- #1
Luckeris
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Homework Statement
Homework Equations
The Attempt at a Solution
I have no idea how to solve this. Any info would be helpful.
How to Determine the pH of a Water Sample?
- Thread starter Luckeris
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- Determination Ph Water
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Discussion Overview
The discussion revolves around determining the pH of a water sample, including definitions, calculations, and related concepts such as alkalinity and hardness. Participants explore both theoretical and practical aspects of pH measurement and its implications in water chemistry.
Discussion Character
- Homework-related
- Technical explanation
- Mathematical reasoning
- Conceptual clarification
Main Points Raised
- Some participants seek clarification on the definition of pH, with one noting it as a quantitative measure of acidity or alkalinity.
- Others provide a mathematical definition of pH as pH = -log [H+], and mention an alternative definition using Hydroxonium ions.
- There is a discussion about the relationship between pH values and hydrogen ion concentration, with participants noting that lower pH indicates higher acidity.
- One participant attempts to calculate pH using a given concentration but initially uses incorrect units, prompting corrections from others regarding the need for molar concentration.
- Participants engage in a detailed calculation of pH, with one arriving at a value of 4.638 after correcting their earlier mistakes in unit conversion.
- There are references to alkalinity and hardness, with participants discussing their definitions and implications in the context of water chemistry.
- One participant mentions the use of complexometric titration for measuring water hardness, while another clarifies the nature of dissolved calcium carbonate in relation to the titration process.
Areas of Agreement / Disagreement
Participants generally agree on the mathematical definition of pH and the approach to calculating it, but there are disagreements regarding the specifics of unit conversions and the implications of water hardness and alkalinity definitions. The discussion remains unresolved on some aspects of water chemistry.
Contextual Notes
Some calculations depend on precise definitions and assumptions about concentrations and units. There are unresolved steps in the calculations presented, particularly regarding the conversion of units and the implications of dissolved versus solid forms of compounds.
Who May Find This Useful
This discussion may be useful for students and individuals interested in chemistry, particularly those studying water quality, pH measurement, and related analytical techniques.
I have no idea how to solve this. Any info would be helpful.
- #2
Borek
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What is pH definition?
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- #3
Luckeris
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Quantitative measure of the strength of the acidity or alkalinity of a solution.
- #4
Borek
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That's s descriptive definition, there is also a specific, mathematical one, much more precise.
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- #5
Luckeris
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The mathematical definition of pH is a bit less intuitive but in general more useful. It says that the pH is equal to to the negative logarithmic value of the Hydrogen ion (H+) concentration, or
pH = -log [H+]
pH can alternatively be defined mathematically as the negative logarithmic value of the Hydroxonium ion (H3O+) concentration. Using the Bronsted-Lowry approach
pH = -log [H3O+]
pH values are calculated in powers of 10. The hydrogen ion concentration of a solution with pH 1.0 is 10 times larger than the hydrogen concentration in a solution with pH 2.0. The larger the hydrogen ion concentration, the smaller the pH.
when the pH is above 7 the solution is basic (alkaline)
when the pH is below 7 the solution is acidic
pH = -log [H+]
pH can alternatively be defined mathematically as the negative logarithmic value of the Hydroxonium ion (H3O+) concentration. Using the Bronsted-Lowry approach
pH = -log [H3O+]
pH values are calculated in powers of 10. The hydrogen ion concentration of a solution with pH 1.0 is 10 times larger than the hydrogen concentration in a solution with pH 2.0. The larger the hydrogen ion concentration, the smaller the pH.
when the pH is above 7 the solution is basic (alkaline)
when the pH is below 7 the solution is acidic
- #6
Borek
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Luckeris said:
OK, can you use information provided and this equation to calculate pH?
- #7
Luckeris
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pH = -log [H+]=-log[0.23*10-2]=2.638 ??
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- #8
Borek
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No, you need molar concentration, not mg/L.
- #9
Luckeris
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m=0.0023g
M(H)=1g/mol
n=m/M=0.0023mol
c=n/V=0.0023mol/l ?
M(H)=1g/mol
n=m/M=0.0023mol
c=n/V=0.0023mol/l ?
- #10
Borek
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Luckeris said:
This is not equivalent to 2.3*10-2mg, but other than that you are on the right track.
- #11
Luckeris
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Oh yeah mili- means *10-3 not *10-1
m=2.3*10-5g
M(H)=1g/mol
n=m/M=2.3*10-5mol
c=n/V=2.3*10-5mol/l
pH = -log [H+]=-log[2.3*10-5]=4.638
Is that it in terms of pH?
m=2.3*10-5g
M(H)=1g/mol
n=m/M=2.3*10-5mol
c=n/V=2.3*10-5mol/l
pH = -log [H+]=-log[2.3*10-5]=4.638
Is that it in terms of pH?
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- #12
Borek
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Yes. Perhaps too many significant figures, but that's correct approach.
Now, look for definitions of both alkalinity and hardness, and think how they apply.
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Now, look for definitions of both alkalinity and hardness, and think how they apply.
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- #13
Luckeris
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Alkalinity - http://www.ehow.com/how_5328969_calculate-alkalinity-caco.html
Hardness - Water hardness is a measure of the amount of calcium and magnesium salts dissolved in water. There are no health hazards associated with water hardness, however, hard water causes scale, as well as the reduced lathering of soaps. Complexometric titration is one of the best ways of measuring total water hardness. Ca2+ + EDTA4- → CaEDTA2-
Indicator (Eriochrome Black T) should be used to determine the end point of titration. Water hardness is usually reported in terms of mg/L of calcium carbonate which could by found from the mass of titrant used.
Hardness - Water hardness is a measure of the amount of calcium and magnesium salts dissolved in water. There are no health hazards associated with water hardness, however, hard water causes scale, as well as the reduced lathering of soaps. Complexometric titration is one of the best ways of measuring total water hardness. Ca2+ + EDTA4- → CaEDTA2-
Indicator (Eriochrome Black T) should be used to determine the end point of titration. Water hardness is usually reported in terms of mg/L of calcium carbonate which could by found from the mass of titrant used.
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- #14
Borek
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Luckeris said:
Good starting point, compare this with the data you are given.
- #15
Luckeris
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So I have Ca in mg/L which was found from CaCO3 + EDTA4- → CaEDTA2- + CO32- or not?
- #16
Borek
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Close, but not exact. You don't have solid CaCO3, but dissolved one. While calcium carbonate is weakly soluble, it is not completely insoluble. In fact, there are no completely insoluble salts.
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