acid : a substance which base : a substance which H +

Transcription

1 4.4. BronstedLowry Theory of A&B acid : a substance which base : a substance which H Typical BronstedLowry AB rxn eqn: eg1) NH 3 H 2 O NH 4 base acid OH eg2) CH 3 COOH H 2 O CH 3 COO H 3 O H 2 O an acid and a base????? H 2 O is said to be amphiprotic Amphiprotic substance: a substance which can If a substance acts as an acid around a stronger base, or a base around a stronger acid, it is an AMPHIPROTIC substance. (eg. H 2 O Note: every BronstedLowry rxn there is an acid and a base on both sides of the rxn eqn N 2 H 5 S 2 N 2 H 4 HS A B B* A* B* & A* are acids and bases for the reverse reaction Acids classified as: Monoprotic releases one proton. Diprotic releases two protons. Triprotic releases three protons. Polyprotic releases many protons Bases classified as: Monobasic accepts one proton. Dibasic accepts two protons. Tribasic accepts three protons. Polybasic accepts many protons Polyprotic acids release H ions : step 1 step 2 step 3 H 3 PO 4 H 2 PO 4 2 HPO 4 3 PO 4 If a substance has a charge and still has an easily removable then the substance is Also, acids which have lost one proton are amphiprotic H 2 S HS S 2 Hebden #1114 1

2 4.5 Conjugate Acids and Bases Conjugate acidbase pair: the pair of molecules in a rxn eqn that. Conjugate acid: the extra proton Conjugate base: the extra proton BronstedLowry eqns have two conjugate AB pairs: eg1) base 2 acid 2 HF H 2 O F H 3 O acid 1 base 1 Conjugate Pair Conjugate A Conjugate B eg1) HF and F H 3 O and H 2 O What is the conjugate B for the following compounds? NH 4 HCO 3 H 2 PO 4 What is the conjugate A for the following compounds? CH 3 COO OH HC 2 O 4 Connect and label the conjugate pairs: a) HCl H 2 O(l) H 3 O Cl b) H 2 SO 4 H 2 O(l) H 3 O HSO 4 Hebden #16, 19 Summary for a BronstedLowry AB rxn: Conjugate Acid Conjugate Base Conjugate Base Form of A form of B form of A Conjugate Acid form of B 2

3 4.6. Strong and Weak Acids and Bases Recall: Concentrated = molarity (M) (mol/l) and Dilute = molarity BUT in chemistry And Strong acid acid Weak acid acid Strong Acid (SA) or Strong Base (SB): 100%: Eg: NaOH (s) Na OH HCl (g) H Cl Weak Acid (WA) or Weak Base (WB): than 100% dissociated: Eg: NH 3 H 2 O (l) NH 4 OH HF H 2 O (l) H 3 O F not complete dissociation eqb arrows Characteristics of Acids and Bases: are STRONG if they: are WEAK if they: dissociate in water do dissociate completely in water have an undefined, or very Ka value have a Ka value have dissociation rxn ( ) have an dissociation rxn ( ) Examples of STRONG Acids (p334): Examples of STRONG Bases (p. 122): PRACTICE: Describe the acid below as: a)monoprotic, b) diprotic, c) triprotic d) strong, e) weak H 2 SO 4 H HSO 4 HSO 4 H SO 4 2 metal hydroxides Which is a stronger acid? HNO 2 _ HPO 4 2 Which is a stronger base? HC 2 O 4 _ CN 3

4 6. The Levelling Effect Strong acids are 100% dissociated in sol n. are all equiv. to H 3 O sol ns of same conc. eg) 1M HI produces 1M H 3 O and 1M I 1M HClO 4 produces 1M H 3 O and 1M ClO 4 Strengths are leveled Similarly, the strong bases are 100% dissociated in sol n. Therefore, are all equiv. to OH sol ns of that conc eg) 1M KOH produces 1M OH and 1M K 1M NaOH produces 1M OH and 1M Na Strengths are leveled Weaker A&B dissociate to different extents, so have unique strengths. Hebden #

5 4.4. BronstedLowry Theory of A&B acid : a substance which donates a proton base : a substance which accepts a proton H Typical BronstedLowry AB rxn eqn: eg1) NH 3 H 2 O NH 4 base acid OH eg2) CH 3 COOH H 2 O CH 3 COO H 3 O acid base H 2 O an acid and a base????? H 2 O is said to be amphiprotic Amphiprotic substance: a substance which can act as either an acid or a base If a substance acts as an acid around a stronger base, or a base around a stronger acid, it is an AMPHIPROTIC substance. (eg. H 2 O Note: every BronstedLowry rxn there is an acid and a base on both sides of the rxn eqn N 2 H 5 S 2 N 2 H 4 HS A B B* A* B* & A* are acids and bases for the reverse reaction Acids classified as: Monoprotic releases one proton. Diprotic releases two protons. Triprotic releases three protons. Polyprotic releases many protons Bases classified as: Monobasic accepts one proton. Dibasic accepts two protons. Tribasic accepts three protons. Polybasic accepts many protons Polyprotic acids release H ions one at a time: step 1 step 2 step 3 H 3 PO 4 H 2 PO 4 2 HPO 4 3 PO 4 If a substance has a negative charge and still has an easily removable hydrogen then the substance is amphiprotic Also, polyprotic acids which have lost one proton are amphiprotic H 2 S HS S 2 Hebden #1114 5

6 4.5 Conjugate Acids and Bases Conjugate acidbase pair: the pair of molecules in a rxn eqn that differ by one proton. Conjugate acid: has the extra proton Conjugate base: lacks the extra proton BronstedLowry eqns have two conjugate AB pairs: eg1) base 2 acid 2 HF H 2 O F H 3 O acid 1 base 1 Conjugate Pair Conjugate A Conjugate B eg1) HF and F HF F H 3 O and H 2 O H 3 O H 2 O What is the conjugate B for the following compounds? NH 4 NH 3 HCO 3 CO 3 2 H 2 PO 4 HPO 4 2 What is the conjugate A for the following compounds? CH 3 COO CH 3 COOH OH H 2 O HC 2 O 4 H 2 C 2 O 4 Connect and label the conjugate pairs: a) HCl H 2 O(l) H 3 O Cl c) H 2 SO 4 H 2 O(l) H 3 O HSO 4 Hebden #16, 19 Summary for a BronstedLowry AB rxn: Conjugate Acid Conjugate Base Conjugate Base Form of A form of B form of A Conjugate Acid form of B 6

7 4.6. Strong and Weak Acids and Bases Recall: concentrated = high molarity (M) (mol/l) and Dilute = low molarity BUT in chemistry And Strong acid concentrated acid Weak acid dilute acid Strong Acid (SA) or Strong Base (SB): dissociate 100%: Eg: NaOH (s) Na OH HCl (g) H Cl Weak Acid (WA) or Weak Base (WB): less than 100% dissociated: Eg: NH 3 H 2 O (l) NH 4 OH HF H 2 O (l) H 3 O F not complete dissociation eqb arrows Characteristics of Acids and Bases: are STRONG if they: dissociate completely in water have an undefined, or very large Ka value have complete dissociation rxn ( ) are WEAK if they: do NOT dissociate completely in water have a defined Ka value have an equilib dissociation rxn ( ) Examples of STRONG Acids (p334): HClO 4, HI, HBr, HCl, HNO 3, H 2 SO 4 Examples of STRONG Bases (p. 122): NaOH, KOH, Mg(OH) 2,Ca(OH) 2,Fe(OH) 3, Zn(OH) 2 PRACTICE: Describe the acid below as: a)monoprotic, b) diprotic, c) triprotic d) strong, e) weak metal hydroxides H 2 SO 4 H HSO 4 b & d HSO 4 H SO 4 2 a & e Which is a stronger acid? HNO 2 > HPO 4 2 Which is a stronger base? HC 2 O 4 < CN 7

8 6. The Levelling Effect Strong acids are 100% dissociated in sol n. are all equiv. to H 3 O sol ns of same conc. eg) 1M HI produces 1M H 3 O and 1M I 1M HClO 4 produces 1M H 3 O and 1M ClO 4 Strengths are leveled Similarly, the strong bases are 100% dissociated in sol n. Therefore, are all equiv. to OH sol ns of that conc eg) 1M KOH produces 1M OH and 1M K 1M NaOH produces 1M OH and 1M Na Strengths are leveled Weaker A&B dissociate to different extents, so have unique strengths. Hebden #