Regents Chemistry Exam June 2024 Question 45
45 In which compound does sulfur have an oxidation state of +4?
(1) K2S (3) SO2
(2) CaS (4) SO3
Solution:
Rules for determining oxidation numbers:
Free, neutral elements have an oxidation number of 0.
Group 1 metals have an oxidation number of +1 (can be found on the Periodic Table)
Group 2 metals have an oxidation number of +2
Oxygen is -2 in all compounds other than peroxide (H2O2)
Hydrogen is +1 unless it is bonded to a metal
The sum of oxidation numbers in a neutral molecule is 0
The sum of oxidation numbers in a charged molecule (ion) is equal to the charge
Let's look at each answer choice. K2S, The oxidation number of K is +1 which you can find on the Periodic Table. We can make an equation to find the oxidation number of S. +1(2)+x = 0 , x=-2
CaS. The oxidation number of Ca found on the Periodic Table is +2. +2+x=0, x=-2 SO2. The oxidation number of O found on the Periodic Table is -2. x+ (2*-2)= 0, X=+4 Choice 3 is the correct answer choice.
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