Potassium chromate solution

Preparing one liter of 0.100 Of potassium chromate. A 0.100 M potassium chromate solution is made by adding enough water to 19.4 g of K2C1O4 to make one liter of solution. 

Weigh out accurately about 0.10 g of analytical grade sodium chloride and about 0.20 g of potassium bromide, dissolve the mixture in about 2.0 mL of water and transfer quantitatively to the top of the column with the aid of 0.3 M sodium nitrate. Pass 0.3 M sodium nitrate through the column at a flow rate of about 1 mL per minute and collect the effluent in 10 mL fractions. Transfer each fraction in turn to a conical flask, dilute with an equal volume of water, add 2 drops of 0.2M potassium chromate solution and titrate with standard 0.02M silver nitrate. 

The theory of the process is as follows. This is a case of fractional precipitation (Section 2.8), the two sparingly soluble salts being silver chloride (Xsol 1.2 x 10 10) and silver chromate (Kso] 1.7 x 10 12). It is best studied by considering an actual example encountered in practice, viz. the titration of, say, 0.1M sodium chloride with 0.1M silver nitrate in the presence of a few millilitres of dilute potassium chromate solution. Silver chloride is the less soluble salt and the initial chloride concentration is high hence silver chloride will be precipitated. At the first point where red silver chromate is just precipitated both salts will be in equilibrium with the solution. Hence ... 

Materials Required Potassium chloride 0.25 g potassium chromate solution (5% w/v in water) 10 ml 0.1 N silver nitrate solution. 

Procedure Weigh accurately about 0.25 g of potassium chloride in a conical flask and dissolve it in 50 ml of DW and titrate with 0.1 N silver nitrate solution, using 2-3 drops of potassium chromate solution as indicator till precipitation of red chromate is indicated. Each ml of 0.1 N silver nitrate solution is equivalent to 0.007455 g of KC1. 

Materials Required Chloral hydrate 4.0 g sodium hydroxide (N) 30 ml sulphuric acid (N) phenolphthalein solution (1.0% w/v in 50% v/v alcohol) 0.1 N silver nitrate solution potassium chromate solution (5% w/v in water). 

Potassium Dichromate Solutions. Preparation of the potassium chromate solution differs for the NIST and BP/EP procedures. For the NIST procedure, a solution of potassium dichromate (0.06 g of dichromate per kilogram of solvent) is prepared in 0.001 N perchloric acid. A 0.001 N perchloric acid solution as the reference is scanned and then the potassium dichromate solutions at 235, 257, 313, and... 

Excess of Potassium Chloride. < >n adding a few drops of potassium chromate solution to It) ee. of the aqueous solution, prepared from h gm. of potassium bromide, dried at 100° (1., and dissolved in 100 ee. of water, the solution should not require more than 25.4 ee. of de.oinormal silver nitrate solution to produce a permanent rod color. 

Barium chromate. [CAS 10294-40-3]. BaCrO yellow precipitate, K,sp = 1.17 < 10-10, formed by reaction of barium salt solution and potassium chromate solution,... 

Other silver compounds include Silver chromate [CAS 7784-01-2] (Ag2Cr04), yellow to red to brown precipitate by reaction of silver nitrate solution and potassium chromate solution. 

Strontium chromate, [CAS 7789-06-2], SrCr04, yellow precipitate (Kjp = 3.75 y 10 ) fonncd by reaction of strontium salt solution and potassium chromate solution. 

It was found that the application of certain strong oxidizing solutions would make polyolefins receptive to inks and adhesives, and Horton5 suggested the use of a strong sulphuric acid-dichromate solution. Later, Ziccarelli6 described a similar process in which a moulding could be treated by immersion in a sulphuric acid-potassium chromate solution. 

Potassium chromate solution a yellow precipitate of barium chromate, practically insoluble in water (3-2 mg t l, Ks = 16 x 10"10) ... 

The addition of acid to potassium chromate solution causes the yellow colour of the solution to change to reddish-orange, owing to the formation of dichromate ... 

Potassium chromate solution yellow precipitate of strontium chromate ... 

Potassium chromate solution no precipitate from dilute solutions, nor from concentrated solutions in the presence of acetic acid (cf. Section III.31, reaction 6). 

Lead acetate solution white precipitate of lead sulphate, PbS04, soluble in hot concentrated sulphuric acid, in solutions of ammonium acetate and of ammonium tartrate (see under Lead, Section III.4, reaction 5), and in sodium hydroxide solution. In the last case sodium tetrahydroxoplumbate(II) is formed, and on acidification with hydrochloric acid, the lead crystallizes out as the chloride. If any of the aqueous solutions of the precipitate are acidified with acetic acid and potassium chromate solution added, yellow lead chromate is precipitated (see under Lead, Section III.4, reaction 6). 

Potassium chromate solution Treat 2 drops of the test solution with 1-2 drops K2Cr04 solution. Note the formation of a yellow precipitate.. Centrifuge and wash. Add 2 drops dilute acetic acid to the precipitate and stir note that the precipitate does not dissolve. 

Potassium chromate solution yellow precipitate of thallium(I) chromate, Tl2Cr04, insoluble in cold, dilute nitric or sulphuric acid. 

Potassium chromate solution no precipitate (difference from thallium(I) salts). 

A potassium chromate solution being added to aqueous silver nitrate, forming silver chromate. 

Preparation of 0.1M Potassium Chromate Solution. Accurately weigh 1.942g of reagent grade K chromate into a 100-ml volumetric flask. Dilute to mark with distd w. Mix well... 

Stannous Chromate has been described by Berzelius as a yellow flocculent precipitate resulting on the addition of stannous chloride to an excess of potassium chromate solution. If, however, dilute potassium chromate solution is added in small portions, wdth constant shaking, to stannous chloride, a greenish-white precipitate is produced which is probably chromic stannate. If the tin solution contains free acid the whole remains dissolved, forming a green solution. 

Colorimetric comparisons have also been made with green chromium-chloride solutions, and it is found that, in general, the sensitiveness is similar to that of potassium chromate solutions. 

Mohr titration, which involves the formation of a coloured precipitate by reaction with the indicator. For example, in the determination of chloride concentration with silver nitrate a small amount of potassium chromate solution is added as an indicator. This results in the formation of a red silver chromate (Ag2Cr04) precipitate at the end-point ... 

After the passage of the gas the liquid is evaporated in a platinum (or porcelain) capsule on the water bath to a volume of 2-3 ml. and then 2 drops of acetic acid are added and the evaporation continued almost to dryness. The residue is redissolved in 2-3 ml. water and again evaporated to dryness to decompose the sodium biacetate which is formed. The residue is once more dissolved in 2 ml. water, a drop of potassium chromate solution added and then titrated with N/40 silver nitrate. It is advisable to carry out a blank determination. The amount of phosgene present in the sample is calculated from the number of ml. of N/40 silver nitrate solution employed in titration. 

Determination of Chlorosulphonic Acid. About i gm. of the sample is introduced into a small glass bulb which is then sealed in the flame and weighed accurately. This bulb is then placed in a tall glass cylinder of about 150 ml. capacity, containing about 100 ml. water. The cylinder is stoppered tightly and shaken violently so as to break the bulb, and then allowed to stand until the cloud which first forms in the cylinder completely disappears. The contents are then transferred to a 500 ml. flask and made up to volume. 200 ml. of the solution are then titrated with a decinormal sodium hydroxide solution, to the methyl-orange end-point, so as to obtain the total hydrochloric and sulphuric acid content. In another 200 ml. the hydrochloric acid is titrated with a decinormal solution of silver nitrate in presence of a few drops of potassium chromate solution, after addition of excess of pure calcium carbonate. 

Table 1.2. Standard Values of Absorbency, A, for Standard Potassium Chromate Solution ...

When aqueous solutions of lead(ll) ion are treated with potassium chromate solution, a bright yellow precipitate of lead(ll) chromate, PbCr04, forms. How many grams of lead chromate form when a 1.00-g sample of Pb(N03)2 is added to 25.0 mL of 1.00 M K2Cr04 solution ... 

Figure 17.20 The solubility of lead chromate becomes lower as the concentration of the potassium chromate solution in which it is dissolved increases. The change is due to the presence of Cr04 - in both lead chromate and potassium chromate. 

---