1.2 Amount of Substance Flashcards
How do you know a chemical reaction has taken place?
Colour change Effervescence Temperature Light Precipitate formed (cloudy) Change in mass Sound pH change
What do the small numbers represent within an equation?
They say how many atoms of that element are within the molecule
What is the Mr?
Relative Molecular Mass
The average mass of a molecule compared to 1/12 of the mass of one atom of carbon-12
What is the Ar?
Relative Atomic Mass
Average mass of an atom compared to 1/12 of one atom of carbon-12
What is used to compared relative masses?
The carbon 12 scale
What unit is used for Mr?
gmol ^-1
How do you calculate the Mr?
Add up all the atomic mass numbers in the molecule
How to work out percentage of an element within a compound?
Ar of element
Divided by
Mr of compound
Multiplied by 100
How do you work out the transition element charges?
They should be given to you as a roman numeral I - 1+ II - 2+ III - 3+ IV - 4+ Etc....
Definition of an element?
A substance in which all the atoms contain the same number of protons
Definition of an atom?
The smallest part of an element that can take part in a chemical reaction
Definition of an ion?
An atom that has either lost electrons to form a positive ion or gained electrons to form a negative ion
Atoms do this to make a full outer shell of electrons
Definition of a molecule?
The smallest particle of a compound (a combination of two or more elements)
Also a name for elements that cannot exist as atoms in a free state
Which elements cannot exist as atoms in a free state?
Diatomic molecules Hydrogen - H2 Nitrogen - N2 Chlorine - Cl2 Iodine - I2 Oxygen - O2 Fluorine - F2 Bromine - Br2
What is the charge of ammonium?
NH4 ^ 1+
What is the charge of chloride, bromide and iodide?
Cl ^ 1-
Br ^ 1-
I ^ 1-
What is the charge of hydroxide?
OH ^ 1-
What is the charge of nitrate and nitrite?
NO3 ^ 1-
NO2 ^ 1-
What is the charge of hydrogen carbonate and hydrogen sulphate?
HCO3 ^ 1-
HSO4 ^ 1-
What is the charges of sulphate, sulphite and sulphide?
SO4 ^ 2-
SO3 ^ 2-
S2 ^ 1-
What is the charges of oxide, carbonate and phosphate?
O2 ^ 1-
CO3 ^ 2-
PO4 ^ 3-
What does aqueous mean?
Dissolved in water
What are the symbols for: hydrochloric acid Sulphuric acid Nitric acid Ethanoic acid
HCl
H2SO4
HNO3
CH3COOH
What are the symbols for ammonia
Carbon monoxide
Sulphur dioxide
Methane
NH3
CO
SO2
CH4
What is the law of conservation of mass?
Total mass of reactants = total mass of products
What are the rules for balancing combustion reactions?
Balance the carbons with CO2
Balance the hydrogen with H2O
Balance the oxygen with O2
What can you use with balancing equations?
Halves for the big numbers
What can you not do when balancing equations?
Use or adjust small numbers to balance
What must you remember about significant figures?
Your answer should always be the same number of significant figures as the smallest significant figure in the question
How do you do empirical formula?
Divide the % or mass of the element by it’s Ar
Divide all the answers by the smallest answer produced
The whole numbers produced shows the EF
You may have to multiply the ratios to create whole numbers
How do you work out the molecular formula?
Mr/EF mass = x
x multiplied by EF
What does a mole contain?
1 mole of any substance contains 6.02 x10 ^23 particles
Or Avagadros number
What is Avagadros number? What contains it?
6.02 x10 ^23
The Ar and Mr of a substance in grams contains Avagadros number of particles
What equation works out moles?
Mass
———
Moles X RFM
What units are used for mass, moles and RFM?
Mass - g
Moles - mol
RFM (Ar/Mr) - gmol ^-1
What do the large numbers represent in balancing equations?
The number of moles
How do you calculate reacting masses?
Check equation is balanced
Use the mass in the question divided by it’s RFM to work out the moles
Use the moles to multiply by the RFM of the substance you are working out
If it asks for the molecules multiply Be Avagadros
If it asks for atoms multiply by Avagadros then the number of the atoms
What is atom economy?
RFM of Useful products
———————————— x100
RFM of ALL the reactants
How can any atom economy be improved?
Find a use for the waste/non useful product
Sell the waste product
What should you remember in atom economy?
Take note of the big numbers when working out the RFM’s
What is significant about impure substances?
You cannot work out the moles or masses of impure substances
What is the second equation that works out moles?
Moles
—————————
Concentration X Volume
What is the unit of volume (in mol, conc, vol)? Converting?
Dm^3
Cm^3 / 1000 = dm^3
What are the units for concentration?
mol dm^3
Or
M
What is the equation for gases at room temperature and pressure?
Volumes
———————
Moles X 24dm^3
What is the equation for gases at standard temperature and pressure?
Volumes
———————
Moles X 22.4 dm^3
What are the conditions for room temperature and pressure?
298K
100kPa
What are the conditions for standard temperature and pressure?
273K
101.3 kPa
What is the ideal gas equation?
V P = n R T
V - volume P - pressure n - moles R - ideal gas constant T - temperature
Units for pressure? Conversions?
Pascals - Pa
kPa X 1000 = Pa
What is the ideal gas constant?
8.31 J k^-1 mol^-1
Units for temperature? Conversions?
Kelvin (K)
Celsius + 273 = Kelvin
Units for volume (in pv=nrt)? Conversions?
m^3
cm^3 / 1000000 = m^3
dm^3 / 1000 = m^3
What is the equation for instrument error percentage?
Number of measurements X Instrument error
——————————————
Measurement value
All multiplied by 100
How can you decrease instrument error?
Increase the measurement value
What do you do if you’re bot told which reactant is in excess?
Find the limiting reagent by working out the moles of both
How to work out the limiting reagents?
Work out the moles of both
Use the moles of one of the reactants to predict the moles of the other reactant
Compare the predicted moles to the actual moles
If the actual moles is greater than the predicted then that reactant is in excess
If the actual moles is smaller than the predicted moles then that reactant is the limiting factor
