there are bunch of mistakes on CHADS quizzes....

[FutureDental88]

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First of all ; He is the only one claiming that Rate constant is based on both catalyst and temperature.


Secondly; on problem 69/180 He saids the PH of [HCL] = 1.0x10-11M so pH = -log (1.0x10-11M) = 11 which is the most basic of the choices.


shouldnt it be more close to 7??


Please correct my thoughts if im wrong in either

 

[annie12]

rate constant is k which DOES depend on catalyst. Rate LAW does not because you have already factored that in rate= k[something][something else] or whatever

 

[AllahIsGreater]

First of all ; He is the only one claiming that Rate constant is based on both catalyst and temperature.


Secondly; on problem 69/180 He saids the PH of [HCL] = 1.0x10-11M so pH = -log (1.0x10-11M) = 11 which is the most basic of the choices.


shouldnt it be more close to 7??


Please correct my thoughts if im wrong in either

-log 1x10^-11 is 11. he is correct on both

 

[flin5845]

First of all ; He is the only one claiming that Rate constant is based on both catalyst and temperature.


Secondly; on problem 69/180 He saids the PH of [HCL] = 1.0x10-11M so pH = -log (1.0x10-11M) = 11 which is the most basic of the choices.


shouldnt it be more close to 7??


Please correct my thoughts if im wrong in either

You may be getting rate constant (k) and equilibrium constant (K) mixed up.... the rate constant (k) is in fact based on both a catalyst and temperature. If you look at Arrienous equation from which the rate constant is derived k=e^-Ea/RT.... where Ea is the energy of activation (and a catalyst will lower the Ea therefore changing the k) and T which is temperature (and messing with the temp will also change k)

However, the equilibrium constant (K) can only be changed by Temperature.

as far as the pH of [H+] = 1.0x10-11M is pH 11. Think about how how much 1x10-11 really is......it is like nothing and what that really means is that there is very little [H+] in solution....and if there is no H+ the pH is going to be basic....

Chad is the man...he knows his stuff.

 

[FutureDental88]

2. TRUE or FALSE: Changes in the temperature or the introduction of a catalyst will affect the rate constant of a reaction


2. FALSE. The rate constant is not dependant on the presence of a catalyst. Catalysts, however, can effect the total rate of a reaction.





Im getting more and more confused... whats correct.. Majority of websites + books say rate constant is only temperature based..

 

[FutureDental88]

ph of a LOW molar concentration of STRONG acid can NOT be basic... where do you guys get that from...


here is a calculation i found on another similar problem..

Calculate the pH of 1.0x10-10M HCl
Major species:
H+ Cl- H2O HCl
1.0x10-10M 1.0x10-10M 1.0x10-7M 0
pH=-log[H+]
What's the sum of 1.0x10-10+ 1.0x10-7
pH=-log[1.0x10-7]
pH=7.00

 

[flin5845]

2. TRUE or FALSE: Changes in the temperature or the introduction of a catalyst will affect the rate constant of a reaction


2. FALSE. The rate constant is not dependant on the presence of a catalyst. Catalysts, however, can effect the total rate of a reaction.





Im getting more and more confused... whats correct.. Majority of websites + books say rate constant is only temperature based..

google arrhenius equation..

 

[flin5845]

ph of a LOW molar concentration of STRONG acid can NOT be basic... where do you guys get that from...


here is a calculation i found on another similar problem..

Calculate the pH of 1.0x10-10M HCl
Major species:
H+ Cl- H2O HCl
1.0x10-10M 1.0x10-10M 1.0x10-7M 0
pH=-log[H+]
What’s the sum of 1.0x10-10+ 1.0x10-7
pH=-log[1.0x10-7]
pH=7.00

The only thing that I saw on his quizzes was he was asking for the most basic solution. The quizzes get mixed up when you take them, so your 68 is different every time. But this question asked the pH of [H+] of 1x10^-11....the pH is 11.. I do not know if this is the exact question. you might want to copy and paste the whole question.

 

[FutureDental88]

yes.. he was asking for which compound was most basic; and said that HCL was most basic because it had a PH of 11. But a HCL concentration of [HCL] = 1.0x10-11M is not 11. Its a common mistake people apparently believe.. Because an Acid compound can never be basic. It can only get very close to 7.


But would still like to have that confirmed by someone who is certain of their thing..

 

[FutureDental88]

here is the problem asked :

Which of the following solutions is most basic?

Pure water

0.001M NH3

[H+]=1.0x10-11M

pOH=12

 

[wenjie1988]

He said in his video that 10^-10M HCl would be close to ~7, so you are right on this one.

 

[addis4ever]

here is the problem asked :

Which of the following solutions is most basic?

Pure water

0.001M NH3

[H+]=1.0x10-11M

pOH=12

that is the most basic i think because the pH [H+]=1.0x10-11M is 11.
pOH=12 is pH=2
0.001M NH3 = 1X10^-3M NH3, pOH= 3, pH= 11 but NH3 is a weak base so its really not true that its pH is that high.
pure water is neutral i believe.

 

[flin5845]

First of all ; He is the only one claiming that Rate constant is based on both catalyst and temperature.


Secondly; on problem 69/180 He saids the PH of [HCL] = 1.0x10-11M so pH = -log (1.0x10-11M) = 11 which is the most basic of the choices.


shouldnt it be more close to 7??


Please correct my thoughts if im wrong in either

I agree with you on [HCl]=1x10^-11 would be neutral. Chad says this in his video...

The QUESTION you asked about is not referring to HCl it is just asking about the [H+]....and with an [H+] of 1x10^-11 the pH of the solution is 11...

 

[egan]

2. TRUE or FALSE: Changes in the temperature or the introduction of a catalyst will affect the rate constant of a reaction


2. FALSE. The rate constant is not dependant on the presence of a catalyst. Catalysts, however, can effect the total rate of a reaction.





Im getting more and more confused... whats correct.. Majority of websites + books say rate constant is only temperature based..

k = A exp (–Ea/RT) is the Arrenhius equation which I think Chad talks about for a bit. Lowering the Ea(with a catalyst) or increasing the temperature will increase k(and the overall rate). Hope this helps

 

[JustwantDDS]

I agree with you on [HCl]=1x10^-11 would be neutral. Chad says this in his video...

The QUESTION you asked about is not referring to HCl it is just asking about the [H+]....and with an [H+] of 1x10^-11 the pH of the solution is 11...

yeah for the strong acid its ~neutral
but that didnt specify what acid, just said H+

 

[wenjie1988]

You would have to assume the [H+] dissociated from a strong acid because you can't calculate pH of a weak acid using [H+] alone, you would also need the Ka... and since Ka is not given, it's probably a strong acid.

 

[Cool Beans]

You would have to assume the [H+] dissociated from a strong acid because you can't calculate pH of a weak acid using [H+] alone, you would also need the Ka... and since Ka is not given, it's probably a strong acid.

Actually, you definitely can't assume this. The question states that [H+] = 1x10^-11. This also implies:
pH = 11
pOH = 3
[OH-] = 1x10^-3

Adding a strong acid or any acid for that matter could never produce the basic solution given here. The wrong assumption is that H+ had to come from an acid. H+ is always present in any aqueous solution due to the auto-ionization of water. Here it's less than the 1x10^-7M concentration we'd see in pure water because the solution is basic.

As far as the other question goes it is straight from the Arrhenius equation as others have stated previously. Both the temperature and a catalyst (by lowering the activation energy) can affect the Rate constant whereas only temperature can change the value of an Equilibrium constant.

Hope this helps!

 

[rah08e]

Wait so both NH3 and H+ have a pH of 11. How can you determine which is more basic?

 

[Cool Beans]

Wait so both NH3 and H+ have a pH of 11. How can you determine which is more basic?

If you're referring to 0.001M NH3, the pH isn't 11. If it were a strong base it would be 11. But NH3 is a weak base and doesn't dissociate completely and we'd need a Kb value to determing the exact pH but at the very least we know the pH will be lower (less basic) than 11.

Hope this helps!