Chap16-Part5

Chap16-Part5 - Combined Effects: Some General Rules 1) An...

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Combined Effects: Some General Rules 1) An anion that is the conjugate base of a strong acid will not affect the pH. Example: HCl + H 2 O H 3 O + + Cl - The reaction is essentially irreversible. Cl - has no effect. 2) An anion that is the conjugate base of a weak acid will increase the pH. Example: HCN + H 2 O CN - + H 3 O + CN - removes protons, causing a decrease in [H + ] and a pH increase. 1
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Combined Effects: Some General Rules 3) A cation that is the conjugate acid of a weak base will decrease the pH. Example: CH 3 NH 3 + + H 2 O CH 3 NH 2 + H 3 O + CH 3 NH 3 + generates protons, causing an increase in [H + ] and a pH decrease. 4) The cations of group 1A and heavier members of group 2A will not affect the pH. Example: NaOH Na + + OH - The reaction is essentially irreversible. Na + has no effect. 2
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Combined Effects: Some General Rules 5) Other metal ions will decrease the pH. 6) When a solution contains equal concentrations of both the conjugate base of a weak acid and the conjugate acid of a weak base, the ion with the larger equilibrium constant, K a or K b , will have the greater influence on the pH. 3
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Predict whether aqueous solutions of the following compounds are acidic, basic or neutral. a) CrBr 3 c) LiI e) K 3 PO 4 d) (CH 3 NH 3 )Cl 4
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CrBr 3 CrBr 3 Cr 3+ + 3 Br - Br - will not affect the pH as it an anion of a strong acid. Cr 3+ is a metal ion (group 6B) not belonging to group 1A or 2A and will cause a pH decrease. The solution will be
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This note was uploaded on 09/13/2011 for the course CHEM 102 taught by Professor Todd during the Spring '08 term at UNC.

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Chap16-Part5 - Combined Effects: Some General Rules 1) An...

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