Amount Of Substance Flashcards
Define relative atomic mass
Relative atomic mass is the average mass relative to 1/12th the mass of an atom of carbon-12
Define relative molecular mass
Relative molecular mass is the mass of that molecule relative to 1/12th the mass of an atom of carbon-12
One mole of a substance contains…?
The Avogadro’s number of particles (L)
6.022x1023
Define Avogadro’s constant
Number of particles/atoms/ions in one mole of substance
1mole of an element has the mass in grams equivalent to what?
It’s mass number. It will contain 6.022x1023 atoms of that element
1mole of Mg 24 equals to what?
24.00g = 6.022x1023 atoms
Write the equation that links mass of 1mol, mass of 1 atom and Avogadro’s constant
Mass of 1 mol= mass of atom/ molecule/ 6.022 x 1023
What is the equation to convert the mass in grams to kilograms using avogadros constant
24/ 6.022x1023 x 1000 = 3.98x10-26kg
Note
1/2 x m /L x 1000 x d2/t2 = 1/2 x m / 1000 x L x d2/t2
Formula for relative atomic mass
Ram = isotopic mass x percentage abundance/ 100
Note
C3H6O2N+ / C3H5O2 NH+
Give the ideal gas equation
PV= nRT
Give the units for the ideal gas equation
P= pa
V= m3
n = number of moles
R= 8.31
T= k
Give the formula for concentration
Conc(mol/dm-3) = mass(mol)/ volume(dm3)
Give the formula for number of moles
Number of moles = mass in grams/ Mr or Ar
What is 1 mole of carbon equivalent to?
6.022x1023
What is 1/2 mole of H20 equivalent to?
6.022x1023 / 2
What is 1 mole of H2O equivalent to?
(6.022x1023)x 3 because it contains 3 atoms
What is mole ratio?
Number in front of element or compound used in calculating number of moles
How can you calculate the Ar of an element in grams e.g Chromium
52.00/ 6.022x1023 = 8.635x10-23g
How to calculate the number of a particle
L x mass in g/ Ar
How do you convert cm3 to dm3 and back?
•Cm3 divided by 1000 equals dm3
• dm3 multiplied by 1000 equals cm3
How do you convert dm3 to m3 and back
• dm3 divided by 1000 equals m3
• m3 multiplied by 1000 equals dm3
How do you convert cm3 to m3 and back
•Cm3 divided by 1000000 equals m3
• m3 multiplied by 1000000equals cm3
How do you convert Celsius to kelvin
• Celsius + 273 equals kelvin
• kelvin - 273 equals Celsius
How do you convert Kpa to Pa and back
• Kpa multiplied by 1000 equals Pa
• Pa divided by 1000 equals Kpa
Define the term empirical formula
Simplest whole number ratio of atoms in a compound
what are standard conditions in the ideal gas equation?
25C/ 298K
1atm/ 100kPa
write the full word equation of the ideal gas equation
pressure x volume = number of moles x gas constant x temperature
Define percentage yield
The % of a product produced by a reaction, compared to a theoretical maximum
How would you calculate percentage yield
mass of useful product/ expected mass of useful product x 100
What can the percentage yield of a practical be used to investigate
Efficiency of practical techniques and whether reactions proceed are estimated
What is molecular formula?
The actual number of atoms present in an element in a compound.
Suggest why washing a conical flask with some distilled water does not give an incorrect result
does not react
what is crystallization
a separation technique used to separate dissolved solids from a liquid
The student used a wash bottle containing deionised water when approaching the end-point to rinse the inside of the conical flask
Explain why this improved the accuracy of the titration
• Ensures all ethanedioic acid/sodium hydroxide reactants are in the mixture/solution
• Acid/ sodium hydroxide would be in the sides of the flask
How do you calculate an empirical formula with decimals?
Multiply it by values until you get all non decimal values for your answer e.g C= 1, H= 1.60
5x1= 5 and 5x1.60=8
C5H8
Define limiting factor
Chemical that gets used up because there isn’t enough of it which also limits the amount of product formed
Define excess
There is more than enough of this chemical so more will be left over
Define theoretical yield
Largest amount of product (maximum yield) that can be made assuming no problems
Define actual yield
Amount of product you can make in an experiment (usually less than theoretical yield)
Give reasons for why the actual yield is usually less than the theoretical yield
• Human errors-specific
• Equipment errors
• Side reactions
• Reaction didn’t finish
• Reaction was reversible
What variables can be used to calculate percentage yield and give their equations
• Mass: actual mass/theoretical mass x 100
• Moles: Actual mole/theoretical mole x 100
Define atom economy
Percentage value that indicates what % of our reactants are turned into useful products. We can also determine how wasteful a reaction might be
List the factors that atom economy can determine?
• How efficiently raw materials are turned into the target product
• High atom economy means less waste is produced
• This also shows that there is a limited production of by-products that have no use
• By-products can be sold
• High atom economies minimise environmental impact and saves raw materials and increases sustainability
• Determines whether we should make a chemical in a particular way
What effect can decrease atom economy
Equilibrium
What type of reactions produce 100% atom economy
• When one product is produced
Give the formula of atom economy
Mass/Mr of desired product/ total mass/Mr of reactants x 100
What decimal point should percentages be in
1 decimal point
Silver oxide, Ag2O can be reduced by passing hydrogen gas over the heated oxide. The maximum mass of silver that could be obtained from 2.32g of silver oxide is?
Ag 2O + H2 ->H2O + 2Ag
Moles = mass/Mr
Mr Ag2O = 232
Moles Ag2O = 2.32/232 = 0.01
2:1 ratio so 0.02 moles of Ag will form
Mass = moles x Mr = o.o2 x 108 = 2.16g
1 mole of any gas occupies how much volume?
24dm-3
How do you calculate which substance is in excess
moles= mass/Mr then compare which is the highest. That is the limiting reagent. This is to understand which substance affects the amount of a particular product formed
Explain how time of flight mass spectrometry distinguishes between ions with different masses
• Positive ions are accelerated
• And detected
• To have a constant kinetic energy
• Lighter ion swill end up moving faster
• Faster ions arrive first at the detector
Why do samples need to be positively charged in time of flight mass spectrometry
So they can be accelerated and detected
What are relative masses
Masses of atoms compared to carbon-12
What is the difference between relative isotopic mass and relative atomic mass
• Isotopic mass is the mass of an atom of an isotope of an element relative to 1/12th the mass of an atom of carbon-12 . And it is usually a while number
• Relative atomic mass is…. And it’s usually a decimal
List the masses that can be measured using a mass spectrometer
• Relative atomic mass
• Relative molecular mass
• Relative isotopic abundance
What is ion drift
The ions renter a region with no electric field, so they just drift through it. Lighter ions will drift through faster than heavier ions
What is the difference between electro spray ionisation and electron impact ionisation
• Electron impact ionisation: The mass/ charge ratio of each peak is the same as the relative mass of that isotope because one electron has been knocked off.
• Electrospray ionisation: The mass/charge ratio of each peak would be one unit greater than the relative mass of each isotope because an H+ ion would have been added
State the type of chemical reaction that occurs when calcium carbonate reacts in a test tube with nitric acid
Neutralisation or acid/base reaction
A student was given a task to determine the percentage purity of a sample of salicylic acid. The method used by the student to prepare a solution of salicylic acid is described below.
* 0.500 g of an impure sample of salicylic acid was placed in a weighing bottle.
* The contents were tipped into a beaker and 100 cm3 of distilled water were added.
* Salicylic acid does not dissolve well in cold water so the beaker and its contents were heated gently until all the solid had dissolved.
* The solution was poured into a 250 cm3 graduated flask and made up to the mark with distilled water.
(a) Give two additional instructions that would improve this method for making up the salicylic acid solution. (4)
Weigh by difference or rinse weighing bottle and add to beaker
Rinse beaker and add washings to graduated flask
Invert flask several times to ensure uniform solution
Use a funnel to transfer to the flask and rinse the funnel
Use a stirrer to prepare the solution and rinse the stirrer
