Pattern formation driven by an acid-base neutralization reaction in aqueous media in a gravitational field

2008 ◽  
Vol 77 (1) ◽  
Author(s):  
A. Zalts ◽  
C. El Hasi ◽  
D. Rubio ◽  
A. Ureña ◽  
A. D’Onofrio
2019 ◽  
Vol 91 (3) ◽  
pp. 489-496 ◽  
Author(s):  
Youssouf D. Soubaneh ◽  
Steeven Ouellet ◽  
Caroline Dion ◽  
Jonathan Gagnon

Abstract N,N,N-Trimethylchitosan (TMC) represents a rare example of cationic polysaccharides and numerous studies have shown its potential in biological and biomedical applications. TMC with high degrees of quaternization (DQ) were synthesized from N-methylation of N,N-dimethylchitosan (DMC), which was obtained by reductive alkylation of high molecular weight chitosan in a simple step process and in good yields. The effects of base and solvents were evaluated on the quaternization reaction. The N-methylation of DMC was performed selectively by CH3I and carbonate in water where quaternization was achieved quantitatively with a low degree of O-methylation (17 %). Moreover, the greener procedure allows easy recovery and purification by conventional filtration as a carbonate salt, in which the anion can be exchanged by an acid-base reaction. Quantification of DQ involving 1H NMR integration of methyl peaks must be performed on protonated TMC. High field NMR spectra of TMC showed two specific chemical shifts for anomeric peaks (5.0 and 5.4 ppm) that can also be used for the determination of DQ. This latter method avoids the superimposition problems with other pyranosyl peaks.


2016 ◽  
Vol 17 (3) ◽  
pp. 509-522 ◽  
Author(s):  
James M. Nyachwaya

The objective of this study was to examine college general chemistry students' conceptual understanding and language fluency in the context of the topic of acids and bases. 115 students worked in groups of 2–4 to complete an activity on conductometry, where they were given a scenario in which a titration of sodium hydroxide solution and dilute hydrochloric acid was tracked by measuring electrical conductivity. Students were asked to write a balanced equation for the reaction, provide a particulate level drawing of the reactants and products, write a net ionic equation for the reaction, predict how electrical conductivity would change with the addition of sodium hydroxide to the acid, provide a sketch of their prediction, and explain their sketch. As students worked on the activity, conversations in their groups were audio recorded. Their written responses and audio conversations were analyzed to decipher conceptual understanding and language fluency. Results showed widespread lack of conceptual understanding as well as a lack of language fluency. Students struggled with very basic ideas regarding acid–base chemistry, such as identifying the right species involved in the neutralization reaction, and providing symbolic and sub-microscopic representations (an aspect of the language of chemistry) of the acid–base reaction. Most students could not accurately predict how electrical conductivity would change as the neutralization reaction progressed. None of the groups provided an accurate sketch depicting the trend of electrical conductivity. Most of the groups did not correctly apply acid–base neutralization ideas to the context of conductometry, indicating that students were not able to transfer knowledge of acid–base neutralization to this new context.


2008 ◽  
Vol 18 (24) ◽  
pp. 6394-6397 ◽  
Author(s):  
Yoshiya Ikawa ◽  
Hiroaki Ogawa ◽  
Hiroyuki Harada ◽  
Hiroyuki Furuta

1980 ◽  
Vol 119 (2) ◽  
pp. 375-377 ◽  
Author(s):  
Bolesław Wàligóra ◽  
Maria Paluch
Keyword(s):  

1988 ◽  
Vol 53 (7) ◽  
pp. 1574-1578 ◽  
Author(s):  
Karel Komers ◽  
Antonín Lyčka ◽  
Josef Jirman ◽  
Ivan Kolb

A redbrown intermediate has been isolated from a reaction mixture of 2-naphthol and the activated sludge, and its structure has been determined on the basis of its IR, MS, and especially 2D 1H and 13C NMR spectra. It corresponds to 4-(2-hydroxy-1-naphthyl)-6-hydroxy-1,2-naphthoquinone (I). In aqueous media I behaves as an acid-base indicator with the colour transition from yellow to redbrown. The concentration dissociation constants of I have been determined spectrophotometrically: K1 = 3·47 . 10-7, K2 = 3·80 . 10-10 for the standard state c0 = 1 mol dm-3, 298 K, 105 Pa.


2018 ◽  
Vol 63 (8) ◽  
pp. 3150-3156 ◽  
Author(s):  
Marija R. Popović-Nikolić ◽  
Gordana V. Popović ◽  
Kristina Stojilković ◽  
Maja Dobrosavljević ◽  
Danica D. Agbaba
Keyword(s):  

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