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Preparation of reagents: Stock/Bench Reagents Friday, February 4, 2011
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HOW TO PREPARE STOCK SOLUTION INTRODUCTION: Commercially produced chemical reagents such as acids and ammonia are highly concentrated solutions. For instance; commercial concentrated tetraoxosulphate (VI) acid, H2SO4 is approximately 18 – molar. In order to prepare solutions of lower concentrations for titration, and for qualitative analysis, a calculated volume of the concentrated solution is taken from the stock solution and then added to a specified volume of distilled water. However the volume of such a solution to be taken depends on the information provided by the manufacturer on the label pasted on the stock bottle. For instance; the label on the stock bottle of concentrated H2SO4.
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t 2011 (2) March (1) t February (1)
Interpretations
HOW TO PREPARE STOCK SOLUTION
(a) The specific gravity of 1.80 means that the stock solution is 1.80 times heavier than an equal volume of water; i.e. 1cm3 of the stock acid solution weighs 1.80g or 1000cm3 (1dm3) of stock solution weighs 1.80 x 1000 = 1800g.
(b) The 98% by mass means: 98g of the acid (solute) is in 100g of solution i.e. 100g of stock solution contains 98g of H2SO4. 1800g (mass of 1dm3 of solution) contains (98/100) * 1800= 1764g. i.e 1dm3 of stock solution contains 1764g of pure H 2SO4, therefore its mass concentration = 1764g/dm3. Hence, its molar concentration, C= 1764 per dm3/98g per mole = 18.0mole per dm3 I.e. the concentration of the stock solution is 18.0 molar H2SO4 General formula: How to calculate molar concentration. Generally, the original molar concentration, Co of a chemical substance of molar mass, M grams per mole in a commercial product of P% by mass and of density (or specific gravity) d gram per cm3 is given as Co = (10 * P * d)/M or Co = 10Pd/M Where Co = Molar concentration of stock reagent P = Percentage purity (% purity) d = density or specific gravity M = Molar mass Example: Calculate the molar concentration of commercial trioxonitrate (V) acid of specific gravity 1.42 and 70.0% of acid (HNO3 = 63.0) Co = ? P% = 70, d = 1.42, m = 63 Co = 10Pd = 10 * 70 * 1.42 =15.8mole per dm3 M 63 General formula: How to calculate volume of solution to be diluted. Take H2SO4 for example; prepare 500ml of 0.1m of H2SO4 from concentrated H2SO4 Specific gravity = 1.82, % purity = 97%, molar mass = 98 To know the concentration: Molarity = 10 * P * d = 10 * 1.82 * 97 =18.01M M 98 Then, the amount of H2SO4 required to prepare 0.1M H2SO4 in 500ml can be expressed as follows: C1V 1 = C2V 2 Where C1 = original concentration; V 1 = volume required from the original solution. C2 = concentration required, V 2 = volume of new concentration required. C1 = 18.01m, V 1 =?, C2 = 0.1m, V 2 = 500ml V1=C2V 2=0.1×500=2.78ml C1 18.01 Therefore, 2.78ml of concentrated H2SO4 will be required to prepare 0.1m of H2SO4 in 500ml. CONCENTRATED LIQUID ANALYTICAL REAGENTS REAGENT
% PURITY
R.M.M.
CH3COOH
99.5
60
S.G. SPECIFIC GRAVITY 1.05
NH3
35
17
0.88
HCl HF HNO3
36 48 70
36.5 20 63
1.18 1.18 1.42
HClO3
60
84.5
1.53
H3PO4
85
98
1.69
H2SO4
97 or 98
98
1.82
Side-Bench Reagents The following is a list of reagents required to carry out chemical analysis, and which should be readily available in reagent bottles on the side-bench in the laboratory. The directions for preparing the solutions are given. Note: When diluting any concentrated acid, always add Acid to Water – never add water to acid. Dilute HCl, 2 molar: Add 200cm3 of concentrated acid to 800cm3 of water. Dilute HNO3, 2 molar: Add 125cm3 of concentrated acid to 875cm3 of water. Dilute H2SO4, 1 molar: Add 55cm3 of the concentrated acid to 500cm3 of water, make up to 1dm3 with distilled water. Dilute Ethanoic (acetic) acid, 2 molar: Dilute 114cm3 glacial acids with water to 1dm3. Ammonia solution, 2molar: 153cm3 commercial product per dm3 Sodium Hydroxide, 2molar: Dissolve 80g of pellets (or solids) in distilled water and make up to 1dm3 with distilled water. Store in a reagent bottle with plastic stopper. Ammonium trioxocarbonate (IV) (NH4)2CO3, 2 molar: Dissolve 160g of commercial solid in a mixture of 200cm3 of conc. Ammonia solution and 800cm3 of water. Ammonium ethanedioate (oxalate): Make a saturated solution, filter, and use the filtrate. Barium chloride, 0.5molar: Dissolve 122g of solid in 1dm3 of water. Bromine water: Add 5cm3 of bromine to every 100cm3 of water shake well and store in amber coloured bottle. Bromine in tetra chloromethane (carbon tetrachloride), CCl: Add 5cm3 of bromine to every 1000cm3 of CCl4 solution. Shake well to dissolve, store in amber coloured (dark) bottle.
Calcium chloride, 0.5molar: Dissolve 55g of solid in water and make up to 1dm3. 2, 4-dinitrophenylhydrazine: Dissolve 2.0g of the solid in 10cm3 of concentrated H2SO4. Add this solution to 200cm3 of absolute ethanol, dilute to 500cm3 with water, thoroughly, allow to stand, then filter and use the filterate. Fehling’s solution A: Dissolve 35g of hydrated CuSO4 in water, add few drops of concentrated H2SO4 and dilute to 500cm3 with water. Fehling’s solution B: Dissolve 60g of pure NaOH and 173g of Rochette salt (sodium potassium tartar ate) in 500cm3 of water, filter if necessary. Mix equal volumes of Fehling’s solutions A and B just before use. Hydrogen peroxide: 20-volume commercial product; or dilute 200cm3 of 100-volume commercial product with water and make up to 1dm3. Store in a dark bottle. Lead ethanoate (acetate), 0.5molar: Dissolve 95g of solid in 500cm3 of water. Shake with about 5g of calcium hydroxide in 1dm3 water. Allow to stand for a few hours. Filter and use the filter ate. Iron (III) chloride: Dissolve 67g of the crystals in 200cm3 of water. Mercury (II) chloride, 0.25molar: Dissolve 7.0g of solid in 500cm3 of water Methyl orange indicator: Dissolve 1.0g of solid in 1.5dm3 of boiling water. Methyl red indicator: Dissolve 1.0g of solid in 600cm3 of ethanol, and dilute to 1dm3 with water. Phenolphthalein indicator: Dissolve 1.0g of the solid in 500cm3 of ethanol and 50cm3 with water. Potassium heptaoxodichromate (VI) (K2Cr2O7): Dissolve 1g of K 2Cr2O7 in a mixture of 200cm3 of water and 40cm3 of 1mol/dm3 H2SO4. Potassium tetraoxomanganate (VII) KMnO4(aq): Dissolve 1.5g of KMnO4 in a mixture of 400cm3 of water and100cm3 of 1mol/dm3 H2SO4. Store in amber coloured bottle. Potassium hexacyanoferrate(II), 0.25molar: Dissolve 105g of solid in 1dm3 of water. Potassium iodide, 0.5molar: Dissolve 83g of solid in 1dm3 of water. Silver trioxonitrate (V), 0.1molar: Dissolve 17g of solid in 1dm3 of water. Store in amber coloured (dark) bottle. Sodium trioxocarbonate(IV), 1.0molar: Dissolve 53g of solid in 500cm3 of water. Sodium hydrogen tetraoxophosphate(V), 1.0molar: Dissolve 60g in 500cm3 of water. Starch solution: Make a paste with 1.0g of soluble starch in a small amount of water and add about 100cm3 of boiling water. Boil the mixture for a while to obtain a clear solution. Prepare when ready to use. Tin(II) chloride, 1.0molar: Dissolve 56g of solid crystals in 500cm3 of 1.0molar HCl solution. To prevent oxidation, add a few pieces of tin metal. Barium trioxonitrate(V), 0.5mol/dm 3: Dissolve 130g of solid in 1000cm3 of water. Lime water (Ca(OH)2(aq): Dissolve 25g of Ca(OH)2 in 1dm3 of distilled water, shake, stir and then keep with tight cover for a day, decant the clear and colourless solution later filter and later keep the filtrate in a corked reagent bottle. Iodine solution: Dissolve 120g of solid iodine in 1000dm3 of distilled water to which 3.5g KI have been dissolved before. Disodium trioxosulphate(II) (Na2S 2O3.5H2O), 1mol/dm 3: Dissolve 248g of solid in 1dm3 of distilled water. Preparation of Reagents in %w/w, %w/v and %v/v Preparation of reagent in %w/w: It means a particular weight of a solute in 100g of solution. For example 98%w/w H2SO4 means: 98g of the acid (solute) is in 100g of solution, i.e. 100g of stock solution contains 98g of H2SO4. Preparation of reagent in %w/v: It means a particular weight of a solute in 100cm3 of solution. For example, 20%w/vNa2CO3 means: 20g of Na2CO3 in 100cm3 of solution. Preparation of reagent in %v/v: It means a particular volume of a solute in 100cm3 of solution. For example, 10%v/v acetone means: 10cm3 of acetone in 100cm3 of solution.
Posted by How to prepare reagents at 11:46 AM
10 comments: Prakash shai December 27, 2012 at 1:04 AM Barium Chloride is used in the purification of water saturated solution in caustic chlorine plants and also in the Barium Chloride Exporters India manufacture of heat treatment salts, case hardening of steel Reply
Robert Melon January 6, 2014 at 4:29 AM I would like to recommend your article on Barium Hydroxide. You can also refer Barium Hydroxide Manufacturers. for more information. Reply
Robert Melon January 11, 2014 at 3:02 AM Thank you for providing clear information on this. you can also refer Barium Chloride Manufacturer. Reply
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Worldofchemicals Media December 2, 2016 at 10:04 PM
Reply
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Idowu October 4, 2017 at 8:34 AM This is very instructive and educative. Reply
Unknown March 21, 2018 at 10:14 AM Thanks so much, it was detailed Reply
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