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Quizzes > Science > Chemistry

Empirical Formula of Ca2 and I- Quiz: Test Your Compound Naming Skills

Ready for a naming compounds quiz? Dive into our empirical formula challenge!

Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art style quiz graphic on empirical formula Ca2 I compound naming chemical nomenclature on teal background

This quiz helps you work out the empirical formula of Ca2 and I- and practice naming the compound. Use it to spot gaps before a test and build speed. For a quick refresher, see our ionic formula guide , then keep practicing with a compound naming quiz .

What is the empirical formula for a compound formed between Ca2+ and I- ions?
Ca2I2
CaI2
CaI
Ca2I
The compound must be electrically neutral, so one Ca2+ ion combines with two I- ions to form CaI2. This gives a net charge of zero. The empirical formula shows the simplest whole-number ratio. .
What is the proper IUPAC name for CaI2?
Calcium iodide(II)
Calcium diiodide
Calcium(II) iodine
Calcium iodide
Ionic compounds are named by stating the cation name followed by the anion root with an "-ide" suffix. Prefixes like "di-" are not used in ionic nomenclature. Thus CaI2 is called calcium iodide. .
What is the charge on an iodide ion?
-1
-2
0
+1
Iodine is a halogen in group 17 and gains one electron to achieve a full octet, giving it a -1 charge. The resulting ion is written as I-. .
What is the oxidation state of calcium in CaI2?
+1
-2
+2
0
Calcium is an alkaline earth metal (group 2) and loses two electrons to form Ca2+. In CaI2, calcium's oxidation state is therefore +2. .
Which type of bond is formed between Ca2+ and I-?
Metallic
Hydrogen
Ionic
Covalent
Ionic bonds form between positively charged cations and negatively charged anions. Calcium donates electrons to iodide, resulting in electrostatic attraction. This is characteristic of ionic compounds. .
What does an empirical formula represent?
The percentage composition by mass
The exact number of atoms in a molecule
The atomic masses of elements in the compound
The simplest whole-number ratio of elements in a compound
An empirical formula indicates the simplest integer ratio of atoms in a compound, not the actual number of atoms in a molecule. It is useful for ionic compounds and many solids. .
How many iodide ions are required to balance one Ca2+ ion?
Four
One
Three
Two
Each iodide ion carries a -1 charge, so two I- ions are needed to balance the +2 charge of one Ca2+ ion. This yields the formula CaI2. .
Which symbol correctly represents the iodide ion?
I
I-
IO3-
I2
The iodide ion is the monatomic anion of iodine with a -1 charge, written as I-. Molecular iodine is I2, not the ion. .
Why are numerical prefixes like "di-" not used when naming ionic compounds like calcium iodide?
Because ionic compound naming does not use prefixes for ion counts
Because calcium can only have one oxidation state
Because iodide ions are monatomic
Because "di" is reserved for organic compounds
In ionic nomenclature, the number of ions is implied by charge balance rather than prefixes. Prefixes like "di-" are used in covalent compound names, not in ionic ones. .
What is the oxidation number of calcium in calcium iodide?
+1
0
-1
+2
Calcium, as a group 2 element, loses two electrons to form Ca2+. In ionic compounds, this is its oxidation number. .
The formula mass of CaI2 is closest to which value?
256 g/mol
317 g/mol
268 g/mol
294 g/mol
Calculate: Ca (40.08) + 2 × I (126.90) = 293.88 g/mol, which rounds to 294 g/mol. This is the formula mass of CaI2. .
What is the percent by mass of iodine in CaI2? (Use Ca=40.08, I=126.90)
86.4%
72.0%
13.6%
40.8%
Mass of I2 = 2 × 126.90 = 253.80; total mass = 293.88. Percent I = (253.80/293.88)×100 ? 86.4%. .
Which compound is isoelectronic with calcium iodide in terms of empirical formula?
BeF2
NaCl
MgO
CaCl2
Isoelectronic species share the same charge ratio pattern. CaCl2 also has one Ca2+ and two Cl- ions, matching CaI2's formula pattern. .
What type of crystal structure does CaI2 adopt?
Fluorite
Zinc blende
CdI2-type layered
NaCl-type
Calcium iodide crystallizes in the cadmium iodide (CdI2) motif, which features layers of iodide ions with Ca2+ in octahedral holes. .
Which factor most directly affects the solubility of CaI2 in water?
Colour of container
Temperature
Magnetic field
Pressure
Solubility of most ionic salts, including CaI2, varies significantly with temperature. Higher temperatures generally increase solubility. .
True or False: In aqueous solution, calcium iodide dissociates completely into Ca2+ and 2 I- ions.
True
False
Ionic compounds like CaI2 dissociate fully in water into their constituent ions, yielding Ca2+ and two I- ions. This complete dissociation drives conductivity in solution. .
Which of the following compounds has an empirical formula analogous to CaI2 from group 2 metals?
AlI2
MgI2
FeI2
CuI
Group 2 metals form M2+ ions that pair with two I- ions, giving MI2. Magnesium is in the same group, so MgI2 is analogous to CaI2. .
The iodide ion has a larger ionic radius than calcium ion. What is the primary reason for this size difference?
Higher nuclear charge in the iodide ion
Additional electron-electron repulsion in the iodide ion
Stronger ionic bond in CaI2
Higher oxidation state of calcium
When iodine gains an electron to form I-, electron-electron repulsion increases and the electron cloud expands. Calcium loses electrons, reducing its radius. .
In the CdI2-type structure of CaI2, what is the coordination number of Ca2+?
8
6
4
12
In the CdI2 structure, each Ca2+ sits in an octahedral site coordinated by six I- ions. Octahedral geometry corresponds to a coordination number of six. .
Which species is isoelectronic with Ca2+?
Cl-
Ar
Ne
K+
Ca2+ has lost two electrons (atomic number 20 ? 18 electrons), matching the electron configuration of argon (Ar). Isoelectronic species share the same electron count. .
Which experimental observation best supports the ionic nature of CaI2?
It conducts electricity when molten
It is soluble in organic solvents
It has a low melting point
It forms covalent bonds
Ionic solids conduct electricity only when their ions are free to move, such as in the molten state. This behavior is a hallmark of ionic compounds. .
In a flame test, which color is characteristic of calcium ions from CaI2?
Brick red
Violet
Green
Blue
Calcium imparts a brick-red (orange-red) color to a flame during a qualitative flame test. This is used to identify Ca2+ in compounds. .
What is the molar concentration of a solution prepared by dissolving 5.00 g of CaI2 in enough water to make 0.100 L?
0.340 M
0.085 M
0.170 M
0.051 M
Moles of CaI2 = 5.00 g / 293.88 g/mol ? 0.0170 mol. Molarity = 0.0170 mol / 0.100 L = 0.170 M. .
Which analytical technique would best confirm the crystal structure of solid CaI2?
UV-visible spectroscopy
Infrared spectroscopy
X-ray crystallography
Mass spectrometry
X-ray crystallography directly measures atomic positions in a crystal lattice and is the definitive method for determining crystal structures. Other techniques provide different information. .
In a non-stoichiometric variant of CaI2 with excess iodide ions, which type of defect is most likely to form?
Anion vacancies
Calcium vacancies
Frenkel defects
Interstitial calcium
Extra iodide ions introduce a negative charge imbalance, which is compensated by creating Ca2+ vacancies (cation vacancies). This maintains overall charge neutrality. .
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Study Outcomes

  1. Determine the Empirical Formula of Ca2+ and I- -

    Apply charge balance principles to derive the empirical formula of Ca2 and I- and understand how ions combine to form neutral compounds.

  2. Apply Chemical Naming Rules -

    Use IUPAC conventions to accurately name ionic compounds in our naming compounds quiz and reinforce your understanding of systematic nomenclature.

  3. Identify Cations and Anions -

    Recognize and distinguish between positive Ca2+ and negative I- ions to determine correct stoichiometry in a compound nomenclature test.

  4. Analyze Charge Neutrality -

    Evaluate how charges balance between Ca2+ and I- to ensure the formation of a neutral ionic compound.

  5. Practice Empirical Formula Skills -

    Engage with targeted empirical formula practice questions to reinforce your skills in determining formulas for ionic compounds.

  6. Assess Your Ionic Naming Proficiency -

    Test and track your ability to name ionic compounds correctly through an interactive chemical naming rules quiz.

Cheat Sheet

  1. Identifying Ion Charges -

    Calcium as a Group 2 metal loses two electrons to form Ca2+, while iodine gains one electron to form I - . Recognizing these charges is crucial for writing the empirical formula of Ca2 and I - . (Source: University of Arizona Chemistry Department)

  2. Deriving the Empirical Formula -

    The empirical formula reflects the simplest whole”number ratio: one Ca2+ ion pairs with two I - ions, giving CaI2. Divide subscripts by their greatest common factor to ensure the lowest ratio. (Source: Purdue University General Chemistry)

  3. Naming Ionic Compounds -

    Follow IUPAC rules by naming the cation first ("calcium") and the anion second with an "-ide" suffix ("iodide"). This yields calcium iodide for CaI2. Consistency with these rules ensures clear chemical communication. (Source: IUPAC)

  4. Stoichiometry in Ionic Lattices -

    In the solid lattice, each Ca2+ is typically surrounded by six I - ions, but the bulk formula remains CaI2. Understanding this coordination helps explain properties like solubility and lattice energy. (Source: Royal Society of Chemistry)

  5. Criss-Cross Method Mnemonic -

    Use the criss-cross trick: write the absolute value of each ion's charge as the other's subscript and simplify if possible. A helpful phrase is "Cal I two" to remember CaI2. This mnemonic makes empirical formula practice quick and fun. (Source: ACS Educational Materials)

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