Determining your waters ppm (mg/L) Alkalinity (as CaCO3) via Bromocresol Purple indicator and 1N HCl

[Silver_Is_Money]

1st priority: Someone please check my work as seen below for mistakes.

Required items list:
1N HCl (1 Normal Hydrochloric Acid)
Bromocresol Purple indicator solution
10 mL Graduated Cylinder
50 mL Graduated Cylinder
100 mL Beaker
Eye Dropper or Pipet

Colors Of Bromocresol Purple indicator in water:
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~pH 6.3 and above = purple
~pH 6.0 = violet
~pH 5.6 = violet/yellow
~pH 5.4 = yellow/violet
~pH 5.2 and below = yellow

Process Steps:
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1) Calibrate the delivery of your chosen eye-dropper or pipet: Add drops of 1N HCl Acid from your eye-dropper or pipet into a clean and dry 10 mL Graduated Cylinder until you reach 5 mL, and record the number of drops required to reach 5 mL.

2) Divide answer from #1 by 5. Record the 'number of drops divided by 5' result as your Eye-Dropper or Pipet's "Drops per mEq"

(Whereby: 1.0 mL of 1N Acid = 1 mEq of acid)

3) Measure out exactly 50 mL of your water to be tested for Alkalinity within a 50 mL Graduated Cylinder, then transfer this 50 mL of water into a 100 mL beaker.

(Note: 50 mL = 0.050 Liters = 1/20 of a Liter as your sample size)

4) Add a few drops of Bromocresol Purple indicator to your water and gently swirl (your water should initially become violet to most likely purple)

5) Add to your water individual drops of 1N HCl Acid via your "Drops per mEq" calibrated eye-dropper or pipet, and gently swirl after each drop until you achieve a transition in color to violet/yellow or yellow/violet. Record the counted number of drops of 1N HCl this required. Your water should now be at about pH 5.4-5.6.

6) Determine the mEq's of acid delivered:
mEq's of acid delivered = # of drops from step #5 divided by "Drops per mEq" from step #2.

7) Multiply the line #6 determined mEq's by 20 to determine the mEq's/L (mEq's per Liter) of Alkalinity titrated for your water.

8) Multiply the line #7 result by 50 to convert mEq's into the ppm (mg/L) of Alkalinity removed from your water via acid titration whereby to reach pH 5.4-5.6.

(Note: Multiply by 50.04345 instead of 50 if you are highly persnickety)

9) Divide the line #8 result by 0.87 if you stopped titrating (adding acid drops) at ~violet/yellow (~pH 5.6). Or divide the line #8 result by 0.89 if you stopped titrating at ~yellow/violet (~pH 5.4).

The #9 Result = "Total Alkalinity (as CaCO3)" in ppm (or mg/L) for your water.

 

[Silver_Is_Money]

Methyl Red indicator should work decently also. Titrate from yellow to first faint hint of persistant orange-red. Deep orange-red means you have gone too far over to the acid side.

 

[Silver_Is_Money]

Bromocresol Purple color change photo:

If this is accurate, your titration may need to go a wee tad more toward yellow than I initially thought. Yellow/yellow (as seen here for the pH 5.0 sample vile) is claimed for this indicator to occur at 5.2pH and below.

 

[Silver_Is_Money]

Methyl Red (among others):

 

[Silver_Is_Money]

If you use Methyl Orange indicator and titrate from yellow until you see the first hint of persistant orange you will be at about pH 4.3, which is the point where Alkalinity has been titrated to zero ppm (mg/L). So for this indicator step #8 gives you the ppm (mg/L) of Alkalinity (as CaCO3) directly, and there is no need for step #9.

 

[Silver_Is_Money]

Bromocresol Green may be the best of the bunch. It should be relatively easy to titrate to a target of pH 4.5 with this indicator. Close enough to pH 4.3 for this indicator to also use step #8 to yield the ppm (mg/L) of Alkalinity (as CaCO3) directly, with no need for a step #9 final tweaking adjustment. But if you are persnickety, divide by 0.99.

 

[Silver_Is_Money]

Most all of the available pH indicators (with the 0-14 pH scale at the top):

 

[JJinMD]

Would a pool water test kit work for this? I have a taylor kit that measures total alkalinity in ppm, but I can't find any info about what is the actual chemical (R-0008) that is titrated with Sulfuric acid. This measures with an indicator color change from green to red.

 

[Silver_Is_Money]

Would a pool water test kit work for this? I have a taylor kit that measures total alkalinity in ppm, but I can't find any info about what is the actual chemical (R-0008) that is titrated with Sulfuric acid. This measures with an indicator color change from green to red.

The chart above shows a mixture of Bromocresol Green and Methyl Red transitioning from green to red at about 5 pH, so it should work. At pH 5 the step #9 divisor would be on the order of ~0.96. As long as the Sulfuric Acid is 1N it should work as described above. If it is not 1N, it would work, but differently than as described above.

 

[Bilsch]

Don't more brewers have a pH meter these days?
Also burettes are pretty cheap on Amazon.

 

[Silver_Is_Money]

A well calibrated pH meter will work. Just keep adding drops of 1N HCl or 1N H2SO4 or 1N HNO3 until the pH meter indicates a steady 4.3-4.4 pH, then follow the above steps, but skip step #9. I'll admit that a Burette eases the burden of going through drops calibration.

Burette or drops, you 'may' however conclude that it is easier and more repeatable to just use an indicator and train your eyes to recognize when the pertinent target color has been reached.