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Ionic Bonding and Solubility in Double Replacement Reactions
Introduction: In double replacement reactions, two different ionic compounds will exchange metal ions. Remember that in ionic bonding electrons are given up by metals and taken in by nonmetals in order to fill the outer (valence) electron shells of the atoms. When this happens, positive and negative ions are formed which are then attracted to each other by the opposite charges. If one of the new ionically bonded compounds that is formed is not soluble in water, it will form a precipitate (p). A precipitate is a solid powder that slowly sinks to the bottom of the solution.
Ex: copper sulfate + sodium carbonate ---------> copper carbonate (p) + sodium sulfate
or CuSO4 + Na2CO3 ---------> CuCO3 (p) + Na2SO4
You may refer to the table of solubilities provided to find out which compound formed the precipitate. If you do not detect a precipitate being formed, there was probably no exchange or both new compounds were also soluble in water. You can also use the solubility table to predict which compounds will produce precipitates.
Some of the ions involved are polyatomic ions. These are groups of ions that as a unit either gain or lose electrons and become an ion. Polyatomic ions behave as a single unit and the atoms composing it do not separate. If the ion has a negative charge, it has gained one or more electrons. If an ion has a positive charge, it has lost one or more electrons. Some charges on polyatomic ions are given below. These will help you to balance equations.
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MnO4-1
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SO4-2
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CO3-2
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C2H3O2-1
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NO3-1
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PO4-3
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OH-1
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NH4+1
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Materials: Spotting plate and dropper bottles with a variety of chemical solutions.
Method: CAUTION!! Some chemicals may be POISONOUS!
Wear Goggles and Apron. Rinse skin or clothing if in contact with chemical solutions.
Be careful NOT to mix droppers between bottles. This would contaminate solutions.
1. Write the chemical formula next to the name of the solution below:
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potassium iodide
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sodium bicarbonate
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sodium carbonate
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potassium ethanoate
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calcium chloride
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sodium phosphate
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barium chloride
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copper (II) sulfate
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magnesium sulfate
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copper (II) chloride
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sodium chloride
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lead (II) nitrate
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silver nitrate
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calcium hydroxide
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potassium nitrate
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zinc sulfate
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sodium hydroxide
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nickel (II) sulfate
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potassium permanganate
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Iron (II) chloride
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2. Choose two of the solutions you would like to mix together. Add three drops of one solution to a well on the spotting plate. Next add three drops of the other solution to the same well. Mix with a gentle swirl. Do not add more than two solutions at a time to the same well.
3. If a precipitate forms, write your observations on the data table and the balanced equation for that reaction.
Data Table:
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Observations
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Balanced chemical reaction (reactants -----> products)
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