Moles, Formulae, and Victor Meyer's Method

Flashcards covering key definitions, mathematical relationships, experimental techniques (Victor Meyer's method), empirical and molecular formulas, and equation balancing from the lecture notes.

How is one mole of an element defined based on carbon-12?

One mole of an element is the amount that contains the same number of atoms as there are in $12.000\,\text{g}$ of carbon-12.

What is the definition of Avogadro's constant ($N_A$)?

The number of atoms in a $12\,\text{g}$ sample of carbon-12.

What is the exact value of Avogadro's constant given in the notes, and what is its value approximated to 3 significant figures?

The exact value is $6.0221367 \times 10^{23}$, which is approximated to 3 significant figures as $6.02 \times 10^{23}$.

What two symbols are used to represent Avogadro's constant?

$N_A$ and $L$.

What formula relates the number of particles to the amount in moles ($n$)?

$\text{number of particles} = N_A \times n$ (or $\text{Avogadro constant} \times \text{amount in moles}$).

What formula relates the mass ($m$), molar mass ($M$), and amount in moles ($n$)?

$n = \frac{m}{M}\,\text{mol}$ (or $\text{amount (in moles)} = \frac{\text{mass}}{\text{molar mass}}$).

What is the definition of Relative Atomic Mass ($A_r$)?

The number of times the average mass of one atom of that element is heavier than one-twelfth the mass of one atom of carbon-12 (or the weighted average mass of an atom of an element compared with $1/12$ of the mass of an atom of carbon-12).

What is an atomic mass unit (amu)?

The amount of matter that has a mass of one-twelfth that of carbon-12.

What is molar mass ($M$), and what are its units?

The mass of that substance expressed in grams, with the unit $\text{g}\,\text{mol}^{-1}$ or $\text{g/mol}$.

What is the definition of relative isotopic mass?

The mass of an atom of an isotope as compared to $1/12$ of the mass of an atom of carbon-12.

What is the definition of Relative Molecular Mass ($M_r$)?

The sum of the relative atomic masses of all atoms in one molecule of that substance (or the weighted average mass of one molecule of an element or compound compared with $1/12$ of the mass of an atom of carbon-12).

How does formula mass differ in scope from relative molecular mass?

Relative molecular mass refers only to the mass of a molecule, while formula mass also applies to an ion, radical, electron, or any other specified groups or nuclear particles.

What is relative vapour density?

The ratio of the mass of a given volume of a gas or vapour to the mass of an equal volume of hydrogen gas, measured under the same conditions of temperature and pressure.

Why is vapour density a unitless (dimensionless) number?

Because it is a pure ratio of two masses.

What is Victor Meyer's method used to determine?

The Relative Molecular Mass (RMM) or molar mass of volatile liquids or solids.

Which gas law does Victor Meyer's method rely on?

Avogadro's Law.

Why is the volume of displaced air collected over water rather than directly measuring vapor volume in Victor Meyer's method?

Because the vapor would condense upon cooling; measuring the displaced air gives the exact volume the vapor would occupy if it behaved as an ideal gas at room temperature and pressure.

Which laboratory apparatus setup is shown in this diagram?

Victor Meyer's apparatus (used in Victor Meyer's method).

What are the two key limitations of Victor Meyer's method?

1. Volatility Requirement: The compound must have a reasonably low boiling point so it can fully vaporize below the temperature limits of the outer heating jacket.
2. Thermal Stability: The method is invalid for compounds that decompose chemically when exposed to high temperatures.

What is the formula used to calculate Relative Molecular Mass (RMM) from Victor Meyer's method at s.t.p.?

$$\text{RMM} = \frac{22400\,\text{mL} \times \text{mass of volatile substance}}{\text{Volume of air displaced at s.t.p.}}$$

What is an empirical formula?

The simplest formula that shows the component elements in a molecule of a compound and gives the ratios in which these elements are combined (mole ratio).

What are the two formulas given to calculate the mole ratio of an element in a compound?

$\text{Mole ratio} = \frac{\%\text{ by mass of the element in a compound}}{\text{relative atomic mass of the element}}$ or $\text{Mole ratio} = \frac{\text{reacting mass of the element in a compound}}{\text{relative atomic mass of the element}}$.

What are the three steps to calculate the empirical formula of a compound?

1. Divide the % (or mass) of each element by the element's relative atomic mass.
2. Divide each figure obtained by the smallest of those figures.
3. If the results are not whole numbers, multiply them all by 2 (or in rare cases by 3 or 4) to obtain whole numbers.

What does the molecular formula of a compound show?

The actual or exact number of moles of atoms of the component elements in one molecule of the compound.

Which law states that matter can neither be created nor destroyed but can change from one form to another?

The Law of Conservation of Mass.

What named method can be used to balance chemical equations according to the lecture notes?

The simultaneous method.