Lab 6D -- by Ria Park

Lab 6D : Determining the Limiting Reactant an Percent Yield in a Precipitation Reaction

Objectives

1. to observe the reaction between solutions of NaCO₃and CaCl₂
2. to determine which of the reactants is the limiting reactant and which is the excess reactant
3. to determine the theoretical mass of precipitate that should form
4. to compare the actual mass with the theoretical mass of precipitate and calculate the percent yield

Supplies

• Equipment: centigram balance, 2 graduated cylinders(25ml), beaker(250ml), wash bottle, filtering apparatus(ring with stand, Erlinmeyer flask(250ml)+funnel), filter paper, lab apron, safety goggles
• Chemical Reagents: 0.70M  NaCO₃solution, 0.50  CaCl₂solution

Procedure

Part Ⅰ= the Precipitation Reaction(Day 1)

1. lab apron + safety goggles
2. obtain 2 clean, dry 25ml graduated cylinder and one 250ml beaker.
3. 25ml of NaCO₃(aq) in one cylinder & 25ml of CaCl₂(aq) in the other. Record volumes.
4. Pour contents of both cylinders into the beaker. Observe. Record. Allow the contents of the beaker to sit undisturbed for 5 min to see what happens to the suspended soild particles. Meanwhile, do step 5.
5. Get a piece of filter paper and put names on it with a pencil. Weigh and record the mass of it. Set up a filtering apparatus.
6. Lightly wet the filter paper the funnel to keep it in place(using the wash bottle). Swirt the beaker to suspend the precipitate. Pour it carefully & slowly into the filter funnel. Use wash bottle to raise the remaining precipitate from the beaker.
7. Rise the precipitate in the filter paper with wash bottle(to remove NaCl)
8. Remove the wet filter paper and place it on a folded paper towel. Put filter paper(with CaCO₃) in the assigned location to dry.
9. Clean up.
10. Wash hands.

Part Ⅱ= Weighing the dried precipitate(Day 2)

1. Weighing and recording the mass of dry filter paper + CaCO₃precipitate.

Reagent Disposal

Rinse all solutions down the smile with sufficient water. Solid go into the designed containers.

Percent Yield and Purity--- By Tina Zhao

percent Yield= The yield is the amount of product you obtain from a reaction. Suppose we own a factory that makes fertilizers or paint. We will want the highest yield possible, for the lowest cost.

The formula for percent yield is:

Example:

The medical drug aspirin is made from salicylic acid. 1 mole of salicylic acid gives 1 mole of aspirin. Given that the chemical formula for salicylic acid is C₇H₆O₃ and the chemical formula for aspirin is C₉H₈O₄.

In an experiment, 100.0 grams of salicylic acid gave 121.2 grams of aspirin. What was the percent yield?

Solution:

Step 1: Calculate the M_r (relative molecular mass) of the substances.

A_r : C = 12, H = 1, O = 16
So, M_r : salicylic acid = 138, aspirin = 180.

Step 2: Change the grams to moles for salicylic acid

138 g of salicylic acid = 1 mole
So, 100 g = 100 ÷ 138 mole = 0.725 moles

Step 3: Work out the calculated mass of the aspirin.

1 mole of salicylic acid gives 1 mole of aspirin
So, 0.725 moles gives 0.725 moles of aspirin
0.725 moles of aspirin = 0.725 × 180 g = 130.5 g
So, the calculated mass of the reaction is 130.5 g

Step 4: Calculate the percent yield.

The actual mass obtained is 121.2 g
So, the percent yield = 121.2 ÷ 130.5 × 100% = 92.9%

Percent purity= sometimes, the reactant we use is not pure, so before we can calculate how much product will form, we need to use percent purity to calculate how much reactant that actually is availablt to react.



The formula for percent yield is:





The medical drug aspirin is made from salicylic acid. 1 mole of salicylic acid gives 1 mole of aspirin. Given that the chemical formula for salicylic acid is C₇H₆O₃ and the chemical formula for aspirin is C₉H₈O₄.

In an experiment, 100.0 grams of salicylic acid gave 121.2 grams of aspirin. What was the percent yield?

Solution:

Step 1: Calculate the M_r (relative molecular mass) of the substances.

A_r : C = 12, H = 1, O = 16
So, M_r : salicylic acid = 138, aspirin = 180.

Step 2: Change the grams to moles for salicylic acid

138 g of salicylic acid = 1 mole
So, 100 g = 100 ÷ 138 mole = 0.725 moles

Step 3: Work out the calculated mass of the aspirin.

1 mole of salicylic acid gives 1 mole of aspirin
So, 0.725 moles gives 0.725 moles of aspirin
0.725 moles of aspirin = 0.725 × 180 g = 130.5 g
So, the calculated mass of the reaction is 130.5 g

Step 4: Calculate the percent yield.

The actual mass obtained is 121.2 g
So, the percent yield = 121.2 ÷ 130.5 × 100% = 92.9%