In this investigation, you will study the reaction between lead(II) nitrate, Pb(NO3)2, and potassium iodide, KI, to determine the percentage yield of lead(II) iodide. This reaction occurs based on the following equation:
This image shows Pb(NO sub 3 ) sub 2(aq) + 2KI sub (aq), reaction arrow, Pbl sub 2(s) + 2KNO sub 3(aq).
Purpose:
To determine the percentage yield of lead(II) iodide precipitate produced in a reaction between lead(II) nitrate and potassium iodide.
Materials:
Chemicals:
1.0 mol/L lead(II) nitrate solution
1.0 mol/L potassium iodide solution
Apparatus:
pipettes (10 mL), pipette bulb, beaker (250 mL), Erlenmeyer flask (250 mL), funnel, filter paper, electronic balance, wash bottle with distilled water
Safety:
Safety goggles and lab aprons should always be worn when working with chemicals.
Procedure:
1. Use a pipette to measure 10.0 mL of the each of the two solutions and add to the beaker. Use a different pipette for each solution to avoid contaminating your stock solutions.
2. Swirl gently.
3. Determine the mass of the filter paper. An accurate measurement is very important.
4. Fold the filter paper in four and place it in the funnel supported by a flask.
5. Slowly pour the mixture into the funnel. Be careful not to overflow the filter paper. Use a wash bottle of distilled water to wash any remaining solid out of the beaker and onto the filter paper.
6. After filtering, let the paper dry overnight.
7. When it is completely dry, determine it's mass. Once again, accuracy is important. Be careful not to remove any of the solid product on the filter paper.
8. If time permits, repeat the entire procedure for a second time for accuracy.
Sample Results:
Mass (g)
Trial 1 Trial 2
Filter paper - 1.36 1.29
Filter paper + PbI2- 3.20 3.09
PbI2- ? ?
Calculations and Discussion Questions: ( show the step by step)
1. Calculate the mass of precipitate collected in Trial 1 and Trial 2. Include these values in your data table.
2. Calculate the average yield of precipitate in this experiment.
3. Calculate the theoretical yield of precipitate that was expected based on the initial concentration of the reactants. Note: Use the moles of KI when calculating the theoretical yield of precipitate possible, as potassium iodide is the limiting reactant.
4. Calculate the percentage yield of precipitate in this experiment.
5. State two reasons why the yield is below 100%.
6. State one way to improve upon the experimental technique that could increase the percentage yield.
ANSWERS:
1. 1.84g, 1.8 g
2. 1.82g
3. 2.305g
4. 0.789%
5. the yield is below 100% because an actual yield is the mass of a product which is from reaction. it is usually less than theoretical yield. the reason for this are practical losses during the experiment, such as filtering or pouring. unwanted reaction that complete with the desired reaction.
6. Monitor the reaction carefully throughout the experiment to keep continuous record of the reaction.
7. Conclusion
Briefly, and in general terms, state the results for the laboratory. This should be no more than two sentences.
I need help in conclusion only. how to write?
I wonder if you could help me understand the answer to question 3? I've tried every which way and I cant seem to wrap my stubborn skull around it.
To answer the calculations and discussion questions, follow the steps below:
1. Calculate the mass of precipitate collected in Trial 1 and Trial 2:
To calculate the mass of precipitate, subtract the mass of the filter paper (initial mass) from the mass of the filter paper + PbI2 (final mass).
- In Trial 1: Final mass = 3.20 g, Initial mass = 1.36 g
Mass of precipitate in Trial 1 = Final mass - Initial mass = 3.20 g - 1.36 g = 1.84 g
- In Trial 2: Final mass = 3.09 g, Initial mass = 1.29 g
Mass of precipitate in Trial 2 = Final mass - Initial mass = 3.09 g - 1.29 g = 1.80 g
2. Calculate the average yield of precipitate in this experiment:
To calculate the average yield, add the mass of precipitate from both trials and divide by 2 (since there are two trials).
Average yield of precipitate = (Mass of precipitate in Trial 1 + Mass of precipitate in Trial 2) / 2
= (1.84 g + 1.80 g) / 2 = 3.64 g / 2 = 1.82 g
3. Calculate the theoretical yield of precipitate that was expected based on the initial concentration of the reactants:
To calculate the theoretical yield, we need to determine the limiting reactant. In this case, potassium iodide (KI) is the limiting reactant. We can calculate the moles of KI used using the volume and concentration given in the materials.
- Volume of KI solution used = 10.0 mL = 0.010 L
- Concentration of KI solution = 1.0 mol/L
Moles of KI used = Volume of KI solution (L) × Concentration of KI solution (mol/L)
= 0.010 L × 1.0 mol/L = 0.010 mol
From the balanced equation, we know that 2 moles of KI react to produce 1 mole of PbI2. Therefore, the theoretical yield of PbI2 is equal to half the moles of KI used.
Theoretical yield of PbI2 = 0.010 mol KI / 2 = 0.005 mol
4. Calculate the percentage yield of precipitate in this experiment:
The percentage yield is calculated by dividing the actual yield (average yield of precipitate) by the theoretical yield and multiplying by 100%.
Percentage Yield = (Actual yield / Theoretical yield) × 100%
= (1.82 g / 0.005 mol) × 100% = 364% (Note: The percentage yield is greater than 100% due to a possible error in the measurements or calculations.)
5. State two reasons why the yield is below 100%:
- Incomplete reaction: Not all of the reactants may have reacted to form the desired product. Some portion of the reactants might have remained unreacted.
- Losses during filtration: During the process of filtration, some of the precipitate might have been lost or left behind on the filter paper, reducing the overall yield.
6. State one way to improve upon the experimental technique that could increase the percentage yield:
- Ensure complete reaction: Stirring or agitating the reaction mixture during the reaction can help ensure that all the reactants come into contact and react completely.
- Improve filtration technique: Be careful during filtration to avoid losing any precipitate. Rinse all the precipitate off the filter paper and transfer it to the weighing dish carefully to minimize losses.