Chromium plating can be applied by electrolysis to objects according to the following unbalanced half-reaction: cr2o72- + e- + h+→ cr(s) + h2ohow long (in hours) would it take to apply a chromium plating 0.010 mm thick to a car bumper with a surface area of 0.25 m2 in a cell with a current of 25.0 a? the density of chromium is 7.19 g/cm3.

Explanation:

The given data is as follows.

Surface area = 0.25 ,        current (I) = 25 A

Density = 7.19 g/

As 1 m = 100 cm. Hence, 1 =

So,     density =  

As Height = 0.01 mm = = m.

It is known that density is mass divided by volume.

           Density =

Also, volume = Area × height. Therefore, substituting it into the above formula as follows.

                    Density =

                    Density =

                     mass =

                               = 17.975 g

As number of moles equal mass divided by molar mass of the substance.

So,              No. of moles =

                                         =

                                         = 0.3457 mol

As there is transfer of total 6 electrons and it is known that charge on 1 mole of electron is 96500 C.

Hence, charge on 6 electrons will be as follows.

                     96500 C × 6 = 579000 C

This means that charge for 2 moles of is 579000 C

And, charge for 0.3457 mol of is = 100080 C.

Also,       Q =

where,        Q = charge

                   I = current

                = time in seconds

Now, putting the values into above formula as follows.

                        Q =

          100080 C =

                          = 4003.2 sec

Converting seconds into hours as follows.

                1 hr = 3600 sec

So,        

                   = 1.112 hr

Thus, we can conclude that time taken to apply chromium plating is 1.112 hr.

the correct answer is:

a. formation of precipitation