Amount of Substance Flashcards

Interactive active recall cards for moles, the ideal gas equation, yields, atom economy, and titrations.

Moles & Molar Mass: read all 3 questions and answers

State the definition of a mole.
The SI unit of amount of substance that contains exactly 6.02214076 × 10²³ elementary entities (the Avogadro constant, \(N_A\); commonly rounded to 6.022 × 10²³ mol⁻¹ in exams). Historically defined relative to 12 g of carbon-12.
What is the Avogadro constant?
The number of particles in one mole of any substance, equal to 6.022 × 10²³ mol⁻¹.
State the formula relating moles, mass, and relative molecular mass (\(M_r\)).
\(\text{Moles} = \frac{\text{Mass (g)}}{M_r}\).

Ideal Gas Equation: read all 4 questions and answers

State the ideal gas equation and the SI units for each term.
\(pV = nRT\) where \(p\) is pressure in Pa, \(V\) is volume in m³, \(n\) is moles, \(R\) is 8.314 J K⁻¹mol⁻¹, and \(T\) is temperature in K.
How do you convert volume from cm³ and dm³ to m³?
cm³ to m³: multiply by 10⁻⁶ (or divide by 10⁶); dm³ to m³: multiply by 10⁻³ (or divide by 10³).
How do you convert temperature from Celsius (°C) to Kelvin (K)?
Add 273 (or 273.15) to the temperature in Celsius.
How do you convert pressure from kPa to Pa?
Multiply by 1000 (10³).

Empirical & Molecular Formulae: read all 3 questions and answers

Define empirical formula.
The simplest whole-number ratio of atoms of each element present in a compound.
Define molecular formula.
The actual number of atoms of each element present in one molecule of a compound.
Outline the steps to calculate the empirical formula from percentage composition data.
1. Divide each percentage by the element's \(A_r\) to get moles. 2. Divide each result by the smallest value to get the ratio. 3. Convert to whole numbers.

Yield & Atom Economy: read all 4 questions and answers

State the formula for percentage yield.
\(\text{Percentage Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100\).
State the formula for percentage atom economy.
\(\text{Percentage Atom Economy} = \frac{\sum (\text{coefficient} \times M_r \text{ of desired product})}{\sum (\text{coefficient} \times M_r \text{ of all reactants})} \times 100\).
Why is a high atom economy desirable in industrial processes?
It minimises the production of unwanted waste products, maximises sustainability, and reduces raw material costs.
What is a limiting reagent?
The reactant that is completely consumed first in a reaction, determining the maximum mass of product that can be formed.

Concentration & Titrations: read all 5 questions and answers

State the formula relating moles, concentration, and volume.
Moles=Concentration (mol dm⁻³) × Volume (dm³).
How do you convert concentration from g dm⁻³ to mol dm⁻³?
Divide the concentration in g dm⁻³ by the relative molecular mass (\(M_r\)) of the solute.
What is a standard solution?
A solution of known, accurately determined concentration, prepared by dissolving an exact mass of solute and making up to a precise volume of solution in a volumetric flask.
Why is it important to rinse a burette with the acid/alkali to be used rather than water before a titration?
Rinsing with water would dilute the solution in the burette, resulting in an artificially larger titre volume.
What are concordant titres?
Titre volumes that are within 0.10 cm³ of each other.