Silver nitrate which is AgNO3 and sodium chloride which is NaCl are both soluble in water. When aqueous solutions of the two are mixed a double replacement reaction takes place. It's also called a precipitation reaction, because an insoluble precipitate forms:
`AgNO_3_(aq) + NaCl_((aq))-> AgCl_((s)) + NaNO_3_(aq)`
Written as an ionic equation:
`Ag^+_(aq) + NO_3^+_(aq) + Na^+_(aq) +Cl^-_(aq) -> AgCl_((s)) + Na^+_(aq) + NO_3^-_(aq)`
Solid AgCl (silver chloride) forms because it's not soluble in water.
Precipitation reactions are often represented by net ionic equations, which leave out the aqueous (dissolved) ions that appear on both sides of the equation. The net ionic equation for this reaction is:
`Ag^+_(aq) + Cl^-_(aq)> AgCl_((s))`
The ions that are not included in the net ionic equation are called spectator ions because they are present but don't participate in the reaction.
To determine the outcome of a double replacement reaction, write formulas for products by switching the ions in the reactants. The negative ion of each reactant will be in a compound with the positive ion of the other. Now use a table of solubility rules to determine if either product is insoluble. If so, it will precipitate. If both products are soluble there will be no precipitate. Ions that are aqueous on both sides of the reaction are spectator ions and they cancel out.
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