Color of indicators

You are probably familiar with a variety of aqueous solutions that are either acidic or basic (Figure 4.6). Acidic solutions have a sour taste and affect the color of certain organic dyes known as acid-base indicators. For example, litmus turns from blue to red in acidic solution. Basic solutions have a slippery feeling and change the colors of indicators (e.g., red to blue for litmus). 

As an example, suppose a chemist needs to know the hydrogen ion concentration in a solution containing both 0.010 M benzoic acid, QHsCOOH, and 0.030 M sodium benzoate, QHtCOONa. Of course, he could go to the laboratory and proceed to investigate the colors of indicator dyes placed in the solution. However, it is easier to calculate the value of [H+], using the accurate value of Ka listed in Appendix 2. 

All add solutions taste sour and are more or less corrosive and chemically quite reactive they react with most metals, many of which are corroded and dissolved by acids. Alkaline solutions, also chemically reactive, are caustic (they burn or corrode organic tissues), taste bitter, and feel slippery to the touch. Both acids and bases change the color of indicators (substances that change color, hue, or shade depending on whether they are in an acid or basic environment). 

In this reaction, one of the products is OH-, which is the species of basic character in aqueous solutions. When NaOH dissolves in water, the reaction is not actually an ionization reaction because the Na+ and OH- ions already exist in the solid. The process is a dissolution process rather than an ionization reaction. Substances such as NaOH, KOH, Ca(OH)2, NH3, and amines (RH2N, R2HN, and R3N) are all bases because their water solutions contain OH-. The compounds dissolve in water to give solutions that conduct an electric current, change the colors of indicators, and neutralize acids,... 

Colorl expl liq used as a component of proplnt, and composite expls. The Italian Army Speci-. fication Requirements listed in the pamphlet Capitolato Tecnico Generate per la Fornitura di Esplosivi Propellenti , MD Esercito (1951), CTF 28, are as follows N content 14.10%, alkalinity (as %Na2C03) 0.0023 and stability by 120° German test, 30 mins for red coloration of indicator paper (Ref 28, p 337)... 

Wash down the sides of each of the three flasks with distd w and make a final neutralization with ft.IN NaOH to green color of indicator. Dilute the contents of each flask to 50ml, add 25 ml of 0.25M H.5IOb (using a pipet or buret), mix well and allow to stand for 10 mins or more in order to achieve oxidation. Add 2 drops of the above indicator (to compensate for the bleaching which takes place) and titrate with 0.1N NaOH to a green cqlor... 

BASES taste brackish. They change the color of indicators. They contain a combination of oxygen and hydrogen atoms called "hydroxyl (OH). They neutralize acids. 

PROP A term loosely applied to the hydroxides and carbonates of the alkali metals and alkaline earth metals, as well as the bicarbonate and hydroxide of ammonium. They can neutralize acids, change the color of indicators, and impart a soapy taste and feel to aq solns. 

This concept explains many phenomena, such as the effect of certain substances otha than In/dvogen ion in changing the color of indicators. Another interesting appiicaiioa of the concept is its explanation of salt formation by reaction of acidic oxides and basic oxides. 

Acids, bases, and hydrolysis. Record in TABLE 27.2A1 the colors of indicator solution standards at various pH values that are provided in the laboratory. These will serve as references for all use of indicator solutions in this experiment. 

Change colors of indicators (e.g., litmus turns from red to blue)... 

Markings On/Off symbols, fuses, outlets, colors of indicators lights and buttons, other Machinery E-stop, function and controls, other ... 

The literature data show that many mediods were used for oxoacidity studies and estimation of the acidic properties of melts. One simplest mefliod involves indicator. Acid-base indicators usually employed in aqueous solutions for protic aeidity measurements have been used for acidity studies in molten KNOj-LiNOj at 210 C and KSCN at 200"C. The color of indicator solution, relative to acidity, changes during titration of bases (sodium hydroxide or peroxide) by potassium pyrosulfate, KjSjOy ... 

What would happen if phenolphthalein indicator were added to the water to which sodium metal was introduced Specifically, what color, if any, would the phenolphthalein turn Briefly interpret the result. Hint The colors of indicators can be found in any good introductory or analytical textbook.)... 

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