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Can anbody help me answer these questions?

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  • 15-06-2009 3:11pm
    #1
    damienricefan
    Registered Users Posts: 165 ✭✭


    There just a few questions in my chemistry experiment book I can't answer.

    HYPOCHORITE IN BLEACH:

    Why was the bleach diluted before being placed in the conical flask?

    PREPARATION OF ETHANAL:

    Why is heating not required once addition of alcohol/dichromate has begun?

    Apart from colour change, what else is observed in the flask as the ethanol/dichromate was added to the hot sulfuric acid?

    What colour change occurs when ethanal reacts with acidified potassium manganate solution and what does that indicate?

    What is formed when ethanal reacts with Fehling's and what does this indicate?

    What does formation of silver mirror indicate?

    PREPARATION OF ETHENE:

    Why is the glass wool inserted after the ethanol has been added to the test tube?

    What steps are taken to avoid suckback and why?

    thanks :D


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    #2
    challengemaster
    Registered Users Posts: 16,931 ✭✭✭✭challengemaster


    damienricefan wrote: »
    HYPOCHORITE IN BLEACH:

    Why was the bleach diluted before being placed in the conical flask?
    Bleach is diluted so when you're titrating, you don't have to use excessive amounts of reactants to titrate it against. If you didn't dilute it you'd probably have to fill the burette about 3+ times
    PREPARATION OF ETHANAL:

    Why is heating not required once addition of alcohol/dichromate has begun?
    Isn't it an exothermic reaction? (gives out heat) - off the top of my head, may be wrong

    PREPARATION OF ETHENE:

    Why is the glass wool inserted after the ethanol has been added to the test tube?
    From what I can remember... you want the glass wool to absorb the ethanol in the test tube/hold it in place at the end of the test tube during the reaction
    What steps are taken to avoid suckback and why?

    When you remove the heat source from the test tube, you take the transfer tube out of the water to avoid suckback. Suckback should be avoided because it would cause water to get sucked back into the test tube, firstly, meaning you have to start again, and secondly, the rapid cooling of the test tube could cause it to shatter which would be a health/safety risk.

    /makes note to look up rest


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    #3
    challengemaster
    Registered Users Posts: 16,931 ✭✭✭✭challengemaster


    damienricefan wrote: »
    What colour change occurs when ethanal reacts with acidified potassium manganate solution and what does that indicate?
    Pale pink -> colourless, indicates the ethanal was reduced by the KMnO4
    What is formed when ethanal reacts with Fehling's and what does this indicate?

    A brick red precipitate of Copper (I) oxide Cu2O is formed. The Cu(+2) is reduced to Cu+ ions, shows it's an aldehyde (ketones have no colour change with fehlings)
    What does formation of silver mirror indicate?
    Presence of aldehyde / oxidation has occured. Ketones have a negative result with the silver mirror test.


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