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A Universal indicator is a pH indicator composed of a solution of several compounds that exhibits several smooth colour changes over a pH value range from 1-14 to indicate the acidity or alkalinity of solutions. Although there are several commercially available universal pH indicators, most are a variation of a formula patented by Yamada in 1933.〔''Jap. Pat.'' 99,664, Feb 21, 1933〕 Details of this patent can be found in ''Chemical Abstracts''.〔''Chem Abstr'', 28, 2258 (1934)〕 Experiments with Yamada's Universal Indicator are also described in the Journal of Chemical Education.〔For a discussion of these experiments, as well as recipes for Yamada and other universal indicators, see 〕 A universal indicator is typically composed of water, propan-1-ol, phenolphthalein sodium salt, sodium hydroxide, methyl red, bromothymol blue monosodium salt, and thymol blue monosodium salt.〔"(Universal Indicator )". ISCID Encyclopedia of Science and Philosophy.〕 The colours that indicate the pH of a solution, after adding a universal indicator are: The colours from yellow to red indicate an acidic solution, colours light blue to dark blue indicate bases and green colour that a solution is neutral. Wide range pH test papers with distinct colours for each pH from 1 to 14 are also available. Colour matching charts are supplied with the specific test strips purchased. ==Types of Universal Indicator== A universal indicator is collectively a mixture of indicators which show a colour change in a solution,which interprets how acidic or basic a solution is. A universal indicator can be in paper form or present in a form of a solution. * Paper form: Is a strip of coloured paper which changes colour to red if the solution is acidic and to blue if the solution is basic. The strip can be placed directly onto a surface of a wet substance or few drops of the solution can be dropped onto the universal indicator using a dropping equipment. If the test solution is in dark colour, it is preferable to use paper universal indicator. * Solution: The main components of a Universal indicator, in the form of a solution, are thymol blue, methyl red, bromothymol blue and phenolphthalein. This mixture is important because, each component, loses or gains electrons depending upon the acidity or basicity of the solution being tested. It is beneficial to use this type of a universal indicator in a colourless solution. This will increase the accuracy of indication. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Universal indicator」の詳細全文を読む スポンサード リンク
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