PRACTICAL PHYSICAL CHEMISTRY
MINUTES WASH IT WITH TAP WATER, THEN WITH HCL AND FINALLY WITH DISTILLED WATER 2 OR, SOAK THE VESSEL IN ‘CLEANING MIXTURE’ (EQUAL VOLUMES OF CONCENTRATED H SO AND SATURATED SOLUTION OF K CR O 7 OR NA CR O 7 (PREFERABLY THE LATTER) FOR SEVERAL HOURS POUR OFF THE MIXTURE AND WASH IT THOROUGHLY WITH TAP AND DISTILLED WATER PRESERVE THE CLEANING MIXTURE FOR SUBSEQUENT USE 3 OR, SOAK THE APPARATUS IN A MIXTURE OF CONCENTRATED SULPHURIC AND NITRIC ACIDS POUR OFF THE MIXTURE AND WASH THE APPARATUS THOROUGHLY WITH TAP AND DISTILLED WATER THIS METHOD IS VERY EFFICIENT FOR CLEANING VERY GREASY AND DIRTY APPARATUS AFTER CLEANING, THE APPARATUS MAY BE DRIED BY RINSING IT WITH LITTLE ACETONE AND PASSING A CURRENT OF WARM AIR FILTERED THROUGH THE COTTON WOOL PLUG VOLUMETRIC GLASSWARE SHOULD NEVER BE DRIED IN AN OVEN, FOR THE VOLUME OF THE APPARATUS IS LIABLE TO CHANGE APPARATUS OF BOROSILICATE GLASS, E G , PYREX, MAY BE DRIED IN AN OVEN AT 100-120°C 1 3 CALIBRATION OF VOLUMETRIC GLASSWARE ALL THE VOLUMETRIC GLASSWARE ARE NOW-A-DAYS CALIBRATED IN CM3 (ONE THOUSANDTH PART OF A LITRE; 1 LITRE = 1000 ML = ? 1000 028 CM3) AT THE MEAN ROOM TEMPERATURE (20°C) FOR ORDINARY PURPOSES THE VOLUME MARKED ON AN APPARATUS BY THE MANUFACTURER MAY BE CONSIDERED RELIABLE IN RELATIVE MEASUREMENTS, SUCH AS DOUBLE TITRATIONS, ANY ERROR IN THE VOLUME, IF PRESENT, GETS CANCELLED BUT FOR AN ACCURATE WORK ANY SUCH SMALL ERROR MUST BE DETERMINED, I E , THE APPARATUS MUST BE CALIBRATED 1 3 1 CALIBRATION OF VOLUMETRIC FLASK WEIGH ACCURATELY A THOROUGHLY CLEANED AND DRIED FLASK ON A ROBUST BALANCE FILL THE FLASK WITH AIR-FREE DISTILLED WATER (BOILED AND COOLED) SO THAT THE LOWER EDGE OF THE MENISCUS STANDS AT THE FIXED MARK ON THE NECK REMOVE ANY DROP OF WATER ABOVE THE MARK BY A PIECE OF FILTER PAPER DRY THE OUTER SURFACE AND WEIGH THE FLASK AGAIN AFTER HAVING DETERMINED THE WEIGHT OF WATER CONTAINED IN THE FLASK UPTO THE MARK, OBTAIN THE TRUE VOLUME OF THE VESSEL FROM THE TABLE GIVEN BELOW IN CASE THE ERROR IS CONSIDERABLE, ETCH A NEW RING ON THE NECK THE APPARENT SPECIFIC WEIGHT AND APPARENT SPECIFIC VOLUME OF WATER WEIGHED IN AIR TEMPERATURE °C APPARENT WEIGHT OF 1 CM3 OF WATER (G) VOL CORRES- PONDING TO AN APPARENT WT OF 1 G WATER (CM3) TEMPERATURE °C APPARENT WEIGHT OF 1 CM3 OF WATER (G) VOL CORRES- PONDING TO AN APPARENT WT OF 1 G WATER (CM3) ? 1 ? 1 3 2 CALIBRATION OF PIPETTES IT IS CARRIED OUT BY WEIGHING THE WATER THEY DELIVER FROM THE FIXED MARK THOROUGHLY CLEAN THE PIPETTE TO BE CALIBRATED BY ‘CLEANING MIXTURE’, AND THEN WASH WITH TAP WATER AND DISTILLED WATER SUCK THE AIR-FREE DISTILLED WATER INTO THE PIPETTE UPTO THE MARK AND DELIVER IT, KEEPING THE PIPETTE ALMOST UPRIGHT, INTO A WEIGHED SMALL FLASK WHEN THE LIQUID STOPS RUNNING, ALLOW THE PIPETTE TO DRAIN FOR ABOUT 15 SECONDS, TOUCH THE TIP OF THE PIPETTE AGAINST THE SIDE OF THE VESSEL SO AS TO REMOVE THE LAST DROP OF WATER WHICH COLLECTS AT THE TIP DETERMINE THE WEIGHT OF WATER DELIVERED BY WEIGHING THE FLASK AGAIN FROM THE WEIGHT OF WATER CALCULATE THE TRUE VOLUME OF THE PIPETTE 1 3 3 CALIBRATION OF BURETTES BURETTES ARE MOST SIMPLY CALIBRATED BY OSTWALD’S METHOD WITH THE HELP OF SMALL PIPETTE (GENERALLY 2 CM3), THE VOLUME OF WHICH HAS BEEN ACCURATELY DETERMINED ALTERNATIVELY, IT MAY BE CALIBRATED AS FOLLOWS : FILL THE WELL CLEANED BURETTE WITH AIR-FREE DISTILLED WATER, TAKING CARE THAT NO AIR BUBBLE REMAINS IN THE JET OF THE BURETTE CLAMP IT IN VERTICAL POSITION AND DELIVER 2 CM3 WATER FROM ZERO MARK IN A PREVIOUSLY WEIGHED SMALL FLASK DETERMINE THE WEIGHT OF WATER DELIVERED BY WEIGHING IT AGAIN WITHDRAW SUCCESSIVELY 2 CM3 WATER AND WEIGH AFTER EACH DELIVERY FROM THE WEIGHTS OF 2, 4, 6, 8 CM3 ETC ON THE BURETTE, CALCULATE THE CORRECT VOLUMES TABULATE THE DIFFERENCES (CORRECTIONS) CORRESPONDING TO 2, 4, 6, …, 50 CM3 ALSO PLOT A GRAPH BETWEEN THE BURETTE READING AS ABSCISSA AND CORRECTIONS AS ORDINATES (POSITIVE CORRECTIONS ABOVE AND THE NEGATIVE CORRECTIONS BELOW THE ABSCISSA AXIS) 1 4 CONCENTRATION OF SOLUTION THE CONCENTRATION OF DISSOLVED SUBSTANCE (SOLUTE) IN A SOLUTION IS DETERMINED BY THE AMOUNT CONTAINED IN A DEFINITE WEIGHT (OR VOLUME) OF THE SOLVENT (OR SOLUTION) THERE ARE DIFFERENT WAYS OF EXPRESSING CONCENTRATION OF SOLUTION 1 4 1 EXPRESSING CONCENTRATION IN PHYSICAL UNITS WHEN PHYSICAL UNITS ARE EMPLOYED THE CONCENTRATION OF SOLUTION IS GENERALLY EXPRESSED IN THE FOLLOWING WAYS : 1 IN TERMS OF WEIGHT OF THE SOLUTE PER UNIT VOLUME (LITRE OR DM3) OF SOLUTION : FOR EXAMPLE, 1 G OF NACL PER DM3 OF SOLUTION 2 IN TERMS OF PERCENTAGE COMPOSITION (WEIGHT/WEIGHT %) : IT IS EXPRESSED BY THE NUMBER OF WEIGHT UNITS (G) OF THE SOLUTE IN 100 WEIGHT UNITS (G) OF THE SOLUTION FOR EXAMPLE, 12% AQUEOUS SUCROSE SOLUTION CONTAINS 12 G OF SUCROSE IN 100 G OF SOLUTION FOR THIS, 12 G OF SUCROSE IS DISSOLVED IN 88 G OF WATER TO FORM 100 G OF SOLUTION 3 BY WEIGHT OF SOLUTE PER WEIGHT OF SOLVENT : FOR EXAMPLE, 7 G OF KCL IN 100 G WATER 4 PARTS PER MILLION (PPM) : THIS IS USUALLY USED FOR SOLUTIONS WHERE A SOLUTE IS PRESENT IN A EXTREMELY SMALL QUANTITY IT IS DEFINED AS PPM = × MASS OF SOLUTE MASS OF SOLUTION 1 4 2 EXPRESSING CONCENTRATION IN CHEMICAL UNITS IN TERMS OF CHEMICAL UNITS, CONCENTRATION MAY BE EXPRESSED IN ONE OF THE FOLLOWING WAYS : 1 IN TERMS OF MOLARITY : IT IS EXPRESSED BY THE NUMBER OF MOLES OF THE SOLUTE IN 1 LITRE (DM3) OF SOLUTION IT IS DENOTED BY THE LETTER M FOR EXAMPLE, 0 ? M SOLUTION OF OXALIC ACID (H C O 2H O , MOL WT 126) CONTAINS × ? = G OF THE ACID PER LITRE (DM3) OF SOLUTION 2 IN TERMS OF NORMALITY : IT IS DEFINED AS THE NUMBER OF GRAM EQUIVALENT WEIGHTS OF THE SOLUTE IN ONE LITRE (DM3) OF SOLUTION IT IS USUALLY DENOTED BY THE LETTER N FOR EXAMPLE, N SOLUTION OF OXALIC ACID (EQ WT 63) CONTAINS × = G OF THE ACID IN 1 LITRE (DM3) OF THE SOLUTION 1 N OXALIC ACID SOLUTION IS ALSO ONE-HALF MOLAR ( ) 0 ? M SOLUTION 3 IN TERMS OF MOLALITY : MOLALITY OF A SOLUTION IS EXPRESSED BY THE NUMBER OF MOLES OF THE SOLUTE PER KILOGRAM (1000 G) OF THE SOLVENT IT IS USUALLY DENOTED BY THE LETTER M FOR EXAMPLE, 180 G OF GLUCOSE (MOL WT 180) DISSOLVED IN 1 KG OF WATER WOULD GIVE 1 MOLAL (M) SOLUTION OF GLUCOSE 4 IN TERMS OF MOLE FRACTION OR MOLE PERCENT : THE MOLE FRACTION OF A COMPONENT IN A SOLUTION IS DEFINED AS THE NUMBER OF MOLES OF THAT COMPONENT DIVIDED BY THE TOTAL NUMBER OF MOLES OF ALL THE COMPONENTS IN THE SOLUTION THE SUM OF THE MOLE FRACTIONS OF ALL THE COMPONENTS OF A SOLUTION IS UNITY IN A BINARY SOLUTION THE MOLE FRACTION OF THE SOLUTE WILL BE = MOLES OF THE SOLUTE MOLES OF SOLUTE + MOLES OF SOLVENT AND THAT OF THE SOLVENT WILL BE = MOLES OF THE SOLVENT MOLES OF SOLUTE + MOLES OF SOLVENT FOR EXAMPLE, IF A SOLUTION CONTAINS 1 MOLE OF ETHANOL AND 3 MOLES OF WATER, THE MOLE FRACTION OF ETHANOL = + = ? = × ? = /( ) ( MOLE PERCENT ETHANOL), AND MOLE FRACTION OF WATER = + = ? = × ? = /( ) ( MOLE PERCENT WATER) 1 5 PREPARATION OF STANDARD SOLUTIONS PRECISION OF QUANTITATIVE CHEMICAL MEASUREMENTS SUCH AS VOLUMETRIC AND GRAVIMETRIC ANALYSIS, DEPENDS TO A LARGE EXTENT UPON THE PROCEDURES OF PREPARATION AND STANDARDIZATION OF REAGENT SOLUTIONS A STANDARD SOLUTION, I E , A SOLUTION OF PRECISELY KNOWN CONCENTRATION CAN BE PREPARED BY DISSOLVING A KNOWN (WEIGHED) AMOUNT OF THE SOLUTE INTO A KNOWN AMOUNT OF SOLVENT OR KNOWN VOLUME OF THE SOLUTION THIS METHOD OF PREPARING THE STANDARD SOLUTIONS IS LIMITED ONLY TO THE SUBSTANCES OF PRIMARY STANDARD GRADE A CHEMICAL IS SAID TO BE OF PRIMARY STANDARD GRADE IF IT IS OF HIGH PURITY ( %) 99 ? AND ITS COMPOSITION DOES NOT CHANGE ON EXPOSURE TO ATMOSPHERE SOME OF THE PRIMARY STANDARD GRADE CHEMICALS COMMONLY USED ARE : POTASSIUM DICHROMATE, SILVER NITRATE, FERROUS AMMONIUM SULPHATE, COPPER SULPHATE, SODIUM CARBONATE, OXALIC ACID, ARSENIUS OXIDE, POTASSIUM HYDROGEN PHTHALATE, POTASSIUM IODATE, SODIUM CHLORIDE, SODIUM OXALATE, ZINC SULPHATE ETC IN CASE OF CHEMICALS OTHER THAN THOSE OF PRIMARY STANDARD GRADE, STOCK SOLUTION OF SLIGHTLY OVER-STRENGTH IS PREPARED EXACT CONCENTRATION OF THE SOLUTION IS DETERMINED BY STANDARDISATION, I E , TITRATING ITS KNOWN VOLUME WITH A STANDARD SOLUTION OF A SUITABLE REAGENT A STANDARD SOLUTION OF DESIRED CONCENTRATION, OF COURSE ON DILUTION SIDE, CAN BE OBTAINED BY QUANTITATIVE DILUTION OF THE STOCK SOLUTION 1 SODIUM HYDROXIDE/POTASSIUM HYDROXIDE (0 ? N OR 0 OF CO2 FREE DISTILLED WATER KEEP THE SOLUTION IN A ALKALI RESISTANT BOTTLE THIS GIVES A SOLUTION OF NORMALITY GREATER THAN 0 STANDARDISATION : WEIGH OUT ABOUT 1 G OF A R GRADE POTASSIUM HYDROGEN PHTHALATE (KHC H O 4 - MOL WT 204 ? ) TO NEAREST 0 ? TO 0 ? MG, TRANSFER QUANTITATIVELY INTO A TITRATION FLASK AND ADD ABOUT 40 CM3 OF CO2 FREE WATER TITRATE THE SOLUTION WITH THE ALKALI SOLUTION, USING PHENOLPHTHALEIN INDICATOR, TO JUST APPEARANCE OF FAINT PURPLE COLOUR N (NAOH/KOH) = × ? × WT OF PHTHALATE (G) 204 22 TITRE (CM ) THE ALKALI SOLUTION MAY ALSO BE STANDARISED BY TITRATING WITH A STANDARD OXALIC ACID ( ) H C O 2H O SOLUTION USING THE SAME INDICATOR 2 HYDROCHLORIC/SULPHURIC ACID (0 ? N) : DILUTE ABOUT 9 CM3 OF CONCENTRATED HYDROCHLORIC ACID (11 ? N) OR 3 CM3 OF CONCENTRATED SULPHURIC ACID (36 N) TO 1 DM3 WITH DISTILLED WATER ADD SULPHURIC ACID GRADUALLY TO WATER AND NOT WATER TO THE ACID STANDARDISATION : WEIGH OUT 0 ? G OF PREVIOUSLY DRIED (AT 250°C) AND COOLED PRIMARY STANDARD GRADE SODIUM CARBORATE ( % 99 ? PURITY) TO THE NEAREST 0 ? MG TRANSFER THE SUBSTANCE CAREFULLY TO A TITRATION FLASK, ADD ABOUT 40 CM3 OF WATER AND 2-3 DROPS OF METHYL RED INDICATOR TITRATE THE CONTENTS WITH THE ACID SOLUTION TO JUST APPEARANCE OF RED COLOUR BOIL THE SOLUTION CAREFULLY, TO AVOID LOSS, UNTIL THE COLOUR IS DISCHARGED COOL THE SOLUTION AND TITRATE FURTHER, CONTINUE THE ALTERNATING ADDITION OF THE ACID SOLUTION AND BOILING UNTIL THERE IS APPEARANCE OF FAINT RED COLOUR THAT IS NOT DISCHARGED ON FURTHER BOILING N (HCL OR H SO 4) = × ? × WT OF NA CO (G) 52 99 TITRE (CM ) FOR ROUTINE WORK THE ACID SOLUTION CAN BE STANDARDISED BY TITRATION WITH A STANDARD SODIUM HYDROXIDE SOLUTION USING PHENOLPHTHALEIN INDICATOR 3 AMMONIA SOLUTION (0 ? M) : STRENGTH OF CONCENTRATED SOLUTION OF COMMERCIALLY AVAILABLE AMMONIA IS 14 ? N (APPROXIMATELY) VOLUME OF LIQUOR AMMONIA REQUIRED TO PREPARE 1 DM3 OF 0 ? N = ?× ? = 0 CM APPROX DILUTE 7 ? CM OF LIQUOR AMMONIA TO 1 DM3 (COOL THE LIQUOR AMMONIA BOTTLE USING CRUSHED ICE OR A REFRIGERATOR BEFORE REMOVING THE STOPPER) STANDARDISATION : STANDARDISE THE AMMONIA SOLUTION BY TITRATING WITH A STANDARDISED HYDROCHLORIC ACID SOLUTION USING METHYL ORANGE AS THE INDICATOR 4 POTASSIUM PERMANGANATE : (0 ? N IN ACIDIC MEDIUM OR 0 ? M) IN ACIDIC MEDIUM, KMNO4 (MOL WT 158 ? ) ACTS AS OXIDISING AGENT FOLLOWING THE HALF REACTION MNO 8H H O ? + ? + + + ?? + E MN EQUIVALENT WEIGHT OF KMNO4 = MOL WT = ? = ? 158 WEIGH OUT 3 ? G OF THE PERMANGANATE AND DISSOLVE IN 1 DM3 WATER HEAT THE SOLUTION TO BOILING, FILTER THROUGH GLASS WOOL AND STORE IN A DARK COLOURED BOTTLE STANDARDISATION : WEIGH ABOUT 0 ? G OF A R GRADE SODIUM OXALATE (MOL WT 134, EQ WT 67), DRIED AT 105-110°C AND COOLED IN A DESICCATOR, TO 0 1 0 ?? ? MG TRANSFER THE OXALATE QUANTITATIVELY TO 500 CM3 TITRATION FLASK, ADD 250 CM3 OF DILUTED H2SO4 (1 : 19) AND SHAKE WELL TO DISSOLVE THE OXALATE TITRATE THE SOLUTION WITH PERMANGANATE SOLUTION TO THE APPEARANCE OF FAINT PINK COLOUR WHICH PERSISTS FOR ABOUT 30 S N (KMNO4) = × × WT OF NA C O (G) 67 TITRE (CM ) 5 SODIUM THIOSULPHATE (0 ? M) : WEIGH OUT 25 G OF SODIUM THIOSULPHATE (NA S O 5H O) 2 AND DISSOLVE IN 1 DM3 CO2 FREE DISTILLED WATER, ALONGWITH 0 ? G OF NA CO STANDARDISATION : WEIGH 0 ? G OF DRY A R GRADE POTASSIUM DICHROMATE (MOL MASS 294 ? MG AND TRANSFER THE AMOUNT TO 250 CM3 TITRATION FLASK ADD ABOUT 100 CM3 WATER, 3 G POTASSIUM IODIDE AND 5 CM3 OF CONCENTRATED HCL SWIRL THE CONTENTS AND TITRATE WITH THE THIOSULPHATE SOLUTION, ADDING A FEW DROPS OF STARCH SOLUTION NEAR THE END POINT (STRAW COLOUR OF THE SOLUTION) UNTIL THE BLUE COLOUR CHANGES TO YELLOWISH GREEN N (NA S O ) = WT OF K CR O (G) 49 03 TITRE 2 × ? × (CM ) 6 FERROUS AMMONIUM SULPHATE, MOHR SALT (FESO (NH ) SO 6H O – 0 ?N OR 0 ?M) DISSOLVE 39 ? G (PRECISELY WEIGHED) OF THE MOHR SALT OF A R GRADE IN ABOUT CM OF WATER, ADD 10 CM3 OF CONCENTRATED H SO 4 AND DILUTE TO 1000 CM3 THIS GIVES 0 ?N MOHR SALT STANDARD SOLUTION THE SOLUTION IS NOT STABLE AND SHOULD BE STANDARDISED DAILY STANDARDISATION : TAKE 20 CM3 OF A STANDARD ( ) 0 ?N K CR O 7 SOLUTION IN A TITRATION FLASK, ADD ABOUT 100 CM3 OF WATER AND 20 CM3 OF CONCENTRATED H SO 4 ALLOW THE SOLUTION TO COOL, ADD 2-3 DROPS OF FERROIN INDICATOR AND TITRATE WITH THE MOHR SALT SOLUTION TO THE CHANGE OF GREENISH-BLUE TO PURPLE COLOUR PERSISTING FOR A FEW SECONDS N (MOHR SALT) = × NORMALITY (K CR O ) TITRE (CM ) 7 SILVER NITRATE (0 ? M, MOL WT 169 ? ) : DISSOLVE 4 ? OF A R GRADE SILVER NITRATE, WEIGHED NEAREST TO 0 ? MG, IN DISTILLED WATER TO 250 CM3 TO OBTAIN 0 ? M SOLUTION IF A R GRADE REAGENT IS NOT AVAILABLE, DISSOLVE 4 ? G OF AGNO3 (LABORATORY REAGENT GRADE) IN 250 CM3 OF DISTILLED WATER ALSO, WEIGH OUT 0 ? G OF A R GRADE NACL TO THE NEAREST 0 DISTILLED WATER AND 1-2 CM3 OF 5%, K CRO SOLUTION TO JUST APPEARANCE OF PERMANENT RED TINGE IT IS BETTER TO OBSERVE THE TINGE AGAINST A WHITE BACKGROUND N (AGNO3) = × ? × WT OF NACL (G) 58 44 TITRE (CM ) 8 POTASSIUM OR AMMONIUM THIOCYANATE (KCNS/NH4CNS – 0 ? M) : DISSOLVE ABOUT 9 ? G OF KCNS OR 7 ? G OF NH4CNS IN WATER TO 1 DM3 STANDARDISATION : PIPETTE 50 CM3 OF A STANDARD AGNO3 SOLUTION (SAY 0 ?N) INTO A CONICAL FLASK, ADD ABOUT 40 CM3 OF WATER, 2 CM3 OF CONCENTRATED NITRIC ACID AND ABOUT CM3 OF 8% FERRIC AMMONIUM SULPHATE SOLUTION AS INDICATOR TITRATE THE SOLUTION TO JUST APPEARANCE OF REDDISH-BROWN COLOUR, PERSISTING FOR ABOUT A MINUTE N (KCNS OR NH4CNS) = × N OF AGNO 9 IODINE (0 ? M) : WEIGH OUT ABOUT 13 G OF SUBLIMED IODINE, TRANSFER TO 1 DM3 VOLUMETRIC FLASK CONTAINING ABOUT 100 CM3 WATER AND 60 G OF POTASSIUM IODIDE SHAKE WELL TO DISSOLVE IODINE AND MAKE UP THE SOLUTION TO DM STANDARDISATION : PIPETTE OUT 50 CM3 OF THE IODINE SOLUTION INTO A TITRATION FLASK AND TITRATE WITH A STANDARD NA S O 2 3 SOLUTION, USING A FEW DROPS OF STARCH SOLUTION AS INDICATOR NEAR THE END POINT, UNTIL THE BLUE COLOUR JUST DISAPPEARS N (IODINE) = × N (NA S O ) TITRE (CM ) 2 CONCENTRATION OF AQUEOUS SOLUTION OF COMMON ACIDS AND AMMONIA REGENTS MOLARITY OF CONCENTRATED SOLUTION NORMALITY OF CONCENTRATED SOLUTION VOL REQUIRED TO MAKE 1 DM3 0 ? N (APPROX CM3) HYDROCHLORIC ACID 11 ? 11 ? 8 ? NITRIC ACID 15 ? 15 ? 6 ? SULPHURIC ACID 17 ? 35 ? 2 ? PHOSPHORIC ACID 14 ? 43 ? ACETIC ACID 17 ? 17 ? 5 ? AMMONIA 14 ? 14 ? PREPARATION OF A MIXTURE OF TWO MISCIBLE LIQUIDS (COMPOSITION IN MOLE FRACTION BEING KNOWN) MULTIPLY THE MOLECULAR WEIGHTS OF THE LIQUIDS BY THEIR RESPECTIVE MOLE FRACTIONS IN THE MIXTURE AND MIX THE QUANTITIES SO OBTAINED TO GET THE REQUIRED MIXTURE IF THE DENSITIES OF THE LIQUIDS ARE KNOWN, THEIR VOLUMES TO BE MIXED CAN BE CALCULATED BY DIVIDING THE ABOVE AMOUNTS BY THE RESPECTIVE DENSITIES LET M1 AND M2 BE THE MOLECULAR WEIGHTS AND D1 AND D2 THE DENSITIES ( ) G CM?3 OF THE TWO LIQUIDS IF MOLE FRACTIONS OF THE LIQUIDS IN THE MIXTURE ARE X1 AND X2, THEN AMOUNTS OF THE LIQUIDS TO BE MIXED ARE : W M X G = , W M X G = THEIR RESPECTIVE VOLUMES ARE : V M X D = / CM , V M X D = / CM THUS, TO PREPARE THE REQUIRED MIXTURE OF THE TWO LIQUIDS, MIX EITHER W1 AND W2 G OR V1 AND V2 CM3 OF LIQUIDS 1 AND 2 RESPECTIVELY IF THIS MIXTURE IS TOO MUCH, SUITABLE FRACTION OF THESE AMOUNTS MAY BE MIXED FOR EXAMPLE, IF A MIXTURE OF CH COOC H 5 AND C H OH (RESPECTIVE MOLE FRACTIONS BEING 0 ? AND 0 ?) IS TO BE PREPARED, THEN AMOUNT OF ETHYL ACETATE = ? × = ? 0 26 4 G = ? ? = ? 26 CM AT 20°C AND AMOUNT OF ETHANOL = ? × = ? 0 32 2 G = ? ? = ? 32 CM AT 20°C MIX 26 ? G OR 29 ? CM OF ETHYL ACETATE AND 32 ? G OR 40 ? CM3 OF ETHANOL, OR SOME SUITABLE FRACTION, OR MULTIPLE OF THESE AMOUNTS TO OBTAIN THE DESIRED MIXTURE 1 5 1 CALCULATION OF COMPOSITION OF A MIXTURE IN TERMS OF MOLE FRACTION SUPPOSE W W W , , G, ETC ARE THE AMOUNTS OF CONSTITUENTS 1, 2, 3, ETC OF THE MIXTURE AND M M M , , , ETC ARE THEIR RESPECTIVE MOLECULAR WEIGHTS THEN, NUMBER OF MOLES OF RESPECTIVE CONSTITUENTS IN THE MIXTURE WILL BE W M 1 / (SAY N1), W M / (SAY N2), W M / (SAY N3), ETC HENCE, MOLE FRACTION OF CONSTITUENT X W M W M W M N N N N = + + = + + + / / / MOLE FRACTION OF CONSTITUENT = + + = + + + / / / AND SO ON IF VOLUMES OF THE CONSTITUENTS OF THE MIXTURE ARE KNOWN, THEIR RESPECTIVE AMOUNTS CAN BE OBTAINED BY MULTIPLYING THE VOLUMES WITH RESPECTIVE DENSITIES AT THE TEMPERATURE OF THE EXPERIMENT 1 6 PREPARATION OF SOLUTIONS OF INDICATORS INDICATOR SOLUTIONS ARE PREPARED NORMALLY IN 0 ?% CONCENTRATION, I E , 0 ? G OF AN INDICATOR DISSOLVED IN 100 CM3 OF WATER OR ETHANOL MOST OF ORGANIC INDICATOR SUBSTANCES ARE AVAILABLE IN TWO FORMS : (I) SODIUM SALTS SOLUBLE IN WATER AND (II) FREE ACID FORM SOLUBLE IN ETHANOL BOTH FORMS OF INDICATORS CAN BE USED BUT SODIUM SALTS ARE PREFERRED FOR THE SAKE OF CONVENIENCE PREPARATION OF SOLUTIONS OF INDICATORS FREQUENTLY USED IS SUMMARIZED AS : 1 PHENOLPHTHALEIN (PH 8 ? COLOURLESS, PH 10 ? PURPLE OR PINK) : DISSOLVE 0 ? G OF INDICATOR IN 200 CM3 OF DISTILLED ETHANOL (95%) NEUTRALIZE, IF NECESSARY BY ADDING 0 ? M NAOH SOLUTION DROPWISE UNTIL A FAINT PINK COLOUR APPEARS, THEN JUST REMOVE THE PINK COLOUR WITH A DROP OR TWO OF 0 ? M HCL 2 METHYL ORANGE (PH 3 ? RED, PH 4 ? YELLOW) : DISSOLVE 0 ? G OF SODIUM SALT OF METHYL ORANGE IN 100 CM3 OF DISTILLED WATER 3 METHYL RED (PH 4 ? PINK, PH 6 ? G OF METHYL RED HYDROCHLORIDE IN 100 CM3 OF ETHANOL OR ABOUT 0 OF DISTILLED WATER 4 PHENOL RED (PH 6 ? YELLOW, PH 8 ? RED) : DISSOLVE 0 OF ETHANOL OR 0 ? G OF PHENOL RED SODIUM SALT IN 100 CM3 OF WATER ADD 0 ? M NAOH SOLUTION DROPWISE UNTIL THE COLOUR CHANGES TO ORANGE 5 BROMOPHENOL BLUE (PH 3 ? YELLOW, PH 4 ? BLUE) : DISSOLVE 0 ? G OF BROMOPHENOL BLUE IN ETHANOL OR ITS SODIUM SALT IN 100 CM3 OF WATER 6 THYMOL BLUE (PH 8 ? YELLOW, PH 9 ? BLUE) : DISSOLVE ABOUT 0 ? G OF THYMOL BLUE IN 100 CM3 OF ETHANOL OR 0 ? G OF ITS SODIUM SALT IN 100 CM3 OF WATER 7 FERROIN : DISSOLVE 1 ? G OF 1, 10 PHENANTHROLINE MONOHYDRATE AND 0 ? G OF FERROUS SULPHATE (FESO 7H O) IN 100 CM3 OF DISTILLED WATER THE INDICATOR SOLUTION IS ALSO COMMERCIALLY AVAILABLE 8 LITMUS SOLUTION (BLUE) : DISSOLVE 0 ? G OF THE SOLID COMPOUND IN 100 CM3 OF DISTILLED WATER 9 LITMUS SOLUTION RED : ADD A DROP OR TWO OF DILUTE HCL TO THE ABOVE BLUE LITMUS SOLUTION UNTIL THE COLOUR CHANGES TO RED 10 METHYL VIOLET : DISSOLVE 0 ? G OF INDICATOR POWDER IN 25 CM3 OF 95% ETHANOL AND MAKE UP THE VOLUME TO 100 CM3 WITH WATER 11 SODIUM DIPHENYLAMINE SULPHONATE : DISSOLVE 0 OF BOILED OUT DISTILLED WATER 12 N-PHENYL ANTHRANILLIC ACID : DISSOLVE 1 G OF THE ACID IN 5 CM3 OF 5% NA CO 3 AND DILUTE THE CONTENTS TO 100 CM3 WITH DISTILLED WATER 13 P-NAPHTHOLBENZOIN : DISSOLVE 1 G OF INDICATOR POWDER IN 100 CM3 OF ISOPROPANOL 14 DPD (N, N-DIETHYL-P-PHENYLENEDIAMINE) : DISSOLVE 0 ? G OF DPD OXALATE OR DPD SULPHATE (OR 0 ? G OF ANHYDROUS DPD SULPHATE) IN BOILED OUT DISTILLED WATER CONTAINING 1 CM3 OF DILUTE H SO 4 (1 PART OF H SO + PARTS OF WATER) 15 ERIOCHROME BLACK T : DISSOLVE ABOUT 0 ? G OF THE DYE STUFF IN 100 CM3 OF 95% ETHANOL OR METHANOL THE REAGENT IS STABLE ATLEAST FOR A MONTH 16 CALCON INDICATOR : DISSOLVE 0 ? G OF DYE STUFF IN 50 CM3 OF METHANOL 17 POTASSIUM CHROMATE INDICATOR : DISSOLVE 10 G OF POTASSIUM CHROMATE IN ABOUT 100 CM3 OF DISTILLED WATER ADD A FEW DROPS OF 2 ?% AGNO3 SOLUTION, SUFFICIENT TO PRECIPITATE ANY CHLORIDE (BRICK-RED PPT) FILTER OUT THE PRECIPITATE 18 FERRIC ALUM : DISSOLVE 25 G OF FE SO SO H O ( ) (NH ) 4 IN 100 CM3 OF HOT DISTILLED WATER ADD 10 CM3 OF A R NITRIC ACID AND BOIL UNTIL YELLOW COLOURED SOLUTION IS OBTAINED COOL AND FILTER THE SOLUTION 19 POTASSIUM FERRICYANIDE : DISSOLVE 5 ? G OF THE SUBSTANCE IN 100 CM3 OF DISTILLED WATER 20 STARCH : PREPARE A PASTE OF 0 ? ? ? G OF SOLUBLE STARCH (A R ) WITH DISTILLED WATER ADD THE PASTE TO ABOUT 100 CM3 OF BOILED OUT WATER WITH CONSTANT STIRRING BOIL FOR ABOUT 5 MINUTES, AND COOL THE INDICATOR SOLUTION MUST BE ADDED NEAR THE END POINT OF TITRATION 1 6 1 DRYING AGENTS SOLID SUBSTANCES ARE USUALLY DRIED IN AIR OR IN VACUUM DESICCATOR, BUT FOR DRYING ORGANIC LIQUIDS DIFFERENT TYPE OF DRYING AGENTS ARE USED THE DRYING AGENT SELECTED FOR THE PURPOSE SHOULD NOT REACT WITH THE ORGANIC LIQUID TO BE DRIED THE ORGANIC LIQUID IS PLACED IN CONTACT WITH THE DRYING AGENT FOR SEVERAL HOURS WHEREBY THE MOISTURE IS ABSORBED BY THE DRYING AGENT BY MEANS OF DECANTATION OR FILTERATION THE DRY LIQUID IS SEPARATED FROM THE DRYING AGENT A FEW OF COMMONLY USED DEHYDRATING AGENTS ARE MENTIONED BELOW : 1 MAGNESIUM SULPHATE (MGSO ) 4 : IT IS AN EXCELLENT NEUTRAL DESICCANT, CHEMICALLY INERT AND VERY EFFICIENT, AND WIDELY USED FOR GENERAL DRYING PURPOSES IT FORMS HEPTAHYDRATE I E , ABSORBS 7 MOLES OF WATER PER MOLE 2 CALCIUM SULPHATE (CASO ) 4 : ITS DRYING ACTION IS VERY FAST IT IS VERY EFFICIENT BUT IT HAS LOW DRYING CAPACITY AS TWO MOLES OF IT COMBINE WITH ONLY ONE MOLE OF WATER TO FORM SEMIHYDRATE, 2CASO4 H O 3 SODIUM SULPHATE (NA SO ) 4 : ALTHOUGH IT HAS GOOD CAPACITY TO ABSORB WATER FOR IT FORMS HEPTAHYDRATE (NA SO 7H O) AND DECAHYDRATE (NA SO 10H O) BUT IT IS SLOW IN ACTION IT IS PARTICULARLY USED TO DRY ETHERS 4 CALCIUM CHLORIDE (CACL ) 2 : IT HAS BOTH GOOD EFFICIENCY AND CAPACITY BUT CANNOT BE USED TO DRY ALCOHOLS, AMINES, AMINO ACIDS, AMIDES, ALDEHYDES, KETONES AND ESTERS–ALL OF THESE REACT WITH IT IT IS ESPECIALLY RECOMMENDED TO DRY HYDROCARBONS AND HALIDES 5 POTASSIUM CARBONATE (K CO ) IT IS FAIRLY GOOD DRYING AGENT FORMING DIHYDRATE (K CO 2H ) 2O 6 METALLIC SODIUM : SODIUM REACTS WITH WATER TO FORM NAOH AND H2, AND IT IS USED TO DRY SOME ORGANIC SOLVENTS SUCH AS ETHERS, BENZENE, ETC 1 6 2 PURIFIED WATER FOR CARRYING OUT QUANTITATIVE CHEMICAL MEASUREMENTS IN SCIENCE AND INDUSTRIAL LABORATORIES WATER OF HIGH LEVEL OF PURITY MUST BE EMPLOYED FOR MANY YEARS THE ONLY METHOD OF PURIFICATION AVAILABLE WAS BY DISTILLATION AND DISTILLED WATER WAS UNIVERSALLY EMPLOYED FOR ANALYTICAL PURPOSES IN RECENT DECADES OTHER METHODS INVOLVING THE USE OF ION EXCHANGE RESINS AND REVERSE OSMOSIS HAVE BEEN WIDELY USED TO OBTAIN PURIFIED WATER IN CATION EXCHANGER, H+ IONS EXCHANGE FOR CATIONS AND IN ANION EXCHANGER OH? IONS EXCHANGE FOR ANIONS GIVING RISE TO THE FORMATION OF DEIONISED OR DEMINERALISED WATER HOWEVER, THE PROCESS DOES NOT REMOVE THE UNCHARGED ORGANIC MOLECULES PROFESSIONAL ORGANISATIONS SUCH AS AMERICAN CHEMICAL SOCIETY, THE BRITISH STANDARD 3978 (1987), ISO 3696 (1987), ETC CLASSIFY PURIFIED WATER INTO THREE GRADES I TO III, DEPENDING UPON THE LEVEL OF PURITY 1 GRADE III : IT CAN BE PREPARED BY DISTILLED OF TAP WAER, BY DEIONISATION THROUGH ION EXCHANGE RESINS OR BY REVERSE OSMOSIS WATER OF THIS GRADE IS SUITABLE FOR ORDINARY ANALYTICAL PURPOSES 2 GRADE II : WATER OF THIS QUALITY IS OF HIGH LEVEL OF PURITY AND CAN BE PREPARED BY REDISTILLATION OF GRADE-III WATER IT IS REQUIRED FOR MORE SENSITIVE ANALYTICAL DETERMINATIONS SUCH AS ATOMIC ABSORPTION SPECTROSCOPY, SUBSTANCES PRESENT IN TRACE AMOUNTS 3 GRADE-I : WATER OF THIS GRADE IS ULTRA PURE AND CAN BE OBTAINED BY REDISTILLATION OF GRADE-II WATER IN A STILL CONSTRUCTED FROM FUSED SILICA IT CAN ALSO BE PREPARED BY SUBJECTING GRADE-II WATER TO REVERSE OSMOSIS OR DE-IONISATION WATER OF SUCH A HIGH LEVEL OF PURITY IS USED FOR THE MOST STRINGENT REQUIREMENTS INCLUDING HIGH PERFORMANCE LIQUID CHROMATOGRAPHY AND DETERMINATION OF SUBSTANCES PRESENT IN ULTRA TRACE QUANTITIES 1 7 TEMPERATURE CONTROL THERMOSTAT MANY PHYSICAL PROPERTIES SUCH AS SURFACE TENSION, VISCOSITY, RATE CONSTANT, EQUILIBRIUM CONSTANT, OSMOTIC PRESSURE, VAPOUR PRESSURE, ETC ARE TEMPERATURE DEPENDENT, AND MUST THEREFORE, BE MEASURED AT A KNOWN TEMPERATURE CONTROLLED TO WITHIN ± ? ° 0 01 C OR BETTER LIQUID NITROGEN AT ITS NORMAL BOILING POINT (77 ? K OR ? ?° 195 8 C), DRY ICE-ACETONE BATH, SOLID CARBON DIOXIDE IN EQUILIBRIUM WITH CO2 VAPOUR AT 1 ATM ( ) ? ?° 78 5 C , ICE BATH (ICE IN EQUILIBRIUM WITH WATER AT 0°C), OR MIXTURES OF CRUSHED ICE WITH SALTS (FREEZING MIXTURES) ARE SOME LOW TEMPERATURE BATHS AN IMPORTANT METHOD OF ACHIEVING TEMPERATURE CONTROL IS TO USE A THERMOSENSING DEVICE WITH A FEEDBACK SYSTEM TO CONTROL THE INPUT OF HEATER (OR OF REFRIGERATOR) TO A BATH SO THAT THE TEMPERATURE IS MAINTAINED TO ANY DESIRED ARBITRARY VALUE WITHIN A NARROW RANGE SUCH A DEVICE, KNOWN AS THERMOSTAT, CONSISTS MAINLY OF THE FOLLOWING PARTS : (I) BATH, (II) STIRRER, (III) HEATER (OR REFRIGERATOR), (IV) THEREMOREGULATOR AND (V) RELAY THE BATH CONSISTS OF A LARGE RECTANGULAR TANK OF SUITABLE SIZE (MOST COMMONLY USED SIZE – 45 BY 75 CM IN HORIZONTAL AREA AND 45 CM DEEP) MADE UP OF GLASS OR METAL (STAINLESS STEEL) WITH GLASS WINDOWS IN TWO OR MORE SIDES THE TANK IS FILLED WITH WATER FOR TEMPERATURES UPTO 60°C, OR A SUITABLE OIL SUCH AS HEAVY CYLINDER OIL UPTO 300°C, OR SILICONE OIL FOR HIGHER TEMPERATURES A METALLIC STIRRER OR A CENTRIFUGAL LIQUID CIRCULATION DRIVEN BY AN ELECTRIC MOTOR PROVIDES A GOOD STIRRING OF THE LIQUID IN THE TANK