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DH OF SOLUTIONS, , Introduction..., ction... |, , , , , , The pH is the power of hydrogen ion concentration of a solution. The pH of a solution is, , defined as the negative log (base 10) of its hydrogen ion concentration in gram moles, Per litre of solution., , pH = -log,, [H’], , , , To find the pH of the following samples by using pH paper/universal indicator:, 1. Water (H,0)., , Dilute sodium hydroxide (NaOH) solution., Lemon juice., , Dilute hydrochloric acid (HCI)., , Dilute sodium bicarbonate (NaHCO,) solution., dilute Ethanoic acid (CH,COOH) solution., , THEORY:, , oOaRYNn, , Acids are those substances which give H" ions in aqueous solution. Bases are those substances which give, OH ions in aqueous solution., , PH papers are used to take approximate measurement of pH of a solution., , 1. If pH value is less than 7, the solution is acidic in nature. Lesser the value of pH, the more is the, concentration of H* (aq) ions per litre of the solution., , 2. If pH value is more than 7, the solution is basic (alkaline) in nature. The more the value of pH, lesser, is the concentration of H* (aq) ions per litre of the solution., 3. pH of pure water is 7. Such a solution is neutral towards indicators., , Colour ted orange yellow green indigo violet/blue, PH range 0-3 3-5 4.5-6 6-8 8-11 11-14, , PSTN pee { =, Leal, , , , , , , , | io ee, PH1 pH2 pH3. pH4-—s pH5-— pH6_-— pH7_-s pHB_— pH9- pH10 pHi. pH12. pH13_ pH14, Figure. 1.1 pH paper ., The chart given below shows the colours of pH paper in the solutions of different PH values:, , Strips of pH paper, 6 test tubes and a test tube rack, a beaker filled with distilled water, dropper, a glazed tile,, , a standard pH chart, water, dilute solution of sodium hydroxide, lemon juice, dilute hydrochloric acid, dilute, solution of sodium bicarbonate and dilute solution of ethanoic acid.
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¥, TROD:, , Take 6 test tubes. Rinse each test tube thoroughly with distilled water. Place them in the test tube rack,, Label the test tubes as A, B, C, D, E and F respectively. Then, half fill the test tubes with the Given, solutions, i.e. dilute water to test tube A, dilute NaOH to test tube B, lemon juice to test tube C, HCLity, , test tube D, sodium bicarbonate to test tube E, ethancic acid to test tube F, as shown in Figure. 1.2,, 3. Shake the contents of each tube., , A B Cc D e F, , , , , , , , , , , , , , , , , , , , water___NaOH__lemon. HCI____sodium _ ethanloic, , Blearbonale ache |, , , , strip of pH paper, Figure. 1.2, , Figure. 1.3, , 4. Take five strips of pH Papers. Mark these strips as A, B, C, D, E and F respectively,, , so that each is, used for testing the solution in the corresponding test tubes., , , , , , , , , , , , , , , , , , , , , , , , 5. Now, withdraw few drops of solution from test tube A, and put two drops of it on the PH paper labelled, Aas shown in Figure. 1.3., 6. Note the colour on the PH paper., 7. Rinse the dropper thoroughly with distilled water, before using it to withdraw solution from test tube B., _ 8. Repeat the experiment with solutions in test tubes B, C, D, E and F, testing each with similarly labelled, = PH strips., 9. Compare the colour developed on the pH paper with the colour given on standard pH-colour chart., : Record your observations in the table given below:, DBSERVATION:, Colour Prod Corresponding pH re of, on pH panei value on standard Natures :, pH-colour chart | ese, Ay, 2. Dilute sodium hydroxide, 3. Lemon juice, 4. Dilute hydrochloric acid, 5. Dilute sodium bicarbonate, 6. Dilute ethanoic acid, CONCLUSION:, 1. Test tube A (water) sample matches with colour of PH 7 in standard pH-colour chart and hence, 's, neutral in nature., , 2. Test tube B (NaOH solution) sample matches with colour of, hence, basic in nature., , 0] [LAB Manualxa, , PH 14 in standard pH-colour chart and
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3. Test tube C (lemon juice) sample matches with colour of pH 2 in standard pH-colour chart and hence,, is acidic in nature., , 4, Test tube D (dilute HCl) sample matches with colour of pH 1 in standard pH-colour chart and hence, is, acidic in nature,, , 5, Test tube E (dilute NaHCo, solution) sample matches with colour of pH 9 in standard pH-colour chart, and hence, is basic in nature., , 6. Test tube F (dilute CH3COOH solution) sample matches with colour of pH 3 in standard pH-colour, chart and hence, is acidic in nature., , PRECAUTIONS:, , 1. Good quality and clean pH strips should be used and these should not be touched with wet hands., 2. Separate pH papers should be used for testing different solutions., , Dropper used for one sample should be used for other sample only after washing it with distilled, water., , Test tubes should be cleaned thoroughly with distilled water otherwise the PH value obtained may be, wrong., , After every use, if the dropper is not cleaned thoroughly 2-3 times with distilled water, a wrong pH, value can be obtained.
