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Caustic / Lime Titration
Mar 06^th, 2013, 10:41pm

Can someone lead me through the equation to convert NaOH addition (grams) to Lime?

I completed a caustic soda titration and want to figure out the equivalent grams of lime to achieve the same pH results.

For example, at pH 4.8, 0.53 grams of NaOH was required. I need to determine the Ca(OH)2 equivalent grams.

Thanks in advance, this simple conversion is stumping me tonight.

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parafly0209 YaBB Newbies Offline I love Water and Wastewater.com Posts: 2 Company or Organization: Golder Associates	Re: Caustic / Lime Titration Reply #1 - Mar 6^th, 2013, 10:45pm mol NaOH = g NaOH / (39.9 g/mol) 2 mol NaOH = 1 mol of Lime (why???) g Ca(OH)2 = mol Ca(OH)2 * (74.1 g/mol)
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The Muck Slinger YaBB Newbies Offline I love Water and Wastewater.com Posts: 7 Company or Organization: Private	Re: Caustic / Lime Titration Reply #2 - Mar 7^th, 2013, 5:47am What is the calculation of; Litres [Caustic Soda] (46% Sodium Hydroxide) vs. kg [Dense Soda Ash] ???
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David S.

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Re: Caustic / Lime Titration
Reply #3 - Mar 7^th, 2013, 8:52am

parafly0209 wrote on Mar 6^th, 2013, 10:45pm:

2 mol NaOH = 1 mol of Lime (why???)

The reason for this equivalence is due to the number of hydroxide groups (OH-) present in each molecule. This is the active ion in neutralization of acidic pH values. This is often equated with normality (N). Sodium hydroxide, NaOH, has only one hydroxide group and lime, more correctly referred to as calcium hydroxide Ca(OH)₂, has two hydroxide groups. Therefore one mole of calcium hydroxide has twice the neutralizing capability as on more sodium hydroxide. Keep in mind that the equivalence only applies to pH calculations. If you need to do a mass balance or anything else of that nature it won't apply.

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Stewart

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Re: Caustic / Lime Titration
Reply #4 - Mar 14^th, 2013, 9:03am

Be aware that saying 2 mol NaOH = 1 mol lime assumes that the lime will fully dissolve in your scenario...

This is a good assumption for the NaOH, but not always a good one for lime - it depends on how much you are dosing, and the chemistry of the receiving water, and the chemistry of the water once "finished".

Also, I assume by "lime" you mean hydrated lime (Ca(OH)2)?

Really, the best way to figure out the equivalent lime dose is to actually titrate with a dilute lime slurry of known concentration...

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