What is the oxidation state of Cr in each compound? b. CrO3

Video transcript

All right. Hi everyone. So this question is asking us to determine the chemical formula of the below compound. Then determine the halogens oxidation number. The compound in question being perchloric acid option A says HCLO two with an oxidation state of positive three. Option B says HCO three with an oxidation state of positive five. Option C says HCL 207 with an oxidate oxidation state of positive six. And option D says HCLO four with an oxidation state of positive seven. Now recall it perchloric acid has a chemical formula of HCLO four. So by using this chemical formula, we can go ahead and find the oxidation state of our halogen which is chlorine in this case. Now, for the purposes of this question, right? Because the oxidation state of chlorine is currently not known to us. I'm going to treat it as a variable in this case. X because by recalling the oxidation states of my other atoms in this case, hydrogen and oxygen, I can use that to solve for my ex starting off with hydrogen. Now recall that hydrogen can generally have an oxidation state of either positive or negative one. It's a positive one when hydrogen is connected to a non metal, but it's negative one when the hydrogen is connected to either metals or boron. And it just so happens that all atoms in perchloric acid are nonmetals. So hydrogen is going to have an oxidation state of plus one or positive one. And oxygen, oxygen generally has an oxidation state of negative two. Now, some exceptions do apply if the compound itself is either a peroxide or a super oxide. But those exceptions don't apply in the case of perchloric acid. So here oxy sorry oxygen is going to have an oxidation state of negative two. So I can use these oxidation states and I can use them to solve for eggs like I mentioned previously, right? Because recall that when you add the oxidation states of each individual atom multiplied by the number of each atom in your compound, that sum total should be equal to the charge of your compound, which in this case happens to be zero. Right? So here, in addition to taking into consideration the oxidation states, you also have to consider the number of each atom in your compound. It just so happens that we only have one hydrogen, we have one hydrogen, but we have four atoms of oxygen and perchloric acid. So in my equation, I should be multiplying my negative two, which is the oxidation state of oxygen by four. And so when I simplified this expression, I get that one added to X and subtracted by eight gives me or is equal to zero. So at this point, I can go ahead and solve for X to give me positive seven. So the oxidation state for chlorine and perchloric acid. In other words, my X is equal to positive seven. So my answer is going to be option D in the multiple choice, the chemical formula of perchloric acid is HC four and the oxidation state of my halogen chlorine is positive seven. So with that being said, thank you so very much for watching and I hope you found this helpful.