#chem 162-2008 homework 6th week

#Chem 162-2008 homework 6th week
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(Note that my algebra-solving calculator requires my setting up equations involving “,X” and lots of parentheses. Ignore these equations.) Brønsted-Lowry Acids and Bases *21. For each of the following pairs, write an equation in which the first species given acts as a Brø nsted- Lowry acid. (a) HIO 4 , NH 3 (b) H 2 O, NH 2 OH (c) H 3 BO 3 , NH 2 - (a) HIO 4 + NH 3 IO 4 - + NH 4 + (b) H 2 O + NH 2 OH OH - + NH 3 OH + (c) H 3 BO 3 + NH 2 - H 2 BO 3 - + NH 3 *23. For each of the following, identify the conjugate acid-base pairs. (a) HOClO 3 + H 2 O H 3 O + + OClO 2 - (b) HSeO 4 - + NH 3 NH 4 + + SeO 4 2- (c) HCO 3 - + OH - CO 3 2- + H 2 O (d) C 5 H 5 NH + + H 2 O C 5 H 5 N + H 3 O + (a) HOClO 3 and OClO 2 - is a conjugate acid-base pair. H 2 O and H 3 O + is a conjugate acid-base pair. (b) HSeO 4 - and SeO 4 2- is a conjugate acid-base pair. NH 3 and NH 4 + is a conjugate acid-base pair. (c) HCO 3 - and CO 3 2- is a conjugate acid-base pair. OH - and H 2 O is a conjugate acid-base pair. (d) C 5 H 5 NH + and C 5 H 5 N is a conjugate acid-base pair. H 2 O and H 3 O + is a conjugate acid-base pair. *25. Identify the species that is amphiprotic, and write two equations for its reaction with H 2 O(l) that illustrate its amphiprotic character: HI, H 2 PO 4 - , NH 4 + , H 2 CO 3 , CO 3 2- . HI is not amphoteric because it can lose a proton, but can’t accept a proton (due to the I - being an extremely weak base). H 2 PO 4 - is amphoteric. H 2 PO 4 - + H 2 O HPO 4 2- + H 3 O +
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H 2 PO 4 - + H 2 O H 3 PO 4 + OH - NH 4 + isn’t amphoteric, because it can lose a proton to become NH 3 , but it has no electrons available to gain another proton becoming NH 5 2+ . H 2 CO 3 is not amphoteric, because it can lose a proton, but it cannot gain a proton to become H 3 CO 3 + . CO 3 2- is not amphoteric, because it can gain a proton, but it has no proton to lose. Molecular Structure and the Strengths of Acids and Bases *31. Identify the stronger acid in each pair, and explain your choice. (a) H 2 S or H 2 Se (b) HClO 3 or HIO 3 (c) H 3 AsO 4 or H 2 PO 4 - (d) H 2 Se or HBr (e) HN 3 or HCN (f) HNO 3 or HSO 4 - (a) H 2 Se is stronger, because in vertical groups (binary groups) the lower acid has a weaker H-X bond, which makes it a stronger acid. (b) HClO 3 is a stronger acid. The strength of the H-O bonds are approximately equal, but the greater electronegativity of the Cl vs the I makes HClO 3 a stronger acid. (c) H 3 AsO 4 is a stronger acid, because removing another hydrogen from H 2 PO 4 - results in the formation of a doubly negatively charged substance, which doesn’t form easily due to it being high energy.
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