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    c) Why is it necessary to filter off the zinc before the second titration takes place?

    If you titrated the iron (II) against manganate to oxidise it to iron (III), the zinc would reduce it straight back to iron (II). That would then have to be oxidised by more managante and there'd be an endless cycle. So you'd need an infinite quantity of manganate and never reach an end point.
    is this correct?


    Last, Kc, at high temperature the value is high and when the temperature lowers the Kc value increases more, does this mean the reaction is exothermic? but does it mean the forward reaction is exo? but I thought that Kc decreases if forward temp is exothermic
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    (Original post by otrivine)
    c) Why is it necessary to filter off the zinc before the second titration takes place?

    If you titrated the iron (II) against manganate to oxidise it to iron (III), the zinc would reduce it straight back to iron (II). That would then have to be oxidised by more managante and there'd be an endless cycle. So you'd need an infinite quantity of manganate and never reach an end point.
    is this correct?


    Last, Kc, at high temperature the value is high and when the temperature lowers the Kc value increases more, does this mean the reaction is exothermic? but does it mean the forward reaction is exo? but I thought that Kc decreases if forward temp is exothermic
    You're right that zinc is a reducing agent and (suffice to say) it will interfere with the titration ...

    You perhaps are being a little excessive when you say an infinite amount as the zinc is also finite! Let's just say that it will reduce the iron(III) as its formed until it's used up.
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    (Original post by charco)
    You're right that zinc is a reducing agent and (suffice to say) it will interfere with the titration ...

    You perhaps are being a little excessive when you say an infinite amount as the zinc is also finite! Let's just say that it will reduce the iron(III) as its formed until it's used up.
    Thanks and what about the Kc thing , I mentioned above
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    (Original post by otrivine)
    Thanks and what about the Kc thing , I mentioned above
    Kc = products/reactants

    When the forward reaction is exothermic it is inhibited by increased temperature.

    Increasing the temperature lowers the value of kc ...
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    (Original post by otrivine)
    c) Why is it necessary to filter off the zinc before the second titration takes place?

    If you titrated the iron (II) against manganate to oxidise it to iron (III), the zinc would reduce it straight back to iron (II). That would then have to be oxidised by more managante and there'd be an endless cycle. So you'd need an infinite quantity of manganate and never reach an end point.
    is this correct?


    Last, Kc, at high temperature the value is high and when the temperature lowers the Kc value increases more, does this mean the reaction is exothermic? but does it mean the forward reaction is exo? but I thought that Kc decreases if forward temp is exothermic
    Kc is easy fam. remember temperature does affect Kc. a change in temperature causes the position of equilibrium to move, but this change will alter the value of the equilibrium constant Kc. if the temperature change means more product is formed, kc will rise. if it means less product is formed, kc will decrease.
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    (Original post by charco)
    Kc = products/reactants

    When the forward reaction is exothermic it is inhibited by increased temperature.

    Increasing the temperature lowers the value of kc ...
    this is not correct. If it is endothermic, it will increase the value of kc.
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    (Original post by iamgreatness)
    this is not correct. If it is endothermic, it will increase the value of kc.
    If you read what I said ...

    When the reaction is EXOTHERMIC ... blah blah
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    (Original post by charco)
    Kc = products/reactants

    When the forward reaction is exothermic it is inhibited by increased temperature.

    Increasing the temperature lowers the value of kc ...
    Do you mean more exo ,Kc is more?

    So if Kc is 1.53 awt low temp and becomes 2.34 at lower temp does this mean reaction is exothermic ?if so why
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    (Original post by charco)
    If you read what I said ...

    When the reaction is EXOTHERMIC ... blah blah
    OK, try and make it more clear, it was very ambiguous.
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    (Original post by otrivine)
    Do you mean more exo ,Kc is more?

    So if Kc is 1.53 awt low temp and becomes 2.34 at lower temp does this mean reaction is exothermic ?if so why
    do you need any help?
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    (Original post by otrivine)
    Do you mean more exo ,Kc is more?

    So if Kc is 1.53 awt low temp and becomes 2.34 at lower temp does this mean reaction is exothermic ?if so why
    Check out this interactive on the effect of temperature on equilibria ...
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    wow, thank you! Did you also get my pm Charco
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    Hi, Otrivine,

    My is Laura,

    Can you help me (b) (i) and (ii) please. I am stuck with these questions.




    Ethanoic acid can be manufactured by the followingreaction, which is carried out between150 °C and 200 °C.

    CH3OH(g)+ CO(g) CH3COOH(g)

    a) Amixture 17.6 moles of methanol and 19.6 moles of carbon monoxide is allowed toreach equilibrium at 175°C in a container with volume 5 dm3. It wasfound that 12.2 moles of ethanoic acid had been formed.
    i) Write down an expression for Kcfor this reaction (1 mark)
    ii) Calculate the concentrations of methanol andcarbon monoxide present at equilibrium. Show your working.
    (4 marks)
    iii) Hence calculate Kc (to 3significant figures) including its units
    (2 marks)

    b) How,if any, would addition of extra carbon monoxide affect the following? Justifyyour answers.

    i) The value of the equilibrium constant forformation of ethanoic acid
    (2 marks)
    ii) The equilibrium yield of ethanoic acid.
    (2 marks)
 
 
 
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