1 NH 3 H 3 O NH 4 H 2 O 2 NH 3 H 2 O NH 4 OH 3 NH 4 Clsolid H 2 O NH 4 Cl 4 NH

1 nh 3 h 3 o nh 4 h 2 o 2 nh 3 h 2 o nh 4 oh 3 nh 4

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1. NH 3 + H 3 O + NH + 4 + H 2 O 2. NH 3 + H 2 O NH 4 + + OH - 3. NH 4 Cl(solid) + H 2 O NH + 4 + Cl - 4. NH + 4 + H 2 O NH 3 + H 3 O + correct 5. The term is misleading, because the am- monium ion is not an acid. 6. NH + 4 + OH - NH 3 + H 2 O Explanation: 007 1.0points The generic equation Base - + H 2 O HBase + OH - can be used to account for the pH of which salt? 1. NH 3 2. KClO 3 3. NaHCOO correct 4. BaBr 2 5. ZnCl 2 Explanation: This hydrolysis equation applies only to anions from weak acids. HClO 3 , HBr and HCl are strong acids. NH 3 is a weak base. 008 1.0points What is the pH of a solution made by mixing 0.05 mol of NaCN with enough water to make a liter of solution? K a for HCN is 4 . 9 × 10 - 10 and K w = 1 × 10 - 14 . Correct answer: 11 . 0044. Explanation: [OH - ] = radicalbig K b C = radicalbigg K w K a C = radicalBigg 1 × 10 - 14 4 . 9 × 10 - 10 (0 . 05) = 0 . 00101015 [H + ] = K w [OH - ] = 1 × 10 - 14 0 . 00101015 = 9 . 89949 × 10 - 12 pH = - log[H + ] = - log(9 . 89949 × 10 - 12 ) = 11 . 0044 009 1.0points What is the pH of a 0 . 19 M solution of hy- droxylammonium bromide (NH 3 OHBr)? K b for hydroxylamine (NH 2 OH) is 6 . 6 × 10 - 9 . 1. 3.510 2. 9.549 3. 18.45 4. 3.270 correct 5. 4.451 6. 3.120 7. 3.400 8. 3.030 Explanation: M NH 3 OHBr = 0 . 19 M K b =6 . 6 × 10 - 9 It’s a salt of a weak base (BHX). This means you need a K a for the weak acid BH + . Use
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avila (gsa368) – Homework 7 – fakhreddine – (50415) 3 K a = K w K b and you’ll get the K a = 1 . 51515 × 10 - 6 . You CAN use the approximation for the equilibrium which means that [H + ] = radicalbig K a · C BH + = 0 . 000536543 M pH = - log(0 . 000536543) = 3 . 2704 010 1.0points What is the pH of a 0 . 3 M solution of pyri- dinium chloride (C 5 H 5 NHCl)? K b for pyri- dine (C 5 H 5 N) is 1 . 5 × 10 - 9 . 1. 9.327 2. 2.849 correct 3. 2.699 4. 5.176 5. 8.824 6. 4.673 7. 2.609 8. 7.000 9. 3.219 10. 2.979 Explanation: M C 5 H 5 NHCl = 0 . 3 M K b = 1 . 5 × 10 - 9 It’s a salt of a weak base (BHX). This means you need a K a for the weak acid BH + : K a = K w K b = 1 . 0 × 10 - 14 1 . 5 × 10 - 9 = 6 . 66667 × 10 - 6
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