The endpoint color for the alkalinity of circulating water is not distinct
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We use methyl red-bromocresol green as an indicator for the alkalinity of our circulating water; the endpoint is reached when the color changes from green to pink. But lately, the endpoint either fails to show color or the color does not persist. I also asked a few people, and they said it has something to do with chloride ions; too many chloride ions are present, which prevents the endpoint color from being visible. However, the workshop added some calcium chloride to the circulating water, and as a result the endpoint color became more distinct when we were measuring alkalinity. I would be greatly grateful if someone experienced could give me some advice!
It is recommended that you use a pH meter to determine the end point of the titration directly. The phenomena you observe indicate interference from the indicator; however, using a pH meter can resolve such problems, as the bromocresol green indicator may not have been oxidized, which leads to inaccurate indication of the end point
Thank you. I do indeed use a pH meter to indicate the endpoint of titration at the moment, but I want to know what factors actually influence the indicator in indicating the endpoint.
Generally, there are two reasons: first, there are oxidizing or reducing substances in the water body that shield the indicator; second, some metal ions can complex with the indicator, thereby causing it to become deactivated or ineffective. You can refer to texts on analytical chemistry or the latest manuals for laboratory technicians – these are available on forums as well
You can try using phenolphthalein as an indicator to determine what is causing the issue.
I agree with the person above; using phenolphthalein as an indicator would be better. We all use phenolphthalein as an indicator.
First, the landlord needs to clarify one thing: chloride ions do not affect the indicator. To inhibit fungal growth in industrial circulating water, chlorine-based oxidants are usually added, and it is these oxidizing substances that affect the indicators. Secondly, calcium chloride is added to industrial circulating water in order to appropriately increase alkalinity, which is likely a step to prevent corrosion. In accordance with GB/T 15451-95 \"Determination of alkalinity in industrial circulating cooling water\", boiling is required for 2 minutes when titrating the alkalinity with methyl orange until the endpoint is reached. The main purpose is to remove CO2 dissolved in water. Did the original poster follow the standard procedures exactly in this step?
If a pH meter is used to indicate the endpoint, what is the pH value at that endpoint?