Heavy metals like lead (Pb²⁺) and copper (Cu²⁺) are often present in wastewater, sometimes in concentrations hazardous to human health and the environment. These contaminants originate from corroding pipelines or improper disposal of substances like paint and solvents. Removing such ions is essential to prevent contamination. This lab aims to extract lead and copper ions from a 50 mL wastewater sample through precipitation reactions using disodium sulfate (Na₂SO₄) and dipotassium carbonate (K₂CO₃).
Educational Goals
To separate and quantify lead and copper ions in wastewater by inducing precipitation and filtration, while analyzing the effectiveness of the extraction process.
- Understanding chemical precipitation: Gain knowledge of precipitation reactions and their application in removing heavy metal ions from solutions.
- Quantitative analysis skills: Develop the ability to measure and weigh substances accurately, ensuring precision in experimental results.
- Application of filtration techniques: Learn proper filtration methods to separate solid precipitates from liquid mixtures.
- Environmental relevance: Appreciate the importance of wastewater treatment in mitigating heavy metal contamination.
- Data recording and analysis: Practice recording observations and interpreting results to evaluate the success of the experiment.
Protocol
- Weigh a filter paper and find its mass in the results table.
- Measure 50 ml of wastewater with the graduated cylinder and pour the sample into Erlenmeyer flask #1.
- Weigh 0.64 g (0.24mL) of disodium sulfate.
- Place the disodium sulfate in the Erlenmeyer flask #1.
- Mix with the glass rod; and observe the precipitation of lead.
- Place the filter paper in the funnel, which is positioned on Erlenmeyer flask #2.
- Stick the filter paper to the wall of the funnel using a little distilled water.
- Wait for the excess water to drain into the Erlenmeyer flask and empty the latter into the recovery tray.
- Filter the mixture to extract the precipitate.
- Allow the filter paper to dry for 10 seconds; then weigh the filter paper + precipitate set. The mass is found in the results table.
- Repeat steps 1 to 9 with the filtrate (Erlenmeyer #2) and the dipotassium carbonate.
- You can also repeat the experiment with different salts, found on the top shelves.
Anticipated Outcomes
- Effective Precipitation of Lead and Copper:
- Lead ions (Pb²⁺) will react with disodium sulfate to form lead sulfate (PbSO₄), a white precipitate that is insoluble in water.
- Lead and copper ions will also precipitate with carbonate (CO3)2- and hydroxide OH-
- Copper ions (Cu²⁺) will react with dipotassium carbonate to form copper carbonate (CuCO₃), a blue-green precipitate.
- Quantifiable Mass of Precipitates:
- The mass of the lead sulfate precipitate is expected to closely align with theoretical values, approximately 1.44 g based on stoichiometric calculations.
- The mass of the copper carbonate precipitate is anticipated to be around 1.41 g, as calculated prior to the experiment.
- Observations Consistent with Theory:
- The wastewater color will shift during each precipitation step: bluish after lead precipitation (due to remaining copper ions) and clear after copper precipitation (as most ions are removed).
- Filter papers will retain distinct white and blue-green precipitates for lead and copper respectively.
- Understanding Deviations:
- Slight variations in precipitate mass may occur due to experimental factors such as incomplete drying of the filter paper or minor inaccuracies in reagent measurements.
- Skill Development:
- Participants will gain proficiency in using lab equipment, including precise weighing, measuring, and filtering techniques.
- Data collection and analysis skills will be honed by comparing experimental results with theoretical predictions.
- Environmental Implications:
- This experiment reinforces the importance of chemical methods in wastewater treatment, providing insights into reducing heavy metal contamination.
| Sample | Filter Paper Mass (g) | Filter Paper + Precipitate (g) | Precipitate Mass (g) |
| Lead | 1.02 | 2.48 | 1.44 |
| Copper | 1.04 | 2.45 | 1.41 |
Summary of Assignment by Grade Range
Grades 9-10
- Focus: Foundational knowledge of precipitation and filtration techniques.
- Activities:
- Measure and weigh materials accurately.
- Observe and document changes during the precipitation reactions.
- Complete provided data tables with experimental results.
- Goals:
- Understand the basic principles of solubility and chemical reactions.
- Develop hands-on experience with laboratory tools such as balances, graduated cylinders, and filtration apparatus.
- Cultivate accurate data recording and error analysis.
Grades 11-12
- Focus: Application of stoichiometric calculations and advanced analysis.
- Activities:
- Perform stoichiometric calculations to predict masses of precipitates.
- Analyze experimental deviations and propose explanations for observed differences.
- Extend the experiment using alternative reagents to observe additional precipitation reactions.
- Goals:
- Apply theoretical knowledge to practical laboratory scenarios.
- Develop critical thinking and problem-solving skills by assessing experimental outcomes.
- Deepen understanding of wastewater treatment relevance.
College-Level/Advanced Students
- Focus: In-depth exploration of environmental applications and reaction mechanisms.
- Activities:
- Design modifications to the experiment to improve yield or address environmental concerns.
- Conduct comparative analyses using different salts and reaction conditions.
- Research the environmental impact of heavy metal contamination and mitigation strategies.
- Goals:
- Build expertise in experimental design and execution.
- Explore the broader implications of laboratory techniques on environmental sustainability.
- Refine analytical and presentation skills by reporting findings.
Laboratory essentials
Instruments
Numeric balance
Weigh-in basket
Spatulas
Glass rod
Funnel & filters
3x 250mL Erlenmeyers
10mL graduated cylinder
70mL graduated cylinder
Products
Ammonium sulfate (powder)
Calcium acetate (powder)
Copper acetate (powder)
Potassium acetate (powder)
Lead acetate (powder)
Sodium acetate (powder)
Ammonium carbonate (powder)
Calcium carbonate (powder)
Copper carbonate (powder)
Potassium carbonate (powder)
Lead carbonate (powder)
Sodium carbonate (powder)
Calcium hydroxyde (powder)
Copper (II) hydroxyde (powder)
Potassium hydroxyde (powder)
Lead (II) hydroxyde (powder)
Sodium hydroxyde (powder)
Ammonium nitrate (powder)
Calcium nitrate (powder)
Copper nitrate (powder)
Potassium nitrate (powder)
Lead nitrate (powder)
Sodium nitrate (powder)
Calcium sulfate (powder)
Copper sulfate (powder)
Potassium sulfate (powder)
Lead sulfate (powder)
Sodium sulfate (powder)
Waste water (liquid)