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Related Concept Videos

pH Scale02:41

pH Scale

78.1K
Hydronium and hydroxide ions are present both in pure water and in all aqueous solutions, and their concentrations are inversely proportional as determined by the ion product of water (Kw). The concentrations of these ions in a solution are often critical determinants of the solution’s properties and the chemical behaviors of its other solutes. Two different solutions can differ in their hydronium or hydroxide ion concentrations by a million, billion, or even trillion times. A common means of...
78.1K
pH01:24

pH

141.8K
The potential of hydrogen (pH) is a measure of the acidity or basicity of a water-based solution determined by the concentration of hydronium ions (H3O+). In one liter of pure water at neutral pH, there are 1×10−7 moles of hydronium ions. However, the extensive range of hydronium ion concentrations present in water-based solutions makes measuring pH in moles cumbersome. Therefore, a pH scale was developed to convert moles of hydronium ions into the negative logarithm of the hydronium...
141.8K
Buffers02:56

Buffers

171.7K
A solution containing appreciable amounts of a weak conjugate acid-base pair is called a buffer solution, or a buffer. Buffer solutions resist a change in pH when small amounts of a strong acid or a strong base are added. A solution of acetic acid and sodium acetate is an example of a buffer that consists of a weak acid and its salt: CH3COOH (aq) + CH3COONa (aq). An example of a buffer that consists of a weak base and its salt is a solution of ammonia and ammonium chloride: NH3 (aq) + NH4Cl...
171.7K
Indicators02:39

Indicators

57.2K
Certain organic substances change color in dilute solution when the hydronium ion concentration reaches a particular value. For example, phenolphthalein is a colorless substance in any aqueous solution with a hydronium ion concentration greater than 5.0 × 10−9 M (pH < 8.3). In more basic solutions where the hydronium ion concentration is less than 5.0 × 10−9 M (pH > 8.3), it is red or pink. Substances such as phenolphthalein, which can be used to determine the pH of a solution, are...
57.2K
Determining the pH of Salt Solutions04:08

Determining the pH of Salt Solutions

46.3K
The pH of a salt solution is determined by its component anions and cations. Salts that contain pH-neutral anions and the hydronium ion-producing cations form a solution with a pH less than 7. For example, in ammonium nitrate (NH4NO3) solution, NO3− ions do not react with water whereas NH4+ ions produce the hydronium ions resulting in the acidic solution.  In contrast, salts that contain pH-neutral cations and the hydroxide ion-producing anions form a solution with a pH greater than 7. For...
46.3K
Titration of a Strong Acid with a Strong Base01:23

Titration of a Strong Acid with a Strong Base

9.1K
During the titration of a strong acid with a strong base, pH calculations are primarily based on the concentration of residual hydronium or hydroxide ions. Initially, a strong acid like hydrochloric acid fully dissociates, creating hydronium and chloride ions, resulting in a low pH. The addition of a strong base like sodium hydroxide alters the concentration of hydronium ions by neutralizing them. As more base is added, the pH gradually increases. At the equivalence point, all hydronium ions...
9.1K

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Measuring Phagosome pH by Ratiometric Fluorescence Microscopy
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Measuring Phagosome pH by Ratiometric Fluorescence Microscopy

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Two New Standards for the pH Scale.

Bert R Staples1, Roger G Bates1

  • 1Institute for Materials Research, National Bureau of Standards, Washington, D.C. 20234.

Journal of Research of the National Bureau of Standards. Section A, Physics and Chemistry
|January 14, 2020
PubMed
Summary
This summary is machine-generated.

Two new primary pH standards, potassium dihydrogen citrate and sodium carbonate/bicarbonate, extend the National Bureau of Standards (NBS) pH scale. These stable solutions offer reliable pH measurements at 25°C and across a range of temperatures.

Keywords:
Aciditycarbonatecitrateemfhydrogen electrodepHstandards for pH

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Area of Science:

  • Analytical Chemistry
  • Physical Chemistry

Background:

  • The National Bureau of Standards (NBS) pH scale requires reliable primary standards for accurate measurements.
  • Existing standards have limitations in stability or range.

Purpose of the Study:

  • To introduce two new primary pH standards to supplement the existing NBS scale.
  • To extend the upper limit of the NBS pH scale.

Main Methods:

  • Preparation and characterization of potassium dihydrogen citrate and sodium bicarbonate/carbonate solutions.
  • Electromotive force (emf) measurements using cells with hydrogen and silver-silver chloride electrodes.
  • Determination of pH(S) values at 11 temperatures (0-50 °C).

Main Results:

  • A 0.05 molal potassium dihydrogen citrate solution established as a primary standard with pH 3.776 at 25°C.
  • A 0.025 molal sodium bicarbonate and sodium carbonate mixture established as a primary standard with pH 10.012 at 25°C.
  • The new carbonate standard extends the NBS pH scale above 9.180.

Conclusions:

  • The proposed citrate and carbonate solutions serve as valuable primary pH standards.
  • These standards enhance the accuracy and range of the NBS pH scale.
  • The stability of the citrate standard offers advantages over existing tartrate and phthalate standards.