Education • All: 4.2: Precipitation Reaction

PRECIPITATION REACTION

Finely divided solid (s). One or both products must precipitate, that is create an insoluble compound:

$\large \fn_cm \\\overset{AX}{Ionic\;Compound}\;+\;\overset{BY}{Ionic\;Compound}\;\rightarrow \;\overset{Ionic}{BX}\;+\overset{Ionic}{AY}$

SOLUBILITY RULES

ALWAYS soluble:

$\large \dpi{120} \fn_cm \\ {\color{DarkBlue} Group\;I\;Metals,\;NH_{4}^{+},\;NO_{3}^{-},\;CH_{3}COO^{-}}$

MOSTLY insoluble:

$\large \dpi{120} \fn_cm \\ {\color{Purple} CO_{3}\;^{2-},\;PO_{4}\;^{3-},\;Ag^{+},\;Hg_{2}\;^{+2},\;Pb\;^{2+}}$

PRECIPITATION / METATHESIS / DOUBLE REPLACEMENT

REACTIONS

Example:

Write the molecular, ionic and net ionic equation, for the reaction between Barium Chloride and Potassium Sulfate.

Step 1 (Molecular Equation)

Write the balance equation. Refer to the solubility rules to see if there's and insoluble product. If so, it means the reaction occurs since there's a precipitate.

MOLECULAR EQUATION:

$\large \dpi{120} \fn_cm \\ BaCl_{2}\;(aq)\;+\;K_{2}SO_{4}\;(aq)\;\rightarrow \;2KCl\;(aq)\;+\;{\color{Purple} BaSO_{4}\;(s)}$

Step 2 (Ionic Equation)

Write out all the ions for the aqueous compounds and cross out everything that's the same in both sides of the equation (Called Spectator ions)

IONIC EQUATION:

$\large \dpi{120} \fn_cm \\ Ba^{2+}\;+\;\underline{2Cl^{-}}\;+\;\underline{2K^{+}}\;+\;SO_{4}\;^{2-}\;\rightarrow \;\underline{2K^{+}}\;+\;\underline{2Cl^{-}}\;+\;BaSO_{4}\;(s)$

Step 3 (Net Ionic Equation)

Write out the remaining elements/compounds.

NET IONIC EQUATION:

$\large \dpi{120} \fn_cm \\ Ba^{2+}\;(aq)\;+\;SO_{4}\;^{2-}\;(aq)\;\rightarrow \;BaSO_{4}\;(s)$

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4.2: Precipitation Reaction

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