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pH measurement Lesson Plan Prepared by: Tabbasum Fatima Class : X Subject : Chemistry.

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Presentation on theme: "pH measurement Lesson Plan Prepared by: Tabbasum Fatima Class : X Subject : Chemistry."— Presentation transcript:

1

2 pH measurement

3 Lesson Plan Prepared by: Tabbasum Fatima Class : X Subject : Chemistry

4 The term "pH" was first described by Danish biochemist Søren Peter Lauritz Sørensen in pH is an abbreviation for "power of hydrogen" where "p" is short for the German word for power, potenz and H is the element symbol for hydrogen. The H is capitalized because it is standard to capitalize element symbols. The abbreviation also works in French, with pouvoir hydrogen translating as "the power of hydrogen".hydrogen

5 Definition of pH pH is a measure of hydrogen ion concentration; a measure of the acidity or alkalinity of a solution.hydrogenconcentrationacidityalkalinitysolution A number which expresses the degree of acidity or alkalinity of a solution. The pH of a neutral solution is 7.0, of an acid solution less than 7.0, of an alkaline solution more than 7.0.

6 Logarithmic Scale The pH scale is a logarithmic scale that usually runs from 1 to 14. Each whole pH value below 7 (the pH of pure water) is ten times more acidic than the higher value and each whole pH value above 7 is ten times less acidic than the one below it.

7 Example, A pH of 3 is ten times more acidic than a pH of 4 and 100 times (10 times 10) more acidic than a pH value of 5. So, a strong acid may have a pH of 1-2, while a strong base may have a pH of A pH near 7 is considered to be neutral.

8 What Is the pH of the Stomach? Your stomach secretes hydrochloric acid, but the pH of your stomach isn’t necessarily the same as the pH of the acid.

9 Example The pH of your stomach varies, from 1-2 up to When you eat, the stomach releases proteases and hydrochloric acid to aid in digestion. The proteases that cleave proteins work best in an acidic environment or low pH. so after a high-protein meal, your stomach pH may drop to as low as 1 or 2. After digestion pH returns to a resting level of about 4 or 5.

10 Is a Negative pH Possible? Any acid that yields a concentration of hydrogen ions with a molarity greater than 1 will be calculated to have a negative pH. For example: The pH of 12M HCl is calculated to be -log(12) =

11 you can't accurately measure extremely low pH with a glass pH electrode and it is difficult to tell whether the pH is lowered by the increased hydrogen ion activity more than it is raised by incomplete dissociation. Negative pH is possible, but not something you can show.

12 How To Calculate pH ?

13 Calculate pH and [H + ] pH = -log 10 [H + ] [H + ] = 10 -pH Example: Calculate the pH for a specific [H + ]. Calculate pH given [H + ] = 1.4 x M pH = -log 10 [H + ] pH = -log 10 (1.4 x ) pH = 4.85

14 Example: Sodium hydroxide is commonly used as a drain cleaner.If the concentration of OH - is 1.0x10 -5 M. Find the concentration of [H + ] ions and also tell that the solution is acidic basic or neutral? Solution: Kw = [H + ] [OH - ] 1.0x = [H + ] 1.0x10 -5 [H + ] = 1.0x / 1.0x10 -5 = 1.0 x = 1.0x M As 1.0x M is < 1.0x M, the solution is basic.

15 Measurement of pH By pH paper By indicator paper By litmus paper

16 By pH paper pH paper is dipped in the solution. Observe the change of colour and compare it to the chart. Each colour is linked to a specific pH value.

17 By litmus paper Litmus paper may be blue or red. Litmus paper is dipped in the solution. Observe the change of colour. An acid turns blue paper red. An base turns red paper blue.

18 By indicator paper Indicators are organic compounds and change colour within small pH change. We add few drops of an indicator to an aqueous solution of unknown pH and measure pH from the solution. Example: Methyl red changes colour from red to yellow at pH6.

19 Use of Litmus Paper Take solutions in separate test tubes and label them. Dip red and blue litmus paper in each solution. Note the colour change. Result: This test will classify each solution as acid or base or has pH less than 7 or greater.

20 Thank You


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