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AQA Chemistry Unit 3 GCSE 24.05.12

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    (Original post by Wintabix)
    Hey, for the silver nitrate question, did you guys put yes? Because I thought if you add silver nitrate and forms a white precipitate, there're chloride ions present :P
    yeah white silver chloride is produced
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    Guys, aluminium was WRONG, and chloride was RIGHT =P
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    (Original post by flumpyfi)
    Can someone please tell me if I’d get the mark for these dodgy answers:

    Why the student was surprised
    Because the solubility increased as the temperature increased but decreased when the temperature reached 68 degrees – the solubility rose then fell.

    2a) (Alkali metal properties)
    -Very reactive
    -Low melting points and boiling points

    3a) (Properties of transition metals)
    -Malleable so can be easily shaped into a ring.
    -Very unreactive so will last longer.

    4b) (pH of weak acids and strong acids)
    -Weak acid will have a higher pH than a strong acid BECAUSE a strong acid completely ionises in water forming H+ ions whereas a weaker acid only partially dissociates forming H+ ions.
    I think you should be fine with those answers, just depends how picky the mark scheme is tbh:P
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    (Original post by Fifi96)
    i put 810 are you sure they ignore the symbols? :/ hope so haha x
    yeah its alright if you just write 810
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    (Original post by maxtate)
    Guys, aluminium was WRONG, and chloride was RIGHT =P
    well said
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    (Original post by flumpyfi)
    Can someone please tell me if I’d get the mark for these dodgy answers:

    Why the student was surprised
    Because the solubility increased as the temperature increased but decreased when the temperature reached 68 degrees – the solubility rose then fell.

    2a) (Alkali metal properties)
    -Very reactive
    -Low melting points and boiling points

    3a) (Properties of transition metals)
    -Malleable so can be easily shaped into a ring.
    -Very unreactive so will last longer.

    4b) (pH of weak acids and strong acids)
    -Weak acid will have a higher pH than a strong acid BECAUSE a strong acid completely ionises in water forming H+ ions whereas a weaker acid only partially dissociates forming H+ ions.
    Think theyre all fine, except for the last one, i think you had to stress that the pH was UNDER 7, not just that the weak acid has higher, or you couldve specified e.g. weak is 4-7, strong is 1-4 ,dunno though ull most likely get
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    Any thoughts on grade boundaries/ums?
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    (Original post by maxtate)
    It wasnt, the energy required to break bonds was higher than energy released from making...
    Err, I swear the energy released when forming new bonds was greater than the energy needed to break bonds so that's why it was exothermic and energy was released..? That's also why the energy change was negative..
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    (Original post by emily_p3)
    Any thoughts on grade boundaries/ums?
    I thinkk for Unit 2 about 35 A*, Unit 3 34, (personally, i think it should be higher, cuz it was too easy LOL, but aqa usually does it reallyyy low =P)
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    Do you think it is okay if I put:

    the weak acid will have a higher pH (closer to 7) because it isn't fully ionised

    ?? Thanks
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    oh god :s

    what did everyone put for the magnesium and sodium one? 3marks
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    Aw that test was great If you did loads of past papers then you'll have noticed loads of similar questions .

    Also why do transitional metals have similar properties?!
    I rambled on about 3rd and 4th electron shell overlap which meant electrons could further fill the shells? I'm pretty sure I didn't get the full 2/2 but I'm hoping for a mark! If anyone knows, pleeeeeeeeeeeease share
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    (Original post by OHNOGEM)
    oh god :s

    what did everyone put for the magnesium and sodium one? 3marks
    The magnesium starts off dissolved, therefore the water is made hard, however the sodium is exchanged for the magnesium, therefore the magnesium is given off as a solid, meaning the water is then soft. (I think)
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    (Original post by catastrophe)
    Aw that test was great If you did loads of past papers then you'll have noticed loads of similar questions .

    Also why do transitional metals have similar properties?!
    I rambled on about 3rd and 4th electron shell overlap which meant electrons could further fill the shells? I'm pretty sure I didn't get the full 2/2 but I'm hoping for a mark! If anyone knows, pleeeeeeeeeeeease share
    Most elements depend on their outermost electrons for their properties. Because the outer shells are not filling up when going through the transition metals, but the inner shells, the properties will not change as much.
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    (Original post by SaraBB)
    for the two tests it asked about, the first one i think she said it had aluminum ions...i put no because the precipitate didn't turn from white to colourless, it stayed white

    and the second one (i think it was chloride ions) i put yes it did have them cause it formed a white precipitate (for the halide test)

    please tell me i got something right...
    i put no for the chloride as well because they used hydrochloric acid rather than nitric acid and therefore the chloride ions in the hydrochloric acid is what made the precipitate
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    (Original post by catastrophe)
    Aw that test was great If you did loads of past papers then you'll have noticed loads of similar questions .

    Also why do transitional metals have similar properties?!
    I rambled on about 3rd and 4th electron shell overlap which meant electrons could further fill the shells? I'm pretty sure I didn't get the full 2/2 but I'm hoping for a mark! If anyone knows, pleeeeeeeeeeeease share
    Transition metals have the same number of electrons in the 4th energy level and the 3rd energy level is being filled up (can hold up to 18 electrons).. Not quite certain of the chemistry behind it haha just learned the answer off by heart


    This was posted from The Student Room's iPhone/iPad App
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    (Original post by catastrophe)
    Aw that test was great If you did loads of past papers then you'll have noticed loads of similar questions .

    Also why do transitional metals have similar properties?!
    I rambled on about 3rd and 4th electron shell overlap which meant electrons could further fill the shells? I'm pretty sure I didn't get the full 2/2 but I'm hoping for a mark! If anyone knows, pleeeeeeeeeeeease share


    Its because they all contain a full inner/3rd shell and also they usually contain the same amount of electrons in their outer shell.
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    (Original post by maxtate)
    Most elements depend on their outermost electrons for their properties. Because the outer shells are not filling up when going through the transition metals, but the inner shells, the properties will not change as much.

    (Original post by EllieHyman)
    Transition metals have the same number of electrons in the 4th energy level and the 3rd energy level is being filled up (can hold up to 18 electrons).. Not quite certain of the chemistry behind it haha just learned the answer off by heart


    This was posted from The Student Room's iPhone/iPad App

    (Original post by mohib96)
    [/B]

    Its because they all contain a full inner/3rd shell and also they usually contain the same amount of electrons in their outer shell.
    Thanks for the replies! 0/2 for me then haha .
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    Anyone doing an unofficial mark scheme?
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    (Original post by emily_p3)
    well said
    Don't mean to be a downer but surely as they used dilute hydrochloric acid rather than nitric acid, then the precipitate was formed due to the chloride ions in the acid rather than in the egg shell and therefore it can't be proved whether it did contain chloride ions??

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Updated: May 30, 2012
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