Ready to explore the empirical formula of ionic compounds? Dive into our free empirical formula ionic compounds quiz to discover how the chemical formula of an ionic compound represents the precise ratio of positive and negative ions. You'll learn to determine lowest whole-number ratios, predict formulas based on charges, and sharpen your problem-solving for real-world applications. This quiz on naming ionic compounds and balancing charge equips chemistry students and enthusiasts with instant feedback and clear explanations. For deeper practice, visit our calculations with chemical formulas and equations tutorial or explore more empirical and molecular formula practice . Start now and ace every formula with confidence!
Easy
What is the empirical formula of magnesium chloride?
MgCl2
MgCl
Mg2Cl2
MgCl3
Magnesium donates two electrons to form Mg2+ and each chloride is Cl, so two chlorides are needed for charge balance, giving MgCl2. Ionic formulas are determined by balancing positive and negative charges. Chemguide reference.
Which of these compounds is ionic?
NaCl
CO2
H2O
CH4
NaCl consists of sodium cations and chloride anions held by electrostatic attraction, making it ionic. The others are molecular covalent compounds. Khan Academy on Ionic Bonds.
Determine the simplest formula for calcium oxide.
CaO
Ca2O2
CaO2
Ca2O
Calcium forms Ca2+ and oxide is O2 so they combine in a 1:1 ratio, giving CaO. Simplest ionic formulas reduce to lowest whole-number ratios. Chemguide reference.
What is the empirical formula of aluminum oxide?
Al2O3
AlO
AlO3
Al3O2
Aluminum forms Al3+ and oxide is O2. Balancing 3+ and 2 charges requires 2 Al and 3 O, yielding Al2O3. Chemguide reference.
What charge does the chloride ion carry in ionic compounds?
1?
1+
2?
2+
Chlorine gains one electron to complete its octet, becoming Cl with a single negative charge. This is fundamental for writing ionic formulas. Chemguide reference.
What is the empirical formula of potassium bromide?
KBr
K2Br
KBr2
K2Br2
Potassium forms K+ and bromide is Br, so they combine in a 1:1 ratio to yield KBr. Empirical formulas show the simplest whole-number ratio. Chemguide reference.
What is the empirical formula of lithium nitride?
Li3N
LiN
Li2N
LiN2
Lithium is Li+ and nitride is N3; three Li+ ions are needed to balance one N3, giving Li3N. Chemguide reference.
Determine the empirical formula of calcium fluoride.
CaF2
CaF
Ca2F
CaF3
Calcium is Ca2+ and fluoride is F; two F ions balance one Ca2+, giving CaF2. This is the simplest ratio. Chemguide reference.
Medium
A compound contains 40.0% sulfur and 60.0% oxygen by mass. What is its empirical formula?
SO2
SO3
S2O3
S2O
Assuming 100 g, S = 40 g/32.06 gmol1 ? 1.25 mol, O = 60 g/16.00 gmol1 = 3.75 mol. Divide by 1.25 to get a 1:3 ratio, SO3. Chemguide on empirical formulas.
A compound is 52.2% Mg, 13.0% C, and 34.8% O by mass. What is its empirical formula?
MgCO3
MgC2O4
Mg2CO3
MgC3O6
For 100 g, moles: Mg 2.15, C 1.08, O 2.17. Divide by the smallest (1.08) ? Mg:2, C:1, O:2, giving MgCO3. Chemguide on empirical formulas.
What is the empirical formula of sodium carbonate?
Na2CO3
NaCO3
Na2C2O3
Na3CO2
Sodium is Na+, carbonate is CO3 2; two Na+ ions balance the charge of CO3 2, giving Na2CO3. Chemguide reference.
From 0.5 mol Ca, 1 mol C, and 1.5 mol O, what is the empirical formula?
CaCO3
Ca2CO3
CaC2O3
CaC3O4
Divide all mole values by 0.5 (smallest): Ca:1, C:2, O:3, giving CaC2O3. But CaC2O3 reduces to CaCO1.5, not whole; proper ionic formula is CaCO3 if you account for carbonate as CO3 2. Chemguide on empirical formulas.
What is the formula of the ionic compound formed between Fe3+ and O2-?
Fe2O3
Fe3O2
FeO
FeO3
Fe3+ and O2 combine in ratios of two Fe3+ (total +6) and three O2 (total ?6), giving Fe2O3. Charge balance dictates the simplest whole-number ratio. Chemguide reference.
What is the ionic charge on an aluminum ion?
1+
2+
3+
2?
Aluminum loses three electrons to achieve a stable octet, forming Al3+. This is its common oxidation state in ionic compounds. Chemguide reference.
What is the empirical formula of barium phosphate?
Ba3(PO4)2
Ba(PO4)2
Ba3PO4
Ba2(PO4)3
Phosphate is PO4 3, barium is Ba2+; three Ba2+ (total +6) balance two PO4 3 (total ?6), yielding Ba3(PO4)2. Chemguide reference.
A compound is 69.9% iron and 30.1% oxygen by mass. What is its empirical formula?
Fe2O3
FeO
Fe3O4
FeO3
For 100 g, moles Fe = 1.250, O = 1.881. Divide by 0.625 ? Fe2, O3, yielding Fe2O3. This matches the iron(III) oxide stoichiometry. Chemguide on empirical formulas.
Hard
A compound contains 46.5% zinc and 53.5% sulfur by mass. What is its empirical formula?
ZnS
Zn2S
ZnS2
Zn3S2
Assuming 100 g, Zn = 0.712 mol, S = 1.672 mol; divide by 0.712 ? Zn1, S?2.35, which rounds to 1:1 yielding ZnS. Charge balance (Zn2+, S2) confirms ZnS. Chemguide reference.
Elemental analysis gives 18.5% Li, 26.7% P, and 54.8% O. What is the empirical formula?
Li3PO4
LiPO4
Li2P O4
Li3P2O8
For 100 g, moles Li=2.67, P=0.86, O=3.42; divide by 0.86 ? Li3.1, P1, O3.97, rounding to Li3PO4. This matches lithium phosphates formula. Chemguide reference.
Analysis yields 40.1% Ca, 18.5% P, and 41.4% O by mass. What is the empirical formula?
Ca3(PO4)2
Ca2P2O8
CaP2O6
Ca3PO6
For 100 g: Ca=0.50 mol, P=0.60 mol, O=2.59 mol; divide by 0.10 ? Ca5, P6, O25 reduces to Ca3, P2, O8, which corresponds to Ca3(PO4)2. Chemguide reference.
What is the empirical formula of aluminum sulfate?
Al2(SO4)3
Al(SO4)2
Al2SO4
Al3(SO4)2
Sulfate is SO4 2 and aluminum is Al3+. Two Al3+ (total +6) balance three SO4 2 (total ?6), giving Al2(SO4)3. Chemguide reference.
What is the simplest formula for the compound of magnesium and phosphorus?
Mg3P2
MgP
Mg2P3
MgP2
Magnesium is Mg2+ and phosphide is P3; three Mg2+ (total +6) combine with two P3 (total ?6), yielding Mg3P2. Chemguide reference.
What is the empirical formula of iron(III) phosphate?
FePO4
Fe3(PO4)2
Fe(PO4)3
Fe2PO4
Iron(III) is Fe3+ and phosphate is PO4 3; one of each balances charge to give FePO4. Chemguide reference.
Identify the empirical formula of strontium nitride.
Sr3N2
SrN
Sr2N3
SrN2
Strontium is Sr2+ and nitride is N3; three Sr2+ (total +6) balance two N3 (total ?6), yielding Sr3N2. Chemguide reference.
Expert
A compound has mass percentages: 28.39% Mg, 21.59% Al, and 49.99% O. What is its empirical formula?
MgAl2O4
Mg2AlO4
MgAlO2
Mg2Al2O4
For 100 g: Mg=1.17 mol, Al=0.80 mol, O=3.12 mol; dividing by 0.39 ? Mg3, Al2, O8 reduces to MgAl2O4. This is the spinel structure empirical formula. Chemguide on empirical formulas.
Elemental analysis yields 33.38% Ca, 15.69% C, and 50.93% O by mass. What is the empirical formula?
CaCO3
Ca2CO3
CaC2O5
CaCO2
For 100 g: Ca=0.83 mol, C=1.31 mol, O=3.18 mol; dividing by 0.83 yields Ca1, C1.6 (~1), O3.8 (~3), rounding to CaCO3. This matches calcium carbonate. Chemguide reference.
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Study Outcomes
Understand Empirical Formula Concepts -
Explain what the empirical formula of ionic compounds represents and distinguish it from molecular formulas, reinforcing your grasp of simplest ion ratios.
Determine Ion Ratios -
Calculate the simplest whole-number ratio of cations and anions to derive an empirical formula ionic compounds require for charge balance.
Apply Naming Rules -
Use systematic naming conventions in our quiz on naming ionic compounds to match compound names with their correct formulas.
Interpret Formula Representations -
Analyze how the chemical formula of an ionic compound represents the ratio of ions and the overall neutral charge of the compound.
Construct Ionic Formulas -
Combine given cations and anions to write accurate empirical formulas of ionic compounds, ensuring proper subscripts and neutrality.
Cheat Sheet
Empirical vs. Molecular Formulas -
In chemistry, the empirical formula of ionic compounds shows the simplest whole”number ratio of ions, while the molecular formula gives the actual numbers of each atom in a molecule. For example, hydrogen peroxide has the molecular formula H₂O₂ but the empirical formula HO. Remember: the empirical formula ionic compounds represent the most reduced form of the ratio.
Identifying Ion Charges and Balancing Ratios -
To write correct ionic formulas, first determine each element's common charge using group numbers (e.g., Group 1 metals are +1, Group 17 nonmetals are −1). Then balance the total positive and negative charges so the chemical formula of an ionic compound represents electrical neutrality, like Al³❺ and S²❻ combining to Al₂S₃. A quick check is that the sum of oxidation numbers equals zero.
Writing Empirical Formulas Step-by-Step -
Begin by converting mass percent or grams to moles for each element, then divide all mole values by the smallest mole number to find whole”number ratios. For instance, a compound with 40% Ca and 60% F by mass converts to moles giving a 1 Ca:2 F ratio, so the empirical formula is CaF₂. This systematic approach ensures accuracy every time.
Common Ionic Compound Naming Rules -
Naming ionic compounds typically pairs the cation name followed by the anion name ending in "-ide" (e.g., NaCl is sodium chloride). For polyatomic ions, memorize common names like nitrate (NO₃❻) and sulfate (SO₄²❻) from reputable university sources. Accurate naming reinforces your ability to reverse the quiz on naming ionic compounds into flawless formula writing.
Quiz Practice and Memory Tricks -
Regularly test yourself with free online quizzes on naming ionic compounds to reinforce key concepts and spot weak areas. Use the criss-cross method (swapping ion charges to become subscripts) as a mnemonic to form empirical formulas swiftly. Consistent practice not only boosts confidence but also engrains the empirical formula of ionic compounds process in your mind.
