Amount of Substance Flashcards
Relative atomic mass (Ar) definition
the mean mass of element compared to 1/12th of an atom of C-12
Relative molecular molecular (Mr) defiition
the mean mass of molecule compared to 1/12th of an atom of C-12
Avogadro constant
No. of particles in a mole
Ideal gas equation
pV=nRT
p=pressure (Pa/Nm^2)
V=vol (m^3)
n=moles (mol)
R=universal gas constant (8.31 JK-1mol-1)
T=temp (K) - C to K=+273
Empirical formula definition
Simplest whole number ratio of atoms of each element in a compound
Molecular formula definition
Actual no. of atoms each element in a compound
% yield equation
% yield= actual yield/theoritical yield
With mass or moles
Atom economy equation
(molecular mass of desired product/sum of molecular masses of all reactants)x100
Advantages of a high atom economy
-economic
Less time and machinery needed to separate desired product from by-products+waste=more product can be sold
Efficiently use of raw materials=less money spent on waste disposal and sourcing raw material
- environmental
Less waste produced+less hazardous materials used=more sustainable
-ethical
Aligns with ethical standards of sustainability=reflects commitment to responsible environmental stewardship+less burden on waste on communities
How to write ionic equations
- Split ionic compounds into ions
- identify spectator ions and cancel out
- rewrite equation w only the ions that react
Stoichiometry definition
Ratio of moles that are reacting+being produced (can tell from balanced equation)
Relationship bw empirical and molecular formula
Divide relative molecular mass of molecular formula by the relative molecular mass the empirical formula
What is a limiting reagent?
Reagents that are used up in a reaction+determine how much product is made
What does % yield tell us?
- practical efficiency of a procedure
- how much is lost to obtain product
Reasons for less than 100% yield
- reversible reaction
- reaction may not go to completion
- product may be lost when its separated from the reaction mixture eg. Filtration, transfer of liquids
- reactants may react in other reactions
Atom economy definition
A measure of how many atoms in the reactants form the desired product
What does atom econmony tell us
- waste produced by a specific reaction
- how many atoms r wasted in theory
Conc definition
A measure of the amount of solute dissolved in a given amount of solvent/solution
Conc equation
c=n/V or m/V
Units moldm-3 or gdm-3 (multiply/divide by Mr)
Types of uncertainty
-
readings
Values from a single judgement when using a piece of equipment eg. Thermometer (only one place to read from) -
measurements
Values taken as a difference between judgements of 2 values eg. Ruler (2 places to read from)
Values of uncertainty
No smaller than +/- 1/2 of smallest division
Quote same d.p as values given
Uncertainty equation
% uncertainty=(uncertainty/reading)x100
Gas volumes
Equal vols of gases under the same conditions ie temp and pressure have the same no. of moles/molecules
Gas volumes equation
No moles=vol (dm3)/molar vol (dm3mol-1)
At RTP: no moles=vol/24
What is an ideal gas?
- molecules act as rigid spheres
- pressure=collisions bw molecules+walls of container
- collisions are perfectly elastic
- temp is proportional to avg KE of molecules
- no intermolecular forces bw gas molecules (in the model, irl they do)
- vol occupied by molecules themselves=neglible relative to vol of container
