AOS Flashcards
What is the definition of moles?
The amount of substance that contains as many particles as there are in 12 grams of carbon 12
How do you calculate number of moles?
Mass divided by mr in compounds
Mass divided by ar in singular elements
What is avogadro’s constant?
What is the value of avogadro’s constant?
The amount of particles in one mole of any substance
6.022 times 10 to the power of 23
What 6 things are examples of particles?
Ions
Protons
Atoms
Molecules
Neutrons
Electrons
How do you calculate number of particles?
Number of particles = moles X avogadro’s constant
What is relative formula mass?
The mass of an ionic compound
What is the equation for density?
What is the density of water?
Mass divided by volume
1.00g/cm^3
What are 2 ways concentration can be defined?
The number of moles dissolved in 1dm^3 of solvent (mol dm^3)
The mass of solute dissolved in 1dm^3 of solvent (g/dm^3)
What are the 2 concentration calculations?
Concentration = moles divided by volume
Concentration = mass divided by volume
How do you convert from g/dm^3 to mol/dm^3?
You divide by the Mr
Define molar volume
The volume that 1 mole of gas would occupy
How do you calculate the mass of a substance using balanced equations?
1) find moles of your known
2) find moles of unknown using ratio
3) multiply by mr to find the mass
How do you work out the limiting reactant?
1) find the moles of all your reactants
2) find the moles you have of each one
3) if you have less moles than you need of any of your reactants then that is the limiting one
How do you use the limiting reagent to calculate mass or moles of other reactants or products?
Ratio of unknown divided by the ratio of the limiting reagent and then multiply by the moles of the limiting reagent - this will give you moles of unknown which can then be used to calculate mass.
How do we calculate the volume of gases in standard conditions?
We use volume in cm^3 = moles X 24.8
How do we calculate volume of gases in other conditions?
We used the ideal gas equation :
Vp = nRT
Volume in m^3
Pressure in Pa
R = Gas constant 8.31
T = temperature in kelvins
What is Avogadro’s law?
Equal volumes of different gases of the same pressure and temperature will contain equal numbers of particles therefore one mole of any gas occupies 24.8dm^3 in standard conditions.
What are the standard conditions?
Temperature = 298 kelvin
Pressure = 100KPa
How did you convert from temperature in degrees Celsius to kelvin?
You add 273
Define percentage yield
The percentage yield of chemical reactions show how much product was actually made compared to the amount of product that was expected
Define theoretical yield and how it is calculated
The maximum mass of product that is expected to be obtained from the chemical reaction - it is calculated by using the reacting masses in balanced equations
Define actual yield and how it’s calculated
The mass of product that is actually obtained from the chemical reaction - it is usually given in the question but the percentage yield equation can be rearranged to calculate it.
What is the equation for percentage yield?
Percentage yield = (actual yield / theoretical yield) x 100
How do you calculate theoretical yield from equations?
1) calculate the moles of your known
2) calculate the moles of your unknown
3)calculate the mass of unknown which is the theoretical yield
What are the 5 common acids to remember?
What salts do they form?
Hydrochloric acid (HCl) - Chloride salts
Sulfuric Acid (H2SO4) - Sulfate salts
Nitric Acid (HNO3) - Nitrate salts
Carbonic Acid (H2CO3) - Carbonate salts
Phosphoric Acid (H3PO4) - Phosphate Salts
What ions are involved in Hydrochloric acid and Sulfuric Acid?
Cl minus
SO4 2 minus
What ions are involved in nitric acid, carbonic acid and phosphoric acid?
NO3 minus
Po4 3 minus
What are titrations?
What is the other definition for it?
A very accurate way of determining the unknown concentration of a substance
Volumetric analysis
What do you usually do before carrying out titrations? And why?
Make a standard solution
It is used to find the concentration of the second solution with which it reacts
Why is a hydrogen with a positive charge considered a proton?
It is considered a proton because hydrogen atoms only have one electron and one proton therefore losing the electron leaves it with a proton only
What are the 2 monoprotic acids and why?
Hydrochloric acid and Nitric acid
When they dissociate into their ions they only release one hydrogen
What are the 2 Diprotic acids?
Sulfuric acid and carbonic acid
When they dissociate into their ions they release 2 hydrogen ions
What is the triprotic acid?
Phosphoric acid - dissolves into 3 hydrogen ions and one PO4 3 minus
What is a back titration?
A titration method where the concentration of a reagent is determined by reacting it with a known amount of an excess reagent, then the remaining excess is titrated against another reagent
When are back titrations used?
In acid - base titrations when the acid or more commonly the base is an insoluble salt so direct titration endpoint would be hard to see or the reaction would occur slowly
What is the method for back titration calculations?
1) calculate the original moles of the excess reagent
2) calculate the moles of the remaining excess which is used in the titration (this is unreacted from original)
3) work out how many moles of excess reagent actually reacted in original
4) calculate the moles and mass of the substance in question
What does chemical formulae tell us?
They tell us how many of each kind of atom make up a substance
What are 3 types of substances?
Monotomic
Diatomic
Polyatomic
What are the 7 diatomic elements?
Hydrogen
Nitrogen
Chlorine
Bromine
Oxygen
Fluorine
Iodine
How do you convert from the molecular formula to the empirical formula?
Divide all the numbers in the molecular formula by the highest common factor which will give you the empirical numbers
Define molecular formula
The number of atoms of each element in a molecule
Define empirical formula
The simplest whole number ratio of atoms of each element in a compound
How do you calculate the empirical formula if there is no HCF?
If there is no HCF then the molecular formula is the same as the empirical formula
How do you calculate the empirical formula from percentages / mass?
1) Write the symbols of the elements present
2) Write the percentage or mass of each underneath
3) Divide the percentage or mass of each by their Ar
4) Divide both answers by the smallest one
5) Find the simplest whole number ratio - use denominator method or round if + or - 0.05 of whole number
How do you calculate the mass of an element in a substance / compound?
(Ar of the element x No of atoms of the element divided by the mr of the compound ) multiplied by mass of the compound
What is the difference between an hydrated and and anhydrous salt?
Hydrated salts contain water trapped in the crystals of the salt and anhydrous salts contain no water
How are hydrated salts shown in chemical formulae?
There is a dot after the salt and then the number of water molecules in each crystal followed by H2O
What is important about calculating the Mr of hydrated salts?
You must include the water molecules
How do you convert from empirical formula to molecular formula?
Molecular formula = empirical formula X (mr of compound divided by the mr of the empirical formula)
Mr or compound is always given in question
What is atom economy?
What percentage of total atoms you start with end up in the desired product - it is a measure of efficiency of chemical reactions
Why are high atom economy reactions usually better? (3)
They are usually more environmentally friendly as they produce less waste, use fewer raw materials and use less energy
How do you calculate atom economy using mass?
Atom economy = (mass of desired products / total mass of products) X 100
How do you calculate atom economy using Mr?
(Mr if desired products X balancing numbers) divided by (sum of all (mr X balancing numbers) for all products)
All multiplied by 100
