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37 Cards in this Set
- Front
- Back
How are atoms ionised in electrospray ionisation? |
The sampleis dissolved in a volatile solvent and forced through a hypodermic needleattached to a positive terminal of a high voltage supply. This produces a finemist of positive ions which has lot electrons to the power supply. The solventevaporates from the droplets into the vacuum until they are travelling assingle ions. |
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How are atoms ionised in electron impact? |
A gaseoussample is put into the ionisation chamber where a hot filament (electron gun)emits high speed electrons. These knock off electrons from the sample whichform positively charged ions. |
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How are ions detected in mass spectrometry? |
The ions hita negatively charged plate. The positive ions gain an electron from thedetector causing a current to flow. The flight times are recorded. The size ofthe current is proportional to the abundance of the species and gives a measureof the number of ions hitting the plate. |
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Which method of ionisation is used for bigger molecules such as proteins? |
Electrospray ionisation |
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Define ionisation energy |
The enrgy required to remove one mole of electrons from a mole of atoms in the gaseous state. |
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What's the trend in IE across a period? Why? |
Increases Nuclear charge increases, atomic radius decreases. Electrons have stronger attraction to nucleus. |
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What happens from group 2-3 when looking at ionisation energies? |
IE decreases, as electron enters 'd' orbit- which is further from the nucleus. |
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What happens from group 5-6 when looking at ionisation energies? |
IE decreases as there will be a paired electron in orbital, paired electrons repel each other so are easier to remove. |
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What is the trend in IE down a group? Why? |
Decrease in IE. Outer electron moves to an a orbit further from the nucleus |
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Define Empirical formula |
The formula which represents the simplest whole number ratio of the atoms of each element present in the compound. |
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What's the trend in electronegativity down a group? |
Decreases Less shielding by electrons in inner shells |
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Trend in electronegativity across a period? |
Increases Nuclear charge increases but inner main levels remains the same and atom becomes smaller. |
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2 Bond pairs shape + Angle? |
Linear 180 |
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3 Bond pairs Shape and angle? |
Trigonal planar. 120 |
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4 Bond pairs Shape and Angle |
Tetrahedral 109.5 |
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5 Bond pairs Shape + Angle? |
Trigonal Planar 120 90 |
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6 Bond pairs Shape + Angle? |
90 |
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Define Enthalpy change. |
The heat transferred in a chemical reaction at constant temperature. |
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Standard Enthalpy of Formation |
The enthalpy change when one mole of substance isformed from its constituent elements under standard conditions, all reactantsand products being in their standard state. |
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Standard Enthalpy of Combustion |
The enthalpy change when one mole of substance iscompletely burnt oxygen under standard conditions, all reactants and productsbeing in their standard states. |
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Hess’s Law? |
Theenthalpy change for a chemical reaction is the same, whatever route is takenfrom reactants to products. |
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Mean bond enthalpy |
The average energy required to break a bond |
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LeChatelier’s principle |
If a reaction is subjected to a change inconcentration, temperature or pressure, the position of equilibrium will moveto oppose the change. |
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Oxidation |
Loss of electrons |
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Reduction |
Gain of electrons |
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Oxidising agent |
Accepts electrons |
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Reducing agent |
Electron donor |
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Trend in atomic radius across a period? Why? |
Decreases. As you move across, the more protons the element has.This means a stronger nuclear charge to pull electrons closer. There are noadditional electron shells to provide shielding so the size of the atomdecreases.� |
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Trend in atomic radii down a group? Why? |
Increase. The atoms of each element have one extra complete mainlevel shell so the outer electron main shell is further from the nucleus. |
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Define first ionisation energy? |
The energy required to convert a mole isolated gaseousatoms into a mole of singly positively charged gaseous ions by removing a moleof electrons. |
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Trend in melting and boiling points across a period? |
The melting/boiling pointsincrease from sodium to aluminium because of the strength of the metallicbonding, the charge on the ions increases so more electrons join the sea ofdelocalised electrons that holds the lattice together. The melting point ofnon-metals with molecular structures depends on the size of the van der waalsforced between molecules. Silicon is macromolecular with strong covalent bondswhich require a lot of energy to overcome. Phosphorous, sulphur andchlorine are molecular substances, van der waals forces are weak and need lessenergy to overcome so they have lower boiling/melting points. Of these, sulphuris the biggest molecule so needs more energy to overcome more van der waalsforces. |
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Uses of calcium? |
CaO and CaCO3 isused to remove sulphur dioxide from flue gases.Ca(OH)2 is used in agriculture toneutralise acid in soils. |
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Uses of Magnesium? |
Used to extract titaniumfrom its ore. (TiCl4)Mg(OH)2 is used in indigestion tablets asan antacid (milk of magnesia). |
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Uses of Barium |
Used in ‘barium meals’ ,BaSO4 is opaque to x-rays so makes tissues show up in x-ray imaging.BaCl2 can be used to test for sulfateions. |
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Test for sulfate ions? |
Acidified BaCl2 is added tothe solution. If a white precipitate of BaSO4 isformed then sulfate ions are present. HCl is used to acidify the solution toget rid of impurities of sulfites and carbonates which would also produce awhite precipitate. |
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Solubility rules for hydroxides (group 2) |
(Add pic) |
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Solubility rules for Sulphates (group 2) |
(add pic) |