【Daily Question】Chemical Engineering Principles 334: Determination of Water Alkalinity (March 4)
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This post was last edited by “Back to Cambridge” on March 21, 2016, at 15:10. Starting today, the Chemical Engineering Theory section will launch the “Question of the Day” activity, aimed at helping everyone reinforce their basic knowledge in chemical engineering. Subsequently, series such as “Fundamentals of Chemical Engineering”, “Mass Transfer and Separation”, “Chemical Thermodynamics”, and “Chemical Process Engineering” will also be introduced. We hope for your active participation! Wishing you all a Merry Christmas~~ For replies to the “Question of the Day” activity, answers can be viewed directly; however, the thread will be closed after one day! ! To encourage everyone’s continued participation this year! You get 3 wealth rewards just for participating, and an additional 4 wealth points for correct answers~~~ Short answer question: What is the basic principle behind measuring the alkalinity of water? Answer: Alkalinity is the amount of substances in water that can accept hydrogen ions; these substances can all react with strong acids. Therefore, appropriate indicators can be used along with standard solutions to titrate them, and then alkalinity can be calculated using the laws of moles, with the result expressed in terms of molar concentration.
Alkalinity refers to the amount of substances in water that can undergo neutralization reactions with ions and strong acids (HCl or H2SO4). The substances that contribute to alkalinity in water are primarily carbonate alkalinity produced by carbonates, bicarbonate alkalinity produced by bicarbonates, and hydroxide alkalinity resulting from the presence of hydroxides.
Alkalinity is the amount of substances in water that can accept hydrogen ions; these substances can all react with strong acids. Therefore, appropriate indicators can be used to titrate them with standard solutions, and then alkalinity can be calculated based on the law of moles, with the result expressed in terms of molar concentration.
What is the basic principle behind measuring the alkalinity of water? The alkalinity in water is determined using a continuous titration method. First, using phenolphthalein as an indicator, titrate with the HNO3 standard solution until the solution changes from red to colorless; the volume used is P (mL) ； Then, using methyl orange as an indicator, the solution was further titrated with HNO3 of the same concentration; the color changed from orange-yellow to orange-red, and the volume used was M (mL).
The alkalinity in water is determined using a continuous titration method. First, using phenolphthalein as an indicator, titrate with the HNO3 standard solution until the solution changes from red to colorless; the volume used is P (mL) ； Then, using methyl orange as an indicator, the solution was further titrated with HNO3 of the same concentration; the color changed from orange-yellow to orange-red, and the volume used was M (mL).
Bicarbonate, the substance that contributes to alkalinity in water, can coexist with sulfate, and hydroxide can also coexist with it. However, bicarbonates and hydroxides cannot coexist; they undergo the following reaction in water: HCO3‑ + OH‑ = CO32‑ + H2O. It can be seen that in addition to existing separately as carbonates, bicarbonates, and hydroxides, there are also two combinations of alkalinity. Therefore, there are five forms of alkalinity in water, namely: (1) Bicarbonate alkalinity, HCO32‑ ； (2) Carbonate alkalinity CO32－ ； (3) Hydroxide alkalinity OH– ； (4) Bicarbonate and carbonate alkalinity HCO3‑ + CO32‑ ； (5) Carbonate and hydroxide alkalinity: CO32‑ + OH‑. What is the relationship between various alkalinity levels in water? Alkalinity in water is determined by the method of acid-neutralization with salts. Two indicators are used to indicate the end point of the titration when titrating the alkalinity of water.
We generally use the acid-base reagent method to test the alkalinity of water
Alkalinity in water refers to the amount of substances present in water that can undergo neutralization reactions with ions and strong acids such as HCl or H2SO4. The substances that contribute to alkalinity in water include carbonate alkalinity, which results from carbonates; bicarbonate alkalinity, which results from bicarbonates; and hydroxide alkalinity, which arises from the presence of hydroxides.
What is the basic principle behind measuring the alkalinity of water? The determination of alkalinity is based on a neutralization reaction; that is, the basic substances in water can undergo a chemical reaction with acids, so an appropriate indicator can be used along with a standard acid solution for titration.
Alkalinity is commonly determined using the acid-base titration method. The principle of this method is to titrate the water sample with an acid solution until a specified pH value is reached; the end point of the titration is determined by the color change of an acid-base indicator at that pH value. In other words, the titration is stopped when the phenolphthalein indicator changes from red to colorless, at which point the pH of the solution is 8.3. The hydroxide ions in the water have been neutralized, and at this stage the carbonates are converted into bicarbonates； However, when titration is carried out until the methyl orange indicator changes from its original light orange-yellow color to orange-red, the pH value of the solution being tested is 4.4–4.5, indicating that the bicarbonates in the water have been neutralized. Based on the amounts of various solutions consumed upon reaching these two different endpoints, the contents of carbonates and bicarbonates in the water, as well as the alkalinity of the water, are calculated.
Alkalinity is the amount of substances in water that can accept hydrogen ions; these substances can all react with strong acids. Appropriate indicators can be used to titrate them with standard solutions, and then the value can be calculated.