2.1.3 Amount of Substance Lecture Notes

Comprehensive practice flashcards covering mole concepts, calculations, gas laws, and sustainability in chemistry based on the lecture transcript.

What is the symbol and unit for amount of substance?

The unit is the mole, and its symbol is mol.

What is the value and definition of the Avogadro constant ($N_A$)?

The number of particles per mole, which is $6.02 \times 10^{23}\,mol^{-1}$.

Define molar mass and state its typical units.

Molar mass is the mass per mole of a substance, with units of $g\,mol^{-1}$.

Define molar gas volume ($V_m$).

The gas volume per mole of gas molecules, with units of $dm^3\,mol^{-1}$ or $cm^3\,mol^{-1}$.

What is the difference between an empirical formula and a molecular formula?

The empirical formula is the simplest whole number ratio of atoms of each element in a compound, while the molecular formula is the actual number and type of atoms of each element in a molecule.

How many grams are in 1 tonne?

$1,000,000\,g$ (or $1000\,kg$).

What is the conversion factor between $dm^3$ and $cm^3$?

$1\,dm^3 = 1000\,cm^3$.

How do you convert degrees Celsius ($^{\circ}C$) into Kelvin ($K$)?

$0^{\circ}C = 273\,K$. To convert, add $273$ to the Celsius temperature.

Define the mole based on carbon-12.

The mole is the amount of substance ($n$) which contains as many elementary particles as there are atoms in exactly $12\,g$ of carbon-12.

What is the formula to calculate the number of moles ($n$) from the number of particles?

$$n = \frac{\text{number of particles}}{6.02 \times 10^{23}}$$

What are the elements that exist as diatomic molecules?

$H_2$, $N_2$, $O_2$, $F_2$, $Cl_2$, $Br_2$, $I_2$, and $At_2$.

Define relative atomic mass ($A_r$).

The weighted mean mass of an element compared with $1/12th$ of the mass of an atom of carbon-12.

What is the formula for calculating the percentage by mass of an element in a compound?

$$\frac{\text{relative mass of atoms of the element in the compound}}{\text{total relative mass of the compound (Mr)}} \times 100$$

How is the number of moles ($n$) calculated from mass ($m$) and molar mass ($M$)?

$$n = \frac{m}{M}$$

What is the molar gas volume ($V_m$) at room temperature and pressure (RTP)?

Approximately $24.0\,dm^3\,mol^{-1}$ or $24,000\,cm^3\,mol^{-1}$.

State the Ideal Gas Equation and the units for each variable.

$pV = nRT$, where $p$ is pressure in $Pa$, $V$ is volume in $m^3$, $n$ is moles, $R$ is the gas constant ($8.314\,J\,mol^{-1}\,K^{-1}$), and $T$ is temperature in $K$.

How do you calculate the number of moles ($n$) for a solution when the volume is given in $cm^3$?

$n = \frac{c \times V}{1000}$, where $c$ is concentration in $mol\,dm^{-3}$ and $V$ is volume in $cm^3$.

What are the steps to prepare a standard solution from a solid?

1. Measure mass by difference. 2. Dissolve in a small amount of water. 3. Transfer to a volumetric flask with washings. 4. Fill to the graduation line with distilled water (meniscus). 5. Stopper and invert to mix.

Define percentage uncertainty for a volumetric measurement.

$$\left( \frac{\text{number of readings} \times \text{uncertainty of equipment}}{\text{quantity measured}} \right) \times 100$$

What is the formula for percentage yield?

$$\text{\% yield} = \left( \frac{\text{actual yield}}{\text{theoretical yield}} \right) \times 100$$

Define the term 'limiting reagent'.

The reactant that is not in excess and is used up completely in a reaction, thereby determining the amount of product formed.

What is the formula for percentage atom economy?

$$\text{\% atom economy} = \left( \frac{\text{sum of molar masses of desired product}}{\text{sum of molar masses of all products}} \right) \times 100$$

Why do addition reactions have a high atom economy?

They have an atom economy of $100\%$ because only the desired compound is formed and there are no by-products.