can anyone help me plz?!?!?!?!?! i'm dumb! (1 Viewer)

[nomz]

hi, i've got my half yearly the first day back at skool and i'm starting to stress coz i really can't do anything- i'm jst stoopid. Anywayz i was wondering if anyone could help me with sum questions-
How do you tell whether something undergoes alpha or beta decay or fission?
How do you write redox equations with more than one thing in the solution or on the electrodes?
eg Mg / Mg 2+ // I-, I2/ pt
Whats a primary standard?
The heat of combustion of ethanol is 1360kJ. What mass of ethanol needs to be burnt to raise the temperature of water to 77oC if 50% of the heat released by the ethanol is lost to the surroungings?
If you can help i'd appreciate it heaps, but if no one can its cool coz i'll probably fail anyways

 

[Xayma]

Fission splits into two parts.

Alpha decay is where a Helium nucleus He²⁺ seperates the atomic mass will drop by 4 and atomic number by 2. It is caused by an excess in nucleons.

Beta decay (you dont need to know what type) is caused by the proton/neutron ratio being out of whack (either too many protons/neutrons)

A Standard is a solution of known concentration, that is first used to find the concentration of another solution.

The heat of combustion question you need to know the initial temp and mass of water but 4.18kJ is required to raise 1kg of water by 1 degree.

 

[CM_Tutor]

For a cell like Mg | Mg²⁺ || I^-, I<sub>2</SUB> | Pt, you have a magnesium electrode in a solution of magnesium ions, connected via a salt bridge to a solution containing both iodide ions and iodine, and there is a platinum electrode (inert) in the solution. If you look at the reduction potentials, magnesium metal is easily oxidised, so you have:

Mg_(s) ---> Mg²⁺_(aq) + 2e^- E = +2.36 V
I_{2 (aq)} + 2e^- ---> 2I^-_(aq) E = +0.62 V

So, overall, Mg_(s) + I_{2 (aq)} ---> Mg²⁺_(aq) + 2I^-_(aq) E_cell = +2.36 + +0.62 = +2.98 V

I have posted on the topic of standards not that long ago, search on my username and 'standard', and I'm sure you'll find much more information.

 

[~*HSC 4 life*~]

Originally posted by CM_Tutor
I have posted on the topic of standards not that long ago, search on my username and 'standard', and I'm sure you'll find much more information.

...And i'm sure that if you search ANY of Cm Tutor's posts you'll find much more information lol :uhhuh:

 

[xiao1985]

Originally posted by nook
The heat of combustion of ethanol is 1360kJ. What mass of ethanol needs to be burnt to raise the temperature of water to 77oC if 50% of the heat released by the ethanol is lost to the surroungings?

u need the initial temperature of water for this one... and specific method... xayma has already said it =)

 

[CM_Tutor]

Here's a link: http://www.boredofstudies.org/community/showthread.php?s=&threadid=29650&highlight=standard

 

[Xayma]

So a primary standard is the solute and not the solution?

 

[CM_Tutor]

As I said in that thread, the term standard is used to refer to both the solid and the solution, so you must decide from context which way the term is being used.

 

[nomz]

thanx heaps every1 you helped alot! yeah the heat of combustion question didn't have an initial temp or anything which is what confused me...