Ch.3 - Mass Relationships in Chemical Reactions

McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook

McMurry 8th Edition

Ch.3 - Mass Relationships in Chemical Reactions

Problem 124b

Chapter 3, Problem 124b

(b) If the molecular weight is 326.26, what is the molecular formula?

Verified step by step guidance

Step 1: The first step in determining the molecular formula is to calculate the empirical formula weight. This is done by adding up the atomic weights of all the atoms in the empirical formula.

Step 2: Once you have the empirical formula weight, divide the molecular weight by the empirical formula weight. This will give you a ratio, which should be a whole number or very close to a whole number.

Step 3: If the ratio is not a whole number, round it to the nearest whole number. This is because the molecular formula must contain whole numbers of atoms.

Step 4: Multiply each subscript in the empirical formula by the ratio you calculated in step 2. This will give you the molecular formula.

Step 5: Check your work by calculating the molecular weight of the molecular formula you determined. It should match the given molecular weight.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molecular Weight

Molecular weight, or molar mass, is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is calculated by summing the atomic weights of all atoms in a molecule, which can be found on the periodic table. Understanding molecular weight is crucial for determining the composition and stoichiometry of chemical compounds.

Empirical Formula

The empirical formula represents the simplest whole-number ratio of the elements in a compound. It provides insight into the relative proportions of each element but does not convey the actual number of atoms in a molecule. To derive the molecular formula from the empirical formula, one must know the molecular weight of the compound.

Molecular Formula

The molecular formula indicates the actual number of each type of atom in a molecule of a compound. It is derived from the empirical formula by multiplying the subscripts by a whole number, which is determined by dividing the molecular weight by the empirical formula weight. This formula is essential for understanding the structure and reactivity of the compound.

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Determining Molecular Formulas

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Textbook Question

An unidentified metal M reacts with an unidentified halogen X to form a compound MX2. When heated, the compound decomposes by the reaction: When 1.12 g of MX2 is heated, 0.720 g of MX is obtained, along with 56.0 mL of X2 gas. Under the conditions used, 1.00 mol of the gas has a volume of 22.41 L.(a) What is the atomic weight and identity of the halogen X?

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Textbook Question

Ethylene glycol, commonly used as automobile antifreeze, contains only carbon, hydrogen, and oxygen. Combustion analysis of a 23.46 mg sample yields 20.42 mg of H2O and 33.27 mg of CO2. What is the empirical formula of ethylene glycol? What is its molecular formula if it has a molecular weight of 62.0?

(a) Polychlorinated biphenyls (PCBs) were compounds used as coolants in transformers and capacitors, but their production was banned by the U.S. Congress in 1979 because they are highly toxic and persist in the environment. When 1.0 g of a PCB containing carbon, hydrogen, and chlorine was subjected to combustion analysis, 1.617 g of CO₂. and 0.138 g of H₂O were produced. What is the empirical formula?

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Textbook Question

(c) Can combustion analysis be used to determine the empirical formula of a compound containing carbon, hydrogen, oxygen, and chlorine?

The symbol CO stands for carbon monoxide, but the sym-bol Co stands for the element cobalt. Explain.

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Textbook Question

Correct the error in each of the following statements:(a) The formula of ammonia is NH3(b) Molecules of potassium chloride have the formula KCl. (c) Cl-is a cation.(d) CH4 is a polyatomic ion

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