Qualification > Sciences
ALL CIE CHEMISTRY DOUBTS HERE !!
Deadly_king:
--- Quote from: Ancestor on November 20, 2010, 03:05:40 pm ---I am trying :
(i) Silicon(IV) carbide (SiC) / Silicon(IV) nitride (Si3N4).
(ii) To overcome it's melting point (their melting points are considerably high)/ To have it in the liquid state.
(iii) Oxygen (or oxygen compound) from atmosphere, by heating.
--- End quote ---
Nice try but I don't think your answer to the second question is correct. It's not necessary that it turns into liquid for combustion to take place.
(ii) For it to reach activation energy.
The rest is good :D
Deadly_king:
--- Quote from: Hissa on November 20, 2010, 02:41:58 pm ---I have some few questions :(
1) Increasing the temperature of the propanoic acid solution causes the pH to decrease.
What does this tell you about the enthalpy of dissociation?
2) Why is an indicator usually added in iodine/thiosulphate titrations but not in titrations involving potassium managanate (VII)?
--- End quote ---
1) According to the information given an increase in temperature causes the pH to decrease. Decrease in pH implies the solution becomes more acidic, i.e there is more H+ present in the solution.
Hence we can deduce that an increase in temperature has caused propanoic acid to dissociate more. In other words the enthalpy change is endothermic. this is because according to Hess's law, an increase in temperature will cause the equilibrium to shift so as to oppose the change which is in this case decrease temperature.
Since the forward reaction for dissociation was favoured, dissociation is an endothermic process. ;)
2) Iodine and thiosulfate are colourless compounds which will react together to form colourless solutions. Hence we will never be able to identify the end-point unless an indicator is used.
Potassium Manganate however is purple in colour and will turn colourless as it is being titrated. Therefore the point at which the solution changes from purple to colourless will be the end-point. This can be observed with our own bare eyes. ;D
Hope it helps :)
Twinkle Charms:
thank you guys =]
~ Miss Relina ~:
guys can anyone explain what is the ground state of an atom (related to the elctronic configuration)
alsowhat is the electron density maps ???
??? ???
need help asap
Deadly_king:
--- Quote from: Relina on November 29, 2010, 10:38:48 pm ---guys can anyone explain what is the ground state of an atom (related to the elctronic configuration)
alsowhat is the electron density maps ???
??? ???
need help asap
--- End quote ---
Atoms can exist in 2 states: Ground state and Excited state
The ground state of an atom is when its electronic configurations are at their lowest energy level. In other words all the electrons orbiting around the nucleus will be in the lowest sub-shells.
Excited state is just the opposite as the electrons may be found in higher energy sub-shells. An atom is more likely to undergo reactions in the excited state rather than the ground state since it has more energy.
Take Sodium for example, its electron configuration is: 1s2 2s2 2p6 3s1
Electrons that are excited have moved to another shell. So if a Sodium atom was excited it would still have the same amount of electrons but a different configuration. Example: 1s2 2s2 2p6 3p1
Electron density maps are used by scientists during an experiment called the X-ray crystallography so as to estimate the location of electrons around the nucleus of a molecule.
If you need more information about it, click here. ;)
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