investigate a range of plant pigment to evaluate their effectiveness asw acid-base indicators?
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You can extract plant pigments, preferably from brightly coloured plants or parts of plants, either by boiling with water or crushing in a mortar and pestle with alcohol. Red cabbage gives good results. Boil some red cabbage in water until you have a good depth of colour. Then you can test it with different acids and bases (try vinegar, baking soda, household ammonia etc) and note the colours. Other good things to try are strongly coloured fruit juices, tea, red wine and of course brightly coloured flowers.
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hydrochloric acid, acetic acid (vinegar), boric acid, sulphuric acid, ascorbic acid(vitamin c) etc.
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Food colouring and bleach.
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I've found the Munsell Book of Color the best reference for comparing colours:\nhttp://www.it.lut.fi/ip/research/color/database/munsell.html\nI own a book given as a reference below, but it is mostly for plant leaves and probably lacks the right colour chips for all shades of mango. But it is waaay easier to find than the Book of Color! (And actually USE.)
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I did a demonstration on the affects of acid rain on plants once.  I used 5 identical, healthy house plants and watered them everyday with varying ratios of a water:vinegar mixture.  Pure water, 5 parts water:1 part vinegar, 5:2, 5:3, 5:4 and so on.  I recorded my observations each day for 10 days.  The impact that the acidity had on the plants with high vinegar ratios was pretty neat to watch and document.  You of course would have to explain how the vinegar acted like acid rain would but there are plenty of resources for this on the net.
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http://www.ebroadcast.com.au/lookup/encyclopedia/so/Soil_pH.html\n\nSoil pH\n\nSoil pH is an indication of the alkalinity or acidity of soil. It is based on the measurement of pH, which is based in turn on the concentration of hydrogen ions (H+) in a water or salt solution.\n\n\nWhen in balance (pH 7) the soil is said to be neutral. The pH scale covers a continuum ranging from 0 (very acidic) to 14 (very alkaline or basic). It is however uncommon to find soils at either extreme of this range. Under many conditions soils tend to become more acid or alkaline over time if steps are not taken to maintain a balance. \n\npH is important for the organic gardener for several reasons, including the fact that many plants and soil life forms prefer either acid or alkaline conditions, that some diseases tend to thrive when the soil is alkaline or acidic, and that the pH can affect the availability of nutrients in the soil. \n\nTable of contents [showhide]  \n1 Nutrient availability in relation to soil pH \n2 Soils and acidity \n3 Soil life and pH \n4 pH and plant diseases \n5 Determining pH \n6 Altering soil pH \n7 See also \n \n \n\n\n\nNutrient availability in relation to soil pH \nThe majority of food crops prefer a neutral or slightly acidic soil, because the solubility of most nutrients necessary for healthy plant growth is highest at at pH 6.3-6.8. Some plants however prefer more acidic (e.g., potatos, strawberries) or alkaline (brassicas) conditions. \n\nWhen the pH falls below 5.5, most major plant-nutrient minerals (those needed in substantial quantities to promote healthy plant growth include nitrogen (N), phosphorus (P), potassium (K), sulphur (S), magnesium (Mg), and calcium (Ca)) and some micronutrients[?] (elements important to plant growth in very small amounts) become insoluble and hence unavailable for uptake by plant roots. \n\nMany cationic (positively charged) nutrients such as zinc (Zn2+), aluminium (Al3+), iron (Fe2+), copper (Cu2+), cobalt (Co2+), and manganese (Mn2+) are soluble and available for uptake by plants below pH 5.0, although their availability can be excessive and thus toxic in more acidic conditions. In more alkaline conditions they are less available, and symptoms of nutrient defficiency may result, including thin plant stems, yellowing (chlorosis[?]) or mottling of leaves, and slow or stunted growth. \n\npH levels also affect the complex interactions among soil chemicals. Phosphorus (P) for example requires a pH between 6.0 and 7.0 and becomes chemically immobile outside this range, forming insoluble compounds with iron (Fe) and aluminium (Al) in acid soils and with calcium (Ca) in calcareous soils. \n\nThis table indicates the availability of several nutrients at various pH values: \n\n  Acid  Neutral Alkali  \n  4   4.5 5   5.5 6   6.5 7   7.5 8   8.5 9   9.5 10 \nnitrogen, N       \nphosphorus, P         \npotassium, K         \ncalcium, Ca       \nmagnesium, Mg       \nsulfur, S     \niron, Fe     \nmanganese, Mn       \nboron, B       \ncopper, Cu       \nzinc, Zn       \nmolybdenum, Mo     \n\n\n\nSoils and acidity \nUnder conditions in which rainfall exceeds evapotranspiration (leaching) during most of the year, the basic soil cations (Ca, Mg, K) are gradually depleted and replaced with cations helds in colloidal[?] soil reserves, leading to soil acidity. Clay soils often contain Fe and hydroxy Al, which affect the retention and availability of fertilizer cations and anions in acidic soils. \n\nSoil acidification may also occur by addition of hydrogen, due to decomposition of organic matter, acid-forming fertilisers, and exchange of basic cations for H+ by the roots. \n\nSoil acidity is reduced by volatilization and denitrification of nitrogen. Under flooded conditions, the soil pH value increases. In addition, nitrate fertilizers containing cations such as Ca, K, or Na also increase the soil pH value. \n\n\nSoil life and pH \nA pH level of around 6.3-6.8 is also the optimum range preferred by
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Water is crucial to photosynthasis, but you may be surprised at the results of other liquids (that are water based of course, everything else will kill the plant---fast!) Just play around with it, that is the fun of experiments. Try some liquids that are more acidic and some that are more basic. Sprite, asprin dissolved in water.... Maybe try coffee--I know that coffee grounds work as a great compost and make plants grow faster and fuller. Who know? Good luck & have fun!
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one way is chlorophyll fluorimetry,a method of studying light absorption by photosynthetic pigments in marine algae.\nthis sight might help good luck.
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Try Copper Test by points
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Here's one source that has a "universal indicator (pH 2-10)".  It may not be the only one:\n\nBromothymol Blue 0.08%\nMethanol (solvent)\nMethyl Red Hydrochloride 0.04%\nPhenolphthalein 0.02%\nThymol Blue  0.1%
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drift wood will lower pH as it releases tannic acid as it soaks.\n\npeat moss will have the same effect , but will release humic acids.
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Identification test for Citric Acid:\n\nAdd a few milligrams of your substance to a solution containing 15mL of pyridine and 5mL of acetic anhydride.  If citric acid is present, a bright red color is produced.
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go to this site - nice color picture\n\nhttp://www.ct-botanical-society.org/galleries/aristolochiaserp.html
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Well if I remember this right...NASA was doing experiments a few years ago with rhubarb and pumpkin plants. The C02 oxygen exchange was the greatest. Also there was something about a genetically engineered algae they were trying out
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pH level, buffering capacity (alkalinity), general hardness and salinity
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http://www.taoherbfarm.com/herbs/resources/acidplants.htm\nCopy and paste above link into your browser
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Acidic \n\nbelow 6 acidic above 7 basic