Ask me for chemistry help! (1 Viewer)

[kittyful]

sorry guys another question,
how do you know which salt is acidic, basic or neutral? i know it has something to do with cation/anion being the conjugate base/acid of another base/acid.
but idk how you know it.
thnks again and again.

To find if a salt is acidic, basic or neutral you have to look at it.

Like CH3COONa
Is a basic salt because it contains the conjugate base of a weak acid and a conjugate acid of a strong base

 

[imZerroo]

k CH3COO- is a conjugate base of a weak acid
but how do you know Na+ is a conjugate acid of a strong base?

also as per that i assume that conjugate bases of strong acids are strong bases?
wow i really need to study hard tonight

 

[imZerroo]

oh wait

NaOH + H+ --> Na+ +H2O

so Na+ is a conjugate base of NaOH
got it
nvm my previous q.

 

[kittyful]

NaOH is a strong base

 

[s2 SEductive]

i can remember the equations, but how does it prove its amphoteric? looking by that do you look at Al's oxidation state?

Try looking at this:
An amphoteric oxide is an oxide that can act both as an acid and as a base. An example is aluminium oxide, Al2O3. It reacts with acids to form the corresponding aluminium salt, and with bases to form salts called aluminates.

Example reactions

Al2O3 + 6HCl → 2AlCl3 + 3H2O
Al2O3 + 2NaOH → Na2Al2O4 + H2O

or this:

Aluminum*)oxide is an amphoteric compound by being both 1. acidic and 2. alkaline
1. acidic
It will dissolve in hydroxide (an alkaline solution):
Al2O3 + 2OH- + 3H2O --> 2 Al(OH)4- aluminate anion



2. alkaline
It will dissolve in acidic H+ solution:
Al2O3 + 6H+ --> 2Al3+ + 3H2O

I think it mean's it can act as an acid and base, judging by the examples. It's probably all you have to write as an answer.

 

[imZerroo]

ok i got it
thnks a lot people.
please stay here a while? i still have chemical monitoring to do :L

 

[s2 SEductive]

ok i got it
thnks a lot people.
please stay here a while? i still have chemical monitoring to do :L

Lol Nice
Do you have an exam tomorrow?

 

[imZerroo]

yup
started studying at 6.30
coz imma big guy.

 

[s2 SEductive]

yup
started studying at 6.30
coz imma big guy.

Lol GoodLuck, Hopefully you can memorise all that content in a few hours.

 

[Reikira]

Hey guys i have question about something that i cant really understand. Here's the question

A student wished to find the heat of combustion of ethanol.

He used a spirit burner to heat 250g of water in a breaker. The water temperature rose from 15degrees to 31degrees. During this combustion the burner lost 0.90g in the mass due to ethanol burning

Calculate the heat of combustion of ethanol in kJ Mol-1






any1 care to explain how u do it please?

 

[UnrealAnchovies]

Hey guys i have question about something that i cant really understand. Here's the question

A student wished to find the heat of combustion of ethanol.

He used a spirit burner to heat 250g of water in a breaker. The water temperature rose from 15degrees to 31degrees. During this combustion the burner lost 0.90g in the mass due to ethanol burning

Calculate the heat of combustion of ethanol in kJ Mol-1






any1 care to explain how u do it please?

1. get all your measurements ready:
delta t (change in temp) = 31-15 = 16 degreesC
m = 250 g
C (specific heat capacity of water) = 4.18J/g/degreeC

2. calculate heat released
i.e. delta h = 250g x 4.18J/g/degreeC x 16 degreesC
the degrees celsius and grams cancel and you're left with: delta h = 16720 J

3. you want kJ not J

so delta h = 16720/ 1000 = 16.72 kJ

4. calculate mols of ethanol
n(C2H5OH) = 0.90 grams/ 46.068 grams/mol
grams cancel, :. n(C2H5OH) = 0.0195 mols

5. divide delta h by the mols of ethanol = 857.4 kJ/mol

 

[UnrealAnchovies]

question: describe the effect of CFC's to humans and evaluate the success of steps taken to alleviate the 'problems' caused by CFC's

 

[Reikira]

1. get all your measurements ready:
delta t (change in temp) = 31-15 = 16 degreesC
m = 250 g
C (specific heat capacity of water) = 4.18J/g/degreeC

2. calculate heat released
i.e. delta h = 250g x 4.18J/g/degreeC x 16 degreesC
the degrees celsius and grams cancel and you're left with: delta h = 16720 J

3. you want kJ not J

so delta h = 16720/ 1000 = 16.72 kJ

4. calculate mols of ethanol
n(C2H5OH) = 0.90 grams/ 46.068 grams/mol
grams cancel, :. n(C2H5OH) = 0.0195 mols

5. divide delta h by the mols of ethanol = 857.4 kJ/mol

Thanks man, greatly appreciate it.

 

[kittyful]

question: describe the effect of CFC's to humans and evaluate the success of steps taken to alleviate the 'problems' caused by CFC's

Mention the Montreal Protocol that started in 1987 - where all countries signed a treaty thing, to stop using CFCs but rather use replaces such as HFCs and HCFCs

 

[UnrealAnchovies]

describe factors of the haber process which require monitoring

 

[FCB]

lets say [H+] of phosphoric acid is 2M
so pH will be -log[2x3] yup?
but if it ionises 10% (making this up btw), then pH= -log(2x3x10%)
am i right?

please tell me im right.

They only ever refer to strong acids when calculating the pH or they will tell you the degree of ionisation and you work out pH

 

[Reikira]

describe factors of the haber process which require monitoring

- Temperature
- IF temp too high, favours the reverse reaction, decreasing yield of ammonia
- IF temp too low, not enough energy for the gases to react thus once again reducing the yield of ammonia

- Pressure
- IF pressure too low, favours the reverse reaction
- Pressure cannot be too high, as it will be expensive and dangerous

 

[kittyful]

describe factors of the haber process which require monitoring

Factors that need montioring - temp and pressure - Liquefaction - stiometric ration

 

[mangoz]

- Temperature
- IF temp too high, favours the reverse reaction, decreasing yield of ammonia
- IF temp too low, not enough energy for the gases to react thus once again reducing the yield of ammonia

- Pressure
- IF pressure too high, favours the reverse reaction
- Pressure cannot be too low, as it will be expensive and dangerous

Adding on.
Monitoring so that the catalyst doesnt get poisoned
No oxygen so no explosions through combustions
1:3 ratio
Removing the ammonia so more yield is achieved .
Yeah i just listed them, didn't really go through it. I think thats it...

 

[UnrealAnchovies]

this has turned into a marathon thread, which is better.