What are the seven steps in Stochiometry

Question

How to complete a stoichiometry graph using :actual yield, mole ratio, theoretical yield, balanced chemical reactions, percentage, percentage yield

Answer 1

Danielle,

 

A stoichiometry graph is used to experimentally determine the stoichiometry (coefficients) in a reaction. It depends upon measuring the amount of product produced by a series of amounts of the reactants.

 

Suppose we have a reaction between reactants A and B that produces a product C, mA + nB = pC + ..., but we don't know the coefficients of the reactants, m and n.

 

We know that A and B react with a specific mole ratio of m/n even though we do not know what the value of that ratio is.

 

We also know that if we combine m+d moles of A with n moles of B that d moles of A will go unreacted: B is the limiting reactant. Similarly, if we combine m moles of A with n+d moles of B that d moles of B will go unreacted: A is the limiting reactant.

 

Assume that C forms a precipitate that we can isolate (filter and dry) and that the amount of C tells indicates how much of A and B react stoichiometrically. In most mixtures there will be either some unreacted A or some unreacted B left in the solution.

 

Of all the possible mole ratios of A and B, that is, for all the (m+d)/n and m/(n+d), only m/n will not be limited by the lesser amount of one or the other reactant and will give the largest measured amount of product C.

 

Our procedure is:

1. mix up a series of mole ratios of A to B
2. measure the amount of the product C produced in each one,
3. plot the amount of precipitate against the initial mole ratios, and
4. find the mole ratio that produces the largest amount of product as it will be the one where A and B are mixed in the stoichiometric ratio m/n.

 

The way that you will create the series of mole ratios of A to B is to, first, create, say, one molar solutions of each. Since each solution has a certain number of moles per volume, you can calculate the number of moles in any particular volume of each solution.

 

Mixing a series of solutions of A and B together with the same total volume, say, 50 ml, makes it easy to calculate the  mole ratio of each solution as the ratio of their volumes.

 

Without seeing your lab instructions with the definitions of all seven quantities, I expect that you must create a table with each of those quantities in one column and with one row for each 50 ml mixture that you create.

 

Actual Yield is the mass of precipitate produced.

Mole Ratio is the ratio of volumes of A to B that you mixed to get 50 ml.

Balanced Chemical Reaction uses the mole ratio with the maximum product to set the coefficients of the reaction.

Theoretical Yield is prediction of the masses of precipitate produced based on the initial moles mixed together and the Balanced Chemical Reaction. This is a series of limiting reactant calculations.

I don't see a difference between Percentage and Percentage Yield since they are both (to me) the ratio of the Actual Yield to the Theoretical Yield multiplied by 100 to make them a percentage.

 

I hope this is enough to help you understand what's going on and to set up your graph of amount of precipitate to mole (volume) ratios and your table of results.

 

Michael.