chemical Indicators

acids and bases

1. By: KIRTI GARG

2. DIFFERENT TYPES OF INDICATORS AND p H SCALE

3. 1. Acid base Indicator 2. Some acid base indicators 3. Litmus 4. Methyl orange 5. Phenolphthalein 6.Bromothymol blue 7. Universal indicator 8. pH indicator 9 . Olfactory indicator 10. redox indicator 11. Uses of indicator CONTENTS

4. I ndicators are chemical substances that are used to find out whether a given solution is  acidic  or  alkaline  by showing a color change.Acid -base indicators are used to determine when one has added enough acid to a base to neutralized the base. So, in a titration the color of the indicator must shift at the pH of the end point. The pH of the endpoint is that calculated from the salt solution. The indicator, added to the solution, must have a different color when the solution has excess base verses the color when there is an excess of acid . Acid base indicator

5. Several acid-base indicators are listed below. Tried-and-true indicators include: thymol blue, tropeolin OO, methyl yellow, methyl orange, bromphenol blue, bromcresol green, methyl red, bromthymol blue, phenol red, neutral red, phenolphthalein, thymolphthalein , alizarin yellow, tropeolin O, nitramine , and trinitrobenzoic acid. Data in this table are for sodium salts of thymol blue, bromphenol blue, tetrabromphenol blue, bromcresol green, methyl red, bromthymol blue, phenol red, and cresol red . some common acid base indicators

6. phenolphthlein : base (pink) ; acid (clear) methyl red: acid (red) ; base (yellow) bromocresol green : base(blue ) ; acid (yellow) litmus : base (blue) ; acid (red ) thymolphthalein : base (blue) ; acid (clear) Some acid base indicators are explained further. For example

7. litmus Litmus  is a  water soluble  mixture of different  dyes  extracted  from  lichens. It is often absorbed onto filter paper to produce one of the oldest forms of pH indicator, used to test materials for acidity. Blue litmus paper turns red under  acidic conditions and red litmus paper turns blue under  basic. Neutral litmus paper is purple . Litmus can also be prepared as an aqueous solution that functions similarly. Under acidic conditions, the solution is red, and under basic conditions, the solution is blue.

8. Methyl orange Methyl orange  is a pH indicator frequently used in titrations because of its clear and distinct colour change. Because it changes colour at the pH of a mid strength acid, it is usually used in titrations for acids. Unlike a universal indicator, methyl orange does not have a full spectrum of colour change, but has a sharper end point . In a solution becoming less acidic, methyl orange moves from red to orange and finally to yellow with the reverse occurring for a solution increasing in acidity .

9. phenolphthalein Phenolphthalein   is a chemical compound with the formula C 20 H 14 O 4  and is often written as " HIn " or " phph " in shorthand notation. Phenolphthalein is often used as an indicator in titrations. For this application, it turns colorless in  acidic solutions and pink in basic solutions. Phenolphthalein is insoluble in water and usually is dissolved in alcohols for use in experiments. It is a weak acid, which can lose H + ions in solution. The phenolphthalein molecule is colorless, and the phenolphthalein ion is pink.

10. Bromothymol blue Bromothymol blue  (also known as  bromothymol sulfone phthalein , and  BTB ) is a pH indicator for weak acids and bases. It is mostly used in applications that require measuring substances that would have a relatively neutral pH (near 7), such as managing the pH of pools and fish tanks. A common use is for measuring the presence of carbonic acid in a liquid. It is typically sold in solid form as the  sodium salt of the acid indicator.

11. UNIVERSAL I NDICATOR A Universal Indicator is a mixture of indicators which give a gradual change in colour over a wide pH range - the pH of a solution can be approximately identified when a few drops of universal indicator are mixed with the solution.There are now also available wide range pH test papers with distinct colours for each pH from 1 to 14. Colour matching charts are supplied with the specific test strips purchased. The universal indicator is made from magnesium hydroxide with a pH value of 4. A universal indicator is typically composed of water, propan-1-ol, phenolphthalein sodium salt, sodium hydroxide, methyl red,  bromothymol blue monosodium salt, and  thymol blue monosodium salt.

12. PH scale pH is the expression of universal indicator. At a low pH, a weak acid indicator is almost entirely in the HIn form, the colour of which predominates. As the pH increases - the intensity of the colour of HIn decreases and the equilibrium is pushed to the right. Therefore the intensity of the colour of In -  increases. An indicator is most effective if the colour change is distinct and over a low pH range. For most indicators the range is within ±1 of the p K ln  value: - please see the table below for examples, to the right is a model of the acid form of each indicator - with the colour of the solution at the turning point . A pH paper is a piece of paper dipped in universal indicator telling whether acid or base. pH indicator

13. A pH scale reading of  less than 7  indicates an  acidic  medium. A pH scale reading of  more than 7  indicates a  basic  medium. A pH scale reading  equal to 7  indicates a  neutral  medium or solution (pure distilled water). A pH scale reading of  2  indicates a  strong acid . A pH scale reading of  13  indicates a  strong base . A pH scale reading of  6  indicates a  weak acid . A pH scale reading of  8  indicates a  weak base . p H scale

14. pH

15. OLFACTORY INDICATORS An  Olfactory indicator  is a substance whose smell varies depending on whether it is mixed with an acidic or basic solution. Olfactory indicators can be used in the laboratory to test whether a solution is a base or an acid, a process called  olfactory titration . Onion , clove oil and vanilla extract are examples. An olfactory indicator works on the principle that when an acid or base is added to it, then different odour can be detected in bases whereas odour remains same in acids.

16. REDOX INDICATORs A  redox indicator   is an indicator which undergoes a definite color change at a specific electrode potential. The requirement for fast and reversible color change means that the oxidation-reduction equilibrium for an indicator redox system needs to be established very quickly. Therefore only a few classes of organic redox systems can be used for indicator purposes. Sometimes colored inorganic oxidants or  reductants  are also  incorrectly  called redox indicators. Almost all redox indicators with true organic redox systems involve a proton as a participant in their electrochemical reaction. Therefore sometimes redox indicators are also divided into two general groups: independent or dependent on  pH .

17. 1.Testing the acidity or basicity of soils, as some plants grow best in slightly acidic soils (such as azaleas and pineapples) while others grow best in slightly basic soils (such as violets ) 2. Pineapples and violets have very different soil requirements Because soil is dark in colour, a white inert solid such as barium sulfate is mixed with the soil before the indicator is added. 3.The colour of the indicator can be seen on the white solid. Everyday uses of indicators include:

18. 4.If a soil is found to be too acidic, it can be partially neutralised by adding a weak base such as powdered limestone (calcium carbonate). 5.If a soil is found to be too basic, it can be partially neutralised by adding a weak acid such as ammonium sulfate. 6.Testing home swimming pools, as they need to be approximately neutral. 7.Monitoring liquid wastes, such as those from photographic processing, as liquids discharged into the sewerage system must be nearly neutral to avoid causing corrosion .

19. THANK YOU