QUANTITATIVE CHEMISTRY Flashcards
(16 cards)
What is the empirical formula of a compound?
The simplest whole number ratio of atoms of each element in a compound.
What is the molecular formula of a compound?
The actual number of atoms of each element in a molecule.
What does hydrated mean in chemistry?
A substance that contains water molecules within its crystal structure.
What does anhydrous mean?
A substance that does not contain water molecules in its structure.
What is water of crystallisation?
Water molecules that are chemically bonded within the crystal structure of a compound.
How can water of crystallisation be removed from a salt?
By heating the hydrated salt to constant mass.
Why do we heat a substance to constant mass?
To ensure all water of crystallisation has been removed and decomposition is complete.
How do you calculate the relative formula mass (Mr) of a hydrated compound?
Add together the relative atomic masses (Ar) of all atoms in the compound, including water of crystallisation.
How can you determine the empirical formula of a compound?
From the mass or percentage composition of each element, convert to moles, then simplify the ratio.
How do you calculate the moles of water of crystallisation in a salt?
Use mass or percentage data to find moles of salt and water, then determine the simplest ratio.
How do you calculate the concentration of a solution in mol/dm³?
Divide the number of moles of solute by the volume of the solution in dm³.
How do you calculate moles of solute from concentration and volume?
Moles = Concentration (mol/dm³) × Volume (dm³)
How do you calculate mass of solute from concentration and volume?
Use moles = concentration × volume, then mass = moles × Mr.
What is the formula for atom economy?
(Mass of desired product ÷ Total mass of products) × 100
Why is a high atom economy important?
It reduces waste and cost, making the process more sustainable and economical.
How do you determine the mass of water in hydrated crystals (Prescribed Practical C5)?
Measure the mass before and after heating to constant mass; the difference is the mass of water lost.
