Introductory Chemistry Exam 3 Review – Step-by-Step Study Guidance

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Topic: Chemical Formulas and Ratios

This question tests your understanding of how to write chemical formulas based on the ratio of atoms in a compound.

Chemical formula: A representation of the elements in a compound and the ratio of their atoms.
Subscript: The small number written to the lower right of an element symbol, indicating the number of atoms of that element in the compound.

Identify the elements involved: carbon (C) and sulfur (S).
Determine the ratio: 1 carbon atom for every 3 sulfur atoms.
Write the chemical formula by placing the correct subscripts after each element symbol to reflect the ratio.

Topic: Counting Atoms in Chemical Formulas

This question tests your ability to interpret chemical formulas and count the total number of a specific atom present.

Subscript: Indicates the number of atoms of an element in a molecule.
Parentheses: Used to group polyatomic ions; the subscript outside the parentheses multiplies all atoms inside.

Identify the polyatomic ion: PO4 is phosphate.
Notice the subscript outside the parentheses: (PO4)4 means there are 4 phosphate ions.
Each phosphate ion contains 4 oxygen atoms. Multiply the number of phosphate ions by the number of oxygen atoms per ion: .

Topic: Precipitation Reactions and Solubility Rules

This question tests your ability to predict the products of a double displacement reaction and identify insoluble compounds (precipitates).

Precipitate: An insoluble solid formed from a reaction in solution.
Solubility rules: Guidelines to predict whether an ionic compound will dissolve in water.

Write the formulas for the reactants: barium nitrate (Ba(NO3)2) and potassium sulfate (K2SO4).
Predict the products by exchanging the cations and anions: Ba2+ pairs with SO42–, and K+ pairs with NO3–.
Write the formulas for the products: BaSO4 and KNO3.
Use solubility rules to determine which product is insoluble (forms a precipitate).

Topic: Solubility and Precipitation Reactions

This question tests your ability to predict whether a precipitate will form when two aqueous solutions are mixed, based on solubility rules.

Precipitate: An insoluble solid that forms in a solution during a chemical reaction.
Solubility rules: Used to determine if a compound is soluble or insoluble in water.

For each pair of reactants, predict the products by exchanging ions (double displacement reaction).
Write the formulas for the possible products for each pair.
Apply solubility rules to each product to determine if any are insoluble (form a precipitate).
Identify which set of reactants produces an insoluble product.

Topic: Writing Molecular Equations for Double Displacement Reactions

This question tests your ability to write a balanced molecular equation for a reaction between two aqueous ionic compounds.

Molecular equation: Shows all reactants and products as neutral compounds.
Double displacement reaction: A reaction where the cations and anions of two compounds exchange partners.

Write the formulas for the reactants: Pb(C2H3O2)2 (aq) and KBr (aq).
Predict the products by exchanging the cations and anions: Pb2+ pairs with Br–, and K+ pairs with C2H3O2–.
Write the formulas for the products: PbBr2 and KC2H3O2.
Balance the equation by adjusting coefficients as needed.