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    Someone Ask me AP Chem Questions

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    Ahmed
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    Re: Someone Ask me AP Chem Questions

    Post by Ahmed on Sat May 08, 2010 1:13 pm

    No...what did I do wrong?


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    Re: Someone Ask me AP Chem Questions

    Post by Justice on Sat May 08, 2010 1:44 pm

    Ahmed there is a mistake with your units -3 for units!!
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    Re: Someone Ask me AP Chem Questions

    Post by Justice on Sat May 08, 2010 1:46 pm

    You basically have (g)(g^-1c^-1)(c)-> kj/mol
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    Re: Someone Ask me AP Chem Questions

    Post by Ahmed on Sat May 08, 2010 2:31 pm

    The sig figs are correct. WHat are you talking about??

    Also I see now. The units for specific heat is J/(g-k)

    So all those numbers are Joules. But the percentage still shouldn't change.


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    Re: Someone Ask me AP Chem Questions

    Post by Justice on Sat May 08, 2010 2:56 pm

    i was talking about the units not sig figs lol
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    Re: Someone Ask me AP Chem Questions

    Post by Justice on Sat May 08, 2010 2:57 pm

    Mailman took of -3 in the beginning of the year cause i did that too. You have to a careful, diligent, studious student
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    Re: Someone Ask me AP Chem Questions

    Post by Justice on Sat May 08, 2010 3:09 pm

    what is the pH of 3M of HCl?
    you do -log[3] beacuse the HCl is a strong acid. But u get a negative number. Explain it?
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    Re: Someone Ask me AP Chem Questions

    Post by Ahmed on Sat May 08, 2010 4:18 pm

    Ok my diligient studious comrade. Wink

    As for your Q:

    -log([H+]) = -log(3) = -0.477

    However, the experimentally derived data should be a bit higher, because at such high concentrations not all of the HCl ionizes.


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    Re: Someone Ask me AP Chem Questions

    Post by Justice on Sat May 08, 2010 6:28 pm

    But how can the pH level be negative? Isn't the scale from 1-14?
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    Re: Someone Ask me AP Chem Questions

    Post by Ahmed on Sat May 08, 2010 6:43 pm

    The molarity is so large so it won't dissociate completely. However, if you do the experiment in real life the number will be greater by a little.

    Ask me a good question please Very Happy


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    Re: Someone Ask me AP Chem Questions

    Post by The Banker on Sat May 08, 2010 6:59 pm

    the answer to the Q i asked was +/- 167 J :S
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    Re: Someone Ask me AP Chem Questions

    Post by Ahmed on Sat May 08, 2010 7:06 pm

    That can't be right. It has to be 83.6 J...and I thought you wanted a percentage btw.


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    Re: Someone Ask me AP Chem Questions

    Post by The Banker on Sat May 08, 2010 7:17 pm

    temperature rise= (24.5-17.4)+/-0.4 = 7.1+/-0.4 degrees Celsius

    Percentage error caused by the thermometer = +/-0.4+ (100/7.1)= +/-5.63%

    Heat produced= 100g*4.18jg^-1C^-1= 2968J

    Error in value of heat produced= +/-5.63% of 2968J= +/-167J
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    Re: Someone Ask me AP Chem Questions

    Post by Ahmed on Sat May 08, 2010 7:19 pm

    That's not the heat produced.
    The forumla is Q=mC(delta)T

    You didn't use Delta T at all.


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    Re: Someone Ask me AP Chem Questions

    Post by The Banker on Sat May 08, 2010 7:20 pm

    Marwa wrote:temperature rise= (24.5-17.4)+/-0.4 = 7.1+/-0.4 degrees Celsius

    Percentage error caused by the thermometer = +/-0.4+ (100/7.1)= +/-5.63%

    Heat produced= 100g*4.18jg^-1C^-1= 2968J

    Error in value of heat produced= +/-5.63% of 2968J= +/-167J
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    Re: Someone Ask me AP Chem Questions

    Post by Ahmed on Sat May 08, 2010 7:21 pm

    Heat produced= 100g*4.18jg^-1C^-1= 2968J
    ^^^Where did you use it here?


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    Re: Someone Ask me AP Chem Questions

    Post by The Banker on Sat May 08, 2010 7:24 pm

    my bad..
    Heat produced= 100g*4.18jg^-1C^-1*7.1= 2968J
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    Re: Someone Ask me AP Chem Questions

    Post by Ahmed on Sat May 08, 2010 7:25 pm

    In the 2nd step why did you do add the percentage error to (100/7.1)?


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    Re: Someone Ask me AP Chem Questions

    Post by The Banker on Sat May 08, 2010 7:26 pm

    my bad again.. multiply em..
    +/-0.4*(100/7.1)= +/-5.63%
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    Re: Someone Ask me AP Chem Questions

    Post by Ahmed on Sat May 08, 2010 7:30 pm

    But why did you do this fraction: (100/7.1)?


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    Re: Someone Ask me AP Chem Questions

    Post by The Banker on Sat May 08, 2010 7:41 pm

    ahmed, i honestly have no idea.. it would make more sense if it was 7.1/100
    but thats what the answer says, and i'de trust the answers more slanty
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    Re: Someone Ask me AP Chem Questions

    Post by Ahmed on Sat May 08, 2010 7:48 pm

    Ok...another Q?


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    Re: Someone Ask me AP Chem Questions

    Post by The Banker on Sat May 08, 2010 7:54 pm

    calculate the mass of sodium carbonate decahydrate, Na2CO3.10H2O, needed to make up 250 cm^3 of 0.0500 mol dm^-3 solution.

    this one is nice n easy..
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    Re: Someone Ask me AP Chem Questions

    Post by Ahmed on Sat May 08, 2010 7:59 pm

    Remind me again...1cm^3=1 mL right?


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    Re: Someone Ask me AP Chem Questions

    Post by The Banker on Sat May 08, 2010 8:02 pm

    yup.. but why would u need that in this Q?

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