Help with Polyatomic Ions

Help Questions

AP Chemistry › Help with Polyatomic Ions

Questions 1 - 3

1

When the ionic compound is put in water, it dissociates to produce which of the following ions?

$NH_4^+\ \text{and}\ NO_3^-$

$N^+,\ H^+,\ \text{and}\ O^{2-}$

$NH_4^+,\ N^+,\ \text{and}\ O^{2-}$

$NH_3,\ H^+,\ \text{and}\ NO_3^-$

$H^+,\ N^{3+},\ \text{and}\ O^{2-}$

Explanation

and are known as polyatomic ions. When a compound made up of polyatomic ions ionizes in water, it separates into the original polyatomic ions, not the individual elements.

$NH_4NO_3\rightarrow NH_4^++NO_3^-$

2

Which of the following polyatomic ions has a net charge of ?

$CO_{3}$

$PO_{4}$

$NO_{2}$

$ClO_{3}$

Explanation

For this question, you need to have the charges of polyatomic ions memorized. This will tell you that of the answer choices only the carbonate ion has a net charge of .

Chlorate: $ClO_{3}^-$

Nitrite: $NO_{2}^-$

Phosphate: $PO_{4}^{3-}$

Carbonate: $CO_{3}^{2-}$

3

What is the correct molecular formula for phosphoric acid?

$H_{3}PO_{4}$

$H_{3}PO_{3}$

$H_{3}P$

$H_{3}PO_{3}$

None of the answer choices are correct

Explanation

Phosphoric acid combines a single phosphate ion with three hydrogen ions. The correct molecular formula is $H_{3}PO_{4}$ .

$PO_{4}^{3-}+3H^{+}\rightarrow H_{3}PO_{4}$

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