Question #09e54

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Question #09e54

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Answer 1 · 2015-07-03T09:48:02

You go by the oxidation numbers of potassium and oxygen.

Explanation:

You're actually looking for oxidation number, not charge.

The oxidation state of chromium in potassium dichromate, $K_{2} C r_{2} O_{7}$ $K_2Cr_2O_7$ , can be determine with two things in mind

the oxidation states of potassium and oxygen;
thefact that the compound is neutral.

Potassium is a group 1 metal, which means that its oxidation state is always $+1$ $"+1"$ . On the other hand, oxygen is a nonmetal that almost always has an oxidation state of $-2$ $"-2"$ .

So, start by writing down what you know

$+ 1 K_{2} ? C r_{2} - 2 O_{7}$ $stackrel(color(blue)(+1))(K_2) stackrel(color(green)(?)) (Cr_2) stackrel(color(blue)(-2))(O_7)$

The compound is neutral, which means that the oxidation states of all atoms that make up the compound must add up to give zero.

Since you have 2 potassium, 2 chromine, and 7 oxygen atoms, you'll get

$2 \cdot (+ 1) + 2 \cdot ? + 7 \cdot (-2) = 0$ $2 * (color(blue)(+1)) + 2 * color(green)("?") + 7 * color(blue)(("-2")) = 0$

$2 + 2 ? - 14 = 0 \Rightarrow ? = \frac{14 - 2}{2} = +6$ $2 + 2? - 14 = 0 => ? = (14-2)/2 = color(green)("+6")$

The oxidation state of chromium in potassium dichromate is indeed $+6$ $"+6"$ .

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Question #09e54

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