THINGS I FORGET
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How do p orbitals form pi bonds
Pi bonds form by SIDEWAY OVERLAP of P orbitals So they are at 90 degrees to each other
Test for sulfates
ADD BaCl2 AND HCL white precipitate is there is sulfate ions OR acidified Bacl2
Define dynamic equilibrium
Forward and backward reactions occur at the same rate Concentration of reactants and products remain constant
2 ways in which to improve a titration
Repeat whole experiment Take more than 1 sample( so more than 1 titration can be carried out)
When drawing a titration curve what do I need to include
A STEEP RISE AT THE START Vertical section is amount of acid and alkali VERTICAL SECTION SHOULD BE BETWEEN PH 6 AND 10 NOT MORE NOT LESS BUT THIS VARIES
Explain how recrystallization reduces amount of soluble impurities
Both acid and soluble impurities dissolve in hot water/solvent Impurities are soluble in cold solvent So impurities remain in solution Impurities remain in filtrate
Why is ionisation energy always endothermic
Ionization energy is endothermic because energy must be continuously absorbed to break the strong electrostatic attraction between a positively charged nucleus and a negatively charged electron. Because electrons are bound to the atom, removing them requires energy input to overcome this attraction, making the process endothermic.
For nitration of benzene why is temperatures of below 55 required
To prevent further substitution of di/tri nitrobenzene
Why is phenol more reactive than benzene
Lone pair of electrons on oxygen overlaps with pi cloud Which activates benzene ring making it more susceptible to attack
Why does benzene go through substitution rather than addition(2)
Delocalisation of pi electrons in the ring makes benzene more stable Addition removes stable arrangement
Assumptions of calculating pH of weak acid
Conc of H+ equals conc of A- as they disassociate in a 1:1 ratio Amount of disassociation is small so amount of acid has remained constant
Why is there a GENERAL INCREASE in first ionisation energy across a period
Going across a period, number of protons increases making electrostatic attraction between nucleus and outer electrons greater so smaller radius Electrons are being added to the same shell which has the same shielding effect
What provides evidence for existence of quantum shells
Atomic emission spectra Successive ionisation energies
What provides evidence for electron subshells
First ionisation energy of successive elements
Physical properties of ionic compounds
High melting points(strong electrostatic forces between ions) Conductor of electricity when in solution or molten(ions are free to move) Brittle
What provides evidence for existence of ions
Electrolysis of Copper chromate as Cu2+ ions migrate to cathode and turn blue And CrO42- migrate to positive electrode and turn yellow
What is covalent bonding
Strong Electrostatic attraction between between 2 nuclei and the shared paired if electrons between them
Explain the effect of multiple bonds on bond strength and length
Multiple bonds have a greater electron density between them This causes greater force of attraction between nuclei and electrons between them, causing shorter bond length and greater bond strength
How do London forces form
Electrons move constantly and randomly Electron density fluctuates and this causes neighbouring electrons to have a temporary dipole These consecutive temporary dipoles causes induced dipolew
Why does ice have a lower density than water
The molecules are held further apart by the hydrogen bonds than in liquid water and this explains lower density of ice
Factors affecting strength of metallic bonding
1)Proton number- more protons means stronger metallic bonding 2) Number of delocalised electrons per atom(more delocalised electrons the stronger the bond) 3) Size- smaller ion stronger bond
Calcium reacts with COLD water to produce calcium hydroxide and hydrogen What would you observe in this reaction
Fizzing/effervescence White precipitate of calcium hydroxide
How do I know if a group 2 hydroxide is not soluble
If it appears as a white precipitate
Why are group 2 carbonates more thermally stable down the group
Cations get bigger and have less of a polarising effect and distortion the carbonate ion less. This means the C-O bond is weakened less so it breaks down easily