Cyclophosphates as ligands for cobalt(III) in water.
Examination of cyclotriphosphate and cyclotetraphosphate as ligands for Co(III) in aqueous solutions revealed that cyclotetraphosphate affords stable complexes as a hemilabile ligand, while cyclotriphosphate exhibits facile hydrolysis.
The mechanism of the hydrolysis of polyphosphates. VI. The effect of cations on the hydrolysis of cyclo-tri- and cyclo-tetraphosphates.
The effect of cations on the rate of the hydrolysis of cyclo-tri- and cyclo-tetraphosphates was studied by adding metal chlorides to aqueous solutions of the ring phosphates. The concentrations of the phosphates and metal chlorides were 0.025 mol dm−3 and 0.1 mol dm−3 respectively. Alkali-metal cations retarded the hydrolysis of both the cyclo-phosphates in acidic media and accelerated it in basic media. The following sequence of efficiency resulted: Li+>Na+>K+. Magnesium, calcium, and nickel(II) cations retarded the hydrolysis of the cyclo-phosphates in the pH range of 1.0–2.0 or 1.0–2.7, while they accelerated it in the pH regions higher than 2.7 or 3.5. A copper(II) ion retarded the hydrolysis at pH 1.0, and accelerated it in the pH ranges higher than 2.0. An aluminium ion highly accelerated the hydrolysis of both the ring phosphates at pH 1.0 and 2.0.
Communicative Competence: Theory and Classroom Practice
ABSTRACT Within the framework of viewing communicative competence as a prerequisite to linguistic competence, rather than vice versa, this paper considers the following: (1) the nature of communicative competence; (2) the implications of communicative competence for second language teaching; and (3) ways in which the teacher can begin to make a foreign language program more meaningful. Communicative competeuce is defined as what native speakers know which enables them to interact effectively with each other. Implications for the language teacher include: (T) the need for tests which measure the ability to use language; (2) the irrelevancy of sequencing surface features; (3) the need for emphasis on non-lizguistic aspects of communication; and (4) the need to re-examiLe attitudes toward students and language teaching. Practical suggestins for implementing communicative competence in the classroom include the use of spontaneous role-playing, discussions, games, radio, and the telephone. (AM)