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Suppose that the diffusion current in a polarogram for reduction of Cd2+at a mercury electrode is14μ´¡If the solution containsof 25mLof0.50mMCd2+what percentage ofCd2+is reduced in the 3.4 min required to scan from-0.6to-1.2V?

Short Answer

Expert verified

The percentage of cadmium ion which can be reduced in polarogram is 0.12%.

Step by step solution

01

Define Molarity.

At any point in an electric circuit the charge is the product of current I and time.

q = l . t

The number of moles of electronsreactreacts in a reaction with a given timeis

Reacted moles=l.tnF

02

 Determine the Molarity of Cadmium.

Given,

l=14×10-6At=3.4min=204sec

Number of moles of electrons is given as

role="math" =(14×10-6A)(204sec)96485C/mol=2.9×10-8mol

The reduced cadmium ion is calculated as =2.9×10-8mol2=1.48×10-8mol

The 25mL of cadmium ions with has =25×0.5×10-31000=1.25×10-5moles

Reduced \% of cadmium ions=1.48×10-8moles1.25×10-5moles×100

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Most popular questions from this chapter

(a) At what cathode potential will Sb(s)deposition commence from 0.010MSbO+solution at pH 0.00? Express this potential versus S.H.E. and versusAg|AgCI. (Disregard overpotential, about which you have no information.)

SbO++2H++3e-→Sb(s)+H2OE°=0.208V

(b) What percentage of0.10MCu2+could be reduced electrolytically to Cu(s)before0.010MSbO+in the same solution begins to be reduced at pH 0.00?

Write the chemical reactions that show that 1 mol of I2 is required for 1 mol of H2O in a Karl Fischer titration.

cd2+was used as an internal standard in the analysis of Pb2+by square wave polarography. Cd2+gives a reduction wave at -0.60 V and Pb2+gives a reduction wave at –0.40 V. It was first verified that the ratio of peak heights is proportional to the ratio of concentrations over the whole range employed in the experiment. Here are results for known and unknown mixtures:

The unknown mixture was prepared by mixing 25.00(±0.05)mLof unknown (containing only Pb2+) plus 10.00(±0.05)mLof 3.23(±0.01)×10-4MCd2+and diluting to 50.00(±0.05)mL.

(a) Disregarding uncertainties, find [Pb2+]in the undiluted unknown.

(b) Find the absolute uncertainty for the answer to part (a).

Consider the following electrolysis reactions.

Cathode:H2O(l)+e-⇌12H2(g,1.0bar)+OH-(aq,0.10M)

Anode:Br-(aq,0.10M)⇌12Br2(l)+e-

  1. Calculate the voltage needed to drive the net reaction if current is negligible.
  2. Suppose that the cell has a resistance of2.0Ω and a current of 100 mA. How much voltage is needed to overcome the cell resistance? This is the ohmic potential.
  3. Suppose that the anode reaction has an overpotential of 0.20 V and that the cathode overpotential is 0.40 V. What voltage is needed to overcome these effects combined with those of parts (a) and (b)?
  4. Suppose that concentration polarization occurs [OH-]s. at the cathode surface increases to 1.0 M and[Br-]s at the anode surface decreases to 0.010 M. What voltage is needed to overcome these effects combined with those of (b) and (c)?

What are the advantages of using a microelectrode for

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