Acid-base equilibria
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I am doing a titration between limewater and hydrochloric acid but can not choose between methyl orange and screened methyl orange as my indicator can you please tell me which one to use and why and what is the difference between them?
You can use either indicator. Screened methyl orange is methyl orange mixed with a green dye. The reason for adding a dye is to make the colour change at the end point sharper.
Some people find it hard to spot the end-point when the colour change is from red to orange-yellow as it is in normal methyl orange.
In the presence of the dye the colour change is from magenta to green. At the end point the indicator is grey at the end point. The eye is very sensitive to grey tones so it is possible to detect a very sharp end point with the screened version of the indicator.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
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updated: 11 January 2005
