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Old 05-19-2010, 08:03 AM
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Default Calculating PH Levels HELP!!!!

I have to write a report about the experiment I did with my group on enzyme activity in different pH and temperatures. I need to calculate the pH levels of the following solutions:

5mL of H2O2 + 1mL of 0.1M HCl
5mL of H2O2 + 1mL of 1M HCl
5mL of H2O2 + 1mL of 0.1M NaOH
5mL of H2O2 + 1mL of 1M NaOH

and I don't know what to do I've read some information on the internet and it says the pH is the negative log of the molarity. so it has an example:

pH of a 0.0025 M HCl solution = -log(0.0025) = 2.6

but since I have a combination of 2 chemicals, is it -log(M1+M1) or -log(M1) + -log(M2)? If you can help me it would be greatly appreciated
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Old 05-19-2010, 08:06 AM
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I really wish I did Chemistry, you're post just excites me...

*gets distracted by something and walks away*
Sorry Im no help.
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Old 05-19-2010, 08:06 AM
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So this is like a Stoichometry equation. Umm.....
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Old 05-19-2010, 08:09 AM
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Originally Posted by Spock View Post
So this is like a Stoichometry equation. Umm.....
Come on Spock!!! you can do this! you nearly saved the romuluns from their planet being destroyed so ofcourse you can work out a simple chemistry problem!
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Old 05-19-2010, 08:13 AM
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Come on Spock!!! you can do this! you nearly saved the romuluns from their planet being destroyed so ofcourse you can work out a simple chemistry problem!
Aw, what. Chemistry is my worse subject. I'll have one panthetic attempt at it.
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Old 05-19-2010, 08:28 AM
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Quote:
5mL of H2O2 + 1mL of 0.1M HCl
1. [H2O2] 5mL divided by 1000 = 0.005L

2. -log(0.005) = 2.3

1. [HCl] -log(0.001) = 3

I suppose you just add them? 2.3 + 3 = pH(5.3)

I'm not sure what to do when discriminating between moles.

I don't want to do any more because I suck at chemistry lol.
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Old 05-19-2010, 08:55 AM
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I have found something, but I am not sure it will help.

HCL + NAOH ph

EDIT: Sorry won't help u use H2O2 , I was reading ucorrect...
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Old 05-19-2010, 09:08 AM
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Ask Autumnshire, she must have covered this back in the day. I have not, so I was just going on logical deduction.
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Old 05-19-2010, 09:14 AM
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Should still work, you just need to replace some the info with the hydrogen peroxide and then logically follow the steps. I think I could get the answer now using that guide. But I'm escaping soon.
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Old 05-19-2010, 09:38 AM
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Quote:
Originally Posted by Spock View Post
Should still work, you just need to replace some the info with the hydrogen peroxide and then logically follow the steps. I think I could get the answer now using that guide. But I'm escaping soon.
Hopefully, but I remember from my high school years that chemistry was strange and deduction didn't work often
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Last edited by Na'vi_supporter; 05-19-2010 at 09:40 AM.
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  #11  
Old 05-19-2010, 11:34 PM
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Quote:
Originally Posted by Spock View Post
1. [H2O2] 5mL divided by 1000 = 0.005L

2. -log(0.005) = 2.3

1. [HCl] -log(0.001) = 3

I suppose you just add them? 2.3 + 3 = pH(5.3)

I'm not sure what to do when discriminating between moles.

I don't want to do any more because I suck at chemistry lol.
Ah not to worry, Astrophysics and data analysism was your strong points in Star Trek.
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Old 05-20-2010, 12:34 AM
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I'm having chemistry flashbacks, thanks for ruining my night.
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Old 05-20-2010, 12:40 AM
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I'm having chemistry flashbacks, thanks for ruining my night.
Haha yeah I come here to get away from school.
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Old 05-20-2010, 07:26 AM
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Quote:
Originally Posted by tm20 View Post
I have to write a report about the experiment I did with my group on enzyme activity in different pH and temperatures. I need to calculate the pH levels of the following solutions:

5mL of H2O2 + 1mL of 0.1M HCl
5mL of H2O2 + 1mL of 1M HCl
5mL of H2O2 + 1mL of 0.1M NaOH
5mL of H2O2 + 1mL of 1M NaOH

and I don't know what to do I've read some information on the internet and it says the pH is the negative log of the molarity. so it has an example:

pH of a 0.0025 M HCl solution = -log(0.0025) = 2.6

but since I have a combination of 2 chemicals, is it -log(M1+M1) or -log(M1) + -log(M2)? If you can help me it would be greatly appreciated
Kids these days, don't they teach you anything? Just kidding. You are on the right track.

First question. You mean H20 (water) or H2O2(hydrogen peroxide)? Pure H2O2 is dangerous and adding HCl just makes it worse. Hope it's just a book problem. Heck H2O2 in water is a weak acid in itself. It's go to be water.

If it is actually water then you are correct about how to calculate it. 5ml H2O and 1ml of .1M HCl would give .0167M HCl. Then do the negative log thing.

For bases (NaOH) you use the fact that [H+][OH-] = 10 to the minus 7

That's how I remember it and I haven't touched a chemistry book for 25 years.
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Old 05-20-2010, 10:26 AM
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Quote:
Originally Posted by txen View Post
Kids these days, don't they teach you anything? Just kidding. You are on the right track.

First question. You mean H20 (water) or H2O2(hydrogen peroxide)? Pure H2O2 is dangerous and adding HCl just makes it worse. Hope it's just a book problem. Heck H2O2 in water is a weak acid in itself. It's go to be water.

If it is actually water then you are correct about how to calculate it. 5ml H2O and 1ml of .1M HCl would give .0167M HCl. Then do the negative log thing.

For bases (NaOH) you use the fact that [H+][OH-] = 10 to the minus 7

That's how I remember it and I haven't touched a chemistry book for 25 years.
thanks for the help, but i'm still confused. BTW yes it is hydrogen peroxide. we had to test the rate of activity of catalase in acidic and basic environments and so the group leader decided to do it this way (although it seemed like he didn't know WTF he was doing as the first 1 and half hours or so was wasted by him "testing" the experiment )

And also, the hydrogen peroxide is 6%..... whatever that means.
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