Laboratory Preparation & Procedure
Materials:
- 24-well plate
- glass stirring rod
- 150-mL beaker
- deionized water
- paper towels
- transfer pipettes
- 0.1 M AgNO₃
- 0.1 M Zn(NO₃)₂
- 0.1 M Pb(NO₃)₂
- 0.1 M Fe(NO₃)₃
- 0.1 M NaNO₃
- 0.1 M NaOH
- 0.1 M Na₂SO₄
- 0.1 M Na₃PO₄
- one unknown cation solution
Safety:
Wear goggles and gloves. Collect all liquids and rinses in the waste beaker. Rinse skin with water if contacted. Clean wells thoroughly to avoid cross‑contamination.
Procedure:
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Obtain a 24-well plate and set up a 3 × 6 grid for testing five known cation solutions & your unknown solution as shown in your data pages.
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In the first column, place three drops of silver nitrate solution (AgNO₃) into each of the three wells.
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In the second column, place three drops of sodium nitrate solution (NaNO₃) into each of the three wells.
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In the third column, place three drops of zinc nitrate solution (Zn(NO₃)₂) into each of the three wells.
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In the fourth column, place three drops of lead nitrate solution (Pb(NO₃)₂) into each of the three wells.
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In the fifth column, place three drops of iron(II) nitrate solution (Fe(NO₃)2) into each of the three wells.
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First row: Add three drops of 0.1 M sodium hydroxide (NaOH) to each well containing a cation solution.
- Using your glass stirring rod, stir each mixture gently, being sure to wash the glass stirring rod with deionized water & drying with a paper towel each time between solutions. This is extremely important to avoid cross-contamination & the appearance of false-positive results.
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Observe and record results in Data Table A, noting whether a precipitate forms (ppt) or not (no ppt) and describing any color or texture changes.
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Second row: Add three drops of 0.1 M sodium sulfate (Na₂SO₄) to each well. Record observations as above.
- Using your glass stirring rod, stir each mixture gently, being sure to wash the glass stirring rod with deionized water & drying with a paper towel each time between solutions. This is extremely important to avoid cross-contamination & the appearance of false-positive results.
- Observe and record results in Data Table A, noting whether a precipitate forms (ppt) or not (no ppt) and describing any color or texture changes.
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Third row: Add three drops of 0.1 M sodium phosphate (Na₃PO₄) to each well. Record observations as above.
- Using your glass stirring rod, stir each mixture gently, being sure to wash the glass stirring rod with deionized water & drying with a paper towel each time between solutions. This is extremely important to avoid cross-contamination & the appearance of false-positive results.
- Observe and record results in Data Table A, noting whether a precipitate forms (ppt) or not (no ppt) and describing any color or texture changes.
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Keep the well plate with known results nearby for direct comparison during unknown identification.
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Obtain an unknown solution containing one or more of the cations used in this experiment (Ag⁺, Fe2+, Na⁺, Pb²⁺, Zn²⁺). Record the unknown number in your data table.
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In the sixth column, place three drops of unknown solution into each of the three wells.
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To the first well of the unknown, add three drops of 0.1 M NaOH. Record observations.
- Using your glass stirring rod, stir the mixture gently, being sure to wash the glass stirring rod with deionized water & drying with a paper towel before moving on.
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To the second well of the unknown, add three drops of 0.1 M Na₂SO₄. Record observations.
- Using your glass stirring rod, stir the mixture gently, being sure to wash the glass stirring rod with deionized water & drying with a paper towel before moving on.
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To the third well of the unknown, add three drops of 0.1 M Na₃PO₄. Record observations.
- Using your glass stirring rod, stir the mixture gently, being sure to wash the glass stirring rod with deionized water & drying with a paper towel before moving on.
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Compare the unknown’s reaction patterns to your known results. Identify the cation(s) present in your unknown and explain your reasoning based on your recorded observations.
