Calculate the formula mass or molecular mass of the...

Calculate the formula mass or molecular mass of the following substances: (a) $\mathrm{Fe}_{2} \mathrm{O}_{3}(\text { rust) }$ (b) $\mathrm{H}_{2} \mathrm{SO}_{4}$ (sulfuric acid) (c) $\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{7}$ (citric acid) (d) $\mathrm{C}_{16} \mathrm{H}_{18} \mathrm{N}_{2} \mathrm{O}_{4} \mathrm{S}$ (penicillin G)

Calculate the formula mass or molecular mass of the following substances:
(a) $\mathrm{Fe}_{2} \mathrm{O}_{3}(\text { rust) }$
(b) $\mathrm{H}_{2} \mathrm{SO}_{4}$ (sulfuric acid)
(c) $\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{7}$ (citric acid)
(d) $\mathrm{C}_{16} \mathrm{H}_{18} \mathrm{N}_{2} \mathrm{O}_{4} \mathrm{S}$ (penicillin G)

Key Concepts

Atomic Mass

Atomic mass is the weighted average mass of an element's isotopes as listed on the periodic table. It is used as a fundamental measurement in chemistry to determine the mass of one atom, and by extension, to calculate the mass of any compound using the number of atoms present.

Molecular (Formula) Mass

Molecular mass, also known as formula mass, is the sum of the atomic masses of all atoms in a compound's chemical formula. This concept is crucial for converting between moles and grams, and it provides a way to compare the masses of different molecules based on their constituent atoms.

Chemical Formula Interpretation

Understanding chemical formulas is essential because it involves identifying the types and numbers of atoms in a molecule. This process allows one to determine the stoichiometric coefficients required for calculating molecular mass, ensuring that each element's contribution is accurately accounted for.

Stoichiometry

Stoichiometry involves using the relationships between the quantities of reactants and products in chemical reactions. In the context of molecular mass calculations, stoichiometry is applied by multiplying the atomic mass of each element by the number of times the element appears in the formula, then summing these values to obtain the overall molecular mass.

Transcript

00:01 To calculate the formula or molecular mass of these different compounds, you're going to need a periodic table, like this one, and the formula of these compounds.

00:16 So for iron three oxide, shown here, we're going to take the subscripts and multiply them by the atomic mass of these individual elements.

00:27 So two times the mass of iron.

00:32 Iron iron is right here on the periodic table, it's 5585, added to three times the mass of oxygen found over here.

00:47 That's 16 .00 or 59 .994, if you have a more precise periodic table, gives 159 .70.

01:02 And this has units of amu.

01:05 If you were calculating molar mass, those are different units.

01:08 But right now you're being asked for formula or molecular mass.

01:12 It has units of atomic mass units or a and mutes.

01:17 Next, we have h2s04.

01:20 So here we're going to do 2 times the molar mass of hydrogen, which is 1 .01, plus the molar mass of sulfur, which is coming over here.

01:38 That's 32 .07, plus 4 times the molar mass of oxygen.

01:44 We already found that.

01:46 That's 16.

01:51 And the sum of those is 98 .09 amus.

01:58 I should mention your mileage might vary for this question.

02:03 Some periodic tables have a lot more than just two significant or two decimal points.

02:10 Some will show all five or six or seven or eight, depending on what's available for that element.

02:16 Some might just only show two decimal places, and you might have an instructor that requires a specific, number of decimal places or a specific number of significant figures for your molar masses or your molecular masses.

02:29 I'm being consistent through this video with two decimal places.

02:36 This particular textbook goes to one decimal place.

02:40 Again, just go with what your instructor requires you.

02:44 So if your numbers are just a little bit off here, that's okay.

02:48 Make sure you're using the periodic table provided by your textbook or your instructor.

02:53 And be consistent with what's asked of you...

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