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    please help!!!

    Ka = 10^-pka
    pka = -logKa

    low/high ka = what
    low/high pka = what

    which combination means its a strong acid???
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    (Original post by BioStudentx)
    I'm struggling to understand! If you post a picture I'll understand better.

    A=(B/C) and A=B/C are the same thing? Haha.
    Maybe, but If I write a Fraction with a horizontal line, I tend to put A not on that line:

    Like imagine this ------- is a line. A fraction has numbers on it and below it. But if the thing the fraction equals is on the line, so for A=B/C it would mean that A/C and B/C are equal because A=B
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    Hardest F325 paper - which year??????
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    (Original post by Jessica Mighall)
    please help!!!

    Ka = 10^-pka
    pka = -logKa

    low/high ka = what
    low/high pka = what

    which combination means its a strong acid???
    A high Ka value means a stronger acid as more of it dissociates. A low pKa value means a stronger acid, it is like pH as in the lower it is, the stronger the acid
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    (Original post by Jessica Mighall)
    please help!!!

    Ka = 10^-pka
    pka = -logKa

    low/high ka = what
    low/high pka = what

    which combination means its a strong acid???
    High Ka= strong acid
    High Ka is low pKa so low pKa is strong acid.

    I remember it by thinking about it like pH. A smaller pH means the acid is stronger so a smaller pKa means the acid is stronger.
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    (Original post by lai812matthew)
    june 2015 4ciii) how do you get 0.12M in C2H5COOH concentration.
    The conc of the 25cm3 sol of ethanoic is 0.48*0.025 but then it is diluted up to 100cm3 so divide by 0.1

    (0.48*0.025)/0.1 = 0.12
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    (Original post by lai812matthew)
    june 2015 4ciii) how do you get 0.12M in C2H5COOH concentration.
    n = cv, n = 0.48x0.035
    n = 0.012mol

    c = n/v
    Total volume = 0.1
    c = 0.012/0.1
    c = 0.12moldm^-3
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    (Original post by GawdHeresEmmie)
    The conc of the 25cm3 sol of ethanoic is 0.48*0.025 but then it is diluted up to 100cm3 so divide by 0.1

    (0.48*0.025)/0.1 = 0.12
    I just did this and I expected there to be more to it, the fact she filled the water up to 100.0, had no relevance?
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    why ph in a standard hydrogen half cell=0?????
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    What's been the highest mark/100 for this paper ever for 90 UMS?
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    (Original post by lai812matthew)
    why ph in a standard hydrogen half cell=0?????
    If you have -log1 = 0

    It's just hydrogen, so the pH is the highest it can get.
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    (Original post by lai812matthew)
    why ph in a standard hydrogen half cell=0?????
    Standard concentrations are 1 mol dm-3 so pH = -log(1) = 0
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    do you need to know the equations for hydrogen-oxygen fuel cells?
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    (Original post by oxfmarfa1)
    do you need to know the equations for hydrogen-oxygen fuel cells?
    I think so, I saw a question come up about it earlier in this thread.
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    (Original post by lai812matthew)
    why ph in a standard hydrogen half cell=0?????
    -log(1)
    cos [H+] = 1 moldm-3
    idk if you do maths or what, but any logarithm with a 1 ln(1), log(1) etc = 0 because x^0 = 1
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    (Original post by Kamara7)
    What's been the highest mark/100 for this paper ever for 90 UMS?
    I'm guessing you mean 90% of the available UMS so 135 UMS? If that's the case then last year it was the highest ever with 87/100. But it was a nice paper.
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    (Original post by Dinasaurus)
    If you have -log1 = 0

    It's just hydrogen, so the pH is the highest it can get.
    You can get negative pH, imagine a solution of HCl with a concentration of 50moldm^-3, the [H+] is gonna be 50 and -Log(50) is negative
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    (Original post by Kamara7)
    What's been the highest mark/100 for this paper ever for 90 UMS?
    If you mean 90% UMS, it was last year at 87/100 for an A*

    If you mean 90 (a C), it was Jan 12 and June 15 at 63

    EDIT: see here https://147a51c371676299402810da40fa...y%20A%20A2.pdf
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    (Original post by JennyMoorcroft)
    Hardest F325 paper - which year??????
    jan 2013
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    (Original post by oxfmarfa1)
    do you need to know the equations for hydrogen-oxygen fuel cells?
    yes
 
 
 
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