F.2 I.S. Question 急!!! (15 點!)

點用 methyl orangre(甲基橙) with hydrochloric acid 試 the acidic regulator in three types of noodles

first i used the pH paper but it didn't work......

Can you show how to used the methyl orange and show the experiment step too?

Please help, i need to do this very important project!!!

HELP!!!

2 個解答

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  • 6 年前
    最愛解答

    Since you're just in F.2, I suppose knowledge in higher studies is not need; however it'd be good if you can take a look into the principle here:

    http://zh.wikipedia.org/wiki/%E6%BB%B4%E5%AE%9A

    First you need to know what kind of acid regulator(s) is in the noodles. I suppose they're alkaline (鹼性).

    You have to extract (提取) the regulator from the noodle samples.

    For example, soak (or boil) a fixed mass (weight) of each of the noodle sample in same volume of distilled water, for a fixed period of time. Better not to use too much or too little water: 100 ml of water and half-a-pack of noodle is a good for a trial.

    This is to leach (dissolve) the regulator in noodle samples.

    Then, filter the mixtures. Add 2 drops of methyl orange into each filtrate.

    I suppose the solutions should be yellow in color -- methyl orange becomes yellow in alkaline solutions.

    If any of the solutions is NOT yellow, then add a small, fixed amount of sodium hydrogencarbonate solution (with same concentration) to ALL samples, until all of them are yellow. (standard addition)

    Then, drop-by-drop, add the hydrochloric acid to the sample. Count the number of drops of acid needed to turn the solution from yellow to red.

    This is to measure the amount of acid needed to react completely with the regulator.

    If you want more "technical" method, you can ask for a burette and learn how to use it; it'll be taught in F.4 Chemistry.

    The relative amount of acid regulator in each noodle sample is proportional to the no. of drops of acid added.

    Remember to include a control, i.e. no noodle & no hydrogencarbonate, just water.

    If you've added the sodium hydrogencarbonate solution in previous step, you should repeat the experiment without noodle (so-called "Blank"), see how much acid is needed. Subtract the result of blank from the results for samples. (standard addition)

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