1Al2(SO4)3 + 3ZnCl2 → 2AlCl3 + 3ZnSO4
The coefficients represents moles. There is 1 mole of Aluminum Sulfate, 3 moles of Zinc(II) Chloride, 2 moles of Aluminum Chloride, and 3 moles of Zinc(II) Sulfate.
Now add all the coefficients/moles.
9 is the sum of all the coefficients.
Answer:
The depth of the damage is given as 
Explanation:
From Fick's second law
![\frac{C_{x}-C_{0}}{C_{s}-C_{0}} = 1 -erf [\frac{x}{2\sqrt{Dt} } ] ...(1)](https://tex.z-dn.net/?f=%5Cfrac%7BC_%7Bx%7D-C_%7B0%7D%7D%7BC_%7Bs%7D-C_%7B0%7D%7D%20%3D%201%20-erf%20%5B%5Cfrac%7Bx%7D%7B2%5Csqrt%7BDt%7D%20%7D%20%5D%20...%281%29)
Where
is the temperature when the skin is damage
is the initial temperature of the skin
is the temperature of the oven
erf is a mathematical function known as error function
D is the thermal diffusivity
x is the depth of the damage
From the question we are given that
= 62°C
= 33°C
D = 
Substituting values into equation one
![\frac{62-33}{200-33} = 1 -erf [\frac{x}{2\sqrt{2.5*10^{-7}} *2} ]](https://tex.z-dn.net/?f=%5Cfrac%7B62-33%7D%7B200-33%7D%20%3D%201%20-erf%20%5B%5Cfrac%7Bx%7D%7B2%5Csqrt%7B2.5%2A10%5E%7B-7%7D%7D%20%2A2%7D%20%5D)
![erf[\frac{x}{1.414*10^{-3}} ] = 0.826\\](https://tex.z-dn.net/?f=erf%5B%5Cfrac%7Bx%7D%7B1.414%2A10%5E%7B-3%7D%7D%20%5D%20%3D%200.826%5C%5C)
Let assume that 
Hence
Looking at the table of error function shown on the first uploaded image
We can use interpolation to obtain the value of z in this manner
z = 0.96
Substituting the value of z into equation 2
35g Mg x 1mol / 24g = 840 mol
Equation is as follow,
Fe₂O₃ + 3 CO → 2 Fe + 3 CO₂
Oxidation:
3 CO → 3 CO₂
Oxidation state of C in CO is +2, and that in CO₂ is +4. So, carbon has lost 2 electrons per mole and 6 electrons per 3 moles hence,
3 CO → 3 CO₂ + 6 e⁻
Reduction:
Fe₂O₃ → 2 Fe
Oxidation state of Fe in Fe₂O₃ is +3 per atom, and that in Fe is 0. So, Iron has gained 3 electrons per atom and 6 electrons per 2 atoms hence,
Fe₂O₃ + 6e⁻ → 2 Fe
Result:
Iron in Fe₂O₃ has been reduced in this reaction and has played a role of oxidizing agent by oxidizing carbon from +2 state to +4 state.
