amount of substances Flashcards
(24 cards)
State Avogadro’s constant.
1 mol = 6.02 × 10²³ particles
Rearrange the particles formula to make moles the subject
moles = particles ÷ 6.02 × 10²³
State the key formula linking moles, mass and Mr.
moles = mass (g) ÷ Mr
Rearrange the above formula to make mass the subject.
Mass = moles × Mr
Concentration and Volume (Solutions)
What are the units for concentration in solution chemistry?
mol dm⁻³
Write the formula to calculate moles when volume is given in cm³
moles = concentration × (volume (cm³) ÷ 1000)
Write the formula to calculate moles when volume is in dm³.
volume (mol dm ^-3) x concentration = moles
Write two rearranged versions of the moles-concentration-volume equation.
Concentration = moles ÷ volume
Volume = moles ÷ concentration
State the ideal gas equation.
pV = nRT
Identify the units for each variable in the ideal gas equation.
p = pressure (Pa), V = volume (m³), n = moles, R = 8.31 J K⁻¹ mol⁻¹, T = temperature (K)
State the conversions for the following:
(a) °C to K
(b) kPa to Pa
(c) cm³ to m³
(d) dm³ to m³
°C to K = +273
kPa to Pa = ×1000
cm³ to m³ = ×10⁻⁶
dm³ to m³ = ×10⁻³
How can the ideal gas equation be combined with another formula to find molar mass?
Combine with Mr = mass ÷ moles
Balancing Chemical Equations
State the two main rules for balancing chemical equations.
Must have equal atoms of each type on both sides.
Only change coefficients, not subscripts in formulas.
Ionic Equations
Describe the four steps to write an ionic equation.
Write the full balanced equation.
Split aqueous ionic compounds into ions.
Remove spectator ions (those appearing on both sides).
Ensure overall charge is balanced.
. Calculating Masses from Equations
Outline the four steps for calculating masses from equations.
Write balanced chemical equation.
Calculate moles of known substance.
Use mole ratio to find moles of desired substance.
Use moles × Mr = mass.
Define the term “empirical formula”
empirical Formula is the Simplest whole number ratio of atoms in a compound.
Define the term “molecular formula”.
Molecular Formula is Actual number of atoms in a molecule.
Define percentage yield and state its formula.
PercentageYield =
(ActualYield ÷ TheoreticalYield) × 100
Explain three reasons why actual yield may be less than theoretical yield.
actual yield is always less than theoretical yield due to: Incomplete reaction
Side reactions
Product lost during purification
Define atom economy
atom economy
measures how many atoms from reactants are used in the desired product.
give the atom economy formula
AtomEconomy =
(Mr of desired product ÷ Total Mr of all reactants) × 100
Give two economic and two environmental/ethical reasons for using reactions with high atom economy.
Economic Benefits:
Efficient use of expensive raw materials and
Less waste disposal cost
Environmental & Ethical Benefits:
Fewer harmful by-products and
More sustainable and greener
What is the formula used to calculate the number of moles from concentration and volume? When volume is given as cm³
Number of moles = (Concentration (mol dm⁻³) × Volume (cm³) )/ 1000
How do you rearrange the formula for moles to calculate the volume in cm³?
Volume (cm³) = (Number of moles × 1000) / Concentration (mol dm⁻³)
