Question

Determine experimentally and theoretically how much zinc iodide can be produced by reacting 2.00 g powdered zinc metal with 2.00 g of solid iodine.

Results: 1.81 g of zinc iodide was collected

1. What was the purpose of the acetic acid?

2. Calculate (hint: which reactant element is diatomic?):

    a. Molar mass of zinc (g/mol)=    

  

    b. Molar mass of iodine (g/mol) =

    c. Molar mass of zinc Iodide =

3. Write the balanced reaction of zinc + iodine (hint: which element is diatomic?):

3. Calculate the theoretical mass of zinc iodide that would be produced if the reaction goes to completion and all product is collected:

a. Calculate from the 2.00 g zinc

b. Calculate from the 2.00 g iodine

4. During the reaction what reactant was completely reacted?

5. What was the actual (experimental) yield of zinc iodide in grams (g)?

6. What is the percent yield? (actual/theoretical x 100 = % yield)

7. Answer the following for the reaction:

    a. Oxidation ½ reaction

     b. Reduction ½ reaction

     c. Substance Oxidized:

     d. Substance reduced:

     e. Oxidizing agent:

     f. Reducing agent:

Answer 1

Answer-

1) Here, acetic acid is acting as a medium that allows the transfer of electrons between reactants.

In the absence of acetic acid, zinc iodide can be hydrolyzed to the zinc hydroxide by the following reaction-

ZnI₂(aq) + 4H₂O(l)   Zn(OH)₂ (s) + 2H₃O⁺ (aq) + 2I^- (aq)

But the acetic acid prevents the formation of zinc iodide by immediately reacting with it according to the following reaction-

Zn(OH)₂ (s) + 2 HC₂H₃O₂ (aq) Zn²⁺ (aq) + 2 C₂H₃O₂^- (aq) + 2H₂O (l)

So the role of acetic acid is to avoid the formation of zinc hydroxide, the reason we do not want zinc hydroxide to form is that its precipitate is also white in color like zinc iodide precipitate, due to which it can be mistaken as zinc iodide.

2) a) The molar mass of zinc is 65.38 gm/mol

b) Iodine is a diatomic molecule and exists in I₂ form

Mass of one Iodine atom = 126.90 gm / mol

Mass of diatomic iodine molecule = 2 x ( 126.90) = 253.80 gm / mol

c) molar mass of zinc iodide = mass of zinc + mass of I₂ =  65.38 + 253.80 = 319.19 g/mol

3) The balanced reaction for zinc and iodine is-

Zn + I₂ ZnI₂

3) a) When 2 gm of zinc is used-

Molar mass of Zinc is 65.38 gm / mol

No. of moles in 2 gm of zinc = 2 / 65.38 = 0.030

Now according to the reaction ,1 mole of Zinc forms 1 mol of zinc iodide

0.030 mole of zinc forms 0.030 mole of zinc iodide

Mass of 1 mole of zinc iodide = 319.19 gm

Mass of 0.030 mole of zinc iodide = (0.030) x (319.19) = 9.575 gm

So 9.575 gm of zinc iodide formed if complete 2 fm of zinc gets reacted

b) When 2 gm of iodine is used-

Molar mass of I₂ = 253.80 gm

No. of moles in 2 gm of iodine = 2 / 253.80 = 0.0078

Now according to the reaction, 1 mole of iodine(I₂) forms 1 mole of zinc iodide

0.0078 mole of iodine forms 0.0078 mole of zinc iodide

Mass of 1 mole zinc iodide = 319.19 gm

Mass of 0.0078 mole of zinc iodide = (0.0078) x (319.19) = 2.49 gm

So 2.49 gm of zinc iodide formed when complete iodine gets reacted.

4) We have 0.030 mole of zinc and 0.0078 mole of iodine(I₂) for this reaction.

Since 1 mole of I₂ can react only with 1 mole of zinc

0.0078 mole of I₂ can only react with 0.0078 mole of zinc, this means there will be some amount of zinc which will be left unreacted

So, Iodine(I₂) reacts completely in this reaction

5) Since 1.81 gm of zinc iodide was collected in the experiment

The actual (experimental) yield of zinc iodide is 1.81 gm.

6) The % yield for this reaction is-

% yield = (actual yield / theoretical yield) x 100

Since iodine is limiting reagent here, the theoretical yield will be according to its concentration.

So the theoretical yield of zinc iodide is 2.49 gm

% yield = (1.81 / 2.49) x 100 = 72.69 %

7)

a) Oxidation-half reaction-

Zn Zn²⁺ + 2 e^-

b) - half-reaction-

I₂ + 2 e^- 2 I ^-

c) The substance which gets oxidized-

Here Zinc has gain electrons which means zinc gets oxidized

d) The substance which gets reduced -

Here iodine gain electron, which means iodine gets reduced

e) Oxidizing agent-

Here Iodine is itself getting reduced. So Iodine iodine is oxidizing agent

f) Reducing agent-

Here zinc is itself getting oxidized. So zinc is reducing agent