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The pH range is commonly given as zero to 14, but a pH value can be less than 0 for very concentrated strong acids or greater than 14 for very concentrated strong bases. [2] The pH scale is traceable to a set of standard solutions whose pH is established by international agreement. [3]
In the Philippines, some universities follow a 4-Point Scale, which resembles or is equivalent to the U.S. grading system. This system uses a grade between 0.00 to 4.00 wherein 4.00 is the highest and 0.00 being a failing mark. Other universities follow a 5-Point Scale, wherein the highest grade is a 1.00 and the lowest is a 5.00 (failing mark).
The main use of litmus is to test whether a solution is acidic or basic, as blue litmus paper turns red under acidic conditions, and red litmus paper turns blue under basic or alkaline conditions, with the color change occurring over the pH range 4.5–8.3 at 25 °C (77 °F). Neutral litmus paper is purple. [2]
Another policy commonly used by 4.0-scale schools is to mimic the eleven-point weighted scale (see below) by adding a .33 (one-third of a letter grade) to honors or advanced placement class. (For example, a B in a regular class would be a 3.0, but in honors or AP class it would become a B+, or 3.33).
The National Achievement Test (NAT) is a standardized set of examinations taken in the Philippines by students in Grades 3,6,10 to 12. The test is designed to determine their academic levels, strengths and weaknesses, as well as their knowledge learnt in major subjects throughout the year.
Beckman Model M pH Meter, 1937 [1] Beckman model 72 pH meter, 1960 781 pH/Ion Meter pH meter by Metrohm. A pH meter is a scientific instrument that measures the hydrogen-ion activity in water-based solutions, indicating its acidity or alkalinity expressed as pH. [2]
The Hammett acidity function (H 0) is a measure of acidity that is used for very concentrated solutions of strong acids, including superacids.It was proposed by the physical organic chemist Louis Plack Hammett [1] [2] and is the best-known acidity function used to extend the measure of Brønsted–Lowry acidity beyond the dilute aqueous solutions for which the pH scale is useful.
In and of themselves, pH indicators are usually weak acids or weak bases. The general reaction scheme of acidic pH indicators in aqueous solutions can be formulated as: HInd (aq) + H 2 O (l) ⇌ H 3 O + (aq) + Ind − (aq) where, "HInd" is the acidic form and "Ind −" is the conjugate base of the indicator. Vice versa for basic pH indicators ...