Colorimetry report PDF

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Summary

This assignment will help people understand the purpose of colorimetry and how it is done. I have also explained calculations and many purposes....

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Introduction: To put it simply, colorimetry is the process used to find out the concentration of coloured compounds in solutions by the application of the Beer Lambert law, which shows that the concentration of a solution is proportional to absorbance. Using a colorimeter is one of the easiest practical to measure the volume you need to determine different concentrations. The colorimeter can measure how much of the light that has been absorbed by the sample. The amount of light that has been absorbed by the sample is related to the concentration of the chemical of interest. It is possible to get numerical values for the amount of light. Using a colorimeter is the most accurate way to measure the concentration of a solution. The following diagram explains: In real life, colorimetry is needed for a couple of things, those are: screen chemicals in water, like chlorine, fluoride, nitrite. To find plant nutrients in the soil, such as ammonia, phosphorus, and nitrate, it is also used to determine the concentration of haemoglobin in blood. Mainly used to monitor the growth of a bacterial or yeast culture. Colorimetry is needed in colour printing, textile manufacturing and paint manufacturing for precise quality inspection. It’s used in many industries which I’ve mentioned, but it’s also used in aspirin and food, e.g., colour changes in meat, fish and poultry can indicate changes in freshness of food. The Beer Lambert law equation is the absorption of light by a solution to the properties of the solution. A standard solution is a solution that contains a precisely known concentration ready from a primary standard. They are used to determine the concentration of other substances, e.g., solutions in titrations. Creating a standard solution of Copper Sulphate Step 1: Press the button to make sure its 0.00g. Weigh out exactly how much CuSO4 you need using a spatula. Accurately weigh out solute using a top pan balance. Step 2: Transfer CuSO4 to deionised water. By pouring the solute down, you wash it down with deionised water, making sure it is all in the beaker. Step 3: Dissolve all the solute in the deionised water with a glass rod.

Step 4: Transfer solution into a 250ml volumetric flask. To do this, use a funnel and a glass stirring rod which helps prevent spillages. Ensure all solution is in the flask. Step 5: Rinse the rod to make sure all the solution is in the volumetric flask. Do the same with the beaker. Now you will know the exact quantity of CuSO4 in the solution. Step 6: Carefully bring the meniscus up to the graduation mark on the volumetric flask. Using a pipette dropper. It should look like a curve. Step 7: Close the volumetric flask and swirl it more than 10 times. This is to make sure you get a uniform solution in the volumetric flask. This is an essential part before you carry out colorimetry. To calculate the mass, take your volume, which was 0.05m. Using the equation, you will do: Mr / 1000 x 0.05 = mass of copper sulphate needed per 0.05m. Ateia’s Group results: Copper sulphate concentration (mol.cm )

1

2

3

Average

0

0

0

0

0

0.2

0.322

0.329

0.321

0.324

0.4

0.650

0.657

0.653

0.653

0.6

0.990

0.995

0.992

0.992

0.8

1.300

1.301

1.301

1.301

1

1.556

1.563

1.566

1.562

3

Absorbance at 635nm

Unknown 1

0.970

0.964

0.961

0.965

Unknown 2

0.253

0.254

0.252

0.253

Equipment list: * Analytical top pan balance * Beaker * Funnel *Cuvette * Clock glass * Glass rod *Pipette dropper *Colorimeter *Spatula *Volumetric flask *Stopper *test tubes Evaluating the accuracy of procedures and techniques used in colorimetry: Once the experiment has been carried out, as the concentration increases so should the absorbance recorded, meaning they are proportional to one another. Each concentration of copper sulphate was tested 3 times, and then a mean average is calculated for all concentrations of copper sulphate. There were 2 unknown concentrations of copper sulphate, and the absorbance was only meant to be determined, following on with a mean average. Using a colorimeter to accurately and skilfully determine the concentrations of samples A and B which are 2 different concentrations of copper sulphate solutions that will be provided. 1. First, preparing your own concentration of CuSO4 by weighing out hydrated copper sulphate solid, then dissolving it in water and making it up to an accurate volume. 2. Accurately dilute your stock solution of CuSO4 solution to produce a series of CuSO4 standard solutions of different concentrations. 3. Select an appropriate filter for the colorimeter that is used to measure the absorbance the CuSO4 solutions. 4. Calibrate the colorimeter according to the instructions I have explained below. 5. Measure and record the absorbance for each of the CuSO4 solutions. 6. Plot a calibration curve of absorbance against concentration of CuSO4. 7. Measure and record the absorbance for sample A and B (unknown concentration of CuSO4 solution) that is already provided. 8. Use the calibration curve to determine the concentrations of sample A and B. The graph will only be plotted correctly if you produce accurate, precise and reliable results from the colorimetry technique. I have plotted the results on my graph below, and the line should go upwards, if it goes downwards, then that means you haven’t measured the concentration of CuSO4 accurately.

Creating dilutions of Copper Sulphate: At first, identify the mass of Na2CO3. (Mass (weighing bottle) +mass (Na2CO3) -(mass (weighing bottle after emptying)15.24g - 12.59g =2.65g Molar mass Na=23 C=12 O=16 2Na x 1C x 3O = molar mass = (2 x 23) + 16 + (3 x 16) =106 Number of mols Table show’s dilution of Copper Sulphate Final concentration (mol.cm3)

0

0.2

0.4

0.6

0.8

1

Volume of copper sulphate solution (cm3)

0

2

4

6

8

10

Volume of distilled water (cm3)

10

8

6

4

2

0

Explain this table: As the volume of copper sulphate increases, the volume of distilled water decreases. The volume of water decreases because particles of CuSO4 crystals lose attraction between one another and start moving continuously then get mixed with water. When water is added to anhydrous copper sulphate, it turns bright blue. Making different concentrations of copper sulphate: As it shows in the table above, take 8cm3 of CuSO4 and add it to the measuring cylinder, then add 2cm3 of distilled water to that volume. Next concentration: take 6cm3 of CuSO4, add to a measuring cylinder, then add 4cm3 of distilled water using a pipette dropper. Next concentration: Add 4cm3 of CuSO4 to measuring cylinder, then add 6cm3 distilled water to it. Do the same with 2cm3 of CuSO4 with 8cm3 of distilled water. Once all concentrations have been made, you then take all the cylinders and invert them until they are fully mixed. You now have different concentrations of copper sulphate. Calibration of the Colorimeter and analytical top pan balance: Calibrating the colorimeter: 1. Press and hold the CAL button on Colorimeter. 2. When red light begins to flash, release the CAL button. 3. When the red light stops flashing, the Colorimeter is calibrated. How you calibrate the analytical top pan balance: • Press and hold the "RE-ZERO" key to enter the calibration mode. • Release the "RE-ZERO" key when the balance displays either

"CAL or CAL 0". • Press the "MODE" key to change the calibration mass value. • Enter the calibration mass value using the following keys: "MODE" key is used to move digit to enter a number; "RE-ZERO" key is used to change a number. Verify that there is nothing on the weighing pan. • Press the "RE-ZERO" key. The balance measures the zero-point.

Method used to investigate unknown concentrations of copper sulphate: (1) Determine the wavelength (colour) of light to use for the colorimetric analysis. (2)Prepare a set of standard solutions of known concentration. (3) Measure the absorbance of each standard solution using the colorimeter. (4) Plot the absorbance vs concentration for each standard solution on a graph. (5) Draw the line of best fit through the data points. This is the calibration curve. (6) Measure the absorbance of the solution of unknown concentration using the colorimeter. (7) Use the calibration curve to determine the concentration of this solution. Risk assessment table:

Determining the unknown concentration: Write out the equation C = m/V, where m is the mass of the solute and V is the total volume of the solution. Put in the values you found for the mass and volume, then divide them to find the concentration of your solution.

Calculation using Calibration Graph: • Prepare a series of solutions of known concentrations. • The absorbance of each solution is measured. • Absorbance over concentration is plotted. Using the calibration curve equation, and the absorbance of the unknown solution, the concentration of the unknown solution can be calculated. The colorimeter can measure the concentration of an unknown solution by the amount of light that shines through it. Method used to investigate unknown concentrations of Copper Sulphate: Having an unknown concentration of Copper Sulphate solution, you need to determine the concentration using a colorimeter, where you simply place the cuvette into the colorimeter, but the clear side facing where the light will go through. Once the red light has been transmitted passed the cuvette, the reading will show how much light has been absorbed by the cuvette. Which will show the unknown concentration by measuring it’s absorbance with the colorimeter.

Evaluating the accuracy of procedures and techniques used in Colorimetry: An improvement for this is to use a syringe with a finer scale. Smaller graduation or another way of improving is to use a measuring pipette to get an accurate result. The aim behind this practical is to measure colours and to quantify the colour of light sources and objects from visual colour matches. Meaning that the eyes are used as a tool to identify if the colour is identical or not....