Explore chapters and articles related to this topic
Symbols, Terminology, and Nomenclature
Published in W. M. Haynes, David R. Lide, Thomas J. Bruno, CRC Handbook of Chemistry and Physics, 2016
W. M. Haynes, David R. Lide, Thomas J. Bruno
classifies any chemical species capable of accepting an electron pair as an acid. Acid dissociation constant (Ka)* - The equilibrium constant for the dissociation of an acid HA through the reaction HA + H2O A- + H3O+. The quantity pKa = -log Ka is often used to express the acid dissociation constant. Actinides - The elements of atomic number 89 through 103, e.g., Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr. [7] Activation energy* - In general, the energy that must be added to a system in order for a process to occur, even though the process may already be thermodynamically possible. In chemical kinetics, the activation energy is the height of the potential barrier separating the products and reactants. It determines the temperature dependence of the reaction rate. Activity - For a mixture of substances, the absolute activity of substance B is defined as B = exp(µB/RT), where µB is the chemical potential of substance B, R the gas constant, and T the thermodynamic temperature. The relative activity a is defined as aB = exp[(µB-µB°)/RT], where µB° designates the chemical potential in the standard state. [2] Activity coefficient ()* - Ratio of the activity aB of component B of a mixture to the concentration of that component. The value of depends on the method of stating the composition. For mole fraction xB, the relation is aB = B xB; for molarity cB, it is aB = B cB/c°, where c° is the standard state composition (typically chosen as 1 mol/L); for molality mB, it is aB = BmB/m°, where m° is the standard state molality (typically 1 mol/kg). [2] Activity, of radioactive substance (A) - The average number of spontaneous nuclear transitions from a particular energy state occurring in an amount of a radionuclide in a small time interval divided by that interval. [1]
Headspace single-drop microextraction combined with nanodrop spectrophotometry for ultra-trace detection of ethanethiol using a suspended drop of AuNPs as a plasmonic sensor
Published in Journal of Sulfur Chemistry, 2023
Mehran Nozari-Asbemarz, Atefeh Abbasi-Ahd, Nader Shokoufi
The AuNPs’ pH is an important parameter affecting the analyte's recovery (Figure 2E). The impact of pH (5–10) on the absorption signal was investigated. The maximum signal was obtained at a pH value of 7. The neutral AuNPs’ pH is 5.7 because the AuNPs are coated with a surface stabilizing reagent named citric acid that maintains dispersion of the AuNPs by electrostatic repulsion. The structure of ethanethiol has an acid dissociation constant (pKa 10.6). Therefore, the ethanethiol adsorbed on the AuNPs had a positive charge. The ethanethiol can exchange the citric acid on the AuNPs with an Au-thiolate bond, which causes neutralization of the negative charge of the AuNPs. The neutralization pH brings up Van der Waals interactions between AuNPs, resulting in aggregation [36]. Hence, in this work, the AuNPs pH was fixed to 7.
Alleviation of boron toxicity in plants: Mechanisms and approaches
Published in Critical Reviews in Environmental Science and Technology, 2021
Tianwei Hua, Rui Zhang, Hongwen Sun, Chunguang Liu
The pH of the soil solution is known to affect B adsorption and its availability to plants (Smith et al., 2013). At neutral soil pH, the most plentiful form of B is a soluble nonionized form, boric acid (H3BO3), which is considered as the available form for plants (Güneş et al., 1999). Boric acid is a weak acid with a low acid dissociation constant and high pK value. At high pH, about ten percent of H3BO3 exists in the form of tetraborate anion, B(OH)4−, which is easily adsorbed by clay minerals (Hutchinson & Viets, 1969). With the increase of soil pH, more B(OH)4− is adsorbed and the decrease of water-soluble B(OH)4− induces depletion of H3BO3. To reduce soil available B (H3BO3), an efficient approach is to increase soil pH by liming (Gupta & Macleod, 1981; Lehto & Mälkönen, 1994; Tsadilas et al., 2005). Besides increasing soil pH, liming can also increase calcium carbonate, which acts as an important B adsorbing surface in calcareous soils (Goldberg, 1997). As reported by Tsadilas et al. (2005), liming significantly increased soil pH, which is negatively correlated with soil available B and tissue B in tobacco leaves.
Efficient and selective use of functionalized material in the decontamination of water: removal of emerging micro-pollutants from aqueous wastes
Published in Environmental Technology, 2023
Ralte Malsawmdawngzela, Lalhmunsiama Siama, Diwakar Tiwari, Seung-Mok Lee, Dong-Jin Kim
Tetracycline (TC) is a widely used antibiotic for the treatment of diseases in humans and animals [13]. Also, it is employed in livestock and aquatic animals. The consumption of TC for veterinary use is significantly high compared to other classes of antibiotics [14,15]. The digestive tract of humans and animals absorbs the TC maximum of Ca 50% and more than half of it is excreted through faeces and urine which may finally enter the aquatic environment [16,17]. The concentration of TC in the aquatic environment is relatively high (i.e. μg/L) due to continuous input through various sources [18]. The prolonged exposure of TC by bacteria resulted in the bacterial antibiotic resistance which is directly or indirectly harmful for human and animal health [19]. Moreover, intensive studies performed on rats have shown that TC reduced the antioxidant enzymes and glutathione levels which further caused the oxidative stress in liver and pancreas of rats [20]. On the other hand, triclosan (TCS) is an antibacterial and antifungal agent frequently employed as personal care products (PPCPs), for instance, washing powders, toothpastes, shampoos, soaps, deodorants, etc. [21]. In an aqueous medium, TCS is having solubility less than 10−6 g/mL but the solubility is increased at higher pH conditions. The acid dissociation constant (pka) of TCS is 7.9–8.1. The growth of terrestrial and aquatic species might be affected by TCS since the TCS is feasibly dissolved in fats and lipids of living organisms [22]. Moreover, the aquatic organisms are indirectly affected by TCS since enzymes carrying proteins are blocked by TCS which may eventually develop bacterial resistance to that particular species [23].