[CHEM] Testing Natural Indicators PDF

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Testing Natural Indicators – Report

Testing Natural Indicators Aim : To prepare and test a range of natural indicators on a batch of solutions possessing varying levels of pH.

Hypothesis : When added to various solutions, results from the natural indicators will vary due to natural discrepancies in plant extracts and pigments.

Equipment : 

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Plant material: purple cabbage leaves; flower petals (e.g. roses, camellias, petunias, hibiscus, violets). Purple cabbage leaves, red rose petals, and watermelon slices were used for the experiment 6 150ml beakers 15 test tubes Hydrochloric acid (0.01 mol/L) Sodium hydroxide (0.01 mol/L) Ammonia (0.01 mol/L) Acetic acid (0.01 mol/L) Water Glass stirring rod Test tube rack (s) 3 Plastic Pasteur pipettes/droppers Heat mat Tripod Gauze mat Bunsen burner Cutting board Cutting knife Crucible tongs (to handle heated beakers)

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Testing Natural Indicators – Report

Procedure : 1) Prepare heating equipment i.e. Bunsen burner, tripod, gauze mat and a heat mat. Also gather necessary materials. 2) Use a cutting board and sharp knife to cut the cabbage leaves into fine shreds. 3) Place the shredded cabbage in the large beaker (about 1-2 cm depth) and cover it with water. Heat the mixture to near boiling on a tripod with a gauze mat and Bunsen burner, and stir with a glass rod. Allow the mixture to cool. 4) Decant the cabbage extract into a clean, labelled beaker and discard the cabbage shreds into a bin. 5) Select the flower and remove its petals. Tear the petals into small pieces and place them into a small beaker. Cover them with water and heat the mixture using the heating equipment to extract the pigments until boiling. Allow the extract to cool on a heat mat when finished. 6) Decant the petal extract into a clean, labelled beaker and discard the petal shreds into a bin. 7) Cut the watermelon into small pieces, heat until boiling, decant into a beaker, and finally allow cooling as well. 8) Pour roughly equivalent amounts of hydrochloric acid into three consecutive test tubes. This will be the set of test tubes for hydrochloric acid. 9) Repeat step (8) for the next four solutions (sodium hydroxide, ammonia, acetic acid, water) with the remaining empty test tubes. There should be five sets of test tubes in total, each set containing a different solution; three test tubes in a set. 10) Using a dropper, add a few drops of the cabbage indicator to the first test tube of the hydrochloric acid set. Record any changes or observations. Repeat for the second unreacted test tube with the next indicator, using a separate uncontaminated dropper. Repeat once again for the third test tube with the next indicator, taking necessary precautions. 11) Repeat step (10) for the next sets of test tubes. Record any concluding observations.

Safety Precautions : Risk Factor Hot equipment, open Bunsen burner flame, boiled water

Hazard Inflammation of skin or possibly scarring. For boiled water, eye damage may also occur.

Shattered glass (if a test tube or beaker is broken)

Cuts and/or scratches.

Control Run the burn under cold water for a few minutes or so and avoid strenuous activity that may exacerbate the injury. Use burn salve to manage to manage the burn. Prevention: Take basic safety precautions when handling hot equipment (allow it to cool down); pay close attention to live flames; wear a lab coat and safety glasses; and handle equipment carefully, e.g. use tongs or test tube holders, etc. Run the cut under clean water to get rid of possible contaminants, sterilise the cut using antiseptics, and apply a bandage to the wound to prevent infection. Prevention: Handle glassware equipment carefully to prevent further breakage; alert a supervising teacher instead of risking (further) injury; take basic safety precautions when handling glassware. 2|Page

Testing Natural Indicators – Report Hydrochloric acid (0.01 mol/L)

Sodium hydroxide (0.01 mol/L)

Ammonia (0.01 mol/L)

Acetic acid (0.01 mol/L)

Corrosive irritation through all routes of exposure (skin, eyes, ingestion, inhalation).

If in contact with skin or eyes, flush the area of exposure with water; do not induce vomiting if ingested: remember to call for the supervising teacher; move to fresh air if inhaled.

Corrosive irritation through all routes of exposure (skin, eyes, ingestion, inhalation).

Prevention: Take basic safety precautions; wear a lab coat and safety glasses; handle the solution carefully; do not directly inhale; work in a well-ventilated area. If in contact with skin or eyes, flush the area of exposure with water; do not induce vomiting if ingested: remember to call for the supervising teacher; move to fresh air if inhaled.

Irritation to eyes and open wounds.

Irritation to eyes and open wounds.

Prevention: Take basic safety precautions; wear a lab coat and safety glasses; handle the solution carefully; do not directly inhale; work in a well-ventilated area. If in contact with skin or eyes, flush the area of exposure with water; do not induce vomiting if ingested and do not wash out with water, small sips of water may cool the throat and keep the airway open: remember to call for the supervising teacher; move to fresh air if inhaled. Prevention: Take basic safety precautions; wear a lab coat and safety glasses; handle the solution carefully; do not directly inhale; work in a well-ventilated area. If in contact with skin or eyes, flush the area of exposure with water; do not induce vomiting if ingested: remember to call for the supervising teacher; move to fresh air if inhaled. Prevention: Take basic safety precautions; wear a lab coat and safety glasses; handle the solution carefully; do not directly inhale; work in a well-ventilated area.

Results : Hydrochloric acid (pH = 1)i Plant material Cabbage

Dark pinkish red

Rose

Red

Watermelon Slightly pink

Acetic acid (pH = 2.87)ii

Purplish pink Bright pink

Slightly pink

Colour of extract Water Ammonia solution (pH = 11.6)iii (pH = 7)

Clear

Green

Lightly pink

Dark green with an earthy brown shade Slightly pink

Slightly pink

Sodium Hydroxide solution (pH = 14)iv Bright yellow, slightly green Brown

Slightly pink

Discussion :

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Testing Natural Indicators – Report Coinciding with the hypothesis, the results from the natural indicators carried due to natural discrepancies in the plant extracts. The purple cabbage indicator had a variety of colour readings from acidic, neutral, to basic: dark pinkish red, clear, and bright-greenish yellow respectively. As such, it would be an effective general indicator. The colour change was due to the presence of a pigment molecule called flavin (an anthocyanin or a plant pigment) which naturally occurred in purple cabbage; such a pigment is also present in apple skin, plums, poppies, cornflowers, and grapes. According to outside sources, anthocyanin turns a red colour in highly acidic solutions; purplish in neutral; greenish yellow in basic.v vi The rose indicator also had a variety of readings, although the colours would be more difficult to distinguish when observing and recording colour changes. Its readings, ranging from acidic, neutral and basic, were: red, lightly pink, and brown. Such colour changes were due to anthocyanins present in red rose petals. The watermelon indicator, however, had no outward readings when added to the variety of solutions at hand. A slightly pink tinge in the tested solutions was a constant result. Such was presumably due to the colour of the extract itself, being a deep red-pink colour. Upon further research, it was found that watermelon did not contain pigments which would react in solutions of varying pH levels. Reliability – The experiment had a low level of reliability. Such was due to the experiment being conducted two times amongst the entire class. The results compared amongst the two groups were also relatively disparate. With respect to sample size, only one test tube of a respective solution was tested with a particular indicator, thus reinforcing the experiment’s low reliability i.e. only one test tube of hydrochloric acid was tested with the cabbage solution: the result gathered from this one test tube might have been skewed due to presiding circumstances that will be detailed upon in the validity. The experiment could be improved by repeating it a greater number of times, while also using a larger sample size for each solution used. Validity – In the experiment, the variables were as follows:  Independent variable: An indicator’s reading in a certain solution.  Dependent variable: The pH of the solutions being tested.  Controlled variable: The solutions being tested for each indicator are kept constant (one test tube of solution for each indicator available); the relative amount of solution in each test tube; the relative amount of indicator solution added to each test tube; the indicators used (each type of indicator being extracted from varying plant materials and utilised in testing solution pH’s throughout the experiment); the molarity of the solutions being tested (where applicable); the atmospheric conditions (stable lab conditions). The controlled variables were maintained throughout the experiment, but there was an issue relating to the number of assumptions made in preparing the planning the experiment. Theoretically, the experiment had a high level of validity if the following assumptions remained undisputed:

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Testing Natural Indicators – Report 

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The glassware equipment was not contaminated. Contamination would possibly lead to skewed and invalid results, either influencing the solutions or the indicators. Such might have been an issue as the beakers and test tubes were not cleaned before being used. An optimal plant sample was gathered for its consequent pigment extraction. I.e. the sample was not aged or decomposing, etc. A sufficient quantity of plant samples was collected for use. If a deficient amount was collected, there would be a scarcity of reacting plant pigments in the concluding indicator. The colour change of the tested solution would thus be too minute, possibly resulting in an invalid observation. With regards to experiment conducted: generous amounts of cabbage, rose, and watermelon samples were used in producing the indicator solutions, thus concentrating the necessary plant extracts. The steps of the experiment were carried out mindfully. While conducting the experiment, skipping a certain solution would result in an incorrect observation, etc. The pigments were extracted properly: i.e. plant material might not have been boiled for a necessary period of time, etc. Observations were taken properly. Accordingly, the following factors might have skewed the concluding results: The test tubes were viewed in low light, hence engendering an invalid recorded result; the test tube was not viewed properly.

Overall, it is discernible that the experiment has a medium level of validity because it relied on only a few assumptions, being the best that could be done with the limited amount of time and resources. The validity could be improved through various means such as: conducting the experiment properly while paying close attention to the procedure (thus allowing for the proper extraction of plant pigments); observing colour changes carefully; cleaning the glassware to prevent contamination; ensuring the collection of optimal plant samples (checking the samples and collecting the fresher kinds, etc.); collecting sufficient amounts of the aforesaid plant samples. Accuracy – The experiment had a medium level of accuracy as, when compared with the observations gathered from external sources such as the internet: as aforesaid purple cabbage typically has a colour range of red, purplish, greenish yellow; from acidic, neutral and basic. The results gathered from this indicator were thus relatively accurate, aside from the result from the neutral reading, wherein a clear result was found. For the rose indicator, outside sources dictate an approximate colour range of dark pink in acids to green in base. vii viii Such roughly correlated with the results gathered from the experiment with no outstanding discrepancies, making it reasonably accurate. Watermelon, however, containing no reactive pigments, did not react by principle and thus comparison with outside sources was fruitless. It can be assumed that the results gathered for the watermelon indicator were accurate. With regards to the measuring instruments utilised in the experiment, there was a medium level of accuracy:  Human observational skills: This was utilised in observing and recording observations during and after the experiment. The method would have been, on a general level, slightly unreliable and thus inaccurate.

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Testing Natural Indicators – Report The glassware and Pasteur pipettes used in the experiment were not given mention as accurate measurements were inessential, possessing little influence over the concluding results. As stated in a prior point, the inherent fallacy of human observational skills might have negatively affected the concluding observations i.e. when using the cabbage indicator. To improve the accuracy of the results and observations: the experiment could be repeated a number of times until consistent results are obtained and, from that, averages on various observations; by paying close attention when discerning colour changes and possibly holding the test tube solutions up to a light source when determining such.

Conclusion : A variety of natural indicators were prepared and tested on a batch of solutions possessing varying pH levels. When added to various solutions, the results from the natural indicators varied due to the natural discrepancies in plant extracts and pigments.

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i http://answers.yahoo.com/question/index?qid=20080608123742AAEFkgH ii http://answers.yahoo.com/question/index?qid=20070320152058AAhUu4i iii http://en.wikipedia.org/wiki/Ammonia iv http://answers.yahoo.com/question/index?qid=20060618005823AAMWms6 v http://chemistry.about.com/od/acidsbase1/a/red-cabbage-ph-indicator.htm vi http://www.cchem.berkeley.edu/demolab/demo_txt/CabbIndic.htm vii http://wiki.answers.com/Q/What_color_when_acid_is_put_on_china_rose_indicator viii http://ejeafche.uvigo.es/component/option,com_docman/task,doc_view/gid,668/...