The PH Scale

Cheemistry

1. The pH Scale Reporter: Krisha Laine Rizala Sindalan Instructor: Mrs. Karen Sale

2. P- power H- hydrogen Thus we define pH as a negative logarithm of the molar concentration of hydrogen ions. pH=-log[H+]

3. The pH scale, first proposed in 1909 by the Danish biochemist S.P.L. Sorensen, to describe the degree of acidity or basicity.

4. The neutral point on the scale is 7, with values below 7, indicating increasing acidity and those above 7, increasing basicity.

5. We might expect that pure water would be completely in the form of H2O molecules, but, it turns out that : about 1 out of every 500 million molecules is split into H + and OH - ions Concentration of hydrogen ions and of hydroxide ions in pure water of 0.0000001 mol /L, or 1x10 -7 M.

6. Note that its value goes down when acidity goes up. Not only in the relationship an inverse one, but also logarithmic.

7. A decrease of 1 pH unit represents a tenfold increase in acidity, and when pH goes down by 2 units, acidity increases factor by 100.

8. Relationship between pH and concentration of Hydronium Ions. Concentration of H 3 O + ( mol /L) pH 1x10 -0 1x10 -1 1 1x10 -2 2 1x10 -3 3 1x10 -4 4

9. EXAMPLE: What is the pH of a solution that has a hydrogen ion concentration of 1x10-5 M? Answer: 5

10. WHAT IS THE HYDROGEN ION CONCENTRATION OF A SOLUTION THAT HAS A pH of 4? Solution: The pH value is 4. This means the exponent of 10 is -4. the hydrogen ion concentration is therefore 1x10 -4 M.

11. Jwk  lol . GET ¼ SHEET OF PAPER MY GORGEOUS AND HANDSOME CLASSMATES. 

12. pH from hydrogen Ion concentration 1.What is the pH of a solution that has a hydrogen ion concentration of 1x10 -11 M?

13. pH from hydrogen Ion concentration 2 .What is the pH of a solution that is 0.0010 M HCI?

14. hydrogen Ion concentration from pH 3 .What is the hydrogen ion concentration of a solution that has a pH of 2?

15. 1. The hydrogen ion concentration, [H + ], of a 0.0010 M HNO 3 solution is 1.0 x 10 -4 M B. 1.0 x 10 -3 M C. 1.0 x 10 -2 M D. 1.0 M

16. 2. What is the pH of a solution that has a hydrogen ion concentration of 1.0 x 10 -11 1 3 10 11

17. 3. Pool water with pH of 8 has a hydrogen ion concentration of A. 8.0 M B. 8.0 x 10 -8 M C. 1.o x 10 -8 M D. 1.0 x 10 8 M

18. The pH of pure water is A. 0 B. 1 C. 7 D. 10 E. 14

19. Which of the following is a reasonable pH for 0.15 M HCI? 0.15 0.82 8.24 13.18

20. Which of the following is a reasonable pH for 0.15 M NaOH ? 0.15 0.82 8.24 13.18

21. Physiological pH (7.4) is the average pH of blood. Which of the following is a reasonable hydrogen ion concentration of a solution at physiological pH? -7.4 M B. 0.6 M C. 6 x 10 -7 M D. 1 x 10 -8 M E. 4 x 10 -8

22. 1. Buffers and Conjugate Acid-Base Pairs Conjugate acid base pair - In the Bronsted -Lowry theory, a pair of compounds or ions That differ by one proton (H + ). examples: HF and F - NH 3 and NH 4 + ion.

23. NH 4 + is an acid; it can donate extra proton. Example: When a base NH 3 accepts a proton, it becomes an acid because it now has a proton that it can donate.

24. EXAMPLES What is the conjugate base of (a) HBr and (b) of HNO 3 and what is the conjugate acid of (c) OH - and (d) of HSO 4 - ? Solution: A . HBr leaves Br - the conjugate base of HBr is Br - . B . Removing a proton from NHO 3 leaves NO 3 - ; the conjugate base of NHO 3 is No 3 - C. Adding a proton to OH - gives H 2 O: the conjugate acid of OH - is H 2 O D. Adding a proton to HSO 4 - gives H 2 SO 4 ; the conjugate acid of HSO 4 - is H 2 SO4

25. EXERCISE WHAT IS THE CONJUGATE BASE OF A (a) HCN AND (b) OF H 3 O+ AND WHAT IS THE CONJUGATE ACID OF (c) SO 4 2- AND (d) OF HCO 3 - ?

26. BUFFER SOLUTION DEFINITION: A buffer solution is one which resists changes in pH when small quantities of an acid or an alkali are added to it . To be able to add a strong acid or base to a solution without causing a large change in the pH, we need to create a buffer solution. A buffer solution contains both a weak acid (HA) and its conjugate base (A - ).

27. Consider the equation for the ionization of acetic acid: HC2H3O2( aq ) H+( aq ) + C2H3o2-( aq ) Where the slight ionization is indicated by a double arrow. If we add sodium acetate to a solution of acetic acid, we are adding the conjugate base of acetic acid- That is, acetate ion thus forming a buffer solution. If we add a little strong base to this solution, it will react with the weak acid: OH - + HC 2 H 3 O 2 H 2 0 + C 2 H 3 O 2 -

28. Do you see that the solution no longer contains the strong base? Instead, it has a little more weak base and a little less weak acid that it did before the reaction. The pH remains very nearly constant. Likewise, if a little strong acid is added it will react with the weak base: H + + C 2 H 3 2 - HC 2 H 3 O 2 The strong acid is consumed, a weak acid takes place, and the solution pH increases slightly.

29. SELF-ASSESMENT QUESTIONS

30. Which of the following pairs is a conjugate acid-base pair ? A.CH 3 COOH and OH - B. HCN and CN - C. HCN and OH - D. HCI and OH -

31. 2. Which of the following is not paired with its Bronsted -Lowry conjugate base or conjugate acid? CH3COO - /Ch 3 COOH F - /HF H 2 O/H 3 O + NH 3 /H 3 O +

32. 3. A buffer solution is made from formic acid (HCOOH) and sodium formate ( HCOONa ). Added acid will react with HCOO HCOOH Na + OH

33. Which of the following pairs could be combines to make a buffer? C 6 H 5 COOH and C 6 H 5 COONa HCI and NaCI HCI and NaOH NH 3 and NO 3

34. Thank you……….