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Author Topic: Uses of metal-acid salt vs acid?  (Read 609 times)

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pcm81

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Uses of metal-acid salt vs acid?
« on: June 10, 2018, 11:34:44 AM »

Greetings.
This question may seem strange, but my google-fu has not provided me with satisfactory answer.

Many "cleaning" agents used tri-sodium-phosphate or other metal reduced acid compound. X-sulphate, X-phosphate etc.
My question is: is there an advantage to using these salts in place of dilute solution of acid?

Seems to me, if you want to dissolve metals, (or for that matter cations in general) you use acid (say when cleaning-up / removing metal oxides). If you want to soapify organics (grease, oil etc) you use base.
Hydroxide of organics, can be a surfactant, but this really falls under using base to clean up organics.

Soo, what’s the reason, benefit, of TSP or other salts? The best thing i can think up is safety for a "common joe". Which by itself is good enough of a reason. I am curios to find-out if there are more "chemically driven" reasons? I have all the proper PPE to run a hot causing blackening bath (think 5lb of NaOh with 2 lb of NaNO3 per gallon of water running at 280 deg F). Is there any reason for me to bother with salts of acids or bases if i can just mix up a dilute acid / base?
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Babcock_Hall

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Re: Uses of metal-acid salt vs acid?
« Reply #1 on: June 11, 2018, 12:32:04 PM »

The pH of dilute phosphoric acid is vastly different versus trisodium phosphate (TSP).  It seems to me that which solution is better depends on what you are trying to clean.  For example, TSP is sometimes used to clean glassware in home brewing.  Naval jelly contains phosphoric acid and is good for rust.
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pcm81

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Re: Uses of metal-acid salt vs acid?
« Reply #2 on: June 12, 2018, 01:45:16 PM »

The pH of dilute phosphoric acid is vastly different versus trisodium phosphate (TSP).  It seems to me that which solution is better depends on what you are trying to clean.  For example, TSP is sometimes used to clean glassware in home brewing.  Naval jelly contains phosphoric acid and is good for rust.

You are right about the ph difference. TSP is alkaline ph, so it would be used to clean organics, while phosphoric acid would be used to clean meals. However to get a ph simmilar to TSP I could use NaOH. I am curios about salt vs acid or base with equivalent ph... is there an appreciable difference?
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Babcock_Hall

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Re: Uses of metal-acid salt vs acid?
« Reply #3 on: June 13, 2018, 06:24:06 AM »

In general, there might be a difference in ionic strength, depending on how each solution is prepared.  However, not all applications would be sensitive to that difference, and simply titrating phosphoric acid with NaOH would produce TSP.
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