Strong versus Weak Acids and Bases

Transcription

1 Strong versus Weak Acids and Bases What they are and how to recognize them. control home - starts the show over right arrow (º) advances to the next slide left arrow (») goes back to the previous slide James B. Condon, 2007, all rights reserved Backgrounds and some graphic copyrighted by Corel Corporation -used by permission.

2 A strong acid or a strong base when dissolved in water forms mostly ions. For example:

3 A strong acid or a strong base when dissolved in water forms mostly ions. For example: HCl(aq) + H 2 O º H 3 O + + Cl less than 1 % more than 99 % on this side is on this side This would be considered a strong acid.

4 A strong acid or a strong base when dissolved in water forms mostly ions. For example: NaOH º Na + + OH So long as there is no solid NaOH left all of the base is in the ionized form. This would be considered a strong base.

5 A strong acid or a strong base when dissolved in water forms mostly ions. For example: HF(aq) + H 2 O º H 3 O + + F more than 99 % less than 1 % on this side is on this side This would be considered a weak acid.

6 A strong acid or a strong base when dissolved in water forms mostly ions. For example: NH 3 (aq) + H 2 O º NH OH more than 99 % less than 1 % on this side is on this side This would be considered a weak base.

7 A strong acid or a strong base when dissolved in water forms mostly ions. For example: Fe(OH) 2 (s) + H 2 O º Fe OH for this hydroxide most remains a solid on this side very little dissolves to form ions on this side This would be considered a weak base because of the slight solubility of the hydroxide.

8 How to tell what type of acid or base is present. A logical question is: how does one tell if one has a strong or weak acid or a strong, weak or slightly soluble base?

9 How to tell what type of acid or base is present. 1) The acids are classified as: P ternary mineral acids P binary mineral acids P organic (carboxylic) acids

10 How to tell what type of acid or base is present. 1) The acids are classified as: P ternary mineral acids P binary mineral acids P organic (carboxylic) acids 2) The bases are classified as: P strong soluble bases (hydroxides) P slightly soluble bases (hydroxides) P weak soluble bases

11 Strong ternary acids Step 1: From the polyion chart (You have learned it, haven t you? ClO ClO 2 BrO BrO 2 IO IO SO 2 SO 3 NO 2 ClO 3 BrO 3 IO 3 2 SO 4 NO 3 ClO 4 BrO 4 IO 4 PO 2 3 PO 3 3 PO 4 3 CO 3 2

12 Strong ternary acids Step 2: replace each with and H in front. HClO HClO 2 HClO 3 HClO 4 HBrO HBrO 2 HBrO 3 HBrO 4 HIO HIO 2 HIO 3 HIO 4 H 2 SO 2 H 2 SO 3 H 2 SO 4 HNO HNO 3 H 3 PO 2 H 3 PO 3 H 3 PO 4 H 2 CO 3 These are the common ternary acids.

13 Strong ternary acids Step 3: In the upper right corner are the strong ternary acids HClO HClO 2 HClO 3 HClO 4 HBrO HBrO 2 HBrO 3 HBrO 4 HIO HIO 2 HIO 3 HIO 4 H 2 SO 2 H 2 SO 3 H 2 SO 4 HNO HNO 3 H 3 PO 2 H 3 PO 3 H 3 PO 4 H 2 CO 3

14 Strong binary acids Step 1: The binary acids (composed of two different atoms) can be discerned from the periodic chart. Look at groups 16 (VI on right) and 17 (VII on right): N O F Ne P S Cl Ar As Se Br Kr Sb Sb I Xe

15 Strong binary acids Step 2: Place one H in front of the group 17 and H 2 in front of group 16: H 2 S H 2 Se HF HCl HBr HI These are the binary mineral acids.

16 Strong binary acids Step 3: The acid in group 17, HCl on down are the strong binary mineral acids: H 2 S H 2 Se These are the binary mineral acids. HF HCl HBr HI Strong Acids

17 Summary of the common mineral acids: HClO HClO 2 HClO 3 HClO 4 HBrO HBrO 2 HBrO 3 HBrO 4 HIO HIO 2 HIO 3 HIO 4 H 2 SO 2 H 2 SO 3 H 2 SO 4 HNO HNO 3 H 2 S H 2 Se HF HCl HBr HI Strong Acids H 3 PO 2 H 3 PO 3 H 3 PO 4 H 2 CO 3 All other common mineral acids that are not delimitated by the red lines above are weak.

18 Organic (or carboxylic) acid Step 1: Any compound that has -COOH is an acid. It is an organic acid and -COOH is called the carboxylic acid group. Examples: CH 3 COOH - acetic acid C 2 H 5 COOH - propionic acid HOOCCOOH - oxalic acid (notice that the first COOH had to be written backwards.) These are all weak acids.

19 Strong bases (or soluble hydroxides) Step 1: A compound with a metal ion followed by one or more OHs is a base. These are the metal hydroxides.

20 Strong bases (or soluble hydroxides) Step 2: These metal hydroxides are further classified a strong bases or slightly soluble bases. How does one know which is which? Looking at the period chart, all metals of group I and metals of group II from Ca on down form the strong bases. LiOH NaOH KOH Ca(OH) 2 RbOH Sr(OH) 2 CsOH Ba(OH) 2 FrOH Ra(OH) 2 All other metal hydroxides are slightly soluble including Mg(OH) 2.

21 Weak slightly soluble bases (or slightly soluble hydroxides) Step 2: All other metal hydroxides are slightly soluble and by vertue of this are weak. Examples: Mg(OH) 2, Fe(OH) 2, Zn(OH) 2, etc. but not LiOH NaOH KOH Ca(OH) 2 RbOH Sr(OH) 2 CsOH Ba(OH) 2 FrOH Ra(OH) 2

22 Weak soluble bases The final class is the weak soluble bases: A compound that has nitrogen in it (except for the acids HNO 2 and HNO 3 ) is a base. These are the weak soluble bases.

23 Weak soluble bases The final class is the weak soluble bases: A compound that has nitrogen in it (except for the acids HNO 2 and HNO 3 ) is a base. These are the weak soluble bases. NH 3 - is a weak soluble base CH 3 NH 2 - is a weak soluble base

24 Out of the jumble of chemicals you should now be able to recognize what is:! A strong acid! A weak acid! A strong base! A slightly soluble hydroxide! A weak soluble base These will be applicable to the next topics - overall reactions versus net ionic reactions and Brønsted-Lowry acids and bases.

25 Strong versus Weak Acids and Bases What they are and how to recognize them. THE END control home - starts the show over right arrow (º) advances to the next slide left arrow (») goes back to the previous slide