1)The equation for the conditional formation constant of an EDTA-metal complex i
ID: 485550 • Letter: 1
Question
1)The equation for the conditional formation constant of an EDTA-metal complex ion is: Kf' = Kf·y4-= [MYn-4] / [Mn+] [Y4-]. The presence in the solution of an auxiliary complexing agent such as tartrate ion, at a given concentration of Y4- would:
lower [Mn+].
have no effect on [MYn-4].
increase [MYn-4].
Increase Mn+
2)EDTA titration of Al3+ at pH 7.00 need to be done with back titration. Why is direct titration not workable?
Al(OH)3 precipitates at pH 7.00 with presence of EDTA.
Al3+ reacts too slowly with EDTA.
Al3+ blocks the indicator used.
Al(EDTA)- is not stable.
3)Calculate the pCu for the titration of 50 mL of 0.020 M Cu2+ at pH 5 after the addition of 10 mL of 0.040 M EDTA.
1.00
2.00
3.00
4.00
4)Which of the following can not be used as auxiliary complexing agent?
Ammonia (NH3)
Tartrate (-OOC-CH(OH)-CH(OH)-COO)
Citrate (C(OH)(CH2COOH)2COOH)
Methanol (CH3OH)
5)How many milliliters of 0.0300 M EDTA are required to react with 30.0 mL of 0.0100 M Al3+?
10.0mL
30.0mL
3.33mL
6.67mL
6)A 100.0 mL aliquot of 0.100 M weak base B (pKb=5.00) was titrated with 1.00 M HClO4. Find the pH after adding 6 mL acid.
8.82
9.00
5.00
9.35
7) 200.0mL aliquot of 0.100M diprotic acid H2A (pK1=3.00, pK2=7.00) was titrated with 1.00M NaOH. How much NaOH is added when solution pH=5.00?
10mL
20mL
30mL
40mL
A.lower [Mn+].
B.have no effect on [MYn-4].
C.increase [MYn-4].
D.Increase Mn+
Explanation / Answer
1) Have increases increase [MYn-4], because role of auilary bind to a metal strongly enough to prevent metal hydroxide from precipitating, but weakly enough to give up the metal when EDTA is added.
2) as Al(OH)3 precipitates at pH 7.00 with presence of EDTA hence it is necessory to do back titration.
3) initial moles of Cu =50*10-3=0.05 mmole
Added moles of EDTA=10*10-3=0.01 mmole
Cu EDTA=0.05/60=8.33*10-4
Excess EDTA=0.01/60=1.66*10-4
pCu=4
4) Methanol not used as auilary titration agent.
5) N1 * V1=N2 * V2
0.03* V1=0.01* 30=10.0 mL
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