CHEM 101 2026 ACTUAL EXAM 1 TEST QUESTIONS WITH ACCURATE SOLUTIONS
Converting between Mass and Number of Molecules
You are given the mass of a compound and the molecular formula. First convert to moles
(using the molar mass from the periodic table) and then to number of molecules using
Avogadro's number.
Mass Percent Composition
You are given the molecular formula of a compound and asked to find the mass percent of
one element that is in its composition. The molecular formula will tell you the # of moles of
the element found in each molecule of the compound. Find the mass percent composition
by using the equation that defines mass percent, mass percent = mass of element in
compound divided by mass of compound multiplied by 100%.
Using Mass Percent Composition as a Conversion Factor
You are given a mass of an element in a compound and the mass percent
composition.Convert between mass of the element and mass of the compound by using
the mass percent composition as a conversion factor. Assume that the sample of the
compound is 100g.
Chemical Formulas as Conversion Factors
You are asked to find the mass of an element in a given amount of volume and a given
density. Use the density to convert between volume and mass --> convert into moles of
compound using mass of compound --> moles of element from moles of compound
(balanced equation) --> mass of element from moles of element using the periodic table.
,Obtaining an Empirical Formula from Experimental Data
Write down given masses of each element present in a sample of the compound. If you are
given mass % comp, assume a 100g sample. Convert each of the masses to moles using
the appropraite molar mass for each element as a conversion factor. Divide the numbers of
moles for each element by the smallest number of moles. If the subscripts are not a whole
number multiply all the subscripts by a whole number to get a whole-number.
Calculating Molecular Formula from an Empirical Formula and Molar Mass
You are given the empirical formula (or must calculate it) and molar mass of a compound
and asked to find the molecular formula. Divide the molar mass by the empirical formula
mass to get a whole number. Multiply the subcripts in the empirical formula by the whole
number to get the molecular formula.
Obtaining an Empirical Formula from Combustion Analysis
Write down given masses of each combustion product and the mass of the sample (if
given). Convert the masses of CO₂ & H₂O into moles --> convert the moles of CO₂ & H₂O
into moles of C & H using chemical formula. If the compound contains an element other
than C & H, find the mass of the other element by subtracting the sum of the masses of C &
H from the mass of the entire sample --> convert the mass of the other element into moles.
Divide all of the moles by the smallest number of moles to get empirical formula.
Balancing Chemical Equations
Write down chemical formulas for each of the reactants and products. Balance atoms that
occur in more complex substances first. Always balance atoms in compounds before
atoms in pure elements. Balance atoms that occur as free elements on either side of the
equation last. Always balance free elements on either side of the equation last. Always
balance free elements by adjusting the coeffecient on the free element. If the balanced
equation contains coefficient fractions, clear these by multiplying the entire equation by
the denominator of the fraction.
, Limiting Reactant and Theoretical Yield
You are given the chemical equation and mass of each reactant in grams and asked to find
the theoretical yield of a product. Determine which reactant makes the least amount of
product by converting from grams of each reactant to moles of the product. The reactant
that produces the least moles of product is the limiting reactant. Convert the moles of
product produced by the limiting reactant into grams of the product to get the theoretical
yield.
Calculating Solution Concentration
You are given the mass of a compound and the volume of a solution and asked to find its
molarity. Molarity = amount of solute (in mol) divided by volume of solution (in L). First use
the molar mass to convert grams of compound into moles of compound. Then use the
number of moles of the compound and divide by the liters of the solution.
Using Molarity in Calculations
You are given the concentration of a compound in a solution. You are asked to find the
volume of the solution that contains a given amount (in moles) of the same compound.
Convert the moles of the compound into liters using molarity.
Solution Dilution
You are given the initial volume, initial concentration, and final concentration of a solution,
and you need to find the final volume. Use this relationship to solve M₁V₁=M₂V₂.
Converting between Mass and Number of Molecules
You are given the mass of a compound and the molecular formula. First convert to moles
(using the molar mass from the periodic table) and then to number of molecules using
Avogadro's number.
Mass Percent Composition
You are given the molecular formula of a compound and asked to find the mass percent of
one element that is in its composition. The molecular formula will tell you the # of moles of
the element found in each molecule of the compound. Find the mass percent composition
by using the equation that defines mass percent, mass percent = mass of element in
compound divided by mass of compound multiplied by 100%.
Using Mass Percent Composition as a Conversion Factor
You are given a mass of an element in a compound and the mass percent
composition.Convert between mass of the element and mass of the compound by using
the mass percent composition as a conversion factor. Assume that the sample of the
compound is 100g.
Chemical Formulas as Conversion Factors
You are asked to find the mass of an element in a given amount of volume and a given
density. Use the density to convert between volume and mass --> convert into moles of
compound using mass of compound --> moles of element from moles of compound
(balanced equation) --> mass of element from moles of element using the periodic table.
,Obtaining an Empirical Formula from Experimental Data
Write down given masses of each element present in a sample of the compound. If you are
given mass % comp, assume a 100g sample. Convert each of the masses to moles using
the appropraite molar mass for each element as a conversion factor. Divide the numbers of
moles for each element by the smallest number of moles. If the subscripts are not a whole
number multiply all the subscripts by a whole number to get a whole-number.
Calculating Molecular Formula from an Empirical Formula and Molar Mass
You are given the empirical formula (or must calculate it) and molar mass of a compound
and asked to find the molecular formula. Divide the molar mass by the empirical formula
mass to get a whole number. Multiply the subcripts in the empirical formula by the whole
number to get the molecular formula.
Obtaining an Empirical Formula from Combustion Analysis
Write down given masses of each combustion product and the mass of the sample (if
given). Convert the masses of CO₂ & H₂O into moles --> convert the moles of CO₂ & H₂O
into moles of C & H using chemical formula. If the compound contains an element other
than C & H, find the mass of the other element by subtracting the sum of the masses of C &
H from the mass of the entire sample --> convert the mass of the other element into moles.
Divide all of the moles by the smallest number of moles to get empirical formula.
Balancing Chemical Equations
Write down chemical formulas for each of the reactants and products. Balance atoms that
occur in more complex substances first. Always balance atoms in compounds before
atoms in pure elements. Balance atoms that occur as free elements on either side of the
equation last. Always balance free elements on either side of the equation last. Always
balance free elements by adjusting the coeffecient on the free element. If the balanced
equation contains coefficient fractions, clear these by multiplying the entire equation by
the denominator of the fraction.
, Limiting Reactant and Theoretical Yield
You are given the chemical equation and mass of each reactant in grams and asked to find
the theoretical yield of a product. Determine which reactant makes the least amount of
product by converting from grams of each reactant to moles of the product. The reactant
that produces the least moles of product is the limiting reactant. Convert the moles of
product produced by the limiting reactant into grams of the product to get the theoretical
yield.
Calculating Solution Concentration
You are given the mass of a compound and the volume of a solution and asked to find its
molarity. Molarity = amount of solute (in mol) divided by volume of solution (in L). First use
the molar mass to convert grams of compound into moles of compound. Then use the
number of moles of the compound and divide by the liters of the solution.
Using Molarity in Calculations
You are given the concentration of a compound in a solution. You are asked to find the
volume of the solution that contains a given amount (in moles) of the same compound.
Convert the moles of the compound into liters using molarity.
Solution Dilution
You are given the initial volume, initial concentration, and final concentration of a solution,
and you need to find the final volume. Use this relationship to solve M₁V₁=M₂V₂.
