Titration: Experiment With Sodium Carbonate

Titration

In the report of titration, finding the unknown concentration we use titration, for example using this method we will find the unknown concentration of the hydrochloric acid using sodium hydroxide to work out the concentration. We need to be very accurate in what and how we do this experiment because if we are not accurate we will not get accurate results, in order to do this we selected certain pieces of equipment to be accurate. For example, we used a glass pipette to be more accurate and accuracy is something that we need to focus on during these experiments. Titration is a technique where a solution of concentration is used to determine the concentration of an unknown solution. And this will be measured in cm3.

Health and safety features of sodium carbonate:

Sodium is only slightly toxic, but large doses may be corrosive to the gastro-intestinal tract where symptoms may include abdominal pain, vomiting, diarrhoea, collapse and death. Overall it is not dangerous unless it is taken in large quantities, usually will just have to seek medical help. To make sure that it does not get inside our systems, you must keep it in a closed container and store inside a cool, ventilated area, this could make experiments slightly more accurate.

In order to make sure that nothing bad happens there are a series of safety features that we should follow, wearing gloves would be a good idea, but more importantly, wearing eye protection. Make sure that you are standing up (so if something spills it isn’t on you). Wash your hands when you’re done, clean up anything that breaks. We tried to make it accurate as possible by rinsing the equipment before using it which helps make it more and more accurate.

• Mass(g) / Test 1 / Test 2 / Test 3 / Average
• 10 10.48 10.47 10.47 10.47
• 20 20.88 20.87 20.85 20.86
• 30 31.11 31.36 31.67 31.38
• 40 42.09 42.18 42.16 42.14
• 50 52.55 52.56 52.57 52.56

When we did this experiment, we had to calibrate a balance. We placed a 5 different masses of weights on a scale. Each weight we know is 10 g and it went up to 50g. we did this to see how accurate the scales are, they are the results^^^.

Looking at the results we can clearly see that they are relatively close and toward the start only are around 0.4-0.5 off of what the mass actually is. As the mass increases, it becomes more and more off of the actual mass. Some are 2 grams off of the actual mass. In order to gain more accuracy you must make sure that you wash the equipment, because this will make it more accurate. This could be the reason why the results changed so much, because we did not wash the equipment in-between tests

Using a 3 decimal place balance we weighed a sample of sodium carbonate as close to 1.4 grams as possible using a weighing boat, insuring that the balance was zeroed. We carefully transferred it to the flask, to make sure that we do not spill anything to avoid losing mass.and added a small amount of water to start dissolving. Once the sodium carbonate started to dissolve we topped up the water to 250 cm3 mark insuring it was mixed well, and making sure that this is accurate, once completely dissolved, the sample was ready to test.

How to improve: to improve this experiment, we have many ways. Firstly we could improve it by using a 4 decimal place balance which could really progress the experiment by making it more accurate. Furthermore, we can use a funnel to avoid spilling water and really making sure that it is completely accurate. Next, we should use warm distilled water because it means that the water will not contain any contaminants that will affect the water and results. Finally, the last improvement, we should use a magnetic stirrer, this allows all the chemicals and substances to fully dissolve and once again give it a better chance at being 100% accurate.

Calculation of moles: to calculate moles of sodium carbonate, (2×25) +12+(3×16)=106

Then we will want to work out the Mr. Using the equation. Moles=mass/Mr to find out the moles which was 1.4/106 = 0.0013 moles in 250cm3

Moles of Na2CO3=0.0013 (in 2503) ÷ 10 = 0.0013 in 25cm3

Titration to standardise hydrochloric acid

Before we begin the experiment we will have to make sure that we are all standing up just encase anything spills, and the stools are underneath the table so no one trips over them and falls on any chemicals, because tripping hazards can mean chemicals getting spills, glass breaking, equipment getting broken, etc. Finally, we will have to make sure that we are wearing the protective glasses. Because if It went in someone’s, it will really damage their sight. And could really affect them.

• Equipment / Equipment capacity / Balance result 1 / Balance result 2 / Balance result 3 / Average / Degree of error
• Burette 50cm3 53.2g 53.2g 53.2.g 53.2g (+)3.2g
• Pipette 25cm3 24.83g 24.81g 25.84g 24.83g (-)0.17g

We basically repeated the idea and methodology of the weighing. We calibrated the pipette and the burette to see what one was more accurate. These are the results.

This shows to us the result, that the burette was very consistent, but it wasn’t consistent at the rate that is should have been, it was consistent at 53.2g which has a (+)3.2g degree of error. IT is basically the same thing with the pipette, it is consistent, but with a (-)0.17g degree of error. We need to take these errors and keep them in mind.

The method we used for titration:

We started off by placing exactly 50ml of hydrochloric acid in the burette. Which we will have to make sure that it is exactly accurate. We want the meniscus on the 0-point line. Which is also a risk of human error. We use a pipette to add 25ml of sodium carbonate to a flask and mixed it with phenolphthalein, this is what our indicator (way of showing the acid strength) is going to be. Now we add our hydrochloric acid one drop at a time and the solution should be going pink. We add one drop to make it as accurate as possible and try and find the exact point in which the solution will be neutralised. This could mean the human eye may not be able to see the colour change, whereas, someone else will think differently, which could be human error. While adding the hydrochloric acid we will be mixing the two solutions to make sure it is all stirred up and the reaction can be successful. Neutralisation, is when the solution inside the flask, goes colourless.

Improvements: to improve, we can use a magnetic stirrer in order to keep a constant stir going to make sure it is changing colour. Furthermore, we should also have a standard. This is where we get the colour we are looking for and then use this to judge the other attempts in order to try and gain some more accuracy

Or, Get multiple people to watch the colour to make sure that it is definitely pink and not almost pink or perfect. Almost use it to act as a maturity vote

Additionally, another method of calculating volume of the liquid that was added from the burette, instead of reading the burette value by eye avoiding human error would be to use electronic equipment. For example, electric stirrers and machines that you can use in order to measure without even beginning to use manual equipment that could bring up the idea of human error.

Finally, another thing to eliminate human error’s the electronic pipette filler, this is something that you can put in a certain amount per dm3 that you want in the pipette and it is exact. This eliminates human error

These are the results we noted down:

• Trial run / Test 1 / Test 2 / Test 3 / Test 4 / Test 5 / Average
• Initial titre (cm3) 0 0 13.9 28.5 0 14.2 11.32
• Final titre (cm3) 14.2 13.9 28.5 43 14.6 30.4 20
• Titre (cm3) 14.2 13.9 14.6 14.5 14.6 16.2 14.76

Na2CO3 + 2HCl 2NaCl + H2O + CO2

1 : 2

Ratio = 1:2

Moles of HCl = 0.0013 x 2 = 0.0026 moles

Concentration of HCl = moles ÷ (volume ÷ 1000) = 0.0026 ÷ (14.56 ÷ 1000) = 0.18 per dm3

0.2 – 0.18 = 0.012 / 0.2 = 0.06 x 100 = 6%

Titration to identify the concentration of sodium hydroxide sample

Ph Indicator method: the first method for finding the Ph level of sodium hydroxide is the same as the method above, we would use an indicator, which is the same method as the standardised Hydrochloric one. We added the acid slowly to the solution, one drop at a time using burette and kept adding it until the liquid became clear. Once it was clear we measured how much acid was used in order to measure the concentration of sodium hydroxide.

pH not being stirred enough may mean that the pH may be too high and cause anomalies

We did a trial run in order to make sure that we knew how to use the equipment and to make sure that the equipment is working properly.

• Trial 1 2 3 4
• Initial 0 0 0 0 0
• Final 27 24.8 22.6 25.3 25.1
• Titre 27 24.8 22.6 25.3 25.1

25.3+24.8+25.1=75.2

75.2/3=25.06

NaOH + HCl=NaCl + H2O

Moles of HCl=volume x concentration=25.06/1000=0.02506 x 0.1899=4.758894×103=moles

Concentration of NaOH=moles/volume=4.758894×103/0.02513=0.1893710306 moles per2

0.2 – 0.1893710306 = 0.011 ÷ 0.2 = 0.055 x 100 = 5.5%—– that is the error

The reason we have a trial run ( a rough titration) is because we can use that as a standard, For example, with colourimetry, we have one already maid flask where we will use the colour of it as a standard to base the rest by, we can use the trial run as a standard to base the rest.

Ph scale method: This method uses a Ph scale. Which means that it can measure the Ph in liquids using this piece of equipment. Make sure that the equipment is clean after every use. So, we had a burette and using this we slowly put acid into the solution of sodium hydroxide that we had in a flask. When set up the burette with 50cm3 of acid and then a flask with 25cm3 of sodium hydroxide with a pipette. We have to make sure that all this is as accurate as we can make it, we then added one cm3 at a time while measuring pH with the pH scale until we use 30cm3

Improvements: An improvement to this method would be further training in the filling and analysing of the burette and pipette. We need to be able to have experience in analysing the meniscus, because the more experience means that we can give a more educated stand on whether the meniscus is at perfect eye level or whether there are air bubbles etc. We can give our say, but with more training we can more confidently say that it is accurate.

Furthermore, we manually stirred the flask by hand, by continuously shaking and spinning it around in order to make sure that it is properly mixed. We can improve this by using a magnetic stirrer, this can make it a lot more accurate. This will affect the Ph because means that it takes more time in between readings.

• Volume of HCl (cm3) / PH (1) / PH (2) / Average
• 0 11.19 11.10 11.145
• 1 11.19 11.00 11.095
• 2 10.92 10.98 10.95
• 3 10.89 10.87 10.805
• 4 10.82 10.79 10.805
• 5 9.62 9.64 9.63
• 6 – – –
• 7 9.34 9.41 9.375
• 8 9.22 9.20 9.21
• 9 9.17 9.01 9.09
• 10 8.68 8.52 8.60
• 11 8.38 7.97 8.175
• 12 7.54 7.51 7.529
• 13 7.36 7.33 7.345
• 14 7.13 7.07 7.10
• 15 6.96 6.81 6.96
• 16 6.8 6.79 6.805
• 17 6.73 6.62 6.76
• 18 6.61 6.5 6.615
• 19 6.51 6.32 6.505
• 20 6.35 9.72 6.325
• 21 9.78 9.72 9.75
• 22 9.25 9.05 9.05
• 23 8.93 8.94 8.935
• 24 3.9 3.55 3.725
• 25 2.8 2.77 2.785
• 26 2.51 2.51 2.51
• 27 2.36 2.36 2.36
• 28 2.25 2.24 2.245
• 29 2.20 2.19 2.195
• 30 2.13 2.12 2.125

Moles of HCl = volume x concentration

15/1000=0.015

0.015 x 0.1899=0.0028485

Concentration of NaOH=0.0028485 ÷ (25/1000) =0.11394 moles per dm3

0.2 – 0.114 = 0.086 / 0.2 = 0.43 x 100= 43%

The graph shows us a steady PH scale initially, and then drops dramatically down from 11 to 9 on the PH scale. Furthermore there are a few anomalies on the graph that could be to human error.

The unknown concentration in supposed to be 0.2 moles per dm3, this allows us to see that the first method is a more accurate than the second one because 0.0101 off the correct concentration, which is a lot better than the second method which was 0.010628964 off of the original. Next time to make it more accurate, we should let the acid and solution settle a lot more and let the pH scale settle before taking a measurement. Not to mention when we were doing it we may have been slightly off when we poured the 1cm3 each time. It could have been slightly off.

The first method may have been more accurate because it was less chance of human error while and the indicator would actually be more accurate. Types of human error would be because humans will see colours differently, for example to some people, a red may seem darker to other people. Additionally, another error is reading the scale differently to other people.

Other results were more accurate, but this could be due to our human error or the fact that we rushed some results and maybe too more time on the other ones which means that it will be a different avg which will affect the end equation that we do. By more accurate, we mean that the average and each individual experiment was closer to the original. This makes their results a more valid set of results and better to use. They probably did better due to the higher quality of team work and management. +

These are some other results from Carlos groups:

Moles of HCL = volume x concentration

= (16÷1000) x 0.18 = 0.00288 moles

Ratio = 1:1

Moles of NaOh = 0.00288 moles

Concentration of NaOH = moles ÷ volume =

0.00288 ÷ (25÷1000) = 0.1152 moles per dm3

Colorimetry:

The aim of our investigation was to find the unknown concentration of copper sulphate.

So we will have to work out how much we will need for 100ml instead of 1 lt. So we know, 249.5 for 1000ml, so we needed to make mass into concentrations so this is the calculation:

1000cm3 – 249.5g of copper sulphate

0.1moles x0.1=24.95÷10 = 2.495 g

2.495g=100cm3 = 0.1m

One thing that we also need to take in to account that we have never done these experiments before, so this could lead to human error, mistakes and more. This means that if we had some training of some sort in order to make it a fairer test.

Method: after working out how much we need for each flask, we will have six flasks labelled with different concentrations, 0, 0.02, 0.04, .0.06, 0.08, 0.10 concentration. And then we will overall make 10ml in each flask, for example, 0.02 would make 2 ml of copper sulphate and then 8ml of distilled water. We do this for every single labelled flask from 0-0.1. We need to make sure that it is all accurate, because we have different people doing different concentrations it may not be as accurate as one person doing it all. Had two anomalous results, this may be due to other people not doing the measurements clearly.

• Concentration moles per dm3 / Volume of copper sulphate solution cm3 / Volume of water cm3
• 0.00 0 10
• 0.02 2 8
• 0.04 4 6
• 0.06 6 4
• 0.08 8 2
• 0.10 10 0

Making dilutions: To make dilutions, you must equal 10cm3 overall of water and copper sulphate. For example, 6cm3 of copper sulphate solution, would mean that we would need 4cm3 of water in order to make a dilution.

What is colorimeter? En.wikipedia.org. (2018).

A colorimeter is an object we use in order to find the concentration of a solution, which in our case, the concentration of copper sulphate. It does this by measuring its absorbance using light, and different colours of light. Overall it is a light sensitive piece of hardware that is used to measure absorbance of light passing through and we will have different options for the shade that we put the light as. For example if we have a blue/green solution (like copper sulphate) we would need to use orange/ red filter, which is 600 nm in order to use the colorimetry correctly.

Calibration: We calibrate using water to make sure that it is 100% ok. So we do a colorimetry test on the water that we use in order to make sure that we can see that it is 100% transparent which means that we can use it. This may not be the most accurate way of calibrating, because it may be relatively old machine, so a new machine may be more accurate and could possibly make it so that there aren’t as many anomalies.

Health and safety: there is not much health and safety to do with the entire experiment, but the main things that you will have to look out for is the copper sulphate. The copper sulphate is a bit of a hazard. Wear goggles, keep away from skin, maybe wear gloves and make sure that it does not get inside you, because it can cause pain, vomiting etc. it is better to be safe, than sorry. Additionally, stand up while doing the tests so you cannot get anything spilled on you. Wear proper gloves when handling cuvettes or the ensure that the frosted side is held to avoid finger prints. So it doesn’t alter the final results

• Concentration / Absorbance / Absorbance / Avg
• 0.00 0 0 0
• 0.02 0.32 0.36 0.34
• 0.04 0.59 0.60 0.595
• 0.06 0.98 0.95 0.965
• 0.08 1.18 1.21 1.195
• 0.10 1.66 1.17 1.685

A-absorbance = 0.14 -0.004 moles per dm3

B-absorbance = 0.28 – 0.01 moles per dm3

C-absorbance = 0.49 – 0.016 moles per dm3

D-absorbance = 0.82 – 0.06 moles per dm3

A-Transmission = 95% – 0.004 moles per dm3

B-Transmission = 45% – 0.014 moles per dm3

C-Transmission = 30% – 0.022 moles per dm3

D-Transmission = 16% – 0.064 moles per dm3

The results on the colorimetry kept flickering so we got two results and make an average in order to gain more accurate results

These graphs are relatively accurate, but they could be more accurate. They were easy to draw, but this does not mean that they are accurate, using computer software of some sort of software that helps the accuracy will make things a lot easier. Or, if you do it on paper, make sure all the intervals.

Discuss: firstly, I’d like to discuss results between the two graphs, they both have anomalies, and this could be because of other people making mistakes and not being as accurate as our groups. Or this could be because we did the same method, just slightly differently to how we did it. Human error is always a factor that the slightest thing we do, can cause anomalies.

Furthermore, comparing the graphs. Graph a (ABSORBANCE) has a better line or best fit, because it is a much smoother and better curve. This could also come down to human error as to why they may not have the same results. For example, C has a difference of 6 and this could come down to the human error messing up the results for c, because the line of best fit is not accurate enough.

Finally, we could use some sort of data tracker, So something like a computer or data logger. This will eliminate the fact of human error when it comes to drawing the graphs we have accurate results that cant have as much human error, because without we would be estimating.