General Chemistry: Mass Relationships in Chemical Reactions

Flashcards covering mass relationships, atomic mass, the mole, percent composition, and reaction stoichiometry based on Chapter 3 lecture notes.

How is atomic mass defined based on the $^{12}C$ isotope?

By definition, $1 ext{ atom } ^{12}C$ weighs exactly $12 ext{ amu}$ or dalton.

What is the average atomic mass of an element?

The weighted average of all naturally occurring isotopes of that element.

What is the mathematical expression for the average atomic mass of an element?

$$ext{Average atomic mass} = ( ext{Weight of 1st isotope} imes ext{\% abundance of 1st isotope}) + ( ext{Weight of 2nd isotope} imes ext{\% abundance of 2nd isotope}) + ext{…}$$

What is the definition of a mole (mol)?

The amount of a substance that contains as many elementary entities as there are atoms in exactly $12.00 ext{ grams}$ of $^{12}C$.

What is the specific value of Avogadro’s number ($N_A$) provided in the text?

$$N_A = 6.0221367 imes 10^{23}$$

What is the conversion factor between grams and atomic mass units (amu)?

$1 ext{ amu} = 1.66 imes 10^{-24} ext{ g}$ or $1 ext{ g} = 6.022 imes 10^{23} ext{ amu}$.

What is the relationship between atomic mass (amu) and molar mass (grams) for an element?

For any element, the atomic mass in amu is numerically equal to its molar mass in grams per mole ($ext{g/mol}$).

What are the two primary formulas for calculating the number of moles ($n$)?

$n = \frac{m}{M_s}$ (where $m$ is mass in grams and $M_s$ is Molar mass) and $n = \frac{N}{N_A}$ (where $N$ is the number of atoms or molecules and $N_A$ is Avogadro’s number).

What is the most direct and accurate method for determining atomic and molecular masses?

Mass spectrometry.

What is the formula for the Percent Composition of an element in a compound?

$ext{Percent composition} = \frac{n imes ext{molar mass of element}}{ ext{molar mass of compound}} imes 100\%$ where $n$ is the number of moles of the element in 1 mole of the compound.

What is the relationship between the Molecular Formula (M.F.) and the Empirical Formula (E.F.)?

$M.F. = n imes (E.F.)$ where $n$ is an integer calculated as $n = \frac{ ext{molar mass of compound}}{ ext{molar mass of E.F.}}$

What is a chemical reaction?

A process in which one or more substances is changed into one or more new substances.

Define the Limiting Reagent (L.R.).

The reactant that is used up first in a chemical reaction.

What is the difference between Theoretical Yield and Actual Yield?

Theoretical Yield is the calculated amount of product that would result if all the limiting reagent reacted, while Actual Yield is the amount of product experimentally obtained from a reaction.

What is the formula for Percent Yield?

$$\% ext{ Yield} = \frac{ ext{Actual Yield}}{ ext{Theoretical Yield}} imes 100\%$$

What is the formula mass of Calcium Carbonate ($CaCO_3$)?

$100 ext{ g/mol}$ (calculated as $40 + 12 + 3 imes 16$).

What name is given to the $C_{60}$ molecule because of its geodesic dome shape?

Buckminsterfullerene or 'buckyball'.