Methyl orange endpoint

Alkalinity and Lime Content. Alkalinity is the ability of a solution or mixture to react with an acid. The phenolphthalein alkalinity refers to the amount of acid required to reduce the pH to 8.3, the phenolphthalein endpoint. The phenolphthalein alkalinity of the mud and mud filtrate is called the and Pp respectively. The P. test includes the effect of only dissolved bases and salts while the P test includes the effect of both dissolved and suspended bases and salts. The methyl orange alkalinity refers to the amount of acid required to reduce the pH to 4.3, the methyl orange endpoint. The methyl orange alkalinity of the mud and mud filtrate is called the and Mp respectively. The API diagnostic tests include the determination of P, Pp and Mp All values are reported in cubic centimeters of 0.02 N (normality = 0.02) sulfuric acid per cubic centimeter of sample. 

Carbonate (as K2C03) Each milliliter of 1 N sulfuric acid required between the phenolphthalein and methyl orange endpoints in the Assay (above) is equivalent to 138.2 mg of carbonate. 

Assay Based on the stated or labeled percentage of Potassium Hydroxide (KOH), accurately weigh a volume of the solution equivalent to about 1.5 g of Potassium Hydroxide, and dilute it to 40 mL with recently boiled and cooled water. Continue as directed under Assay in the monograph for Potassium Hydroxide, beginning with cool to 15°.. .. Carbonate (as K2C03) Each milliliter of 1 N sulfuric acid required between the phenolphthalein and methyl orange endpoints in the Assay is equivalent to 138.2 mg of carbonate. Lead Determine as directed under Lead Limit Test, Appendix IIIB, preparing the Sample Solution as follows Dilute the equivalent of 1 g of Potassium Hydroxide (KOH), calculated on the basis of the Assay, with a mixture of 5 mL of water and 11 mL of 2.7 N hydrochloric acid. Use 2 p,g of lead (Pb) ion in the control. 

The second endpoint (at Vp + Vm, where Vm is the methyl orange endpoint) occurs at pH 4.3 and indicates the conversion of HCOj" into H2CO3 as follows ... 

A sample of water from the overflow of the recarbonation basin that follows a precxpitation/softening process has a pH of 9.0 200 ml of the water require 1.1 ml of 0,02 N H2S04 to titrate it to the phenolphthalein endpoint and 22.3 ml of 0.02 N H2SO4 to titrate it further to the methyl orange endpoint. Assuming the sample contains no calcite particles, what are the total and carbonate alkalinities of the sample in meq/liter and the total alkalinity in mg/liter as CaCOa ... 

Total alkalinity = the meq of acid required/liter of sample to reach the methyl orange endpoint... 

Total alkalinity is based on the volume of titrant required to lower the pH of the sample to the methyl orange endpoint, which is approximated by pH 4.3 in this problem. 

The term free mineral acid is applied to strong acids such as H2SO4 and HCl in water. Pollutant acid mine water contains an appreciable concentration of free mineral acid. Whereas total acidity is determined by titration with base to the phenolphthalein endpoint (pH 8.2, where both strong and weak acids are neutralized), free mineral acid is determined by titration with base to the methyl orange endpoint (pH 4.3, where only strong acids are neutralized). 

Acidity (see Chapter 11, Section 11.6) is determined simply by titrating hydrogen ion with base. Titration to the methyl orange endpoint (pH 4.5) yields the free acidity due to strong acids (HCl, H2SO4). Carbon dioxide does not, of course, appear in this category. Titration to the phenolphthalein endpoint, pH 8.3, yields total acidity and accounts for all acids except those weaker than HCO3 . 

A 200-mL sample of water required 25.12 mL of 0.0200N standard H2SO4 for titration to the methyl orange endpoint, pH 4.5. What was the total alkalinity of the original sample ... 

Primarily the sum of carbonate, bicarbonate and hydrate ions in water, but phosphate, silicate etc. may also contribute partially to alkalinity. Normally expressed as ppm (mg/1) CaC03. Phenolphthalein alkalinity (P Aik.) is that portion of alkalinity titrated with acid to pH 8.2 end-point, while total alkalinity (T Aik. or M Aik.) is that titrated with methyl orange indicator to pH 4.2 endpoint. 

Most water analysis results are rather easily interpreted. However, two simple and useful tests need explanation. These are the P and M alkalinity. The water is titrated with N/30 HC1 to the phenolphthalein endpoint at pH 8.3. This is called the P alkalinity. Similar titration to the methyl orange end point at pH 4.3 is called the M alkalinity. They are reported as ppm CaC03. 

Calculations The total volume of 1 N sulphuric acid consumed in the titration was required to neutralize NaOH and Na Oj, thereby converting the latter first to NaHC03 at the phenolphthalein endpoint and then to H2C03 at the methyl orange end-point. 

Quantitative Determination. — Dissolve 1 gm. of calcined borax in 50 cc. of water, add 1 drop of methyl orange solution, and titrate with fifth normal hydrochloric acid. At least 37.2 cc. of the acid should be necessary to produce the endpoint. 

Orthophosphoric Acid may be titrated with sodium or potassium hydroxide free from carbonate. The equivalent point indicating NaH2P04 occurs at pH = ca. 4-2, which is within the transition range of methyl yellow, methyl orange and bromophenol blue. The endpoint tint should be matched against that of a comparison solution containing about the same concentration of NaH2P04. 

Note For cleaning the Selas crucible after this test use reverse washings with a hot acid (except hydrofluoric)i followed by hot distd w until two successive weighings of dried crucible agree within at least 0.0003 g e)Acidity. Dissolve a 25 g sample (weighed on a trip balance) in 300 ml distd w, add a few drops of methyl orange indicator and titrate with 0.2N NaOH soln to reddish endpoint... 

Titrate the eluate with a standard 0.1000 M NaOH solution (provided) using methyl orange indicator. The endpoint of the titration is reached at the color change of the indicator this will take place within one drop of titrant. Record the volume of titrant added (to the nearest 0.05 ml) at the endpoint. 

Titrations are carried out to end-points , defined by inflection points in titration curves. These theoretical end points are often difficult to determine in practice, so fixed endpoints are now universally used, defined by the change in color of an indicator substance, or by a pH reading. For alkalinity titrations, a pH of about 4.3 is used, as indicated by an electrode or by an indicator such as methyl orange. In other words, any solution having a pH greater than 4.3 is titrated with a standard acid, and the quantity required to lower the pH to 4.3 is reported in milliequivalents per liter of solution (meqL-1).5 Alternatively, this quantity of milliequivalents may be converted into an equivalent quantity of calcite (CaCOs), or of HCCfj". 

Add 4 drops of methyl orange (solution will turn blue) and titrate with 0.02 N H2S04 to a steel gray endpoint. Record mL required for this step only. 

In the determination of total alkalinity a known volume of sample is titrated with a standard solution of a strong acid to a pH value in the approximate range of 4 to 5 and usually in the range 4.5 to 4.8. This endpoint is commonly indicated by the color change of the indicator methyl orange therefore, the total alkalinity is often referred to as the methyl orange alkalinity. The H added is the stoichiometric amount required for the following reactions ... 

H3PO4 NaOH Methyl orange First endpoint... 

So the free active chlorine content is titrated with arsenous acid reagent. Different endpoint detection techniques can be used here. The simplest is to prepare the titrant with a small amount of a color indicator dissolved in it. Methyl orange is a good choice for this. As long as the chlorine is in excess, it destroys the indicator. The endpoint is indicated by the orange color. It shows up more sharply if potassium bromide is added to the water sample. Then the free chlorine stoichiometrically liberates an equal quantity of bromine according to the reaction... 

If the organic material content of the sample is high, then a certain volmne of the titrant is added into the titration flask, together with the potassium bromide crystals, and the sample is added from a burette. The disappearance of the color of the methyl orange indicates the endpoint. 

Neutralization indicators, or acid-base indicators or pH indicators, are auxiliary reagents added to the titrand solution in order to detect the equivalence point in acid-base titrations. They can also be used for an accurate quantitative measure of the pH. Tournesol, a natural pigment extracted from some blue-green lichens, was the first pH indicator to be used (1850). Phenolphthalein and methyl orange were introduced somewhat later (1877 and 1878, respectively). Undeniably, the chief interests in the use of acid-base indicators are their low cost and ease of handling. However, they give rise to less precise and less accurate endpoints than some instrumental methods. 

For samples containing only Carbonate, titration to phenolphthalein endpoint corresponds to the complete conversion of carl>onate to bicarbonate or what is also known as half-neutralisation of carbonate (Reaction 3.14). This means that exactly the same amount of additional acid will be required for lurther titration to methyl orange end- )oint (Reaction 3.15). 

Tocopherol was effective and ascorbic acid ineffective in the protection of citrus oils evaluated by aroma (13). In a typical study, 5 g of orange oil was oxidized in 75-mL open brown bottles at 45°C and was evaluated by a panel after 6 d, at which time it was ranked as off-odor, "terpeney. The peroxide value of the initial oil was zero the oxidized material had a PV of 100. As a result, days to reach 100 PV was used as an endpoint. Comparative antioxidant effects on a number of citrus oils and on D-limonene [cyclohexene, l-methyl-4-(l-methylethenyl)-(R)-5989-27-5] are presented in Table X. BHA is the most active while AP has no activity alone but does synergize with tocopherol. 

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