SQSM-06 - Chapter 6 Acids and Bases 1. 3. Define a...

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Chapter 6 Acids and Bases 6-1 1. Define a conjugate acid-base pair. A conjugate acid-base pair is a weak acid and a weak base that differ by only one proton. 3. Indicate the conjugate base for each of the following: a) OH 1- O 2- b) H 2 O 2 HO 2 1- c) H 2 PO 4 1- HPO 4 2- d) H 3 O 1+ H 2 O e) H 2 SO 3 HSO 3 1- 5. Are all Brønsted bases also Lewis bases? Explain. Yes! Both types of base must have a lone pair to form a covalent bond to an acid. 7. Which of the following are Brønsted bases? a) NaOH yes b) NaCl not in water c) CH 3 OH no d) KCN yes e) KH 2 PO 4 yes 9. Explain how the reaction Ag 1+ + Cl 1- AgCl is a Lewis acid-base reaction. Is it a Brønsted acid-base reaction? Ag 1+ is a Lewis acid that accepts a lone pair on Cl 1- to form a bond that has substantial covalent character. It is not a Brønsted acid-base reaction because no proton is transferred. 11. Write Brønsted acid-base reactions or indicate no reaction if K << 1. a) Aqueous sodium sulfate is added to hydrobromic acid. SO 4 2- + H 3 O 1+ HSO 4 1- + H 2 O (weak base + strong acid) b) Aqueous NH 4 Cl and aqueous KF are mixed. NH 4 1+ + F 1- no reaction (HF, the produced acid, is much stronger than the reacting acid) c) Aqueous sodium cyanide is added a large excess of sulfurous acid. CN 1- + H 2 SO 3 HSO 3 1- + HCN d) Acetic acid and aqueous sodium hypochlorite are mixed. CH 3 COOH + OCl 1- CH 3 COO 1- + HOCl (produced acid is weaker than reacting acid) e) Hydrogen sulfide is bubbled into water. H 2 S + H 2 O no reaction (this is the K a reaction of a weak acid and the extent is very small) 13. Explain why HCl is a strong acid, but HF is a weak acid. The HF bond is much stronger than the HCl bond. 15. What is the predominate phosphorus containing species in a solution prepared by adding some phosphoric acid to a solution containing a large excess of ammonia? NH 3 is strong enough to remove a proton from H 3 PO 4 and H 2 PO 4 1- , but it is too weak to react with HPO 4 2- . Therefore, the predominant phosphorus containing species is HPO 4 2- . 17. What is an autoionization reaction? Write the chemical equation for the autoionization of ammonia. H 3 O 1+ and OH 1- are the strongest acid and base that can exist in aqueous solutions because water reacts with any acids or bases that are stronger than these acids. This is known as the leveling effect . What are the strongest acid and base that can exist in liquid ammonia? Autoionization reactions are reactions between two identical molecules that produce ion. The autoionization of ammonia is NH 3 + NH 3 NH 2 1- + NH 4 1+ . The strongest acid that can exist in liquid ammonia is NH 4 1+ and the strongest base is NH 2 1- . 19. Determine the hydronium and hydroxide ion concentrations in the following solutions: a) detergent; pH = 10.3 [H 3 O 1+ ] = 5 x 10 -11 M [OH - ] = 2 x 10 -4 M b) stomach acid; pH = 2.4 [H 3 O 1+ ] = 4 x 10 -3 M [OH - ] = 3 x 10 -12 M c) beer; pH = 4.2 [H 3 O 1+ ] =6 x 10 -5 M [OH - ] = 2 x 10 -10 M d) milk of magnesia; pH = 10.5 [H 3 O 1+ ] =3 x 10 -11 M [OH - ] = 3 x 10 -4 M 21. Determine the pK a of each of the following acids: a) tartaric acid H 2 C 4 H 4 O 6 K a = 1.0 x 10 -3 pK a = -log (1.0 x 10 -3 ) = 3.00 b) boric acid H 3 BO 3 K a = 5.8
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This note was uploaded on 01/27/2011 for the course CHEM 201 taught by Professor Wilson during the Spring '10 term at N.C. Central.

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SQSM-06 - Chapter 6 Acids and Bases 1. 3. Define a...

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