Page 364 - Chemistry eBook

58 State the trend in ionic radius as the elements in Group 2 are considered in order of increasing atomic number. [1]
59 Explain, in terms of electrons, why the ionic radius of a Group 2 element is smaller than its atomic radius. [1]
Sample Regents Questions
Base your answers to questions 60 and 61 on the information below.
61 State why the entropy of the reactant is less than the entropy of the products. [1]
June 2011 #60
Answer
P.S./Chem.–June ’11 [9] [OVER] +5
Explanation: Let’s take the compound in the reactant that includes Cl: KClO3.
Now let’s apply the rules for oxidation numbers in a compound.
We know that all the oxidation numbers in a compound must equal zero.
So let’s figure out the oxidation states of K and O. Then we can figure out the oxidation state of Cl. K: +1
O: -2 x 3 (subscript) = -6
(+1)+(-6)= -5
If the total oxidation states of a compound must equal zero, then Cl’s oxidation state must equal +5. (+5-5=0)
The balanced equation below represents the decomposition of potassium chlorate. 2KClO3(s) → 2KCl(s) + 3O2(g)
60 Determine the oxidation number of chlorine in the reactant in the equation. [1]
363 © UNIT 10: OXIDATION & REDUCTION