10 Questions
What is the correct way to write the precipitation equation for a reaction between silver nitrate and sodium sulfide?
AgNO3 + Na2S → Ag2S + NaNO3
What is the purpose of predicting which products are dissolved in water or not in a precipitation equation?
To identify the insoluble compound(s)
What happens to the ionic form of the dissolved compound in a precipitation equation?
It is excluded from the final equation
What is the solubility product constant (Ksp) a measure of?
The level at which a solute dissolves in solution
What is the correct way to write the ionic form of silver nitrate in a precipitation equation?
Ag+ + NO3-
What is the purpose of writing a precipitation equation in ionic form for dissolved compounds?
To distinguish between dissolved and undissolved compounds
What is the correct way to predict which products are dissolved in water or not in a precipitation equation?
By looking at the ionic form of the compounds
What happens to the molecular form of the expected product in a precipitation equation?
It is included in the final equation
What is the correct way to weigh a precipitation equation?
By balancing the equation
What is the relationship between the solubility product constant (Ksp) and the solubility of a substance?
Higher Ksp values indicate higher solubility
Study Notes
Precipitation Reactions
- Occur in aqueous solutions, resulting in an insoluble precipitate
- Solubility rules:
- All nitrate and acetate salts are dissolved in water
- Most sulfate salts are dissolved in water, except for BaSO4, PbSO4, Hg2SO4, and CaSO4
- Salts containing alkali metal ions (Li+, Na+, Cs+, and K+) are dissolved in water
- All ammonium compounds (NH4) are dissolved in water
- Halide ions (chloride, bromide, and iodide) dissolve in water, except for silver, lead, and mercury ions
Insoluble Salts
- All hydroxide compounds are insoluble, except for bonding with ammonium and barium ions and alkali metal ions
- All carbonate, sulfite, chromate, and phosphate salts are insoluble, except for bonding with ammonium ions and alkali metal ions
- All sulfide compounds are insoluble, except for bonding with ammonium ions and alkali metal ions
Detection of End Point in Precipitation Reaction
- Methods used to determine the end of the reaction: light scattering, electrodes, and indicators (Mohr's method, Volhard's method, Fajan's method)
Mohr's Method
- Utilizes chromate as an indicator
- Chromate forms a precipitate with Ag+, but the precipitate has a greater solubility than AgCl
- AgCl is formed first, and after all Cl- is consumed, the first drop of Ag+ in excess reacts with the chromate indicator, giving a reddish precipitate
- Conditions: neutral medium (pH 7), as alkaline or acidic solutions can interfere with the reaction
- Error: using a dilute chromate solution, which requires additional Ag+ for the Ag2CrO4 to form, leading to a late equivalent point; can be corrected by determining a blank
Volhard's Method
- Indirect method used for determining anions that precipitate with silver (e.g., Cl-, Br-, and I-)
- Excess Ag+ is added to the unknown solution containing Fe3+ as an indicator
Writing Precipitation Equations
- Write the molecular form of the expected product in the precipitation equation
- Predict which products are dissolved in water or not, and abbreviate accordingly
- Write the equation in ionic form for soluble compounds only, and molecular form for insoluble compounds
- Exclude the ionic form of the dissolved compound from the equation and balance the equation
Solubility Product Constant (Ksp)
- Represents the level at which a solute dissolves in solution
- Higher Ksp value indicates higher solubility of a substance
Learn about precipitation reactions that occur in aqueous solutions, including the formation of insoluble precipitates and predicting the type of precipitate based on solubility rules.
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