CHE2611
ASSIGNMENT 4
FULL SOLUTIONS
Complete Solutions
INORGANIC CHEMISTRY II THEORY
26 JULY 2024
UNISA
2024
,SOLUTION
(i) Oxoacid: An oxoacid is an acid that contains oxygen, hydrogen, and one or more
other elements (usually a nonmetal). These acids have the general formula H𝑛XO𝑚 ,
where X represents the central atom and n and m are integers. Oxoacids typically have
acidic hydrogen atoms attached to oxygen atoms. Examples of oxoacids include
sulfuric acid ( H2SO4 ), nitric acid ( HNO3 ), and phosphoric acid ( H3PO4 ).
(ii) Aqua acid: An aqua acid is an acid that exists as a hydrated ion in an aqueous
solution. Aqua acids are formed when acids dissolve in water and donate hydrogen ions
( H+ ). The term "aqua" refers to the water molecules that are part of the acid structure.
An example of an aqua acid is hydrochloric acid ( HCl ) and acetic acid (CH3COOH)
when it is dissolved in water, forming hydronium ions ( H3O+ ) and chloride ions ( Cl− ).
(iii) Polyprotic acid: A polyprotic acid is an acid that can donate more than one
hydrogen ion ( H+ ) per molecule. These acids have more than one ionizable hydrogen
atom. Polyprotic acids can undergo stepwise ionization, releasing one hydrogen ion at a
time. Examples of polyprotic acids include sulfuric acid ( H2SO4 ), which can donate
two hydrogen ions, and phosphoric acid ( H3PO4 ), which can donate three hydrogen
ions.
(iv) Hydroxoacid: A hydroxoacid, also known as an oxyacid or oxoacid, is an acid that
contains hydrogen, oxygen, and a hydroxyl group ( OH− ). These acids typically have
acidic hydrogen atoms attached to oxygen atoms, and they can also contain other
elements. An example of a hydroxoacid is sulfuric acid ( H2SO4 ), which has two acidic
hydrogen atoms attached to oxygen atoms and one hydroxyl group.
, SOLUTION
2.
1. (a) Pka of oxo acids:
(i) Pauling’s First Rule for predicting the pKa of oxoacids is:
• For the oxoacid OpE(OH)q , 𝑝Ka≈8−5p
This rule means that the pKa of an oxoacid depends on the number of oxygen atoms (p)
attached to the central atom (E), and that the more oxygen atoms there are, the lower
the pKa and the stronger the acid.
(ii) Pauling’s Second Rule for predicting the pKa of oxoacids is:
• The successive pKa values of polyprotic acids (those with q > 1), increase by 5
units for each successive proton transfer.
This rule means that for oxoacids that can donate more than one proton, the pKa value
increases by 5 for each ionization step, making it harder to remove the next proton.
2. b)Tetraoxoanions are anions that have four oxygen atoms bonded to a central atom X.
The structures and charges of the tetraoxoanions of X = Si, P and S are shown below:
SiO44− : A tetrahedron with Si at the center and four O atoms at the vertices. Each O
atom has a single bond to Si and three lone pairs. The charge of 4- is distributed equally
among the four O atoms.
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