Chapter 3 - amounts of substance Flashcards
what is a mole?
1 mole is the amount of substance that contains 6.02 x 10 (^23)
the mass of one mole of an element is?
the relative formula mass in grams
The Avagadro constant value?
6.02 x 10 (^23)
molar mass gives?
the mass in grams in each mole of a substance
units of molar mass are?
gmol (^-1)
NUMBER OF MOLES EQUATION?
n = mass/ molar mass
m/ M
molecule definition
2 or more atoms held together by covalent bonds
Molecular formula definition?
the number of atoms of each element in a molecule
empirical formula definition?
the simplest whole number ratio of atoms of each element in a compound
the empirical formula is important for?
substances that do not exist as molecules - this includes metals, some non metals and ionic compounds. these substances form giant crystalline structures of atoms or ions
analysis definition?
investigating the chemical composition of a substance
what is a hydrated salt?
water molecules are part of their crystalline structure. This water is known as the water of crystalisation
is it very difficult to remove the last traces of what in a hydrated salt?
water
what are assumptions in working out a formula for hydrated salts? 1
1 - all of the water has been lost - only surface of crystals can be seen and some water could be left inside
solution: heat to a constant mass - the crystals are reheated repeatedly until the mass of the residue no longer changes, suggesting all water has been removed
what are assumptions in working out a formula for hydrated salts? 2
2- no further decomposition - many salts decompose further when heated. this can be very difficult to judge if no colour change
1cm (^3) =
1 ml
1 dm (^3) =
1000 cm (^3) = 1000 ml = 1 litre
concentration definition?
the amount of solute, in moles, dissolved in each 1dm (^3) of solution
moles, conc, vol equation
n = c x v
V IN DM (^3)
What is a standard solution?
a soolution of known conc
Convetring from moldm(^-3)
conc x Mr
at the same temp and pressure,
equal volumes of different gases contain the same no. of molecules
molar gas volume definition
the volume per mole of gas molecules at a stated temp and pressure
RTP is abt?
20 degrees and 101 kPa
At RTP, 1 mole gs molecules has a volume of?
approx 24dm (^-3)
RTP gas equation
n = v/24 or 24,000
4 assumptions making up the ideal gas equation?
1- random motion
2- elastic collisions
3- negligible size compared to size of their container
4 - no inter molecular formula
IDEAL GAS equation?
pV = nRT
ideal gas constant, R has a value of
8.314 (given on data sheet)
Temp units for ideal gas equation?
K (Kelvin)
degrees Celsius + 273 = K
pressure units
Pa
volume units
m(^3)!!!!!!
cm (^3) to m(^3)
x 10 (^-6)
dm (^3) to m (^3)
x 10 (^-3)
prob with assumptions for real gases
- when gas molecules are close together, the vol of the molecules compared with the vol of the container becomes sig
- also if gas molecules move slowly, they have less energy and intermolecular forces may become sig
stoichiometry def?
the ratio of the amount in moles of each substance
theoretical yield def
the max poss amount of product
why is theoretical yield diff to achieve?
- the reaction may not have gone to completion
- side reactions may have taken place alongside the main
- purification of the product may result in loss of some of the product
% yield equation?
actual / theoretical yield x 100%
note: both values are in MOLES not GRAMS
limiting reagent def
- the reactant that is not in excess, will be completely used up first, will stop the reaction
calculations MUST be based on what?
limiting reagent
atom economy def
is a measure of how well atoms have been utilised
atom economy assumes a
100% yield
atom economy equation
mr of desired products/ mr of all products x 100%
amount of molecules means use
avagadro’s constant
how many moles
look at formula
salts made by neutralisation have to be
ionic
anhydrous salt =
the water of crystallisation has been removed
hydrated salt =
a salt that has water of crystallisation as a part of its structure
water of crystallisation =
it’s the water that’s bonded as part of the crystal structure in hydrated salts
% error equation
+ or - uncertainty/ quantity measured x100
to reduce % error we can:
- decrease uncertainty (use balance that reads to 3.d.p 0.001)
or - increase quantity measured
molar mass
- mass of one mole of a substance
- takes same value as Atomic/ Molecular/ Formula mass
‘ideal behaviour of gases’ (snap)
- molecules act as tho they are rigid spheres
- molecules are in constant motion
- mols exert a constant pressure on walls of container
- collisions of mols are completely elastic
- as temp ⬆, KE ⬆
what is a crystal?
a substance whose atoms are ordered in a regular 3D pattern
. H(2)O represents…
the number of waters of crystalisation
note: atom economy
USE BIG NUMBERS IN EQUATION
2 types of reaction?
- addition - 100% atom economy, no by-products
- substitution and elimination reactions - < 100% atom economy
