sos, may day! help

[arthurk]

cracking? wont be on exam i thought
lol truetears your knowledge extends beyond the required knowledge of the course

[lacoste]

Write a balanced chemical equation for the cracking of decane to produce pentene.

their solution:
C10 H22 (g) ----> C5H10 (g) + C5H10 (g)   


Is this right? I thought it would be C10 H22 (g) ----> C5H10 (g) + C5H12 (g)

also with the states, are they gases, i thought C1 to C4 are gases then liquids to about C14?

[TrueTears]

Thanks Truetears again, wish i could + karma you again.

Would it be wise to go through every MC option A to D and check for the oxidation numbers, or go through until you get one ie like B the one above and then stop and say its B?    

So if it doesnt change we just move onto the other "SO2 option" and find a decrease?

Cheers!!!

Spot on

[TrueTears]

cracking? wont be on exam i thought
lol truetears your knowledge extends beyond the required knowledge of the course

I think thermal and catalyst cracking are on the course (they help your understanding of fractional distillation, such as the fractional distillation of crude oil), although it's not a very big part of the course.

[TrueTears]

Write a balanced chemical equation for the cracking of decane to produce pentene.

their solution:
C10 H22 (g) ----> C5H10 (g) + C5H10 (g)   


Is this right? I thought it would be C10 H22 (g) ----> C5H10 (g) + C5H12 (g)

also with the states, are they gases, i thought C1 to C4 are gases then liquids to about C14?

As a normal guideline:
1-4 are gases
5-20 are liquids
21+ are solids

[lacoste]

Question 5
A student attempted to determine the amount of sodium chloride in a brand of chicken stock powder. The label on the bottle states the sodium content at 17050 mg per 100 g.

a.   Calculate the amount of sodium, in mol, in 3.0 g of the chicken stock, assuming the label is accurate.





b.   The student dissolves 3.0 g of stock in distilled water and makes up the solution to 250 mL in a volumetric flask. A 20.00 mL sample is taken and excess silver nitrate solution is added to precipitated all the chloride ions as silver chloride.
Using the information provided, calculate the mass of silver chloride that the students would expect to precipitate.


Not too sure with part B.

thanks!!!!!

[Samira]

5)
a)m(Na)= 17050 mg in 100g
           xmg   in 3g
x= (17050*3)/100 = 5115.5 mg

so m(Na)=5115.5 mg in 3g
n(Na) .51155/23= 0.02224 mole

b) Nacl+AgNO3---> NaNO3 + AgCl
n(Na)=(Nacl)= 0.0224 mole
However thats in 250 ml...we need the mole in 20 ml as we took 20 ml sample
so... n(NaCl)= 0.0224*(20/250) =0.001779 mole
n(nacl)=n(AgCl)= 0.001779 mole
m(Agcl) =0.001779* (107.9+35.45) =.255g or 255mg

hope that helps

[lacoste]

a)m(Na)= 17050 mg in 100g
           xmg   in 3g
x= (17050*3)/100 = 5115.5 mg


i got 5115mg not 5115.5 mg, how did you get the extra decimal?

[arthurk]

how are u guys getting in the thousands for mg
if u think about it 4 x 5115 = 20460 mg in 12 g (4 times ur 3 gram calculation) thats already over the mass you had originally.
i think it should be 511.5mg

[Samira]

Soz my mistake it its ment to be 511.5 tyypin error...but the rest of calc i used 511.5 i just typed it up wrong

[lacoste]

thanks!

another q:

IR spectroscopy is an analytical tool often used in organic chemistry. Which of the following
could be distinguished from the other molecules due to the absence of a particularly distinct
and characteristic peak?
(a) CH3CH2CH2CH2OH
(b) CH3CH2CH2COOH
(c) CH3CH2CH2CH2NH2
(d) CH3CH2CH2COOCH3

[d0minicz]

D; as all of the others have peaks around 3000cm^-1 and D doesnt (only has C=O) at 1700cm^-1
the others have OH's and an NH2 soo thats around 3000cm^-1 right

[lacoste]

Yes, its D, thanks dominicz.

cheers!! got it now!!

Is it possible for a different molecule apart from glucose to undergo fermentation?

[TrueTears]

Yes, its D, thanks dominicz.

cheers!! got it now!!

Is it possible for a different molecule apart from glucose to undergo fermentation?

Fermentation is the process of deriving energy from the oxidation of organic compounds. For VCE all you have to know is glucose undergoes fermentation.

[lacoste]

thanks TT!

another one :

QUESTION 3
300 ml of a 0.35 M Ca(OH)2 solution was reacted with 300 ml of 0.40 M HCl .
The pH of the resultant solution is closest to:
A 0.82
B 1.12
C 12.88
D 13.18

Please show working too. thanks!