Chemistry, 31.07.2019 18:20 chanel2371

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.

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Answer from: liyah450

Explanation:

The given data is as follows.

Surface area = 0.25 $m^{2}$ , current (I) = 25 A

Density = 7.19 g/ $cm^{3}$

As 1 m = 100 cm. Hence, 1 $m^{3}$ = $10^{6} cm^{3}$

So, density = $7.19 g/cm^{3} \times \frac{10^{6} cm^{3}}{1 m^{3}}$

As Height = 0.01 mm = $10^{-2} \times 10^{-3}$ = $10^{-5}$ m.

It is known that density is mass divided by volume.

Density = $\frac{mass}{volume}$

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

Density = $\frac{mass}{volume}$

Density = $\frac{mass}{area \times height}$

mass = $7.19 \times 10^{6}g/cm^{3} \times 0.25 \times 10^{-5}m$

= 17.975 g

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

So, No. of moles = $\frac{mass}{\text{molar mass of Cr}}$

= $\frac{17.975g}{\text{52 g/mol}}$

= 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 $Cr^{3+}$ is 579000 C

And, charge for 0.3457 mol of $Cr^{3+}$ is $0.3457 mol \times \frac{579000 C}{2}$ = 100080 C.

Also, Q = $I \times \Delta t$

where, Q = charge

I = current

$\Delta t$ = time in seconds

Now, putting the values into above formula as follows.

Q = $I \times \Delta t$

100080 C = $25 A \times \Delta t$

$\Delta t$ = 4003.2 sec

Converting seconds into hours as follows.

1 hr = 3600 sec

So, $4003.2 sec \times \frac{1 hr}{3600 sec}$

= 1.112 hr

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

Answer from: Quest

what are the two models

explanation:

Answer from: Quest

in the given question, the partial pressure is calculated by using the ideal gas equation, that is, pv = nrt

here, p is pressure, v is volume = 25 l, n is number of moles = 0.0104 moles, r is gas constant = -0.0821 l.atm / mol.k

t is temperature = 273 k

p = nrt / v

p = (0.0104 mol × 0.0821 l.atm / mol.k × 273 k) / 25 l

= 0.0093 atm

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