双指示剂滴定碳酸盐-碳酸氢盐混合物

用两种指示剂分析碳酸盐混合物

Titrations Advanced (University) 55 分钟 ~$14.00

目标

依次使用酚酞和甲基橙两种指示剂，用HCl滴定分析碳酸钠和碳酸氢钠的混合物。

背景

A mixture of Na₂CO₃ and NaHCO₃ has two equivalence points when titrated with acid. Phenolphthalein detects the first (CO₂³⁻ → HCO₃⁻), and methyl orange detects the second (HCO₃⁻ → H₂CO₃). By comparing the volumes at each endpoint, the individual concentrations can be calculated.

安全警告

  • HCl is corrosive
  • Wear safety goggles throughout
  • Handle indicators carefully — they stain

所需PPE

goggles lab_coat

材料

  • Sodium carbonate/bicarbonate mixture (100 mL)
    Unknown composition
  • Hydrochloric acid (HCl) (100 mL)
    0.1M standardized
  • Phenolphthalein indicator (5 mL)
  • Methyl orange indicator (5 mL)
  • Distilled water (200 mL)

设备

50 mL burette Burette stand and clamp 250 mL Erlenmeyer flask 25 mL pipette White tile

步骤

1

Pipette 25.0 mL of the carbonate/bicarbonate mixture into the flask.

2 分钟
2

Add 2-3 drops of phenolphthalein. The solution should turn pink.

1 分钟
3

Fill the burette with 0.1M HCl. Record the initial volume.

3 分钟
4

Titrate until the pink color disappears (first endpoint). Record volume V₁.

10 分钟
5

Without refilling the burette, add 2-3 drops of methyl orange to the same flask.

1 分钟
6

Continue titrating until the color changes from yellow to orange/salmon (second endpoint). Record total volume V₂.

10 分钟
7

Repeat the entire process for concordant results.

18 分钟
8

Calculate: V(phenolphthalein) = V₁, V(methyl orange only) = V₂ - V₁. Use these to find the individual concentrations of Na₂CO₃ and NaHCO₃.

7 分钟

预期结果

V₁ corresponds to the carbonate content, and (V₂ - V₁) includes both the remaining carbonate reaction and the original bicarbonate. For pure carbonate, V₂ - V₁ = V₁. Any excess indicates bicarbonate present.

清理

Neutralize waste solutions before disposal. Rinse all glassware thoroughly.

详情

类别
Titrations
难度
Advanced (University)
时长
55 分钟
预估费用
$14.00
步骤数
8
材料
5

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Frequently Asked Questions

What is the objective of 双指示剂滴定碳酸盐-碳酸氢盐混合物?
依次使用酚酞和甲基橙两种指示剂，用HCl滴定分析碳酸钠和碳酸氢钠的混合物。
How difficult is 双指示剂滴定碳酸盐-碳酸氢盐混合物?
This experiment is rated as Advanced (University). It takes approximately 55 minutes to complete.
What safety precautions are needed for 双指示剂滴定碳酸盐-碳酸氢盐混合物?
Key safety precautions include: HCl is corrosive; Wear safety goggles throughout; Handle indicators carefully — they stain.
What materials are needed for 双指示剂滴定碳酸盐-碳酸氢盐混合物?
The main materials required are: Sodium carbonate/bicarbonate mixture, Hydrochloric acid (HCl), Phenolphthalein indicator, Methyl orange indicator, Distilled water.
What results should I expect from 双指示剂滴定碳酸盐-碳酸氢盐混合物?
V₁ corresponds to the carbonate content, and (V₂ - V₁) includes both the remaining carbonate reaction and the original bicarbonate. For pure carbonate, V₂ - V₁ = V₁. Any excess indicates bicarbonate present.