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    (Original post by pav)
    Does anyone know why ions dissolve in water or polar solvents? is it to do with ionic lattice breaking up and ion-dipoles are forming? if this is the case, how do i expand on it?

    also do we need to know about colourfastness?
    because the delta plus charge on the hydrogen in a water molecule attracts the negative ions and the oxygen that has a delta plus charge in the H2O molecule attracts the positive ions. so the ions separate from the ionic lattice and become surrounded by the water molecules and this particular process of the water molecules surrounding the ions is called hydration.

    and yea i think we do need to know colourfastness
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    (Original post by pav)
    Does anyone know why ions dissolve in water or polar solvents? is it to do with ionic lattice breaking up and ion-dipoles are forming? if this is the case, how do i expand on it?

    also do we need to know about colourfastness?
    Colour fastness is briefly covered in story lines, so i suppose it could come up. What they could ask would be limited though
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    (Original post by Jamesrb)
    When you say finishing off, do you mean reading? From CI?
    Doing the problems

    (Original post by limetang)
    I know I know.
    I only became paranoid today after my biology exam xD
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    (Original post by pearlover)
    because the delta plus charge on the hydrogen in a water molecule attracts the negative ions and the oxygen that has a delta plus charge in the H2O molecule attracts the positive ions. so the ions separate from the ionic lattice and become surrounded by the water molecules and this particular process of the water molecules surrounding the ions is called hydration.

    and yea i think we do need to know colourfastness
    Can you please explain colourfastness to me. What do we need to know regarding it?
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    (Original post by zahre)
    Can you please explain colourfastness to me. What do we need to know regarding it?
    sure thing... a dye needs to have a good colourfast-this means that it won't wash out too easily or fade in the light.. and colourfastness depends on the strenght of the bonding between the dye and the fibre..so the bonding needs to be strong in order for the dye to be colourfast. An example of a good colourfast dye are ones with carboxylic acid groups or sulfonic acid groups in the dye molecule and these can form ionic interactions with fabrics that contain alkaline groups -NH- group and so as the bond between the fibre and dye is ionic interactions its strong and so is a good colourfast dye..
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    (Original post by pearlover)
    sure thing... a dye needs to have a good colourfast-this means that it won't wash out too easily or fade in the light.. and colourfastness depends on the strenght of the bonding between the dye and the fibre..so the bonding needs to be strong in order for the dye to be colourfast. An example of a good colourfast dye are ones with carboxylic acid groups or sulfonic acid groups in the dye molecule and these can form ionic interactions with fabrics that contain alkaline groups -NH- group and so as the bond between the fibre and dye is ionic interactions its strong and so is a good colourfast dye..
    Thanks for explaining. Very helpful.
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    The awkward moment when you realise 10% of the content will appear in the paper.
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    Why exactly do ligands cause orbitals to split?
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    (Original post by Conor 419)
    Why exactly do ligands cause orbitals to split?
    do we need to know about ligands for unit 5?
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    someone provide me with a model answer to why ionic compounds dissolve whereas others ie co2 do not!!!
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    (Original post by Rei5)
    someone provide me with a model answer to why ionic compounds dissolve whereas others ie co2 do not!!!
    was doing the same question on a paper today. from the mark scheme:

    CO2
    A CO2 has instantaneous dipole-induced dipole between molecules;
    BBCO2 forms hydrogen bonds with water (2);
    C detail of imf, eg diagram;

    ions
    D electrostatic forces between ions;
    E ions form ion-dipole bonds with water (or description);
    F hydration description;
    G detail (eg diagram);

    reasons
    H water forms hydrogen bonds with itself;
    J more hydrogen bonds broken than made for CO2/ imf in water stronger than in
    CO2;
    K imf between ions and water stronger than hydrogen bonds/ stronger than imf
    in CO2;
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    Can somebody please confirm this:

    Ka -> pKa = -log10 x ka and

    pKa -> ka = 10^-pka

    Teacher had neglected to teach us this. And I only just realised, sooo, is this right?
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    (Original post by ABCDemily)
    Can somebody please confirm this:

    Ka -> pKa = -log10 x ka and

    pKa -> ka = 10^-pka

    Teacher had neglected to teach us this. And I only just realised, sooo, is this right?
    That's right.
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    (Original post by ABCDemily)
    Can somebody please confirm this:

    Ka -> pKa = -log10 x ka and

    pKa -> ka = 10^-pka

    Teacher had neglected to teach us this. And I only just realised, sooo, is this right?
    Yeah that looks right, although I didn't think we'd ever need to go from pKa to Ka?

    where log is to the base 10:

    Ka = [H+(aq)]^2
    ---------
    [HA]

    pH = -log([H+(aq)])

    pKa = -log(Ka)
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    (Original post by pearlover)
    sure thing... a dye needs to have a good colourfast-this means that it won't wash out too easily or fade in the light.. and colourfastness depends on the strenght of the bonding between the dye and the fibre..so the bonding needs to be strong in order for the dye to be colourfast. An example of a good colourfast dye are ones with carboxylic acid groups or sulfonic acid groups in the dye molecule and these can form ionic interactions with fabrics that contain alkaline groups -NH- group and so as the bond between the fibre and dye is ionic interactions its strong and so is a good colourfast dye..
    won't a good colourfast dye be the one that forms covalent bonds? ( since that is the strongest bond )
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    (Original post by pav)
    Does anyone know why ions dissolve in water or polar solvents? is it to do with ionic lattice breaking up and ion-dipoles are forming? if this is the case, how do i expand on it?

    also do we need to know about colourfastness?
    That H- bonded dyes, like those used on cotton and other cellulose based fibres aren't very colourfast as the bonds are very easily broken when washed/exposed to heat. Then, you get the ionic interactions, between an acid and an alkali group, ie -COOH in the dye and -NH3 in the fibre. Slightly more colourfast as the bonds are stronger, meaning that they will withstand washing and heat.

    The strongest dyes are fibre reactive dyes which covalently bond to the fibres.
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    (Original post by ABCDemily)
    That H- bonded dyes, like those used on cotton and other cellulose based fibres aren't very colourfast as the bonds are very easily broken when washed/exposed to heat. Then, you get the ionic interactions, between an acid and an alkali group, ie -COOH in the dye and -NH3 in the fibre. Slightly more colourfast as the bonds are stronger, meaning that they will withstand washing and heat.

    The strongest dyes are fibre reactive dyes which covalently bond to the fibres.
    so does that mean that dyes that covalent bond with fibres will most colourfast?..also do you know what mordant means?
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    (Original post by pav)
    so does that mean that dyes that covalent bond with fibres will most colourfast?..also do you know what mordant means?
    Yesss. Fibre reactive dyes are the most colourfast.

    Mordant is 'serving to fix colours when dying', basically, it's a fixing agent within dyes, and increases colourfastness?
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    Ahh, this time tomorrow I will be petrified! And wondering how to get to my exam.... Great! I could walk, but it's a long ish way (45 mins) and I don't want to waste that time walking and stressing and then get there all hot and sweaty! Or, If it happens to be raining, soaked!

    But anyway, azo dyes are killing me at the moment! Can read through it all and nod along, yes I understand this, but reading through it with the intention of remembering any of that... Not wanting to happen!

    Think a day of past papers is in order.
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    (Original post by pav)
    so does that mean that dyes that covalent bond with fibres will most colourfast?..also do you know what mordant means?
    I think a mordant is a binding agent, which binds to a surface where a dye is then added and binds to the mordant.
 
 
 
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