#limiting reactant

Lesson 5a: Theoretical, Actual, and Percent Yield.

https://videopress.com/embed/2JEc18wZ?hd=0&autoPlay=0&permalink=0&loop=0 In which we explore theoretical and actual yields! And I make a personal record of how many times I can say, “My bad” onscreen. Trouble accessing the video? Check us out on YouTube! Questions, comments, concerns? Email us at [email protected]. Science rules!! x

Determining Precipitate Yield (g) in Aqueous Solution

This slideshow requires JavaScript. Given Question: Given the reaction: K3(PO4)+ Ni(SO4)→ K3(SO4)(aq)+Ni(PO4)(s), with 100.0 ml of K3PO4 and 200.0 ml of NiSO4 under standard conditions, how many grams of precipitate form?  Step 1: Determine the limiting reactant and the precipitate.  In order to determine the limiting reactant, one must convert all reactants to moles (mol). In this case, we can…

limiting reactant - the reactant that is used up first Excess - The non-limiting reactants. There is more than enough to fulfill the reaction Theoretical yield - amount of product calculated by assuming that the reaction goes cleanly and completely Actual yield - the amount present after separating it from other products and reactants and purifying it

Actual yield is less than the theoretical yield.

For the first question, it is best to know the solubility rules. You should commit them to memory. They are as follows:

Salts containing Group I elements are soluble (Li+, Na+, K+, Cs+, Rb+). Exceptions to this rule are rare. Salts containing the ammonium ion (NH4+) are also soluble. 

Salts containing nitrate ion (NO3-), Chlorate ion (ClO3), Perchlorate ion (ClO4), and acetate ion (C2H3O2) are generally soluble. 

Salts containing Cl -, Br -, I - are generally soluble. Important exceptions to this rule are halide salts of Ag+, Pb2+, and (Hg2)2+. Thus, AgCl, PbBr2, and Hg2Cl2 are all insoluble.

Most silver salts are insoluble. AgNO3 and Ag(C2H3O2) are common soluble salts of silver; virtually anything else is insoluble.

Most sulfate salts are soluble. Important exceptions to this rule include BaSO4, PbSO4, Ag2SO4 and SrSO4 .

Most hydroxide salts are only slightly soluble. Hydroxide salts of Group I elements are soluble. Hydroxide salts of Group II elements (Ca, Sr, and Ba) are slightly soluble. Hydroxide salts of transition metals and Al3+ are insoluble. Thus, Fe(OH)3, Al(OH)3, Co(OH)2 are not soluble.

Most sulfides of transition metals are highly insoluble. Thus, CdS, FeS, ZnS, Ag2S are all insoluble. Arsenic, antimony, bismuth, and lead sulfides are also insoluble.

Carbonates are frequently insoluble. Group II carbonates (Ca, Sr, and Ba) are insoluble. Some other insoluble carbonates include FeCO3 and PbCO3.

Chromates are frequently insoluble. Examples: PbCrO4, BaCrO4

Phosphates are frequently insoluble. Examples: Ca3(PO4)2, Ag3PO4 

Fluorides are frequently insoluble. Examples: BaF2, MgF2 PbF2.

From this information, we can determine that the first set contains compounds that are all soluble in water.

The first step, as with all chemistry problems, is to balance your equation.

Then you plug in your given values for each reactant to find how much product is formed. In this step, you can use any product you want. I chose Mg(OH)2 for no particular reason. Either way, it will give you the same result!

Limiting reactant means "which reactant will run out first?" So there will almost always be an excess reactant. In this case, the excess is H2O. We can find how much remains with a simple stoichiometric equation. Start with your limiting reactant and use a mole-to-mole ratio to find how much excess is used. Then subtract that amount from how much you had to begin with. Sorry about the scan here, the final answer is 10.9 grams. I see now that you wanted that in moles, so you can just divide this number by MM (molar mass in grams/mol). The final answer is .448mol remaining.

You use the same stoichiometric equation to find how much of each product is formed.