Question

1. You work for a crafts supply company, KidKrafts, making calcium carbonate for their chalk products. They have recently decided to add plaster of Paris as one of their products. The key ingredient in plaster of Paris is calcium sulfate (CaSO4). You have been asked to adapt your knowledge of making calcium carbonate from calcium chloride dihydrate (CaCl 2 •2H2O ) and anhydrous sodium carbonate (Na2CO3) to making calcium sulfate. To make the most profit, you will be using the same stock of calcium chloride dihydrate as for the chalk. Therefore, you need to make sure that you use only the necessary amounts of each reactant. Your boss has asked you to not only figure out how to make the calcium sulfate but to prove that you don’t have any excess of either reactant.

a. The first step is figuring out what you need to mix together to make calcium sulfate. You know that the combination of calcium chloride and sodium carbonate worked well to make calcium carbonate in lab. Propose one chemical that you could react with calcium chloride to make calcium sulfate.Give two reasons why the chemical you chose will work. (Hint: What can you replace sodium carbonate with to make calcium sulfate instead of calcium carbonate?)

b. Now that you’ve selected a reactant, write out its (a) complete and (b) net ionic reaction with calcium chloride. You can ignore the waters of hydration on calcium chloride for this step.

c. If you run the reaction above using a solid mixture of exactly the right amount of each reactant, how can you prove that there is no excess? Describe the steps involved with this test. (Hint: Think about how you determined which reactant was in excess in the lab.)

d. Since you are developing a new procedure with a new chemical, you need to check how will you store it at the lab. Look up the MSDS of the reactant you proposed. What does your boss need to keep in mind when storing this chemical?

e. To try out your reaction and test for correct amount, you first need to determine how much of the reactants you need. What mass of your proposed reactant will you need to react with 1.000 g of calcium chloride dihydrate?

Answer 1

# a.

The chemical that we would propose is Sodium Sulfate, Na2SO4

We think this chemical will work because

1) we need sulfate ion to form CaSO4 which is provided by this chemical.

2) It has Sodium ions which form soluble salts , therefore there would not be any interfering precipitate or co-precipitate

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#b

Complete equation

CaCl2 (aq) + Na2SO4 (aq) ----------> CaSO4 (s) + 2 NaCl (aq) ............... Molecular equation

Ca^2+ (aq) + 2Cl^- (aq) + 2Na^+ (aq) + SO4^2- (aq) --------> CaSO4 (s) + 2Na^+ (aq) + 2Cl^- (aq) .... Total ionic equation

Ca^2+ (aq) + SO4^2- (aq) ---------> CaSO4 (s) .....................Net ionic equation

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#c

Step 1 :Take exactly right amount of reactants and dissolve them in water.

Step 2: Mix the solutions of each reactant, and you would see a white precipitate of CaSO4 getting formed.

Step 3 : Separate the precipitate from the remaining solution.

If both the reactants were in exactly stoichiometric amounts, the solution would contain only Na+ (aq) and Cl- (aq) ions as indicated in total ionic equation.

Step 4 : Divide the solution in 2 parts. To one part of the solution add a pinch of sodium sulfate, If it has CaCl2 in excess, excess Ca^2+ ions would react to form CaSO4 again and the solution would turn cloudy white.

But this would not happen in our case, as we have only Na+ and Cl- ions

Step 5: To remaining half, add a pinch of CaCl2. If it has Na2SO4 in excess, SO4 ions would react with Ca2+ to form CaSO4 again and solution would turn cloudy

but our solution only has Na+ (aq) and Cl- (aq) which would not react with CaCl2

So adding either of the reactants to remaining solution does not create more precipitate which proves that both the reactants are in stoichiometric amounts.

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#d

Na2SO4 is relatively safe chemical.

But it still needs to be handled carefully. Na2SO4 is very hygroscopic which means it will attract moisture so it needs to be stored in a dry and well ventilated place . The container should be preferably air tight.

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#e

The balanced equation for this reaction is

CaCl2 . 2H2O + Na2SO4 -------> CaSO4 + 2NaCl + 2 H2O

We have 1 g of CaCl2 . 2H2O

Let's use dimensional analysis to find grams of Na2SO4 needed to completely react with 1 g CaCl2 . 2H2O

1 g CaCl2 . 2H2O * 1 mol/ 147 g * 1 mol Na2SO4 / 1 mol CaCl2 . 2H2O * 142 g/ 1mol Na2SO4

= 0.966 g Na2SO4

0.96 g of Na2SO4 is needed to completely react with 1 g CaCl2 . 2H2O