Scientific Practical Techniques Lab report PDF

Preview

Summary

What is a colorimeter?

- uses

- Advantages and Disadvantages of using Colorimeter

Paper Chromatography

- Titration

- Results

- Evaluation

- Greatly detailed...

Description

A Colorimeter is a light-measure device which can operate by measuring the amount of light that can pass through a solution. It works behind the principle of Beer's Law relating to the Concentration of a specific or unknown sample, its absorbency, the curvature of the container as well as the light that goes through and is being received. A Colorimeter is a Scientific Instrument used in Colorimetry. It is a sensitive light device which can be used to measure the absorbance in a particular wavelength of light by passing through a liquid sample. This device is able to measure the concentration of the color which develops on introducing a specific reagent into a solution. The Colorimeter is able to identify and determine color which can be based on red, blue and green components once the light is absorbed by the sample. Once light passes through the medium, part of the light is being absorbed indicating that it decreases the amount of light transmitted. Overall, this device works by the law of Beer-Lambert which is stated that once the absorption of the light is transmitted through a medium, it means that it is directly proportional to its concentration of the medium. To outline Beer's law, it measures the absorbance of a substance within the medium. This is to determine how well a light is able to easily pass through it. The more concentrated the substance is means that the less light visible would pass through it. The working principle of the Colorimeter is that a ray of light with a certain wavelengths is being passed through a solution and measuring the light which passes through on the other side. The more concentrated the solution is it conveys that more light will be absorbed which can be identified in the difference between the light at its origin and also after it passes through the solution. In order to dictate the concentration of an unknown sample, several sample solutions of a concentration (e.g: Copper Sulfate) solution is tested. Once the process is complete, the results shown is plotted onto a graph with the Concentrations on the Y axis and the Absorbance on the X Axis. This forms a calibration curve. Nonetheless, to be able to measure concentration, results from the unknown sample is compared to the known sample. (Copper Sulfate) The reason being as to why a Colorimeter is used to find the concentration of Copper Sulfate due to the fact that the Copper Sulfate solution is an Inorganic

Compound which the Colorimeter could be able to determine the absorbance of a specific wavelength of light. Not only Colorimeters could determine Inorganic Solutions of only Copper Sulfate but they also are valuable instruments in measuring the quality of water by determining the concentration of Organic Compounds as well as other substances. For instance, a wide range of contaminants and substances of Phosphorus, Fluoride, Pesticides etc. Also when using the Colorimeter to find the concentration of Copper Sulfate solution, before placing it within the Colorimeter slot the deep blue copper sulfate solution would be able to interpret the light which is received by the photocell and to be able to both show the absorbance as well as the transmittance value. The deep blue color solution would show the higher concentration of the colored solution absorbing more of the light or transmitting less of the light if it has a lower concentration. In terms of Colorimeter Technology, major Organic and Inorganic Compounds can be either a decolourised substance or imperceptible to the human eye which is why a Colorimeter is used due to its function in introducing the chemical reagent and light which provides the way in seeing the invisible compounds. Finally Colorimeters are used for the Copper Sulfate solution due to. Although both techniques of Titration and the Colorimeter instrument is accurate depending on what the method is tested on, Colorimeters are believed to be more reliable than the Titration technique. This is because it is sensitive within smaller concentrations indicating that it is much quicker and more reliable. The titration technique however could cause many problems as this method consists of accuracy, concentration and time also meaning that pouring the substance over the Volumetric Flask could go over the line, the materials as well as the solution could pour out of the flask having to repeat the procedure over. The two tools or instruments used to be able to measure the concentration of any solution is with Colorimetry as well as Titration. Titration is recognized as a Volumetric measurement which is measuring an unknown substance by applying another either a reagent or a chemical so that it reacts to make a noticeable change. Being able to know the volume of the chemical added, the results could be also used to calculate how much of the unknown is present. A standard type is an acid-base Titration as a when adding a base, the unknown substance may be an acid or the other way round. Once the chemical neutralizes the unknown substance, the pH would be able to change from its initial value. This change can be detected by adding in an indicator. This process is called Colorimetric Titration due to the fact that the measurements shown by the end of each experiment shows through a change in color. Colorimetry however, involves using an instrument of a Colorimeter that functions to shine a light through a sample. This instrument is able to measure the amount of light reached to a detector from the other side of the sample solution. Once it is identified how much was absorbed it should be remembered that the higher the concentration of the light within the sample, the more light it can absorb at the given wavelength. When measuring the concentration of a Colorimeter, a set of samples called standards with the known concentrations of the chemicals tested and the measurements of the absorbance. Once it is identified with how much light is given within the Colorimeter that is absorbed, the absorbance of the sample from the unknown concentration is measured. There is a significant difference as a result of determining the concentration of unknown dilute solutions with a Colorimeter and the Titration technique. Colorimetry is able to identify how much light is absorbed within the sample. Titration however looks at the exact amount of reagent added. Also, when you determine the concentration of a dilute solution, an instrument is used which is the Colorimeter. Before using the instrument, the Colorimeter is firstly calibrated before it is in operated. This to give consistent readings of data so that the results itself is very precise and not anomalous. On the contrary, the Titration technique only consists of glassware as well as reagents when performing the experiment. However, using the equipment could cause many limitations of the technique itself. The accuracy when performing the method of Titration is that depending on whether the experiment is carefully done, it would give off

accurate as well as a precise result. The accuracy when performing a Titration is that students or those working with experiments in the Laboratory would use a less concentrated solution because as the concentration increases, this decreases the accuracy of the results in the end. Another accuracy when performing Titration is that the Pipettes used are well calibrated and intact. This is to ensure that the readings taken in this instrument is consistent with the other measurements taken and to also determine accuracy of the readings. Also, the main accuracy of Titration is that the procedure is repeated at least three times to give out consistent readings as well as to ensure that the titre value is correspondent so that the calculations are reliable. This is the indication that the average titre within the end of the repeated titrations must be valid. The accuracy of the Colorimeter technique is that when measuring the absorbance of the sample from the unknown concentration is able to easily figure out the amount of chemical it consists. Although both the Titration and Colorimeter techniques have different procedures and a different laboratory method, they similarly use color observations to be able to determine an unknown amount of a substance. ADVANTAGES OF USING COLORIMETER FOR CONCENTRATION The Colorimeter technique only needs an instrument to test the concentration meaning that it can be relatively quick and efficient to use than Volumetric techniques. The instrument is convenient to determine the concentration of an unknown substance which can be organic and inorganic. When the light is being absorbed, the light source is easily controlled as depending on the concentration, it has a mind of its own of how much it absorbs from the unknown substance. Due to the fact that it is a built-in instrument, there are no exposures to radiation from the instrument indicating that it is safe to use.

DISADVANTAGES OF COLORIMETER FOR CONCENTRATION If the concentration is small, the Colorimeter instrument would be unable to detect it and would only absorb a small amount of light as if the concentration is too high, the absorbance will also increase more. The substance used for the Colorimeter instrument can have varied concentrations which could possibly give out an inaccurate result. A matrix effect during the pocess of the Colorimeter technique can easily produce uneven results which the situation could not be controlled. You are unable to see the process occurring as when the light is being absorbed, the method is occurring within the instrument meaning that you are unable to notify anything if there are any problems encountered within the Colorimeter.

Paper Chromatography is a method commonly used scientifically to be able to separate colored chemicals or their substances. The process takes place by the stationary phase of the filter paper which the mobile phase of the solvent is along with the mixture components and runs across the paper. Due to the difference in the affinity with water, the dots separate. Their purpose of Paper Chromatography is to be able to separate a mixture into varied components. A sample which is mixed with a high colored components such as a leaf pigment or ink could allow those that are identifying the paper to easily view it as it separates. The principle of Paper Chromatography is that the substances are distributed between liquid phases as soon as the phase is in the water held within the pores of the filter paper used and the other part is the mobile phase which functions in moving over the paper. The components in the mixture separates because the affinity towards water is difference as well as the mobile phase solvents during the movement of the mobile phase which is under the capillary action of the pores within the paper. Also the principle of Paper Chromatography could be an absorption kind of Chromatography which is happens between the solid and the liquid phase. The constituents of the colored mixture can also be separated due to the difference in the affinity which exists in each mixture component. ADVANTAGES OF PAPER CHROMATOGRAPHY An unknown inorganic or an organic compound can be easily identified using the Paper Chromatography method. Using the Paper Chromatography could analyze as well as provide accurate and precise results. The method is efficient as well as straight forward to be able to easily separate components of . a mixture. It is not time consuming as it is a relatively quick technique to perform.

DISADVANTAGES OF PAPER CHROMATOGRAPHY Using a large quantity of the sample cannot be used within Paper Chromatography. A Complex mixture is unable separate by the process of Paper Chromatography. Paper chromatography is not as effective within a quantitative analysis. It can be the case of this technique being less accurate than other chromatography techniques.

When performing the procedure of Paper Chromatography to separate and purify the mixtures of Amino Acids, the method was fairly a quick technique to perform and can generally provide in the accurate results. However, when doing the Paper Chromatography technique the end result in the paper gave out small dots on the solvent paper which was hard to identify and did not work its way up in the solvent line. The indication was that we were able to obtain an accurate result of the Paper Chromatography from our colleague. To suggest any improvements made within the Paper Chromatography technique, is to place a much smaller drop of the mixture onto the paper as some of the crosses had three or four drops of the amino acid and mixture. Also, to show accuracy within the experiment we should have run and evaluate on the mobile phase system at least twice to compare each result and the A and B mixture should be in a separate mobile phase. To evaluate the way in which the Paper Chromatography was carried out, our hands had to be washed before touching the paper used for the technique. This was the case as it could produce inaccurate results by the end of the experiment when leaving the paper to dry out which means that the paper must be handled on the edges of the paper sheet using gloves. To begin the experiment we firstly used a pencil to be able to draw a line which had to be 2 cm from below the Chromatography paper and leaving 1cm of space at the bottom of the paper also. Once that was done, we then marked six small crosses evenly along the origin line for the 4 known Amino Acids as well as the other two unknown mixtures. A three letter code was then written below each cross using a pencil for each of the amino acids leaving the other two mixtures labelled as A and B. Lastly, the Micropipette were used to apply a drop of the Amino Acids

within the middle of the crosses which are corresponding. This is then repeated for the other crosses. Different Micropipettes are used when applying the mixtures onto each cross to avoid cross contamination. The solvent is then placed into a Beaker in depth of 1.5 cm and allowing the chromatography paper to gently go into the Beaker also. This meant that we ensured that the paper is stood straight and not touching the sides of the beaker to avoid any inaccurate results. The beaker is then covered and given time for the solvent. Once the solvent reaches to the top, the chromatography is removed from the paper which lead us to mark the solvent front line from the paper using a pencil so that that it hangs to air dry. Once the chromatography paper is dry, it is sprayed using locating agent to be able to easily identify the separated amino acids present within the paper. This was performed in an operated Fume Hood to avoid any inhaling of toxic fumes and to keep the Laboratory well ventilated. This was then outlined carefully with a pencil and the Rf Value was also calculated of the Amino Acids used so that the mixture of A and B is identified. AMINO ACIDS GLUTAMIC ACID LYSINE VALINE LEUCINE UNKNOWN

SAMPLE A (Little boy)

SAMPLE B (REFERENCE SAMPLE)

DISTANCE MOVED BY SOLUTE 17.6 cm 17.6 cm 17.6 cm 17.6 cm 17.6 cm

1) 1.4 CM 2) 2.9CM 3 )5.5 CM 4) 3.6CM 5) 12CM 1) 1.4 CM 2) 3.5 CM 3) 6.1 CM

17.6 cm 17.6 cm 17.6 cm 17.6 cm 17.6 cm 17.6 cm 17.6 cm 17.6 cm

DISTANCE MOVED BY SOLVENT 5.3 cm 3cm 11.6 cm 1.5 cm 8 cm

RF VALUE 0.301 0.170 0.659 0.08 0.45

0.079 0.164 0.312 0.204 0.681 0.079 0.198 0.346

4) 6.8CM 17.6 cm 0.386 The purpose of the experiment was to find out whether both of the identified samples and amino acids we used in the technique would determine whether the little boy had Sickle Cell Anemia. Sample A and B both had a similar as well as an exact result of the value 0.079. In conclusion, the results were able to show that comparing with the A sample and B sample, the little boy had the Sickle Cell Anemia.

ADVANTAGES OF USING TITRATION TO DETERMINE CONCENTRATION The method to determine the concentration is a very accurate as well as a reliable method to use. When using the technique to determine concentration, wide reagents as well as chemicals can be used to analyze it.

DISADVANTAGES OF USING TITRATION TO DETERMINE CONCENTRATION Can easily repeat the technique once the solution is too much or too little. Due to the fact that the Titration technique only uses glassware to complete the method, the equipment could easily shatter which is a hazard.

When performing the method to determine the concentration, it does not consist of high trained people to do the procedure as it only provides

Problems could be encountered once a base is added within multiple acids to the sample, the

them to take their time when doing the method and not rush. Is very useful within the work industries to identify fats, the water content as well as whether vitamins are present. They are also used to test for drugs.

Titration technique would not be able to know how much acid is included in the flask. In order for Titration to work, the reagent or chemical must react quickly and instantly and completely in order for the experiment to work.

To evaluate the Titration of NaOH and HCl, the alternatives in the method or procedures when testing the accuracy is to be able to ensure that the equipment is sterilized well so that there the excess solutions from their experiments does not mix with the Titration indicating that the Burette must be rinsed with distilled water at least three times as this allows the accuracy of the Titration when pouring the solution in. The purpose of distilled water during a Titration and a Standard Solution is due to the fact that the water is pure which all the minerals and chemicals have been removed from the liquid. This will not have any side reactions when being mixed with a solution. Another piece of equipment such as the Conical Flask must be washed with distilled water in order to prevent any titrations when repeating a method. Finally, I believe that the improvements stated would be able to increase the number of data collected by using a larger sample of the Titration to give a more precise answer and also the equipment used to measure the solution should be as clear as possible for validity. The mistakes made during the Titration was not tightly closing the Pipette after transferring the Sodium Hydroxide into the Conical Flask. As the solution in the Flask was already measured specifically, even only a droplet of the solution can have a huge effect on the volume as you may have to complete the Titration again. This means to avoid the error, it must be tightly closed so that the solution is kept in the conical flask and avoiding inaccuracy. When preparing the Titration, I firstly rinsed the Burette with distilled water and also a tiny amount of white vinegar. I then filled the burette with white vinegar to record the first burette reading for the rough titration onto a table. With the Conical Flask on my table, I rinsed it as well as a pipette using distilled water and 1M of the Sodium Hydroxide. Using the pipette, I transferred 10cm3 of the 1M of sodium hydroxide into the Conical Flask as well as adding the three drops of Phenolphthalein. As it titrates, the white vinegar from the burette is included into the sodium hydroxide solution so I would be able to constantly swirl the flask until the indicator changes color from a purple to pale pink. This became the second Burette reading for the rough titration which was recorded and also the volume of the vinegar was calculated. I then emptied out the Conical Flask and washed it out using distilled water. This process is repeated however, the vinegar from the burette is added quickly until 2cm3 shorter than the approximate titre. Finally, the vinegar is added in drops and swirling the flask constantly until the indicator changes into a required color. The results was finally recorded onto a table.

References: https://en.wikipedia.org/wiki/Colorimeter_(chemistry) https://www.reference.com/science/colorimeter-measure-e8af79f7f9b69b42?qo=cdpArticles http://education.seattlepi.com/titration-different-colorimetry-4356.html https://www.instrumart.com/MoreAboutCategory?CategoryID=6075

https://www.reference.com/science/relationshi...