Limiting Reactant Lab PDF

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Limiting reactant lab report for Chemistry 1061...

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Recipes in Chemistry – Limiting Reactants (Sometimes You Don’t Have Enough) Name ______________________________ Introduction: When you are cooking in the kitchen you might use a recipe. You measure out a certain amount of this and a specific amount of that to get a perfect pizza or curried rice with a flavor just like your dad’s. In chemistry, we use recipes too. Our recipes are balanced equations. The reactants are like the ingredients needed to produce the products that we hope to make. The coefficients of the chemical reaction give the proportions (or ratios) of each ingredient. In a chemical reaction the coefficients represent the number of moles and we measure out moles using grams or liters. However, there are times when you do not have exactly the right amount of each ingredient (reactant). In cases like this one of the reactants is the limiting reactant and the other is in excess. The limiting reactant controls the maximum amount of product that can be formed; it determines the theoretical yield.

Balanced Reaction:

฀฀฀฀(฀฀฀฀3 )3 (฀฀฀฀) + 3 ฀฀฀฀฀฀฀฀(฀฀฀฀) → ฀฀฀฀(฀฀฀฀)3 (฀฀) + 3 ฀฀฀฀฀฀฀฀3 (฀฀฀฀) orange Pre-Lab Question In your own words, define the terms: a. Supernatant

b. Limiting reactant

c. Excess reactant

d. Theoretical Yield

clear

red-brown

clear

Part I. Which combination creates the greatest amount of solid? Obtain 4 test tubes and add Fe(NO3)3 and NaOH to each tube according to the table below. The illustration shows the test tubes after the reaction has occurred.

Table 1 Reactant

Tube 1

Tube 2

Tube 3

Tube 4

1.00 M Fe(NO3)3

0.50 mL

1.00 mL

1.50 mL

2.00 mL

1.00M NaOH

3.50 mL

3.00 mL

2.50 mL

2.00 mL

Observations (amount of solid, color of supernatant):

Predicted limiting reactant (based on tubes above):

Predicted excess reactant (based on tubes above):

Part II. Determining Excess and Limiting Reactants The supernatant in each reaction tube contains the excess reactant. You can experimentally determine the excess reactant by taking a sample of the supernatant from each tube and adding it to a Fe(NO3)3 solution and a NaOH solution. The excess reactant will react with either the Fe3+ (if OH- is present in the supernatant) or OH- (if Fe3+ is present in the supernatant). When the supernatant from each tubes was added to both NaOH (row A) and Fe(NO3)3 (row B) solutions, the following was observed. Table 2: Write “ppt.” if a precipitate (solid) forms and “NR” if there is no reaction. Substance in the well plate NaOH

Fe(NO3)3

Tube 1

Tube 2

Tube 3

Tube 4

Now, combine your results from Tables 1 and 2 and fill out the following conclusions based on all of the experimental data: Table 3 Tube 1

Tube 2

Tube 3

Tube 4

Observed Limiting Reactant:

Observed Excess Reactant:

Calculations Although you can determine which reactant is in excess and which is limiting through experimentation, you can also do this with calculations using stoichiometry. Using the information in Table 1, calculate the number of moles of each reactant (Fe(NO3)3 and NaOH) present in each tube. Show your work for Tube 1 below Table 4. Table 4 Tube 1 Moles of Fe(NO3)3

Moles of NaOH Mole ratio of Fe(NO3) 3 to NaOH Which reactant is limiting according to the mole ratio? Does the limiting reactant from this table agree with the limiting reactant from Table 3?

Work for Tube 1. Include all units:

Tube 2

Tube 3

Tube 4

Post- Lab Questions 1. In the balanced equation, what is the mole ratio of iron (III) nitrate to sodium hydroxide?

2. In which tube did you have exactly the right amount of each reactant? Explain.

3. In which tubes, was the ratio of iron (III) nitrate to sodium hydroxide smaller than in the balanced reaction? What was the limiting reactant in those cases?

4. In which tubes was the ratio of iron (III) nitrate to sodium hydroxide larger than in the balanced reaction? What was the limiting reactant in those cases?

5. The limiting reactant is the reactant that determines the maximum amount of product formed. We call this the theoretical yield. (You cannot produce any more product than the limiting reactant allows – since it gets completely used up in the reaction). For tube 4 what is the theoretical yield of iron (III) hydroxide (in grams)? SHOW YOUR WORK.

6. If you wanted to produce 5.00 grams of iron (III) hydroxide, how many mL of 1.00 M Fe(NO3)3 would you need if you had excess sodium hydroxide? SHOW YOUR WORK. Use dimensional analysis....