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.

hydrocarbons are organic compounds that contain only hydrogens and carbons. they can be saturated (those which contain only carbon-carbon single bonds) or unsaturated (those which contain carbon-carbon double or triple bonds) in nature. hydrocarbons can undergo several reactions like substitution, elimination etc.  

on substituting one or more hydrogen atoms in hydrocarbon it results in the formation of haloalkane. as the halogen atoms are large compared to the carbon and hydrogen atoms, due to which the molecular weight increases and the bond become polar because of presence electronegative halogen atom and results in the increase in boiling point of the haloalkane.

thus, the correct option is (b) that is the boiling point of the new compound increases on substituting a hydrogen atom with a halogen in a hydrocarbon.