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Finalexam111111so9elab

Finalexam111111so9elab - E xam CH101 001 8:00 am 11:00 am...

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E xam CH101 – 001 April 27 2009, 8:00 am- 11:00 am Name: ID number: 111111
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Hand graded questions: Question H1 The solubility product of a solid hydroxide M(OH) 2 in water at room temperature is: K sp = 1.0 x 10 -18 . H1.1 Write a balanced equation for the solubility equilibrium [2pts] M(OH) 2(s) M 2+ (aq) + 2OH - (aq) H1.2Write the proper expression for the K sp [3pts] K sp =[M 2+ ][OH-] 2
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H1.3 Water always contains some hydroxyl ions. Calculate the [OH - ] that can be present in an (equilibrated) aqueous solution of the metal nitrate M(NO 3 ) 2 with [M 2+ ] = 10 -2 M. [6pts] 1.0 x 10 -18 .= [10 -2 ]. x 2 x =sqrt(10 -16 ) = 10 -8 M for 222222 numbers are different 1pt less for no units; check for consistency with H1.2 H1.4 What is the pH of such a solution? [1 pt] pOH=8 pH=6
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Question H2 Cyanogen has the molecular formula (CN) 2 . The molecule consists of two CN groups that could be linked to each other in three different ways. (CNNC, NCCN, NCNC) H2.1For all three possible ways of linking, compute and write out the Lewis structure(s). [4pt] ER = 32 VE= 18 TP= 9 _____________ - 14 SP= 7 _____________ - LP= 2 | C N -- N C | (-1) (+ 1) (+ 1) (-1) | N C -- C N | all zero | N C -- N C | + 1 -1
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H2.2 Show all lone pairs and –if any- all resonance structures. NONE [3pts] (No resonance because that lead to pentavalent C’s) H2.3 Add the formal charges on the atoms. [3pts] H2.4 Which of the three possible molecules is the most likely (i.e. most stable) one? (State why) [2pts] The middle one |N C-C N| because it has not formal charges
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Question H3 Nickel (Ni) is a fairly noble metal. It is used for many systems where corrosion is undesirable. In contact with carbon monoxide (CO) gas however, it corrodes quickly to form the gaseous nickel carbonyl Ni(CO) 4 molecule. H3.1 Write a balanced chemical equation for the corrosion reaction. The reaction of nickel with carbon monoxide is extensive enough that it can be considered to go to completion. Make sure to indicate the state in which each chemical occurs. [2 pts] Ni(s) + 4CO(g) Ni(CO) 4 (g) H3.2 The reaction is spontaneous at room temperature. What are the signs of the enthalpy and the entropy change? [4 pts] Entropy decreases because the number of gas molecule decreases so S = negative, this makes -T S positive. The reaction is spontaneous so G = H – 300. S is negative. This means that H must be large and negative to overcome the -T S term H3.3 When a gas stream containing nickel carbonyl is led over a hot tungsten wire, nickel metal is deposited on the wire. Can you explain this observation? [3 pts]
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