Testing Tablets

[Old Guard]

I have a commercial customer that uses Accu-Tabs for chlorinating their largest indoor pool. They think that their more recent deliveries of tabs lack the punch of the originals. Is there a way to dissolve X grams of cal-hypo in Y ml of distilled water to see if the tabs are up to the 65% to 73% listed in the SDS?

This is a somewhat academic question as I am pushing them to switch over to liquid chlorine, but I would like to know how to answer the question anyway.

 

[Newdude]

1 gram of 65% calhypo is 34 FC in a 5 gallon bucket. Pour 2/3 of it out, fill it back up and it would be about 11 FC.

You'd need a digital scale that read to the .XX to know it was 1.00 grams even and not somewhere between 1 and 1.5 grams as that would skew the results.

 

[JoyfulNoise]

Only way to know for sure would be to be able to compare an "old" tablet with a "new" one. You'd have to do a typical laboratory standardization procedure (skipping the calibration of your reagents with a known chlorine standard ... not something you'd do in a real lab but you can make the gross assumption that your test kit is accurate). A standardization would look like the follow -

1. Obtain 1 gram of the unknown powder and dissolve it in 1 liter of distilled water
2. After that solution has mixed and dissolved, remove exactly one milliliter of solution and add that to a 100mL Erlenmeyer flask
3. Fill the 100mL flask with DI water up to the fill mark being careful not to overfill the flask
4. Swirl to mix for 1 min
5. Use the diluted mixture as you sample to test FC

In the above procedure, the one gram of powder is dissolved into approximately 1000 grams (1kg) of water. So assuming the weight percent of the calhypo is X wt%, then the resulting solution is roughly X ・(10,000)・(1/1000) ppm. The next 99:1 dilution drops the ppm by another 1/100th or so. So if you started off with 65% cal-hypo, the resulting test solution should be roughly around 6.5ppm. One of the reasons for doing the serial dilution is to avoid some of the adverse effects that come with dissolving a strong oxidizing powder like cal-hypo into a small quantity of water ... not only will the FC be very high, but the pH will be off the charts as cal-hypo strongly raises pH. Serial dilutions makes the resulting test solution look more like "pool water" and less like a chemical stew thus avoiding any interferences or bleaching out of the FC test reagents.

The numbers above are very roughly useful. You might not be able to detect much difference between a 65% cal-hypo sample and a 70% cal-hypo sample but you should see the effect if the starting chemicals are wildly different. You also might want to run the procedure a few times and take an average value and, if you had the time, you should really run a KNOWN chlorine standard against your test kit reagents to ensure that the test kit is still good.

You did say this was an ACADEMIC exercise ...

 

[Old Guard]

Only way to know for sure would be to be able to compare an "old" tablet with a "new" one. You'd have to do a typical laboratory standardization procedure (skipping the calibration of your reagents with a known chlorine standard ... not something you'd do in a real lab but you can make the gross assumption that your test kit is accurate). A standardization would look like the follow -

1. Obtain 1 gram of the unknown powder and dissolve it in 1 liter of distilled water
2. After that solution has mixed and dissolved, remove exactly one milliliter of solution and add that to a 100mL Erlenmeyer flask
3. Fill the 100mL flask with DI water up to the fill mark being careful not to overfill the flask
4. Swirl to mix for 1 min
5. Use the diluted mixture as you sample to test FC

In the above procedure, the one gram of powder is dissolved into approximately 1000 grams (1kg) of water. So assuming the weight percent of the calhypo is X wt%, then the resulting solution is roughly X ・(10,000)・(1/1000) ppm. The next 99:1 dilution drops the ppm by another 1/100th or so. So if you started off with 65% cal-hypo, the resulting test solution should be roughly around 6.5ppm. One of the reasons for doing the serial dilution is to avoid some of the adverse effects that come with dissolving a strong oxidizing powder like cal-hypo into a small quantity of water ... not only will the FC be very high, but the pH will be off the charts as cal-hypo strongly raises pH. Serial dilutions makes the resulting test solution look more like "pool water" and less like a chemical stew thus avoiding any interferences or bleaching out of the FC test reagents.

The numbers above are very roughly useful. You might not be able to detect much difference between a 65% cal-hypo sample and a 70% cal-hypo sample but you should see the effect if the starting chemicals are wildly different. You also might want to run the procedure a few times and take an average value and, if you had the time, you should really run a KNOWN chlorine standard against your test kit reagents to ensure that the test kit is still good.

You did say this was an ACADEMIC exercise

Only way to know for sure would be to be able to compare an "old" tablet with a "new" one. You'd have to do a typical laboratory standardization procedure (skipping the calibration of your reagents with a known chlorine standard ... not something you'd do in a real lab but you can make the gross assumption that your test kit is accurate). A standardization would look like the follow -

1. Obtain 1 gram of the unknown powder and dissolve it in 1 liter of distilled water
2. After that solution has mixed and dissolved, remove exactly one milliliter of solution and add that to a 100mL Erlenmeyer flask
3. Fill the 100mL flask with DI water up to the fill mark being careful not to overfill the flask
4. Swirl to mix for 1 min
5. Use the diluted mixture as you sample to test FC

In the above procedure, the one gram of powder is dissolved into approximately 1000 grams (1kg) of water. So assuming the weight percent of the calhypo is X wt%, then the resulting solution is roughly X ・(10,000)・(1/1000) ppm. The next 99:1 dilution drops the ppm by another 1/100th or so. So if you started off with 65% cal-hypo, the resulting test solution should be roughly around 6.5ppm. One of the reasons for doing the serial dilution is to avoid some of the adverse effects that come with dissolving a strong oxidizing powder like cal-hypo into a small quantity of water ... not only will the FC be very high, but the pH will be off the charts as cal-hypo strongly raises pH. Serial dilutions makes the resulting test solution look more like "pool water" and less like a chemical stew thus avoiding any interferences or bleaching out of the FC test reagents.

The numbers above are very roughly useful. You might not be able to detect much difference between a 65% cal-hypo sample and a 70% cal-hypo sample but you should see the effect if the starting chemicals are wildly different. You also might want to run the procedure a few times and take an average value and, if you had the time, you should really run a KNOWN chlorine standard against your test kit reagents to ensure that the test kit is still good.

You did say this was an ACADEMIC exercise ...

Thanks to you I have the starch-iodine commercial bleach testing kit from Taylor. Using that, I could test the step 1 solution? I think that would result in a fraction of 1%. 10 ml of distilled water then?
By the way, every time I have tested my barreled sodium hypochlorite, it has been ≥ 12%.

 

[JoyfulNoise]

Thanks to you I have the starch-iodine commercial bleach testing kit from Taylor. Using that, I could test the step 1 solution? I think that would result in a fraction of 1%. 10 ml of distilled water then?
By the way, every time I have tested my barreled sodium hypochlorite, it has been ≥ 12%.

Yes the starch-iodine test should give you a good estimate of strength. If you can accurately measure 1 gram of the tablets powder, then you can try 10 grams in 100mL of distilled water. There could be undissolved solids left over if there are binders used in making the tablets. You’ll have to see what you get when you make up the solution; it may need to be filtered to remove any solids.

You might try using a lower concentration, like 1 gram in 100mL of water and then use the 0.05% per drop test protocol in the K-1579 kit. Otherwise, if you use a more concentrated solution, then you need to measure the specific gravity to get the right answer. Just remember that the Taylor starch iodine test gives results in units of % available chlorine.