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1. Consider an amphoteric hydroxide, M(OH)2(s), where M is a generic metal.

M(OH)2(s)<-> M^2+(aq)+ 2OH-              Ksp=8x10^ -16

M(OH)2(s)+2OH- <->M(OH)4^2-             Kf =0.03

 Estimate the solubility of M(OH)2 in a solution buffered at pH =7.0

 

2. The pKb values for the dibasic base B are pKb1=2.10 and PKb2=7.79. Calculate the pH at each of the following points in the titration of 50 ml of a 0.65 M B with 0.65 M HCl

a) before addition of any HCl

b) after addition of 25 ml of HCl

c) after addition of 50 ml of HCl

d) after addition of 75 ml of HCl

e) after addition of 100 ml of HCl

 

3. You prepare a buffer solution from 10 ml of 0.100M MOPS( 3- morpholinopropane- 1- sulfonic acid) and 10 ml of 0.086 M NaOH. 

MOPS Ka = 6.3x 10^-8.     Lidocaine Kb= 8.7 x 10^-7

next you add 1 ml of 4.87x 10^-6 M lidocaine to the this mixture

Denoting Lidocaine as L, calculate the fraction of lidocaine present inthe form LH+

 

4. Phosphoric acid is a triprotic acid with the following pKa values

pKa1=2.148  pKa2= 7.198    PKa3=12.375

you wish to prepare 1L of a 0.0400 M phosphate buffer at pH 7.780. To do this, you choose to mix the two salt forms involved in the second ionisation, NaH2PO4 and Na2HPO4, in a 1L volumetric flask and add water to the mark. What mass of each salt will you add to the mixture? 

 Mass of NaH2PO4 ?

mass of Na2HPO4?

what other combination of phosporic acid and / or its salts could be mixed to prepare this buffer?

check all that apply

a. H3PO4 and NaH2PO4

b. H3PO4 and Na2HPO4

c. H3PO4 and Na3PO4

d. NaH2PO4 and Na3PO4

e.Na2HPO4 and Na3PO4

 

5. You weigh a sample of potassium hydroxide phthalate(KHP) to prepare a primary standard for a titration . You later discover that the KHP was contaminated with sugar. To determine the amount of KHP in the mixture , you take a 6.906g of the mixture and make a 100 ml solution. You then titrate 10 ml of this solution with a 0.1788M sodium hydroxide solution. You find that 15.17 ml of the NaOH solution is needed to reach the endpoint. What is the percent by mass of KHP in the mixture?

 

6.How many moles of solid Mg(OH) 2 should you add to 200 ml of 0.15M lactic acid solution to produce pH 4.0 buffer?

 

 

 

 

 

 

 

 

    • Posted: 5 years ago
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