Mole Concept, Stoichiometry, and Chemical Laws

Comprehensive practice flashcards covering the mole concept, atomic and molecular weights, stoichiometry, equivalent mass calculations, limiting reagents, and the laws of chemical combination.

What are the charges in Coulombs on a single electron, a single proton, and a single neutron?

An electron has a charge of $-1.6 \times 10^{-19}\,C$, a proton has a charge of $+1.6 \times 10^{-19}\,C$, and a neutron has a charge of $0\,C$.

How many electrons, protons, and neutrons are present in an oxide ion ($O^{2-}$), and what is its net charge?

An oxide ion has $10$ electrons, $8$ protons, and $8$ neutrons. Its net charge is $2 \times (-1.6 \times 10^{-19}\,C) = -3.2 \times 10^{-19}\,C$.

How many electrons, protons, and neutrons are present in a single ammonium ion ($NH_4^+$)?

An ammonium ion contains $10$ electrons, $11$ protons, and $7$ neutrons.

What is the numerical value of Avogadro's number ($N_A$), and what does the term 'mole' mean etymologically?

Avogadro's number is $N_A = 6.02 \times 10^{23}$. The word 'mole' is derived from a Greek word meaning a 'heap' or collection.

How many electrons, protons, and neutrons are present in $2\,\text{moles}$ of nitride ions ($N^{3-}$)?

There are $20 N_A$ electrons, $14 N_A$ protons, and $14 N_A$ neutrons.

What is the relationship between the number of atoms of an element in one molecule and the moles of that element in one mole of the substance?

The number of atoms of an element contained in one molecule of a compound is equal to the number of moles of that element in one mole of that compound (e.g., one molecule of $CO_2$ has $2$ oxygen atoms, so one mole of $CO_2$ contains $2\,\text{moles}$ of oxygen atoms).

How is relative atomic mass defined on the modern Carbon-12 scale?

$\text{Relative Atomic Mass} = \frac{\text{Mass of 1 atom of } X}{\frac{1}{12} \times \text{Mass of 1 atom of }^{12}C}$. It is a unitless ratio.

What is the relationship between $1\,\text{amu}$ (or $1\,\text{u}$) and grams?

$1\,\text{amu} = \frac{1}{N_A}\,g = \frac{1}{6.02 \times 10^{23}}\,g$.

How does the mass of one mole of an element in grams relate to the mass of a single atom of that element in amu?

The numerical values are identical: if the mass of $1\,\text{mole}$ of an element is $M\,g$, then the mass of a single atom of that element is $M\,\text{amu}$.

How many helium atoms are present in $52\,\text{amu}$ of helium?

Since one helium atom has a mass of $4\,\text{amu}$, the number of atoms is $\frac{52}{4} = 13\text{ atoms}$.

How do the number of oxygen atoms compare among samples of $16\,g$ of $O$, $16\,g$ of $O_2$, and $16\,g$ of $O_3$?

All three samples contain an equal number of oxygen atoms, exactly $N_A$ ($1\,\text{mole}$) of oxygen atoms.

Among $52\,g$ of He, $52\,\text{moles}$ of He, and $52\,\text{amu}$ of He, which sample contains the highest number of atoms?

$52\,\text{moles}$ of He contains the highest number of atoms ($52 N_A$ atoms, compared to $13 N_A$ atoms in $52\,g$ and only $13$ individual atoms in $52\,\text{amu}$).

What do the chemical terms 'gram-atom', 'gram-molecule', and 'gram-mole' represent?

'Gram-atom' means $1\,\text{mole}$ of atoms, 'gram-molecule' means $1\,\text{mole}$ of molecules, and 'gram-mole' denotes $1\,\text{mole}$ of any chemical entity.

What is the molar volume of an ideal gas at standard temperature and pressure (STP, old convention: $1\,\text{atm}$, $273\,K$)?

The molar volume is $22.4\,dm^3$ ($22.4\,\text{L}$) or $22400\,\text{mL}$.

What is the formula for the density of an ideal gas derived from $PV = nRT$?

$d = \frac{PM}{RT}$, where $P$ is pressure, $M$ is molar mass, $R$ is the universal gas constant, and $T$ is absolute temperature in Kelvin.

What is the relationship between molar mass and vapor density ($VD$) for a gas or volatile substance?

$\text{Molar Mass} = 2 \times VD$.

What is the balanced stoichiometric equation for the complete combustion of a general hydrocarbon $C_xH_y$?

$C_xH_y + \left(x + \frac{y}{4}\right)O_2 \rightarrow x CO_2 + \frac{y}{2} H_2O$.

How is the limiting reagent determined from the initial moles of reactants in a balanced reaction?

Divide the given moles of each reactant by its respective stoichiometric coefficient; the reactant with the minimum value of $\frac{\text{given moles}}{\text{coefficient}}$ is the limiting reagent.

What is the general relationship between equivalent weight ($E$), molar mass ($M$), and the $n$-factor?

$E = \frac{M}{n\text{-factor}}$, where the $n$-factor is always a positive quantity defined per single reacting entity.

What are the $n$-factors (basicities) of phosphoric acid ($H_3PO_4$), phosphorous acid ($H_3PO_3$), and hypophosphorous acid ($H_3PO_2$)?

The $n$-factors are $3$ for $H_3PO_4$, $2$ for $H_3PO_3$, and $1$ for $H_3PO_2$, representing the number of ionizable protons directly bonded to oxygen.

How is the equivalent weight of a metal oxide related to the equivalent weight of the metal ($E$)?

$E_{\text{metal oxide}} = E + 8$, because the equivalent weight of the oxide ion ($O^{2-}$) is $\frac{16}{2} = 8$.

What does the Law of Equivalence state for a general chemical reaction?

Regardless of the stoichiometric coefficients, the number of gram equivalents of all reacting substances consumed is equal to each other and equal to the number of gram equivalents of each product formed.

How is the limiting reagent identified when reactant amounts are expressed in gram equivalents?

The reactant having the lowest number of gram equivalents is the limiting reagent.

What is the formula for the minimum molecular mass of a compound containing an element with a given mass percentage?

$\text{Minimum Molecular Mass} = \frac{100 \times \text{Atomic Weight of element}}{\% \text{ of element}}$, assuming at least one atom of that element per molecule.

Who experimentally proved the Law of Conservation of Mass, and what apparatus was used?

The law was proposed by Lavoisier and experimentally proved by Landolt using an H-shaped glass tube containing reacting solutions (such as $AgNO_3$ and $NaCl$).

What is a recognized exception to the Law of Definite Proportions (Constant Composition)?

Compounds formed from different isotopes of the constituent elements (e.g., $^{12}CO_2$ vs. $^{14}CO_2$ have different mass ratios of carbon to oxygen).

What is Dulong and Petit's Law for solid elements, and which elements are exceptions to it?

$\text{Approximate Atomic Weight} \times \text{Specific Heat (in } cal\,g^{-1}\,^\circ C^{-1}) \approx 6.4$. It does not apply to beryllium ($Be$), boron ($B$), carbon ($C$), and silicon ($Si$).

How is the valency ($x$) of a metal determined using the vapor density method for a volatile metal chloride ($MCl_x$)?

$x = \frac{2 \times VD}{E + 35.5}$, where $VD$ is the vapor density of the metal chloride and $E$ is the equivalent weight of the metal.