How many coulombs are required to plate a layer of chromium metal 0.28 mm thick on an auto bumper with a total area of 0.40 m2 from a solution containing cro2−4? the density of chromium metal is 7.20 g/cm3.

Explanation:

The given data is as follows.

Thickness = 0.28 mm = cm = 0.028 cm

Area = 0.40 = = 4000

As, it is known that volume = area × thickness

So,             Volume =      

                                = 112

As density is mass divided by volume. So, mass of chromium will be calculated as follows.

                   Density =  

            7.20 =      

                      mass = 806.4 g

As, mass of 1 mole of chromium is 52 g. So, number of moles in 806.4 g of chromium will be as follows.

              No. of moles =                            

                                     =

                                     = 15.50 mol

In chromate ion, () charge on Cr is +6. It means that 6 electrons are needed to reduce into Cr.

As, 1 mole of ions require 6 moles of electrons. Therefore, moles of electrons for 15.50 mol will be calculated as follows.

                              6 × 15.50 mol = 93.04 mol

To calculate number of electrons we multiply number of moles by Avogadro's number as follows.

                      =

                     = electrons

There is magnitude of times the charge on an electron is equal to 1 coulomb.

Hence, number of coulombs will be as follows.

              No. of coulombs =

                                           = C

or,                                        = C

Thus, we can conclude that C are required to plate a layer of chromium metal with given data.

c.

explanation: