harder chem stuff Flashcards
benzene facrts
Benzene does not take part in addition reactions. An addition reaction is a benzene ring to a ring with no conjugated system.
Benzene takes part in electrophiles substitution reactions with halogens using aluminium bromide
Nitration if benzene uses concentrated sulphuric acid
To get geometric isomerism there must be restricted rotation
Hydrogen bond are easily solvent
more covalent character means the least difference in electro negativity values
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Bond entahlpy is breaking minus making
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Explain how proton nmr spectroscopy works
Nuclei of atoms behave like tiny magnets and in a strong magnetic field some align with the field (lower energy) whilst the rest align against it (higher energy). The absorption of radiation in the radio frequency of the electromagnetic spectrum causes the 1h nuclei to flip from the lower to higher energy alignment. As they fall back from higher to lower energy alignment emitted radiation is detected and plotted on a spectrum
Explain why there is a series of lines at discrete wavelengths in the emission spectrum of cadmium.
Different energy levels/subshells
Conjugated system and high low energy n frequency etc
the more atoms in a conjugated system:
Smaller energy gap between homo and lumo
A lower frequency of light (longer wavelength, lower energy)
The less atoms in a conjugated system:
a larger energy gap between homo and lumo
A higher frequency of light absorbed (shorter frequency, higher energy)
Order of ems
Gamma rays, x rays, ultraviolet, visible light, infrared, microwave, radio wave
Explain how colour arises in transition metal compounds such as those above. (complexes)
(Ligands) split the degenerate d orbitals (sub shell) into orbitals of different energies.
absorption of visible energy (white light) resulting in complementary colour observed.
2016 3aii d orbital splitting spectrochemical series - Explain why all of the complex ions formed by the Fe3+ ion are paramagnetic.
Less energy is required to promote an electron
Electrons can be promoted between energy levels
In a free transition metal ion (one without ligands) the five d orbitals in the 3d subshell are degenerate (equal in energy). On the formation of a complex for example [Ni(H2O)6]2+ six water ligands surround the central nickel ion forming an octahedral shaped complex. The ligands approach the nickel ion along the x,y and z axes. The electrons in d orbitals that lie along these axes (dz2 and dx2-y2) will be repelled by electrons in the water ligand molecules. These orbitals now have higher energy than the three d orbitals that lie between the axes (dxy, dyz and dxz) and therefore the five d orbitals are no longer degenerate. This is called splitting of d orbitals and is different in octahedral complexes compared to tetrahedral and other shapes of complexes.
The energy difference between the different subsets of d orbitals depends on the ligand and its position in the spectrochemical series (series of order of ligand’s ability to split the d orbitals). CN- >NH3 >H2O>OH- >F- >Cl- >Br- >I-
Transition metal complexes absorb light due to the split in d orbitals. Electrons in the lower d orbitals can absorb energy and move to the higher energy d orbitals. If this energy absorbed in this d-d transition is in the visible region of the electromagnetic spectrum the colour of the transition metal complex will be the complementary colour of the colour absorbed.
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Predicting ph:
The first part of the name of a salt identifies which alkali/base was used to make the salt. Sodium
salts are generally made using sodium hydroxide and potassium salts made using potassium hydroxide as the alkali.
The second part of the name of a salt identifies the acid used to make the salt. Chloride salts are made from hydrochloric acid, nitrate salts nitric acid and sulfate salts sulfuric acid.
Indicator used in ppa/edta reactions
Murexide
How does the buffer work? If acid is added to the mixture the large reserve of A- ions will trap the extra hydrogen ions and convert them to the weak acid. This stabilises the pH. If alkali is added the large reserve of HA molecules will convert the extra OH- to water. This again stabilises the pH.
A typical example of an acid buffer solution would be ethanoic acid and sodium ethanoate. The ethanoic acid is only partly dissociated. The sodium ethanoate salt completely dissociates and provides the conjugate base.
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