Chemistry Unit 1- Amount of Substance

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  • Created by: FireDwarf
  • Created on: 06-09-13 16:53
What is a mole?
A mole is an amount of any substance which contains the same number of atoms of 12g's of carbon 12
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How many atoms does 1 mole of any substance contain?
6.02 x 10^23
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What is Ar?
Relative atomic mass- the average weight of one atom of an element to 1/12th of Carbon 12
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What is Mr?
Relative Molecular Mass- the average weight of one molecule to 1/12th of Carbon 12
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What are the units for Mass, Mr and Moles?
Mass (g), Mr (g), Moles (Mol)
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Mass = Mr x Moles
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How do we complete one with Ch4.7H20?
We work out the number of moles then times it by 7 ( as 7 moles of H20 are per mole of that)
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What is the ideal gas equation about?
It allows the molar vaule of a gas to be worked out if the temperture and pressure is kept constant
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What is the standard temperture and pressure?
273k and 100kPa
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What space does 1 mole of a gas occupy following the ideal gas equation?
22.7 dm^3
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What is the equation?
pv= nRT
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What do the symbols mean?
Pressure (Pa), v (Volume m3), Number of Moles (Mol),R (Gas constant), Temperture (Kelvin)
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How do I convert these units?
Kelvin = +273 to C, Kpa to Pa= 1000, dm3 to m3= /1000, cm3 to m3= /100000
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How do you work out the mass or MR?
Work out the number of moles via pv= nRT (n= moles) and then subtract it into mass = mr x mole
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Democritus said that the smallest piece of matter was the atom, theory wasnt accepted for 2000 years
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1800- Elements composed of atoms, indestructable, atoms of the same element are the same, atoms of diffrent elements are diffrent, compounds, 2 or more elements joined together
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1897- Atom was divisable- discovered electrons- plumb pudding theory- positive charged material with negative charge spread evenly throughout.
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1908- Fired postive charged alpha particals at gold foil- found that some bounced back- this suggested that there was a positive charged center (nucleus) as some deflected.
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1913- Electrons orbit in definate orbits around the nucleus and electrons are placed in energy levels
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Wave Model
Nucleus surrounded by electrons- electrons dont move in orbits but the probable location of an electron can be determined by its energy level. Its called an orbital
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James Chadwick
1932- Discovered the neutron
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Relative masses of the diffrent parts of the atom?
Proton 1, Neutron 1, Electon 1/1836
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relative charge?
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What does a Mass spectrometer do?
Allows you to work out an accurate relative atomic mass, relative molecular mass and other things.
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What must it be first?
In a gaseous state. High vaccum so that the ions dont collide with air molecules which would stop it reaching the detector.
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How does it find the relative atomic mass? ( the stages)
With 4 stages, ionisation, accerleration, deflection and detection
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Beam of electons are fired from an electron gun, causing some electrons to fall off the atom/molecules so they therefore form a positive ion. Most only lose 1 electon forming a 1+ charge. but some can get a 2+ charge.
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These positive ions are then accerlerated via a electric field (negatively charged plate). Their speed depends on their mass, the lighter they are the faster they go.
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These then move into a magnetic field where the field deflects the beam of ions in a circle. The deflection of an ion depends on its m/z value. Heavier ions are deflected less, while lighter ions are deflected more.
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What else is the deflection dependant on?
Strengh of the magnetic field, stronger field, more deflection.
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Gradually increased field which causes the ions to go into the detector one after each other, Ions enter the detector, lose their charge by accepting electrons and create a current which is proportional to the abundance.
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What does this produce?
A mass spectrum where the m/z value is plotted agianst the abundance
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How does it let us find out the Ar?
We can find the diffrent ions in the sample, rather then the diffrent elements. This allows diffrent isotopes to be isolated. We then do low resolution Mass Spec by multiplying the mass numbers (the m/z cause z is 1) by the abundance of each isotope
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Then dividing it by the total abundance.
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What does m/z value mean?
Mass to charge - The Mass number divided by the charge (usually 1+)
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What is the empirical formula?
The simplest whole number ratio of atoms in a compound combined together
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What is the molecular formula?
The actual number of atoms of each diffrent element that make up a molecule of a compound.
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How to do the empirical formula?
Write in list - Take the mass (g) or percentage (%) - Divide it by the AR - Divide the amounts by the lowest amount previously - write it like so ; C2H
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How to do the molecular formula?
Work out the MR of the empirical formula --- Divide the real Mr by empirical Mr to get answer -- then times the empirical by the answer previous
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Equation for concentration, volume or number of moles in solution?
Number of moles = Conc x Volume
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Conc= moles dm^-3 and Volume= dm^3
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How to convert from g dm^-3
mass/MR = number of moles therefore converting it into mol dm^-3
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Work out mass?
Get the number of moles via conc x volume then put this into mass = MR mole
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What is atom economy?
The percentage of atoms which are used for a useful product
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How to do?
Calculated the mass of products (mass = mr mole) and then calculate mass of the product wanted, (check with all products added together = mass of reactants)
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Mass of desired products/ Mass of total reactants
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What is percentage yield?
The amount of yield prodcuced in comparison to the theoretical yield
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Mass of product wanted/Mass of theoretical product wanted
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How to do?
Mass (Mr Mole) of product wanted and then the same for the equation
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How to do?
Mass (Mr Mole) of product wanted and then the same for the equation
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Card 2


How many atoms does 1 mole of any substance contain?


6.02 x 10^23

Card 3


What is Ar?


Preview of the front of card 3

Card 4


What is Mr?


Preview of the front of card 4

Card 5


What are the units for Mass, Mr and Moles?


Preview of the front of card 5
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