Chemistry Problems for Schools on “P-Block Elements – Oxoacids of Halogens”.
1. Why does fluorine form only one oxoacid?
a) High electronegativity of fluorine
b) Large radius of fluorine
c) Presence of a single valence electron
d) High electropositivity of fluorine
Answer: a
Clarification: Fluorine is the most electronegative element on the periodic table. Due to its high electronegativity and small atomic radius, fluorine only forms one oxoacid, HOF known as hypofluorous acid.
2. All halogens form only one oxoacid due to their high electronegativity and small size.
a) True
b) False
Answer: b
Clarification: Only fluorine forms one oxoacid due to their high electronegativity and small size. The other halogens form several oxoacids, most of them cannot be isolated in pure state. They are stable only in aqueous solutions or in the form of their salts.
3. Which of the following is not an oxoacid of chlorine?
a) HCl
b) HOCl
c) HOClO
d) HOClO2
Answer: a
Clarification: HCl, known as hydrochloric acid and is not an oxoacid. All oxoacids have the acidic hydrogen bound to an oxygen atom, in HCl the hydrogen is bound to the chlorine atom making it a Lewis acid.
4. Which of the following is a hypohalous acid?
a) HOClO
b) HOBrO3
c) HOF
d) HOIO3
Answer: c
Clarification: Hypohalous acids are oxoacids in which the hydroxyl group is singly bonded to a halogen. In HOF the hydroxyl group is singly bonded to fluorine making it a hypohalous acid named hypofluorous acid.
5. What is the bond angle of hypochlorous acid?
a) 108°
b) 108.5°
c) 109°
d) 109.5°
Answer: d
Clarification: Hypochlorous acid is an oxoacid of chlorine in which the hydrogen atom is singly bonded to the oxygen atom and chlorine is also singly bonded to oxygen atom forming a bend structure with bond angle 109.5°.
6. How many bonds does chlorine make with oxygen in perchloric acid?
a) 3 double bonds and a single bond
b) 7 single bonds
c) 2 single bonds and 2 double bonds
d) 3 single bonds and a double bond
Answer: a
Clarification: The formula for perchloric acid is HOClO3, in which the chlorine group is attached to 3 oxygen atoms and a hydroxyl group. The 3 oxygen atoms are attached to chlorine through a double bond and the hydroxyl group is singly bonded to chlorine. Thus, there are 3 double bonds and a single bond between oxygen and chlorine.
7. Which of the following shows the correct sequence of acidic strength?
a) HClO4 > HBrO4 > HIO4
b) HClO44 4
c) HClO4 = HBrO4 > HIO4
d) HClO4 > HIO4 > HBrO4
Answer: a
Clarification: As the electronegativity of the halogen decreases, the tendency of the XO3 group to withdraw electrons of the O—H bond towards itself decreases and hence the acid strength of the perhalic acid decreases in the same order.
8. Which the following is the correct order of oxidizing power of perhalates?
a) BrO4–4–4–
b) IO4– > BrO4– > ClO4–
c) IO4–4–4–
d) BrO4– > IO4– > ClO4–
Answer: d
Clarification: Perhalates are strong oxidizing agents, their oxidizing power decreases in the order: BrO4– > IO4– > ClO4–. This can be explained on the basis of their electrode potentials. Although among perhalates BrO4– is the strongest oxidizing agent, yet it is weaker oxidizing agent than F2.
9. Which of the following is the correct order of acidic strength?
a) HClO44 2
b) HClO4 = HClO3 = HClO2
c) HClO4> HClO3 > HClO2
d) HClO2 > HClO4 > HClO3
Answer: c
Clarification: Acidic strength of oxoacids of the same halogen increases with increase in the oxidation number of the halogen. The oxidation number of halogens in HClO4, HClO3 and HClO2 is 7, 5 and 3 so the Acidic strength of HClO4 is greatest followed by HClO4 and HClO2.
10. The acidic strength of HClO4 is lesser than HClO.
a) False
b) True
Answer: a
Clarification: The acidic strength of the oxoacids of the same halogen can be determined by the oxidation number of the halogen in the compound. In HClO4 the oxidation number of chlorine is +7 and in HClO the oxidation number of chlorine is +1. So, the acidic strength of HClO4 is greater than HClO.
Chemistry Problems for Schools,