How to Stoich

By: Jeffrey Tran

What is Stoichiometry?

First of all, what is stoichiometry? Stoichiometry is the relationship between 2 or more elements in a reaction to form a compound, with a ratio of whole numbers.

An Example of Stoichiometry

An ice cream sandwich has 2 cookies and 1 scoop of ice cream in the middle. If you wanted to make 2 ice cream sandwiches, you'd have to double everything(4 cookies and 2 scoops of ice cream). The ratio has to stay the same.
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The steps to completing a stoichiometry problem

The steps to solving a stoichiometry problem is easy:

  1. Solve and balance the given equation
  2. Find the molar mass of everything
  3. Find the limiting and excess reactants by doing 2 mass to mass conversions
  4. Get the limiting reactant and name the product as the theoretical yield
  5. Get the actual yield from the given and find the percent yield

Start with the given

We are given the equation Zinc plus Copper(II) Chloride. Because of the (II) after copper, we know copper has a charge of 2, making the equation Zn+CuCl2. Now you have to solve and balance the equation. The equation would be Zn(s) + CuCl2(aq) -> Cu(s) + ZnCl2(aq). It could also be read as Zinc + Copper(II) Chloride -> Copper + Zinc Chloride.

Learning mole to mole conversions

You are given the starting element and grams in the question(in this case, is 6.14 grams of Zinc). In the second column on the bottom, you put the same element you started with, but with the coefficient in front of it. On top of the second column, you put what you're trying to find(in this case, it's Zinc Chloride), and you put the coefficient in front of it and multiply the top, divide by the bottom.
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doing mass to mass conversions

You start with the given from the question, then you get the molar mass of the given element and put it under 1 mole. Then you put the coefficients of the given element, then the coefficient of the element you're trying to look for. After that, you find the molar mass of the element you're looking for you you put it on top of 1 mole. Then you multiply the top, divide by the bottom.
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Finding the limiting and excess reactant

After you do the mass to mass conversion of one reactant, you do the same for the other reactant, while still looking for the same element. Keep the same amount of grams for both of the starting elements and solve for the same element. Then multiply the top and divide by the bottom, to find which one has a less solution.
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Getting theoretical yield and finding the percent yield

Because we found out that Copper(II) Chloride is the limiting reactant, we say it's the theoretical yield. Then after doing the experiment below, we find the actual yield(which is 15.3 grams of Zinc Chloride). We divide the actual yield from the theoretical yield and multiply it by 100, to get 122.77%.
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zinc and copper chloride react

Video information

In the video above, zinc and copper(II) chloride react, making the solid turn into a darker color. The reaction above was a single replacement reaction.