0.005/25 which gives me the concentration of 0.0002
volume pH Average
1st attempt 2nd attempt 3rd attempt
0 11.7 11.6 11.8 11.7
5 10.6 10.5 10.7 10.6
10 9.8 9.9 9.7 9.8
15 9.2 9.1 9.3 9.2
20 9.1 9.1 9.1 9.1
22 9 8.9 9.1 9
24 9 9 9 9
26 1.9 1.9 1.9 1.9
28 1.8 1.8 1.8 1.8
30 1.8 1.8 1.8 18
Method of titration
Titration is a lab method used to help determine the concentration of the unknown solution. This is done by reacting two solutions. It is important due to being able to calculate the correct concentration of the unknown solution. Titration is used in industry when creating a product to work out the concentration of it due to the fact that it could be applied to skin if was a skin cream or lotion it would have to be a suitable concentration so it wouldn’t burn or cause irritation to the skin.
Aim- To find the concentration of NaOH
Equipment:
I will need a retort stand, burette, burette holder, 25cm3 volumetric pipette, pipette filler, white tile, phenolphthalein (indicator solution), 2 x100ml conical flasks, 100ml beaker, bottle of distilled water, hydrochloric acid, sodium hydroxide and a funnel
Method:
1. Take two conical flasks. Take one of the conical flasks and fill it with exactly 50ml of sodium hydroxide
2. Take the volumetric pipette and measure exactly 25cm3 of sodium hydroxide (from the fist conical flask using the meniscus as a stopping point)
3. Empty the pipette into the empty conical flask and add 2-3 drops of indicator
4. Put the conical flask contacting the 25cm3 of sodium hydroxide that you’ve added the indicator on a white tile
5. Record the start point on the burette (should hydrochloric acid in the burette and it should be on 0)
6. Open the tap on the burette opening it and letting it go down 1cm3 then closing it swirling the conical flask after closing it each time
7. Once the colour looks like it is about to change colour, swirl it around and make sure has changed colour
8. Record the end reading on the burette
9. Using the two readings you obtained (one from a trial run which gives you an idea of what the value should be and other from the experiment ) calculate the amount of hydrochloric acid needed to neutralize sodium hydroxide
Volume pH Average
1st attempt 2nd attempt 3rd attempt
0 12.8 12.9 12.7 12.8
5 12.8 12.7 12.6 12.8
10 12.8 12.7 12.6 12.8
15 12.6 12.7 12.5 12.6
20 12.3 12.4 12.2 12.3
21 12.1 12.2 12 12.1
21.5 12 12 12 12
22 11.9 12 11.8 11.9
22.5 11.7 11.8 11.6 11.7
23 11.4 11.5 11.3 11.4
23.5 10.9 11 10.8 10.9
24 9.8 9.9 9.7 9.8
24.5 4.1 4 4.2 4.1
25 2.6 2.7 2.5 2.6
25.5 2.2 2.2 2.2 2.2
To work out the number of moles in NaOH you do the concentration of NaOH (unknown) times by the volume of NaOH used divided by 1000 which is 25/1000 which gives you 0.025 you then divide the concentration of hydrochloric acid by the 0.025 which would be 0.2/0.025 which gives you 0.005 you then * that by 0.025 which gives you 0.2 moles.
Colorimeter test
Equipment-
I will need a Colorimeter, cuvets, test tubes x6, test tube rack, bottle of distilled water, pipette, pipette filler and a bottle of copper sulphate solution with 10% concentration
1. We measured out 9cm of distilled water into 4 different test tubes
2. I then poured some of the solution which has 10% concentration into test tube
3. I then took 1cm out of that the 1st test tube then put it into the second test tube
4. I then took 1cm out of the 2nd test tube I continued to do that for the rest of the test tubes taking 1cm out of the test tube before
5. I then poured the cuvets full of the solutions from each test tube including a one of just the solution and one of just distilled water
6. I then tested the absorbance by putting it in the colorimeter and starting off by putting distilled water in and zeroing it
7. Then I put in the next percentage of solution into the colorimeter gathered what the absorbance was
8. For all of the test tubes cuvets that I put into the colorimeter I have to put the cuvets with distilled water in a zero it so each are as accurate as the others
Approximate concentration(mol/dm3) Absorbance Average
1st attempt 2nd attempt 3rd attempt
0.0125 0.08 0.07 0.09 0.08
0.025 0.1 0.1 0.1 0.1
0.05 0.18 0.17 0.19 0.18
0.075 0.25 0.26 0.24 0.24
0.1 0.3 0.3 0.3 0.3
0.125 0.35 0.36 0.34 0.35
The unknown concentration had an absorbance of 0.26 which made the concentration 0.085mol/dm3 when followed along the graph and then followed down.
Safety- always wear safety goggles and a lab coat to limit damage from spillages. When using hydrochloric acid make sure if any spillage happens you notify the teacher so they are able to clear it up safely or clear it up before anyone could slip, lean in it and it stain their clothes or put their hands in it then rub their eyes and damage their eyes due to it being adhesive.
When using sodium hydroxide you must make sure to keep lid on at all time other then when pouring as could be a hazard when split as it could cause someone to slip and seriously damage someone
Evaluation
The concentration when titrating hydrochloric acid against sodium carbonate I should have got the concentrating of hydrochloric acid to be 0.2molar. However I got the concentration to be 0.2 molar showing that my results were exactly on the correct value. Meaning that all my results were accurate.
When titrating the known concentration of hydrochloric acid against sodium hydroxide I got the concentration of sodium hydroxide to be 0.025 molar. However the correct concentration was 0.2molar showing that my results were either not accurate or my equipment was accurate. It could also be that I didn’t read off my graph correctly which would also explain me being 0.1975 molar out of the concentration. To improve my titration I could have go down in smaller gaps instead of 0.5 I could have gone down in gaps of 0.25 which would help give me more results and improve my graph.
When doing the colorimeter test I got the concentration of copper sulphate to be 0.08 molar. However the correct concentration should have been 0.1 showing that either the equipment was not accurate enough or I had read of the graph incorrectly. To improve my results from my colorimeter test I should use smaller dilutions rather than the ones I used for example I could have used dilutions of 0.01,0.025,0.04,0.055,0.07,0.085,0.1,0.1,0.25,0.4,0.55 which would help give me more results giving a better variety of results.
References
http://www.bbc.co.uk/schools/gcsebitesize/science/triple_ocr_gateway/how_much/titrations/revision/3/ – I used this method as a guideline to give me an idea of how to write my method
https://www.thestudentroom.co.uk/showthread.php?t=1487313 – I used this to base my calibration of my colorimeter on
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