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how do i write a double replacement reaction (balanced) between sulfuric acid and...

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user9551564 | eNotes Newbie

Posted November 8, 2013 at 3:06 AM via web

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how do i write a double replacement reaction (balanced) between sulfuric acid and magnesium hydroxide

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caledon | High School Teacher | (Level 1) Educator

Posted November 8, 2013 at 3:48 AM (Answer #1)

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A double replacement reaction takes place between two ionic compounds, and follows this pattern:

`(A^+ B^-) + (C^+ D^-) -> (A^+ D^-) + (C^+ B^-)`

The ionic compounds are just trading "partners", so to speak.

The Compounds:

Sulfuric acid has the formula `H_2 SO_4`

It is composed of two Hydrogen ions, with a total charge of +2, and one sulfate ion, with a charge of -2.

Magnesium hydroxide has the formula `Mg(OH)_2`

It is composed of one Magnesium ion, with a total charge of +2, and two hydroxide ions, each with a charge of -1.

The Reaction:


`(H_2^+2)(SO_4^-2) + (Mg^+2)(OH)_2^-2`

Double replacement:

`(H_2^+2)(OH)_2^-2) + (Mg^+2)(SO_4^-2)`

which gives us

`H_2(OH)_2 + MgSO_4`

The hydrogen-hydroxide compound has a formula of

`H_4O_2`

which simplifies to

`2 H_2O`

So, the complete reaction is:

`H_2SO_4 + Mg(OH)_2 -> MgSO_4 + 2H_2O`

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ayl0124 | TA , Grade 12 | Valedictorian

Posted June 2, 2014 at 12:42 AM (Answer #2)

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Think of a chemical reaction as a square dance. Two couples are dancing and then they swap dates. The resulting couples are a mix of the original couples.

`AB + CD -> AD + CB`

In order to write a double replacement, first find your original chemicals.

`H_2SO_4 + Mg(OH)_2 -> ?`

Note the charges on all the ions. Swap the cations...

`H_2SO_4 + Mg(OH)_2 -> MgSO_4 + H_2O`

Remember, matter cannot be created nor destroyed. There should be an equal amount of atoms in each side of the reaction. Therefore, we must balance the equation to get your final answer.

`H_2SO_4 + Mg(OH)_2 -> MgSO_4 + 2H_2O` 

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