Oxidation States and Chromium Compounds

The video tutorial explains how to find oxidation numbers for each element in magnesium dichromate (MgCr2O7). It begins by noting that the compound is neutral, meaning the oxidation numbers must sum to zero. Magnesium, being in group two, has an oxidation number of +2. Chromium, a transition metal, has variable oxidation states, so it is represented as 'x'. Oxygen is consistently -2. An equation is set up to solve for 'x', resulting in an oxidation number of +6 for chromium. The video concludes by mentioning an alternative method using the dichromate ion's charge.

What is the overall charge of the compound MgCr2O7?

• Positive

• Variable

• Neutral

• Negative

What is the oxidation number of magnesium in MgCr2O7?

• +1

• 0

• +3

• +2

Why is the oxidation number of chromium initially unknown?

• It has multiple oxidation states

• It is a non-metal

• It is always zero

• It is a noble gas

What is the oxidation number of oxygen in most compounds?

• +1

• 0

• -2

• -1

How many chromium atoms are present in MgCr2O7?

• 4

• 1

• 2

• 3

What is the oxidation number of each chromium atom in MgCr2O7?

• +6

• +3

• +4

• +5

What is the total contribution of oxygen atoms to the oxidation state in MgCr2O7?

• -8

• -10

• -12

• -14

What is the charge of the dichromate ion (Cr2O7)?

• 1+

• 2-

• 1-

• 2+

What alternative method can be used to find the oxidation number of chromium?

• Using the charge of the dichromate ion

• Assuming chromium is a noble gas

• Using the periodic table

• Guessing based on color