P1: Amount of Substance Flashcards
What is Avagadro’s Constant?
6.022 x 10^23
What does Avagadro’s Constant measure?
The amount of molecules/atoms/particles in one mole.
How would you use coefficients and the moles of one reactant to find the other moles?
Moles of A (what we want to find)=
Moles of B (the moles we have been given)
x
coefficient of A
/ coefficient of B
What is a Limiting Reactant?
Limits the number of particles of the other substances that can react.
What is the excess reactant?
The reactant you have more than enough of.
How do you find the limiting and excess reactants?
- Find the mole ratio from the equation
- Use the mol of B x A/B formula to find mol of A
- Use info provided to see what reactants you have enough of for the reaction
What is the formula using moles and Avagadro’s constant to find paticles?
Moles=
number of particles
/
Avagadro’s Constant
What is an easy 3 step process to balancing equations?
- Write out how many atoms of each element you have
- Find the first ones which are not equal, use a coefficient to equal them
- Amend the rest to dit
What is dissociation?
When ionic compounds dissolve in water, the ions separate and move around independently.
What are spectator ions?
Ions that don’t change in the equation (can be left out of ionic equations)
Tips for balancing equations
- Start with an element that is only in one reactant and product
- Use lowest common multiples
- Can use fractions
- Balance stand alone elements last
What is element molar mass?
Mass in grams of 1 mole of the elements atoms
How would you work out the mass of 1 mole of an element?
Average mass of 1 atom x avagadros
How would you work out molar mass ( g mol-1) from relative atomic mass (Ar)?
They are equal
Ar= 4
Molar mass= 4 g mol-1
How would you work out the molar mass of a giant lattice?
- Find the formula of the smallest repeating unit
- Take the Ar of each element and add up
= relative formula mass
How do you work out moles? (solid)
Moles = mass / Mr
How do you work out conc?
Conc = mol / vol (dm3)
How do you convert between cm3, dm3, and m3?
cm3 > div. 1000> dm3> div. 1000> m3
What is the units of conc?
mol dm-3
or g dm-3
How do you convert between g and mg?
g > x1000> mg
C1V1=C2V2 , what do C and V represent?
Conc
Vol
Explain these properties of gases: Volume, amount, temp, pressure
Volume= the amount of space it takes up.
Amount= number of particles measured in moles
Temp= determined by average speed of particles
Pressure= number of collisions between particles and walls of container
What are the 4 gas laws relating amount, pressure, volume, and temp?
&= directly proportional
Amount & Volume
Volume & Temp
Temp & pressure
Volume and Pressure are not &
What is the ideal gas equation?
PV=nRT
P- pressure (Pa)
V- Volume (m3)
n- number of moles
R- gas constant (JK-1 mol-1)
T- temp (Kelvin)
How do you convert from KPa to Pa?
KPA> x1000> Pa
What is 1Nm-1 equal to?
1Pa
Define Percentage Yield
How efficient the reaction is at converting reactants into products
How do you calculate theoretical yield?
- Balance
- Identify limiting reactant
- Find moles of limiting reactant
- Find amount (moles or mass) of desired product
What is the % yield equation?
% yield= Actual yield / Theoretical yield.
x 100
What does a high % yield mean for cost?
Lower economic and environmental costs
To find the theoretical yield, you need to find the limiting reactant, how?
- Turn the given mass into mol
mass/ Mr - Use the mole ratio
Define percentage atom economy
The percentage of reactants that end up in the desired product, compared to waste products
What is the % atom economy equation?
% atom economy = Mr desired products / total Mr of all reactants
x 100
What are the 4 steps to working out a titration calculation?
- Balance equation
- Calculate how many moles reacted for the solution with a known conc.
mol= vol x conc - Use the mole ratio to calculate the amount of the other solution that reacted
- Use this amount, along with the initial volume to calculate the unknown conc.
conc= mol / vol
What is a titration used for?
To find the amount of solute in solution, to then find conc
Example of a neutralisation reaction
Acid + Base –> Salt + Water
How do you calculate purity?
% Purity= mass of solute / total mass of substance
x 100
What is the empirical formula?
The simplest whole number ratio of elements in a compound
How do you work out the empirical formula?
- Work out ratio of moles or atoms
- if given mass, change to moles
-if given a %, switch to mass 75%=75g
then to moles - Simplify
-divide by the smallest number and convert to whole numbers
(the number after the decimal e.g 0.5, its equivilent fraction, 1/2, times by denominator , x2)
You have the decimals:
.5
.33
.66
.25
.75
What are there equivilent fractions
.5 = 1/2
.33= 1/3
.66=2/3
.25=1/4
.75=3/4
Define molecular formula
The actual number of atoms of each element in a compound
How do you find molecular formulas?
- Find empirical formula
- Find relative forula mass
- Find correct multiple
- Times empirical by multiple
Multiple?
Mr / formula mass
How would you find the percentage of water in a hydrated salt? e.g MgSO4 . yH20
y(18.0) / molar mass of salt + (y x 18.0)
x100
where y= moles of water
18.0= molar mass of water
