College Chemistry - Problem Drill 07: Writing Formulas
Question No. 1 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
1. Binary ionic compounds are made of only two elements, cation and anion – the
simplest compound. If one of the two elements is a metal (or ammonium), the
suffix –ide is added to the non-metal atom. Which of the following formulas is
correct for “sodium oxide”?
Question
(A) SO
(B) S2O
(C) NaO
(D) Na2O
A. Incorrect!
Sodium is symbolized with “Na”, not S.
B. Incorrect!
Sodium is symbolized with “Na”, not S.
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C. Incorrect!
These are the correct symbols, but the charges must be balanced.
D. Correct!
The symbols are correct. The charges are balanced in this formula.
This is a binary ionic compound.
Sodium is Na+.
Oxide is O2-.
Na+Na+O2- would give a neutral compound: Na2O.
The correct answer is (D).
Solution
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Question No. 2 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
2. All halogen atoms have multiple oxidation states and share the similar naming
convention for their acids. Which of the following is the correct formula for bromic
acid or hydrogen bromate?
Question
(A) HBr
(B) HBrO3
(C) HBrO2
(D) HBrO4
A. Incorrect!
This is a binary acid without “O”, therefore it is hydrobromic acid with -1 oxidation
state. It is not bromic acid. Recall chloric acid.
B. Correct!
Good job! Start looking at the parallel of chlorine, since their naming system is the
same (halogen). We know chloric acid is HClO3 with its anion chlorate (ClO3-). The
oxidation state is +5. The same applies to bromic acid HBrO3 with its anion bromate
(BrO3-) and oxidation state of +5.
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C. Incorrect!
This is bromous acid with +3 oxidation state. It is not bromic acid. Recall chloric
acid.
D. Incorrect!
Similar to perchloric acid (HClO4), this is perbromic acid with the highest oxidation
of +7 in the bromine family. It is not bromic acid. Recall chloric acid.
This is an acid. “ic” acids come from “-ate” polyatomic ions.
Chlorate is ClO3-, therefore Bromate is BrO3-.
Chloric acid is HClO3, therefore bromic acid is HBrO3. They all have +5 charges for
the halogen elements.
The correct answer is (B).
Solution
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Question No. 3 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
3. Polyatomic ions consist of more than one atom. Atoms are usually bonded
together covalently. They stay together as a single charged unit. One example is
phosphate, a salt of phosphoric acid. Which of the following formulas is correct for
“Ammonium phosphate”?
Question
(A) NH4PO4
(B) (NH4)3PO4
(C) NH4(PO4)3
(D) (NH4)12PO4
A. Incorrect!
The symbols are written correctly, but not the charges. You must balance the
charges.
B. Correct!
Good job. Ammonium (NH4+) and phosphate (PO43-) are combined to give
ammonium phosphate (NH4)3PO4. The charges are correctly balanced.
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C. Incorrect!
The symbols are written correctly, but not the charges. The charges aren’t
balanced.
D. Incorrect!
Don’t multiply the charge by a subscript within the polyatomic ion.
This is a polyatomic ionic compound.
Ammonium is NH41+
Phosphate is PO43-. You do not multiply the polyatomic ion’s subscript by its
charge.
NH4+NH4+NH4+PO43- would result in a neutral compound: (NH4)3PO4
The correct answer is (B).
Solution
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Question No. 4 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
4. Copper is a multivalent atom with +1 and +2 charge. Which of the following
formulas is correct for “copper (II) hydroxide”?
Question
(A) Cu2OH
(B) CuOH2
(C) Cu(OH)2
(D) Co2OH
A. Incorrect!
The roman numeral doesn’t mean that there are two copper atoms. It means the
copper ion has a charge of +2.
B. Incorrect!
When using a subscript with a polyatomic ion, make sure to use parenthesis.
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C. Correct!
Good job! The symbols are correctly written and the charges are correctly balanced.
D. Incorrect!
The symbol for copper is “Cu”, not “Co”.
This is a polyatomic ionic compound.
The roman numeral gives the cation charge. Copper (II) is Cu 2+
Hydroxide is OHCu2+OH-OH- would give a neutral compound.
Remember to use parenthesis with polyatomic ions:
Cu(OH)2
The correct answer is (C).
Solution
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Question No. 5 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
5. Silicon dioxide is also known as silica, commonly found in sand. Which of the
following is correct for “silicon dioxide”?
Question
(A) SiO2
(B) Si2O
(C) SiO
(D) SO2
A. Correct!
Good job! The “di” indicates there are two oxygen atoms. It is the correct formula
for silicon dioxide.
B. Incorrect!
The “di” is with the oxygen, not the silicon.
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C. Incorrect!
“Di” means two oxygen atoms, O2.
D. Incorrect!
The symbol for silicon is “Si”, not “S”.
This is a binary covalent compound.
Do not worry about charges as they don’t form charges—just write what the
compound says, using the prefixes to designate subscripts. (Remember “mono” is
not used on the first element).
Silicon is Si.
Dioxide is O2.
The correct answer is (A).
Solution
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Question No. 6 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
6. Iron can have +2 and +3 charges, so the naming of such needs to indicate the
charge. Which of the following is correct for iron (III) carbonate?
Question
(A) Fe3CO3
(B) Fe3(CO3)2
(C) Fe2(CO3)2
(D) Fe2(CO3)3
A. Incorrect!
The roman numeral indicates the charge of the iron ion, not the number of atoms in
the subscript.
B. Incorrect!
The roman numeral indicates the charge of the iron ion, not the number of atoms.
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C. Incorrect!
The symbols are correct. The charges are not balanced in this choice.
D. Correct!
The formula is written correctly. Ion (III) means Fe3+.The charges are balanced in
this choice.
This is a polyatomic ionic compound. The roman numerals give the charge of the
cation.
Iron (III) is Fe3+.
Carbonate is CO32-.
Fe3+Fe3+CO32-CO32-CO32- is a neutral compound.
Remember to use parenthesis with polyatomic ions.
The correct formula is Fe2(CO3)3.
The correct answer is (D).
Solution
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Question No. 7 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
7. Binary acids are two-element acids in which hydrogen is combined with a
second non-metal. Which of the following is hydrosulfuric acid?
Question
(A) HS
(B) H2S
(C) H2SO3
(D) H2SO4
A. Incorrect!
You need to balance the charges.
B. Correct!
Good job! A “hydro” acid does not contain oxygen and the charges are balanced.
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C. Incorrect!
A “hydro” acid does not contain oxygen.
D. Incorrect!
A “hydro” acid does not contain oxygen.
The “hydro” acids do not contain oxygen.
“sulfuric” is S2-.
Acids begin with H+.
H+H+S2- is a neutral compound: H2S
The correct answer is (B).
Solution
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Question No. 8 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
8. There are many nitrogen oxide binary compounds where a nitrogen atom can
have various charges. Among them, dinitrogen tetroxide is a powerful oxidizing
agent and is also one of the most important rocket propellants. Which of the
following is dinitrogen tetraoxide?
Question
(A) Ni2O4
(B) N2O4
(C) Ni2O5
(D) N2O5
A. Incorrect!
The symbol for nitrogen is “N”, not “Ni”.
B. Correct!
Good job. This is a binary covalent compound. Use its prefixes for the naming. ”Di”
= 2 and “tetra” = 4. Therefore, its formula is N2O4.
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C. Incorrect!
The symbol for nitrogen is “N”, not “Ni”.
D. Incorrect!
“tetra” stands for “4” atoms of oxygen, not 5.
This is a binary covalent compound. They do not form charges. Use the prefixes to
indicate subscripts.
Dinitrogen is N2.
Tetraoxide is O4.
The correct molecular formula is N2O4.
The correct answer is (B).
Solution
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Question No. 9 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
9. A binary ionic compound contains only two elements, one metal and one nonmetal. Which of the following is calcium fluoride?
Question
(A) Ca2F
(B) CaF
(C) CaF2
(D) C2F
A. Incorrect!
The symbols are correct. The charges aren’t balanced.
B. Incorrect!
The symbols are correct. The charges aren’t balanced.
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C. Correct!
Good job! The +2 charge of the calcium is balanced with 2 fluoride ions with -1
charge each. The formula is correct with the subscript.
D. Incorrect!
The symbol for calcium is “Ca”, not “C”.
This is a binary ionic compound.
Calcium is Ca2+.
Fluoride is F-.
Ca2+F-F- is a neutral compound: CaF2
The correct answer is (C).
Solution
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Question No. 10 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
10. Phosphoric acid is the most important oxoacid (oxygen-containing acid) of
phosphorus, used to make fertilizers. It has many other industrial applications.
Which of the following is phosphoric acid?
Question
(A) HP
(B) H3P
(C) H3PO4
(D) H12PO4
A. Incorrect!
Acids without “hydro” contain oxygen. It should be an oxoacid.
B. Incorrect!
Acids without “hydro” contain oxygen. It should be an oxoacid. H3P or PH3 is
phosphine.
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C. Correct!
The “ic” acid came from the “ate” anion (phosphate PO4-). This is the correct
formula for phosphoric acid. When in doubt, try to draw a parallel on an acid you
know (i.e. sulfuric acid H2SO4).
D. Incorrect!
Don’t multiply the charge of a polyatomic ion by the subscript within the ion. The
charges are not balanced with this formula.
This is an acid. “ic” acids come from “ate” polyatomic ions.
Phosphate is PO43Acids begins with H+
H+H+H+PO43- is a neutral compound: H3PO4
The correct answer is (C).
Solution
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