Quantitative Chemistry Definitions Flashcards
What is a relative mass?
A comparative value (modern compare to an atom of Carbon-12)
Definition of relative atomic mass?
The average mass of an atom of an element of a scale where an atom of Carbon- 12 is exactly 12
Definition of relative molecular mass
The average mass of an element/ compound on a scale where an atom of Carbon-12 is exactly 2 (used with molecules of a element/ compound)
Definition of relative formula mass
The average mass of a formula unit of a scale where an atom of Carbon-12 is exactly 12 (used with ionic/ giant covalent compounds)
How many particles does 1 mole of a substance have in?
6.02 x 10^23 particles (avogadros number)
What is the empirical formula?
The simplest ratio of atoms in each element in a compound
What is the molecular formula?
The actual numbers of atoms of each element in a molecule
Does a molecular formula apply to ionic compounds?
No
Reading (e.g reading from some apparatus) definition
A value found from a single judgement when using a piece of equipment
What is the definition of a measurement?
A value found from the differences between the judgement of two readings
What is a cation?
A positive (metal) ion
What is an anion?
A negative (non-metal) ion
What are ions?
Charged particles formed when atoms lose or gain electrons
What are three substances that contain ions?
Ionic metal-non metal compounds
Ammonium salts
Acids in an aqueous solution
What is a soluble salt?
One which will dissolve in water at room temperature
What is an insoluble salt?
One which will not dissolve in water at room temperature
What is a sparingly soluble salt?
One which will dissolve slightly in water.
What is a limiting reagent?
A reactant that is not in excess (less moles)
What are three reasons why the actual yield from a reaction will be less than the theoretical yield?
- Chemicals can be lost during transfer between containers
- The reaction may be reversible, so not all starting materials may fully react
- There could be other products formed in side reactions.
Atom economy definition
A measure of what proportion of the products are the desired product and how much is waste
Do chemical processes with high atom economies produce more or less waste that ones with a lower atom economy?
Less waste
What are two assumptions that we make when we say a gas is ideal?
There are no forces of attraction between the particles and the size of the particles is negligible.
What does the concentration of a solution tell us?
It tells us how much solute is dissolved in a know volume of a solution.
What is a titration?
A procedure where a solution of known concentration is used to determine an unknown concentration
What are concordant results?
Results withing plus or minus 0.10 cm3
What do you have to assume about the reagents to do with safety in a titration?
You assume all reagents and liquids are toxic, corrosive and flammable
Definition of a standard solution
It is a solution whose concentration is known precisely
What type of indicator is used in a titraition and what colour does it turn at the end point?
Phenolphthalein, turns colourless
What can we do to improve the accuracy in a titration?
Washing splashed down the sides of the conical flask with distilled water near the end point, this improved the accuracy as it makes sure that all the acid has reacted with the alkali so the reaction is complete (no acid on the sides of the flask)
How does the calculated concentration change if the pipette is only washed with water before the titration?
The concentration would be inaccurate and higher than the actual value as the concentration of NaOH would be more dilute, so less acid would be needed, so the value for the volume of acid needed would be lower.
How would the burette only being rinsed with water before the titration affect the calculated concentration of the acid?
The calculated concentration would be lower as the concentration of acid in the burette would be lower so more would be needed to neutralise the alkali.
How would we reduce the percentage uncertainty in titrations (using the biggest source of uncertainty)?
The largest source of uncertainty is the burette, so we would increase the volume of alkali used so that we would need more acid to neutralise it.
What does a back titration involve?
It involves reacting a know mass of an insoluble solid with a known excess of acid/ alkali, so only some of the acid/ alkali will react with the solid and some will remain left over.
The excess acid/ alkali can then be made up into a solution and titrated to determine how much remains.
What does a chemical equation tell us?
What is happening in a reaction
What non-metallic elements exist as diatomic molecules?
Have No Fear Of Ice Cold Beer
Hydrogen
Nitrogen
Fluorine
Oxygen
Iodine
Chlorine
Bromine
Astatine
