chm 108 suroviec fall 2014 chemical quantities. i. reaction stoichiometry given the recipe for 16...

CHM 108SuroviecFall 2014

Chemical Quantities

I. Reaction Stoichiometry

Given the recipe for 16 pancakes: 2 cups flour 2 teaspoons baking powder 2 eggs 1 cup milk

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I. Reaction Stoichiometry

For molecule we have the balanced chemical equation

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A. Mass to Mass Conversions

The question when synthesizing a compound is how much will this reaction make

Using the balanced chemical equation we can answer that.

CaF2 + H2SO4 CaSO4 + 2HF

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II. Limiting Reagents

When carrying out a reaction it is often the case that the reactants are not in exact stoichiometric amounts

One will always be used up first: limiting reagent

One will always be in excess: excess reagent

C6H12O6 (s) + 6O2(g) 6CO2 (g) + 6H2O (l)

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A. Limiting Reactant, Theoretical Yield and Percent Yield

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In the lab we often want to know how much product can be made (theoretical yield) vs. how much we actually made (percent yield)

2Ca(s) + O2(g) 2CaO (s)

If you start with 43.8g of Ca(s) and 32.5g of O2 what is the limiting reagent and theoretical yield?

Example7

Now lets say you did this same reaction (previous slide) and produced 57.42 grams of CaO. What was the percent yield?

IV. Solution Concentration and Stoichiometry

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Working with aqueous solutions is very common in the lab so we need to look at how they are prepared and used.

Solution

Solvent

Solute

A. Solution Concentration9

Molarity is defined as moles/Liter

If 15.5g of Na2CO3 is dissolved into water to make 1.50L, what is the molarity?

B. Using molarity10

How many grams of glucose, C6H12O6, are needed to make a 2.00L solution of 0.750M?

C. Dilution11

HCl comes as a 12M solution, but the experiment calls for 500 mL of 0.100M. How will you make this?

D. Solution Stoichiometry12

What volume (in mL) of a 0.150M HNO3 solution is required to completely react with 37.7 mL of a 0.110 M Na2CO3 solution according to the equation below?

Na2CO3 (aq) + 2HNO3(aq) 2NaNO3 (aq) + CO2(g) + H2O (l)