# Which type of reaction is AlCl_3 + 3 KOH ->Al(OH)_3+ 3 KCl?

Aug 7, 2018

A double replacement reaction

#### Explanation:

none of the atoms or polyatomic ions change the oxidations states, so it is not a oxidation reduction reaction.

The reaction follows the general form of a double replacement

${A}^{+} {B}^{-} \left(+\right) {C}^{+} {D}^{-}$= ${A}^{+} {D}^{-} \left(+\right) {C}^{+} {B}^{-}$
The positive three ion of Al disassociates with the Chlorine -1 ion.
then the still positive +3 ion of Al then combines with the -1 OH

The positive +1 K disassociates with the Hydroxide ion -1 ion then the still positive +1 K ion combines with the -1 Chlorine ion.

This is a classic example of a double replacement reaction.

Aug 7, 2018

This is a double replacement (double displacement) reaction.

#### Explanation:

In a double replacement reaction, the cations in two compounds switch places. The generic reaction is:

$\textcolor{red}{\text{A"color(green)"X" + color(blue)"B"color(purple)"Y}}$$\rightarrow$$\textcolor{b l u e}{\text{B"color(green)"X" + color(red)"A"color(purple)"Y}}$,

where $\textcolor{red}{\text{A}}$ and $\textcolor{b l u e}{\text{B}}$ are the cations and $\textcolor{g r e e n}{\text{X}}$ and $\textcolor{p u r p \le}{\text{Y}}$ are the anions.

One of the products of a double replacement reaction must be water (neutralization), an insoluble gas (such as $\text{H"_2}$ or $\text{CO"_2}$, or a precipitate (an insoluble solid).

$\textcolor{red}{\text{Al"color(green)("Cl")_3("aq") + 3color(blue)"K"color(purple)("OH")("aq)}}$$\rightarrow$${\text{3"color(blue)("K")color(green)("Cl") + color(red)("Al")(color(purple)("OH"))}}_{3}$

When the aqueous $\text{AlCl"_3}$ and aqueous $\text{KOH}$ solutions are mixed, an insoluble solid is produced. We can see that neither of the products is water or an insoluble gas, but one of the products is a precipitate because it is insoluble in aqueous solutions.

We can find out which product is the precipitate by consulting a solubility table like the one below. We can see that compounds containing alkali metal cations, such as $\text{K"^(+)}$, are soluble in aqueous solutions. We can also see that compounds that contain the hydroxide ion, $\text{OH"^(-)}$, are insoluble, and aluminum is not one of the exceptions. Therefore, the precipitate is the compound $\text{Al(OH)"_3}$.

The entire equation with physical states included is:

$\text{AlCl"_3("aq") + "3KOH(aq)}$$\rightarrow$$\text{Al(OH)"_3("s") + "3KCl(aq)}$

We can use a down arrow to show that the solid is a precipitate.

$\text{AlCl"_3("aq") + "3KOH(aq)}$$\rightarrow$$\text{Al(OH)"_3darr + "3KCl(aq)}$