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Empirical Formulae

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Wize University Chemistry Textbook > Stoichiometry

Empirical and Molecular Formulae Problems

4 Activities

A compound has an empirical formula of C2H5O. Its molar mass is 225.305 g/mol. Determine its molecular formula.
More Empirical and Molecular Formulae Problems Questions:
Mass Percentage
A compound containing sodium, chlorine, and oxygen is 25.42 % sodium by mass. A 3.25 g sample gives 4.33 x 1022 atoms of oxygen. What is the empirical formula?
MW Na: 23 g/mol
MW Cl: 35.45 g/mol
Empirical formula
A compound has the following mass composition: C 86.59%, H 8.36% and N 5.05%. What is the empirical formula of this compound?
Gas Stoichiometry
Cyanogen is 46.2 % C and 53.8 % N by mass. 1.00 g cyanogen gas occupies 0.476 L at 25 °C and 750 Torr. Determine the empirical and molecular formula of cyanogen.
Mass Percentage II
A certain metal hydroxide with the formula M(OH)2 is 17.22 % oxygen by mass. What is the identity of the metal, "M" ?
Spring 2017, Practice Exam 1 (CHM2045/UF)
A 7.21 g sample of a LiClO4 · xH2O was heated to drive off the water. The mass was reduced to 4.78 g. What is the formula of the hydrate?
Mass Percentage
A compound containing sodium, chlorine, and oxygen is 25.42 % sodium by mass. A 3.25 g sample gives 4.33 x 1022 atoms of oxygen. What is the empirical formula?
Hint: This is a tricky problem but start by writing the variables that you know.....what can you solve for?
If you're still not sure, my hint is to start with O! We can calculate moles of O, then mass of O, then % mass of O! What should we do next??
Practice: Empirical and Molecular Formula
A sample of a compound contains 1.52 g of N atoms and 3.47 g of O atoms. The molar mass of the compound is between 90.0 g and 95.0 g. Determine the empirical and molecular formulas.
Elements: Mass Percentage
A metal oxide with the formula M2O3 is 21.2 % oxygen by mass. What is the identity of the metal, "M"?
Empirical formula: Hydrates
A 15.67 g sample of a hydrate of magnesium carbonate (MgCO3) was heated, without decomposing the carbonate, to drive off the water. The mass was reduced to 7.58 g. What is the formula of the hydrate?
Empirical Formulae
7. A compound has an empirical formula of CH2O. Its molar mass is 180.01 g/mol. Determine its molecular formula.
Chemical formula: Molecular formula
Part 1: What's the empirical formula for a molecule containing 65.5% C, 5.5% H, and 29.0% O?
Part 2: It was found that the atomic mass of the molecule is 110g/mol. What is the molecular formula?
Molecular Formula from Empirical Formula
p-dichlorobenzene (mM = 147.00 g/mol) is a common disinfectant and deodorant used in industrial applications. It has an empirical formula of C3H2Cl. Determine its molecular formula. You do not need subscripts for your submission. For example, if you answer is the empirical formula, enter it as: C3H2Cl.
Chemical Reactions: Finding an Unknown Empirical Formula from Mass Percentages
A compound containing sodium, chlorine, and oxygen is 25.42% sodium by mass. A 3.25 g sample gives 4.33 x 1022 atoms of oxygen. What is the empirical formula?
Chemical Reactions: Hydrate Question
A 15.67 g sample of a hydrate of magnesium carbonate (MgCO3) was heated, without decomposing the carbonate, to drive off the water. The mass was reduced to 7.58 g. What is the formula of the hydrate?
Chemical Formula: Mass Percentage Problem
A compound is found to contain 50.05 % sulfur and 49.95 % oxygen by weight. What is the empirical formula for this compound? The molecular weight for this compound is 64.07 g/mol. What is its molecular formula?
Note: Empirical formula is the formula that expresses the SMALLEST whole number ratio of atoms present whereas the molecular formula expresses the same ratio as the empirical formula but is the actual number of atoms present in a molecule.
Practice: Mass Percentage
A compound containing sodium, chlorine, and oxygen is 25.42% sodium by mass. A 3.25 g sample gives 4.33 x 1022 atoms of oxygen. What is the empirical formula?
Hint: This is a tricky problem but start by writing the variables that you know.....what can you solve for?
If you're still not sure, my hint is to start with O! We can calculate moles of O, then mass of O, then % mass of O! What should we do next??
Empirical and Molecular Formula: Molar Mass
A sample of a compound contains 1.52 g of N atoms and 3.47 g of O atoms. The molar mass of the compound is between 90.0 g and 95.0 g. Determine the empirical and molecular formulas. Also, calculate the actual molar mass of this compound.