Calculations ⚖️ Flashcards
How do you calculate the relative formula mass of a compound?
Add together all the relative atomic masses of the atoms in a compound.
What is the empirical formula?
The smallest whole number ratio of the atoms of each element in a compound.
What is the molecular formula?
Actual number of atoms of each element in a compound.
What is the law of conservation of mass?
No matter is lost or gained during a chemical reaction.
If a reaction is carried out in a closed system, what can you say about the total mass of the reaction throughout the experiment?
Mass stays constant
What equation links mass, moles and relative atomic mass?
Mass (g) = Moles x Relative atomic mass (Mr)
How can you calculate concentration in g/dm³?
Concentration (g/dm³) = Mass(g) / Volume(dm³)
What is Avogadro’s constant?
The number of atoms, molecules or ions in one mole of a given substance.
The value of the constant is 6.02 x 10^23
What is the mass of 20 moles of calcium carbonate, CaCO3?
Mass = moles x relative atomic mass.
Mr = 100
20 x 100 = 2000 g
What formula links Avogadro’s constant, moles and number of particles?
Number of particles = Avogadro’s constant x Moles
How many atoms are in 3 moles of copper?
Number of atoms = Avogadro’s constant x Moles
= 6.02 x 10^23 x 3
= 1.83 x 10^23
What is a limiting reagent in a chemical reaction?
The chemical that is used up first in a reaction, preventing the formation of more oroduct.
Typically, an excess of one of the reactants is used to ensure that the other reactant is completely used up.
How do you calculate the concentration of a solution in mol dm -3?
Concentration (mol dm -3) = moles / volume (dm3)
How can you convert concentration in g dm-3 to mol dm-3?
Concentration (mol dm-3) = concentration (g dm-3) / Mr
What is meant by the term theoretical yield?
The amount of product that would be collected under perfect reaction conditions.
How do you calculate percentage yield?
Percentage yield = (Actual yield / Theoretical yield) x 100
Why could the actual yield of product be less than expected?
- Incomplete reaction
- Competeing, unwanted side reactions.
- Practical losses, for example some solid may get lost when being transferred between beakers.
What is the atom economy of a reaction?
Atom economy is a measure of the efficiency of the reaction. It looks at the amount of reactants that get turned into useful products.
How can atom economy be calculated?
Atom economy = (Mr of desired product / Mr of reactants) x 100
The _______ the atom economy, the more sustainable and efficient the process’
Higher
