Standard acid solution preparation

Reagents. Standard calcium solution. Prepare a standard solution containing 40.0 mg L 1 calcium by dissolving the calculated quantity of calcium carbonate in the minimum amount of hydrochloric acid and diluting to 1 L in a graduated flask. 

Ammoniacal ethanol is prepared by chilling ten liters of anhydrous denatured ethyl alcohol as commercially purchased in a freezer to well below 0° C. Next, 600 to 750 ml of liquid ammonia is drawn from a pressure cylinder into a 1000 ml graduate in a well ventilated area. The contents of the graduate are carefully poured into the chilled alcohol. The solution is then stirred to mix and warmed to room temperature. The solution should be at least two molar as determined by titration against standard acid solution to a methyl red endpoint. If titration is to be attempted, a little methyl red should be added to the chemical list. 

Prepare from a concentrated solution of sodium hydroxide that has been standardized, ml x N = ml X N. Standardize this dilute solution against a standard acid solution and adjust to 0.05 N if necessary. 

Standard Lead Solution Prepare all lead solutions in 0.1% nitric acid. Use a single-element 1000 p,g/mL lead stock solution to prepare (weekly) an intermediate stock solution (1 p,g/ mL). Prepare (daily) a Standard Lead Solution (10 ng/mL) by diluting the intermediate stock solution 1 100 with 0.1 A nitric acid. 

Procedure Transfer 1.0 mL each of the Standard Solution and the Assay Preparation into separate containers. Add 1.0 mL of a freshly prepared 1 100 furfural solution to each container. Cool the containers in an ice bath for 5 min. Add 13 mL of a dilute sulfuric acid solution, prepared by cautiously mixing 50 mL of sulfuric acid with 65 mL of water. Thoroughly mix the contents in each container, and place them for 10 min in a water bath maintained at 70°. Immediately place the containers in an ice bath for 2 min. Determine the absorbance of each solution in a 1-cm cell at the wavelength of maximum absorbance at about 650 nm. Calculate the quantity, in milligrams, of cholic acid in the sample by the formula... 

Iodate Dissolve 1.1 g of sample in sufficient ammonia- and carbon dioxide-free water to make 10 mL of solution, and transfer to a color-comparison tube. Add 1 mL of starch TS and 0.25 mL of 1 A sulfuric acid, mix, and compare the color with that of a control containing, in each 10 mL, 100 mg of Potassium Iodide, 1 mL of standard iodate solution (prepared by diluting 1 mL of a 1 2500 solution of potassium iodate to 100 mL with water), 1 mL of starch TS, and 0.25 mL of 1 N sulfuric acid. Any color in the sample solution does not exceed that in the control. 

Why is HNO3 seldom used to prepare standard acid solutions ... 

Prepare serial dilutions of standard acid solutions. 

MDI method For determination of 4,4 -diphenylmethane diisocyanate in the atmosphere, 5 litres of air should be drawn through 3 ml of 0-4n hydrochloric acid. After the addition of three drops of a 0-6% (w/v) sodium nitrite solution six drops of 10% (w/v) sulphamic acid should be added and the mixture transferred to a separating funnel containing 2 ml of 1 n sodium hydroxide solution and six drops of a suspension of 0-5 g of 2-hydroxy-3-naphthoic anilide (Brenthol AS) in 50 ml water. This mixture is then shaken and 1 ml of 6n sulphuric acid followed by 3 ml of chloroform are added. This is shaken and the chloroform layer separated off. The colour of this chloroform layer is then compared with standard colour solutions prepared by mixing a solution of cobaltous chloride (as above) with a solution of 32 g anhydrous ferric chloride, 25 ml concentrated hydrochloric acid (SG 20°C 1-18) and 975 ml water. The proportions of these two solutions equivalent to different levels of atmospheric diisocyanate are given in Table 11.3. 

Prepare the standard curve as follows Measure, into separators, 0, 1 0, 2 0, 3-0 and 4 0 ml of standard lead solution [prepared by dissolving 1-60 g of lead nitrate in water and adding 10 ml of concentrated nitric acid and sufficient water to produce 1 litre (=1 0 mg of lead per ml) and diluting this 100 times just before use so that 1 ml of diluted solution contains 10 //g of lead]. Dilute the contents of each separator to 10 ml with a 1 per cent v v solution of concentrated nitric acid in water and proceed as described above under Determination of Lead. Measure the extinctions with chloroform (I) in the comparison cell and prepare a curve relating the extinctions to the number of microgrammes of lead. 

Wash the aqueous layer with 3 ml of carbon tetrachloride, discard the washing and add exactly 10 ml of standard zinc solution (prepared by dissolving 0-044 g of zinc sulphate heptahydrate in 50 ml of 0 01 N sulphuric acid and diluting to 1 litre with water this solution contains 10 //g of Zn per ml). Repeat the titration with the dithizone solution as described above. Let the ml of dithizone solution required be 6. ... 

Solutions of Na2S203 are prepared from the pentahydrate and must be standardized before use. Standardization is accomplished by dissolving a carefully weighed portion of the primary standard KIO3 in an acidic solution containing an excess of KI. When acidified, the reaction between 103 and K... 

Monobasic aluminum acetate is dispensed as a 7% aqueous solution for the topical treatment of certain dermatological conditions, where a combination of detergent, antiseptic, astringent, and heat-dispersant effects are needed (12). The solution, diluted with 20—40 parts water, is appHed topically to the skin and mucous membranes as a wet dressing (13). Burrow s solution, prepared from aluminum subacetate solution by the addition of a specific amount of acetic acid, is also used as a topical wet dressing. Standards of purity and concentration have been estabHshed for both pharmaceutical aluminum acetate solutions (13). Each 100 mL of aluminum subacetate solution yields 2.30—2.60 g of aluminum oxide and 5.43—6.13 g of acetic acid upon hydrolysis. For the Burow s solution, each 100 mL yields 1.20—1.45 g of aluminum oxide and 4.25—5.12 g of acetic acid. Both solutions may be stabilized to hydrolysis by the addition of boric acid in amounts not to exceed 0.9% and 0.6% for the subacetate and Burow s solutions, respectively (13). 

Standard 1/10 N nitrite is used to titrate a solution prepared by dissolving 10—100 mg of sulfamic acid and about 6 mL of (1 + 1) H2SO4 in 300 mL of distilled water at 40—50°C. At the end point, the colorless external potassium iodide starch-paste indicator changes to blue. A 1-mL solution of 1/ION NaN02 is equivalent to 9.709 mg of sulfamic acid. The 1/10 N nitrite titrant solution is standardized using primary standard-grade sulfamic acid. For sulfamate assay determination, the same procedure is used as for sulfamic acid. 

The preparation of cyclohexylmagnesium bromide is described on p. 22. The solution may be standardized by titrating against 0.5 N hydrochloric acid, and exactly one mole equivalent is used in the preparation. Five cubic centimeters of cyclohexylmagnesium bromide solution is slowly added to 20 cc. of water, an excess of the standard acid is added, and the excess acid titrated with sodium hydroxide. If 85 g. (3.5 moles) of magnesium, one liter of dry ether, and 571 g. of cyclohexyl bromide (3.5 moles) are used, a solution results which is about 2 molar. 

A standard method for preparing sodium cyclopentadienide (CjHjNa) is by the reaction of cyclopentadiene with a solution of NaNH2 in liquid ammonia. Write a net ionic equation for this reaction, identify the acid and the base, and use curved arrows to track the flow of electrons. 

The standard of cleanliness which must be achieved has been stated to be that which will allow the subsequent process to be carried out satisfactorily . As an example, the degree of cleanliness required to satisfactorily zinc plate from an acid solution is somewhat higher than that required prior to zinc plate from a high-cyanide alkali zinc solution. This should never be taken as a licence to skimp on surface preparation. However, the arguments over surface-tolerant paint coatings abound and will probably continue. It is to a very large extent true that problems of early failure in metal finishing are traceable to incorrect or insufficient surface preparation. 

For work of the highest precision a comparison solution or colour standard may be prepared for detecting the equivalence point. For 0.05 M solutions, this is made by adding 5 drops of methyl red to a solution containing 1.0 g of sodium chloride and 2.2 g of boric acid in 500 mL of water the solution must be boiled to remove any carbon dioxide which may be present in the water. It is assumed that 20 mL of wash water are used in the titration. 

Procedure B. The experimental details for the preparation of the initial solution are similar to those given under Procedure A. Titrate 25 or 50 mL of the cold solution with standard 0.1M hydrochloric acid and methyl orange, methyl orange-indigo carmine, or bromophenol blue as indicator. Titrate another 25 or 50 mL of the cold solution, diluted with an equal volume of water, slowly with the standard acid using phenolphthalein or, better, the thymol-blue cresol red mixed indicator in the latter case, the colour at the end point is rose. Calculate the result as described in the Discussion above. 

The EGTA solution may be standardised by titration of a standard (0.05M) calcium solution, prepared by dissolving 5.00 g calcium carbonate in dilute hydrochloric acid contained in a 1 L graduated flask, and then after neutralising with sodium hydroxide solution diluting to the mark with de-ionised water, use zincon indicator in the presence of Zn-EGTA solution (see below). 

Discussion. Very pure silver can be obtained commercially, and a standard solution can be prepared by dissolving a known weight (say, 10.787 g) in nitric acid in a conical flask having a funnel in the neck to prevent mechanical loss, and making up to a known volume (say, 1 L for a 0.1 M solution). The presence of acid must, however, be avoided in determinations with potassium chromate as indicator or in determinations employing adsorption indicators. It is therefore preferable to employ a neutral solution prepared by dissolving silver nitrate (relative molecular mass, 169.87) in water. 

Either the Mohr titration or the adsorption indicator method may be used for the determination of chlorides in neutral solution by titration with standard 0.1M silver nitrate. If the solution is acid, neutralisation may be effected with chloride-free calcium carbonate, sodium tetraborate, or sodium hydrogencarbonate. Mineral acid may also be removed by neutralising most ofthe acid with ammonia solution and then adding an excess of ammonium acetate. Titration of the neutral solution, prepared with calcium carbonate, by the adsorption indicator method is rendered easier by the addition of 5 mL of 2 per cent dextrin solution this offsets the coagulating effect of the calcium ion. If the solution is basic, it may be neutralised with chloride-free nitric acid, using phenolphthalein as indicator. 

The standard redox potential is 1.14 volts the formal potential is 1.06 volts in 1M hydrochloric acid solution. The colour change, however, occurs at about 1.12 volts, because the colour of the reduced form (deep red) is so much more intense than that of the oxidised form (pale blue). The indicator is of great value in the titration of iron(II) salts and other substances with cerium(IV) sulphate solutions. It is prepared by dissolving 1,10-phenanthroline hydrate (relative molecular mass= 198.1) in the calculated quantity of 0.02M acid-free iron(II) sulphate, and is therefore l,10-phenanthroline-iron(II) complex sulphate (known as ferroin). One drop is usually sufficient in a titration this is equivalent to less than 0.01 mL of 0.05 M oxidising agent, and hence the indicator blank is negligible at this or higher concentrations. 

Standard arsenic solution. Dissolve 1.320 g arsenic(III) oxide in the minimum volume of 1M sodium hydroxide solution, acidify with dilute hydrochloric acid, and make up to 1 L in a graduated flask 1 mL contains 1 mg of As. A solution containing 0.001 mg As per mL is prepared by dilution. 

For the preparation of standard cobalt solutions, use analytical grade cobalt(II) chloride or spectroscopically pure cobalt dissolved in hydrochloric acid subject solutions containing 0, 5, 10, 25, 50, 100, 150, and 200 jug of Co to the whole procedure. 

Procedure. Dissolve a weighed portion of the substance in which the amount of iron is to be determined in a suitable acid, and evaporate nearly to dryness to expel excess of acid. Dilute slightly with water, oxidise the iron to the iron(III) state with dilute potassium permanganate solution or with a little bromine water, and make up the liquid to 500 mL or other suitable volume. Take 40 mL of this solution and place in a 50 mL graduated flask, add 5 mL of the thiocyanate solution and 3 mL of AM nitric acid. Add de-ionised water to dilute to the mark. Prepare a blank using the same quantities of reagents. Measure the absorbance of the sample solution in a spectrophotometer at 480 nm (blue-green filter). Determine the concentration of this solution by comparison with values on a reference curve obtained in the same way from different concentrations of the standard iron solution. 

Procedure. Take an aliquot portion of the unknown slightly acid solution containing 0.1-0.5 mg iron and transfer it to a 50 mL graduated flask. Determine, by the use of a similar aliquot portion containing a few drops of bromophenol blue, the volume of sodium acetate solution required to bring the pH to 3.5 1.0. Add the same volume of acetate solution to the original aliquot part and then 4 mL each of the quinol and 1,10-phenanthroline solutions. Make up to the mark with distilled water, mix well, and allow to stand for 1 hour to complete the reduction of the iron. Compare the intensity of the colour produced with standards, similarly prepared, in any convenient way. If a colorimeter is... 

Standard tin solution. Dissolve 1.000 g tin in lOOmL of 1 1 hydrochloric acid and dilute with the same concentration of acid to 1 L 1 mL contains 1 mg Sn. Prepare more dilute solutions as required (e.g. 0.01 mg Sn per mL) by dilution with 1 1 hydrochloric acid. 

Preparation of standard titanium solution. Weigh out 3.68 g potassium titanyl oxalate K2Ti0(C204)2,2H20 into a Kjeldahl flask add 8g ammonium sulphate and 100 mL concentrated sulphuric acid. Gradually heat the mixture to boiling and boil for 10 minutes. Cool, pour the solution into 750 mL of water, and dilute to 1 L in a graduated flask 1 mL = 0.50 mg of Ti. 

Procedure. Prepare four test solutions of phenol by placing 200 mL of boiled and cooled distilled water in each of four stoppered, 500 mL bottles, and adding to each 5g of sodium chloride this assists the extraction procedure by salting out the phenol. Add respectively 5.0, 10.0, 15.0 and 20.0 mL of the standard phenol solution to the four bottles, then adjust the pH of each solution to about 5 by the careful addition of 5M hydrochloric acid (use a test-paper). Add distilled... 

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