# Physical I

• Created by: Jessinoch
• Created on: 16-04-18 22:03
What are the 4 essential steps of mass spectrometry?
1. Ionisation (electron impact/electro spray ionisation) 2. Acceleration - positive ions accelerated by electric field to constant K.E. 3. Flight Tube - ions with smaller m/z travel faster 4. Detection - ions reach detector generating small current
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Describe Electron Impact Ionisation
1. Vaporised sample is injected at low pressure 2. Electron gun fires high energy electrons at the sample 3. Knocks an outer electron out and forms positive ions with different charges (X(g) -> X+(g) + e-)
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Describe Electro Spray Ionisation
1. Sample is dissolved in volatile, polar solvent 2. Injected through fine hypodermic needle giving aerosol 3. Tip of needle has high voltage where molecule gains a H+ proton from solvent (X(g) + H+ -> XH+(g))
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What is the difference between choosing when to use electron impact/electro spray ionisation?
Electron Impact is used for elements with low formula mass, it can cause large organic molecules to fragment. Electro Spray is used for larger organic molecules, the softer conditions means fragmentation does not occur.
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What is the equation for velocity?
v = square root of 2KE/m (KE = kinetic energy of particle in J, m = mass of particle in kg, v = velocity of particle in ms^-1)
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What is the equation for time of flight?
t = d square root m/2KE (t = time of flight (s), d = length of flight tube (m), v = velocity of particle (ms^-1)
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What is the difference for the electronic configuration of d-block elements?
When forming ions, 4s are lost before 3d.
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Define first ionisation energy
The first ionisation energy is the enthalpy change when one moles of gaseous atoms forms one moles of gaseous ions with a single positive charge.
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What are the factors that affect ionisation energy?
SANDE (S = shielding, A = attraction to the nucleus, N = nuclear charge D = distance from nucleus), E = amount of electrons)
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When given an ionisation energy table, how can you tell which element it is?
Look for where there is a big jump between numbers and between that group will be the element.
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Why is there a small drop in ionisation energy from Mg to Al?
Al is starting to fill a 3p sub shell, whereas Mg has its outer electrons in the 3s sub shell. The electrons in the 3p sub shell are slightly easier to remove as the 3p electrons are higher in energy and are also slightly shielded by the 3s electrons
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Why is there a small drop from P to S?
Sulphur has 4 electrons in the 3p sub shell and the 4th is starting to doubly fill the first 3p orbital. When the second electron is added there is a slight repulsion between the two negative electrons making the 2nd electron easier to remove
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Define mole
The mole is the amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12
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Define relative atomic mass
Relative atomic mass is the average mass of one atom compared to one twelfth of the mass of one atom of carbon-12
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Define relative molecular mass
Relative molecular mass is the average mass of a molecule compared to one twelfth of the mass of one atom of carbon-12
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How is number of particles calculated?
Moles of substance (in moles) x Avogadro's Constant (6.022 x 10^23)
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How is density calculated?
Mass/volume (density is given in gcm^-3)
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How do you convert from cm^3 to dm^3
Divide by 1000
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How do you convert from cm^3 to m^3
Divide by 1000 000
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How do you convert from dm^3 to m^3
Divide by 1000
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Define empirical formulae
An empirical formula is the simplest ratio of atoms of each element in the compound
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Define molecular formula
A molecular formula is the actual number of atoms of each element in the compound
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How do you make a solution for a titration?
1. Weigh solid on plastic boat 2. Add solid to beaker and reweigh plastic boat (note the difference) 3. Add 100cm^3 distilled water to beaker and stir to dissolve solid 4. Pour solution into graduated flask via a funnel
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How do you make a solution for a titration? continued...
6. Rinse beaker and funnel and glass rod and add washings into the volumetric flask 7. Make up to the mark with distilled water using a dropping pipette for last few drops 8. Invert flask several times to ensure uniform solution
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What is the ideal gas equation?
PV = nRT (P = pressure in Pa, V = volume in m^3, n = moles, R = constant, T = temperature in K)
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Percentage Yield
Actual Yield / Theoretical Yield x 100
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Percentage Atom Economy
Mass of Useful Products / Mass of All Reactants x 100
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What is the method for carrying out a titration?
1. Rinse equipment with distilled water 2. Pipette 25cm^3 of alkali into conical flask 3. Touch surface of alkali with pipette 4. Add acid solution from burette 5. Make sure jet space in burette is filled with acid 6. Add few drops of indicator
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What is the method for carrying out a titration? continued...
7. Use a white tile underneath flask to observe colour change 8. Add acid to alkali whilst swirling the mixture and add acid drowse at end point 9. Note burette reading before and after addition of acid 10. Repeat titration until 2 concordant results
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Percentage Uncertainty
% uncertainty = uncertainty / measurement made of apparatus x 100
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Define ionic bond
The electrostatic force of attraction between oppositely charged ions formed by electron transfer
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Define covalent bond
A shared pair of electrons
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Define dative covalent bonding
When the shared pair of electrons in the covalent bond comes from only one of the bonding atoms
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Define metallic bonding
The electrostatic force of attraction between the positive metal ions and the delocalised electrons
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What are the three main factors which affect the strength of a metallic bond?
1. Strength of nuclear attraction 2. Number of delocalised electrons per atom 3. Size of ion (smaller ion, stronger bond)
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Describe the structure of ionic bonding and give examples
Structure: Giant ionic lattice Examples: sodium chloride/magnesium oxide
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Describe the structure of one type of covalent bonding and give examples
Structure: Simple molecular with vdw forces/permanent dipoles & hydrogen bonds between molecules) Examples: Iodine/Ice/Carbon Dioxide/Water/Methane
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Describe the structure of the other type of covalent bonding and give examples
Structure: Macromolecular with giant molecular structures Examples: Diamond/Graphite/Silicon Dioxide/Silicon
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Describe the structure of metallic bonding and give examples
Structure: Giant metallic lattice Examples: Magnesium/Sodium (all metals)
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What are the properties of ionic compounds?
High boiling/melting points due to strong electrostatic forces of attraction, soluble in water, poor conductivity when solid as fixed in lattice, good conductivity when molten, crystalline solids.
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What are the properties of simple covalent compounds?
Low boiling/melting points due to weak intermolecular forces btwn molecules, poor solubility, poor conductivity when solid (no ions to conduct), poor when molten too, mostly gases & liquids.
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What are the properties of macromolecular covalent compounds?
High boiling/melting points due to strong covalent bonds (lots of them), insoluble, diamond and sand are poor conductors as they can't move, graphite is a good conductor as free delocalised electrons, generally poor when molten, generally solids.
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What are the properties of metallic compounds?
High boiling/melting points due to strong electrostatic forces between positive ions & delocalised electrons, insoluble, good conductivity when solid and molten, shiny metals, malleable as plates of ions can slide over each other.
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Describe the shape of the molecule with 2 bonding pairs
Linear - 180 degrees
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Describe the shape of the molecule with 3 bonding pairs
Trigonal planar - 120 degrees
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Describe the shape of the molecule with 4 bonding pairs
Tetrahedral - 109.5 degrees
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Describe the shape of the molecule with 5 bonding pairs
Trigonal Bypyramidal - 120 and 90 degrees
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Describe the shape of the molecule with 6 bonding pairs
Octahedral - 90 degrees
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Describe the shape of the molecule with 3 bonding pairs and 1 lone pair
Trigonal pyramidal - 107 degrees
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Describe the shape of the molecule with 2 bonding pairs and 2 lone pairs
Bent - 104.5 degrees
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How do you explain the shape of these molecules?
1. State number of bonding pairs and lone pairs 2. State that electron pairs repel to get as far apart as possible 3. If no loner pairs state that bonding pairs repel equally 4. If there are lone pairs state they repel more than b pair 4. State shape
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Define electronegativity
The relative tendency of an atom in a covalent bond in a molecule to attract electrons in a covalent bond to itself
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What are the trends with electronegativity?
1. Increases across period as number of protons increases and atom radius decreases 2. Decreases down a group as distance between nucleus and outer electrons increases and shielding increases
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Define enthalpy change
The amount of heat energy taken in or given out during any change in a system provided the pressure is constant
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What is an exothermic reaction?
When energy is transferred from the system to the surroundings, ΔH = negative, reactants are above products on graph
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What is an endothermic reaction?
When energy is transferred from the surroundings to the system, ΔH = positive, reactants are below products on graph
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Define standard enthalpy change of formation
ΔfH = enthalpy change when 1 mole of the compound is formed from its elements under standard conditions (298K and 100kPA), all reactants and products being in their standard states
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Define standard enthalpy change of combustion
ΔcH = enthalpy change that occurs when 1 mole of a substance is combusted completely in oxygen under standard conditions (298K and 100kPa), all reactants and products being in their standard states
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How do you measure the enthalpy change for a reaction experimentally?
q = mcΔt (q = energy change in J, m = mass of solution, c = heat capacity, t = temperature change)
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Describe how to use q = mcΔt in a question
1. Find the moles of each reactant to find which is in excess 2. Calculate q 3. Answer will be given in Joules 4. ΔH = reactant not in excess/q in joules 5. Change sign (- if exothermic, + if endothermic)
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How would you do the calorimetric method in a lab?
1. Put polystyrene cup in beaker for insulation & support 2. Add solutions to cup and make sure bulb of thermometer is in 3. Measure temperature for 3 mins then add solid 4. Stir and record temperature in intervals
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What errors could occur in the calorimetric method
1. Heat transfer to surroundings (heat loss) 2. Method assumes all solutions have heat capacity of water 3. We ignore heat absorbed by apparatus 4. Reaction of dissolving may be slow/incomplete 5. Density of solution is taken to be same as water
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State Hess' Law
Total enthalpy change for a reaction is independent of the route by which the chemical change takes place
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Define mean bond enthalpy
The enthalpy needed to break the covalent bond into gaseous atoms, averaged over different molecules
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What is the equation for ΔH?
ΔH = ∑bond energies broken - ∑bond energies made
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Draw the Maxwell Boltzmann Distribution
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What happens to the Maxwell Boltzmann Distribution if the temperature if increased?
The curve moves to the right, the mean will move to the right meaning more particles have the activation energy required
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What happens to the Maxwell Boltzmann Distribution if the temperature is decreased?
The curve moves to the left, the mean will move to the left meaning less molecules have the activation energy required
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How is the rate of reaction defined?
The change in concentration of a substance in unit time (moldm^-3s^-1)
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What is the effect of increasing concentration & pressure on rate of reaction?
At high concentrations and pressures there are more particles per unit volume and so the particles collide with a greater frequency and there will be a higher frequency of successful collisions
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What are the 2 features of a dynamic equilibrium?
1. Forward and backward reactions are at equal rates 2. Concentrations of reactants are products stays constant
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State Le Chatelier's Principle
If an external condition is changed the equilibrium will shift to oppose the change
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What effect does increasing temperature have on equilibrium?
The equilibrium will shift to oppose this and move in the endothermic direction to try and reduce the temperature by absorbing heat
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What effect does decreasing temperature have on equilibrium?
The equilibrium will shift to oppose this and move in the exothermic direction to try and increase the temperature by giving out heat
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How do you work out the concentrations of reactants and products in a Kc question?
Draw a table of initial moles, then equilibrium moles, then equilibrium concentration and use that in the Kc expression.
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What affects Kc?
Kc only changes with temperature
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What is Kc?
Kc is the equilibrium constant, the larger the Kc the greater the amount of products, the smaller the Kc the more the equilibrium favors the reactants
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What is an oxidising agent?
It is an electron acceptor
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What is a reducing agent?
It is an electron donor
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## Other cards in this set

### Card 2

#### Front

Describe Electron Impact Ionisation

#### Back

1. Vaporised sample is injected at low pressure 2. Electron gun fires high energy electrons at the sample 3. Knocks an outer electron out and forms positive ions with different charges (X(g) -> X+(g) + e-)

### Card 3

#### Front

Describe Electro Spray Ionisation

### Card 4

#### Front

What is the difference between choosing when to use electron impact/electro spray ionisation?

### Card 5

#### Front

What is the equation for velocity?