ㄚ維 asked in 科學化學 · 1 decade ago

幫我翻譯跟解答這些化學問題有關滴定酸跟鹼

1.what is the equivalence point of a titration? Give a precise definition.

2.how does the equivalence point of a titration differ from the end point?

3.what property of phenolphthalein makes it a useful indicator for acid-base titrations having equivalence points in the pH range from 7 to 9?

4.why must we standardize the NaOH titrant in order to use it to analyze the unknown acid?

5. A buret containing NaOH solution has an initial volume reading of 0.14 mL. 25.00 mL of 0.1000M HCl is titrated to a phenolphthalein end point , which occurs at a final buret reading of 27.16 mL NaOH. What is the molarity of the NaOH titrant?

1 Answer

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    Lv 7
    1 decade ago
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    1. 滴定的當量點是什麼?請給精確的定義.

    當量點是滴定液的計量與分析液中樣品的計量相等的一點.有些物質會有多個當量點,譬如多質子酸.

    2. 滴定的當量點如何與滴定終點不同?

    當量點是化學計量上的平衡點.滴定終點是滴定過程中偵測器訊號產生大變化時,如指示劑變色,發生沉澱,導電度變化,pH值變化,電位變化等等,的一點.這點不一定與當量點重疊,譬如指示劑變色的pH範圍在當量點之外等等.

    3. 酚酞的什麼性質使它成為酸鹼滴定中當量點在pH 7跟9之間有用的指示劑?

    酚酞在pH小於8.2的溶液中呈無色,pH8.2以上時它會失去氫,改變結構而產生粉紅色,由於變色的pH範圍在pH 7和9之間,所以是酸鹼滴定的很有用的指示劑.

    4. 為什麼分析未知酸液之前必須先標定NaOH滴定液?

    標定滴定液確知滴定液的濃度以避免誤差.

    5. 裝有NaOH滴定液的滴管開始的體積讀數是 0.14mL. 25.00mL的0.1000M鹽酸用此滴定液滴定至酚酞終點,滴管最後的體積讀數是27.16mL. NaOH的體積莫耳濃度是多少?

    NaOH用掉的體積為27.16-0.14=27.02mL,套用M1V1=M2V2的公式: 0.1000*25.00=M2*27.02, M2=0.0925M.

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