【Daily Question】Chemical Engineering Principles 380: Methyl Orange Indicator (May 19)
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The last edit to this post was made by Zaihui Kangqiao on 2016-6-13 at 16:59. The Chemical Engineering Theory section is now launching a \"One Question per Day\" activity aimed at helping everyone reinforce their basic knowledge in chemical engineering. Subsequent series will include those on \"Principles of Chemical Engineering\", \"Mass Transfer and Separation\", \"Thermodynamics in Chemical Engineering\", and \"Chemical Process Engineering\". We hope you will give it your active support~~~ Answers to the questions in the \"One Question per Day\" activity can be viewed directly; the thread will be closed after 1 day! ! To encourage continued participation from everyone this year! You get 3 wealth points for participating, and an additional 4 wealth points for answering correctly~~~ Short answer question: What is the color change range of the methyl orange indicator? 3.1-4.4
Methyl orange: Color change range: pH 3.4–4.4. Phenolphthalein: Color change range: pH 8.1–10.0. Litmus purple: Color change range: pH 5.8–8.0. Methyl orange or phenolphthalein can be used for neutralization titrations; methyl orange is convenient for titrating bases with acids, while phenolphthalein is better suited for titrating acids with bases. Litmus has a too wide color change range, and the distinction between its acid color and base color is not clear, so it is generally not used in titrations. The color change range for methyl orange is: yellow at pH 4.4
Color change range: PH 3.1–4.4, changing from red to yellow
PH3.1–4.4 changes from red to yellow. Ps: The date is wrong; it’s the 18th today
The color change range of methyl orange is from red to yellow at pH values of 3.1–4.4
1. Methyl orange is an azo-colored pigment; it is red when the pH is less than 3.1, orange when 4.4 > pH > 3.3, and turns yellow as it dissociates hydrogen ions when pH is greater than 4.4. In other words, solutions in all pH ranges where pH > 4.4 are yellow. The solution is yellow at pH=7. 2. If an acid is used to titrate a base, and the solution turns yellow after adding an indicator before the titration, and it remains yellow at pH=7, how can the end point be determined? If an acid is titrated with a base, and the solution turns red after adding an indicator before the titration, then solutions in all pH ranges where pH > 4.4 are yellow. How can the end point be indicated? 3. As can be understood from the concept of titration jump, there is only a half drop of base (0.02 mL) required to change the pH from 4.3 to 7.0; conversely, only a half drop of acid is needed to change it from 7.0 to 4.3. The ratio of half a drop of solution to the volume of base (or acid) consumed in titration is 0.1%, meaning that the resulting error is also 0.1%. 4. Conclusion: Whether titrating sodium hydroxide with acid or sodium hydroxide with acid, it is feasible to use methyl orange as an indicator with orange as the endpoint for titration, resulting in a titration error of 0.1%.