Determination Of Formulae Flashcards
What are molecules?
Compounds containing two or more atoms held together by covalent bonds.
What is the molecular formula?
This is the number of atoms of each element in a molecule.
What is meant by empirical formula?
This is the simplest whole number ratio of a atoms of each element in a compound.
What is the empirical formula important for?
Substances that do not exist as molecules:
Metals
Some non-metals
Ionic compounds
What do substances that do not exist as molecules form?
Giant crystalline structures of atoms or ions.
What does this abbreviation mean: Mr?
Relative molecular mass
What is meant by relative molecular mass?
This compares the mass of a molecule to the mass of an atom of carbon-12.
How do you calculate the relative molecular mass?
Add together the relative atomic masses of the elements in the compound.
What is the relative formula mass?
This compares the mass of a formula unit with the mass of an atom of carbon-12.
How do you calculate the relative formula mass?
Add together the realise atomic masses of the elements in the empirical formula.
What is the process of investigating the chemical composition of a substance called?
Analysis
What is a hydrated salt?
This is where water molecules are a part of the salt’s crystalline structure.
What is the water of crystallisation?
Water molecules that are bonded into a crystalline structure of a compound
What is meant by the term anhydrous?
Dehydrated
What happens to the crystalline structure without water?
The crystalline structure is lost.
What are the two assumptions made when finding the water of crystallisation through an experiment?
All of the water has been lost.
There is no further decompositio.
Why is it difficult to see whether all of the water in a hydrated salt has been removed?
The colour of the substance may have changed but water may be present inside the crystals.
How do you make sure that all of the water has been removed from a hydrated salt?
Reheat until there is no longer a mass change.
Why is it difficult to judge if the salt has a further decomposition?
It’s difficult to judge if there’s no colour change so a different product could be formed if heated for too long.
