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Preparing, Diluting of solutions of different Strengths & safety measures while Handling them.
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Preparing, Diluting of solutions of different Strengths & safety measures while Handling them.

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  • Solvent substance which does the dissolving. Must b greater thm the 50% of the solution
  • 8. Dun use hands, since finger prints can add weight. Use tongs,tissue or other device.
  • Molality does no

Transcript

  • 1. Weighing & Preparation of Solutions of Different strengths & their Dilution AND Handling Techniques of Solutions 1
  • 2. We will discuss.. 1. Solutions 2. Measuring Chemicals 3. Different chemical concentrations 4. Dilution of stock solutions 5. Labelling 6. Lab safety 7. Conclusions 2
  • 3. • Solution uniform homogenous mixture of two or more substances i.e, solute and solvent. Solution= solute + solvent • Standard solution: very precise solution, usually to 3-4 significant figures, used in quantitative analysis or an analytical procedure. • Saturated solution: a solution that contains the maximum amount of a particular a solute that will dissolve at that temperature • Supersaturated solution: a solution that contains more solute than equilibrium condition allow; it is unstable & the solute may precipitate upon slight agitation or addition of single crystal 3
  • 4. Preparing Solutions Solutions of known concentration can be prepared in a number of different ways depending on the nature of the analyte and/or the concentration required: • Weighing out a solid material of known purity, dissolving it in a suitable solvent and diluting to the required volume • Weighing out a liquid of known purity, dissolving it in a suitable solvent and diluting to the required volume • Diluting a solution previously prepared in the laboratory • Diluting a solution from a chemical supplier. 4
  • 5. Weight Measurements Basic protocol 1: measuring mass using a top-loading Balance 1. Turn on balance and wait for display to read 0.0 g. 2. Place weighing vessel on the balance pan (e.g., creased weighing paper, weigh boat) 3. Press tare button so that display reads 0.0g. 4. Gently add the substance being weighed to the weighing sample. 5. Record mass. 6. Remove weighed sample. 7. Clean spills off balance with brush or absorbent laboratory tissue. Discard any disposable weighing vessel. 5
  • 6. Contd... • Basic protocol 2: measuring Mass using an analytical Balance 1. Turn on balance and wait for display to read 0.0000 g. 2. Check the level indicator & do not lean on table while weighing. 3. Place weighing vessel on the balance pan (e.g., creased weighing paper, weigh boat) 4. Close the sliding doors & wait for stability light indicator, indicating that the weight is stable. 5. Press tare button so that display reads 0.0g. 6. Gently add the substance being weighed to the weighing sample. 7. Record mass. 8. Remove weighed sample. 9. Clean spills off balance with brush or absorbent laboratory tissue. Discard any disposable weighing vessel 6
  • 7. Volume Measurements Micropipettes Volumetric or transfer pipettes 7
  • 8. Volumetric Containers 2. Volumetric flasks 1.Beakers & Erlenmeyer flasks 3. Graduated cylinders 8
  • 9. Procedure for preparing a solution of known concentration from a known amount of a solid material 9
  • 10. Procedure for preparing a solution of known concentration by dilution 10
  • 11. Common Practical Units for Reporting Concentration Name Units Symbol Molarity Moles of solute / litres of solution M Normality Number of EWs solute / Litre of solution N molality Moles of solute / Kg of solvent m Weight % g of solute / 100 g of solution % w/w Volume % mL of solute / 100 mL of solution % v/v Weight-to-Volume % g of solute / 100 mL of solution % w/v •Weight per unit volume e.g., g/L, mg/ml •Parts per million(ppm) or ppb 11
  • 12. 1. Molar solutions • Molarity is number of moles of a solute that are dissolved per liter of total solution. • A 1 M solution contains 1 mole of solute per liter total volume. Example: A 1M solution of H2SO4 contains 98.06 g of sulfuric acid in 1 liter of total solution. "mole" is an expression of amount "molarity" is an expression of concentration. 12
  • 13. Contd.. • "Millimolar", mM, millimole/L. – A millimole is 1/1000 of a mole. • "Micromolar", µM, µmole/L. – A µmole is 1/1,000,000 of a mole. HOW MUCH SOLUTE IS NEEDED FOR A SOLUTION OF A PARTICULAR MOLARITY AND VOLUME? (g solute ) X (mole) X (L) = g solute needed 1 mole L or FW X molarity x volume = g solute needed 13
  • 14. TO MAKE SOLUTION OF GIVEN MOLARITY AND VOLUME 1. Find the FW of the solute, usually from label. 2. Determine the molarity desired. 3. Determine the volume desired. 4. Determine how much solute is necessary by using the formula. 5. Weigh out the amount of solute. 6. Dissolve the solute in less than the desired final volume of solvent. 7. Place the solution in a volumetric flask or graduated cylinder. Add solvent until exactly the required volume is reached, Bring To Volume, BTV. 14
  • 15. 2. Normal Solutions • Normality is defined as the gram Eq.Wt. of the solute per L of the solvent. 1N sol. = 1 EW solute / 1L of sol. • Conc. Of acids and alkalis are usually expressed in this unit. • gram Eq.Wt. is the M.W divided by the no. of H+ or OH- ions released from 1 molecule of the acid or base, respectively in solutions. Eq. Wt. = MW of the substance / replaceable no. of H+ or OH15
  • 16. Example: 1N Sulphuric Acid M.W of H2SO4 = 98 g Each molecule of acid releases 2 H+ ions in solutions. Eq. Wt. = 98/2 = 49 So, 1L of 1N H2SO4 solution contains 49 g of H2SO4 Chemical M.W Eq. Wt. 1N of solution contains NaOH 40 1 40 g KOH 56 1 56g Na2CO3 106 2 53g HCl 36.45 1 45g 16
  • 17. 3. Molal solutions • Molality expresses the no. of moles per 1000 g or 1 Kg of solvent. • It is dependent on the density of solvent. • It is different from Molarity as the later refers to volume of the solution, which is temperature dependent. • Molal solutions are not usually used in biochemical exp. 18
  • 18. 4. Percent solution • Mass percent solutions are defined based on the grams of solute per 100 grams of solution. Example: 20 g of sodium chloride in 100 g of solution is a 20% by mass solution. • Volume percent solutions are defined as ml of solute per 100 mL of solution. Example: 10 mL of ethyl alcohol + 90 ml of H2O (making approx. 100 mL of solution) is a 10% by volume solution. • Mass-volume percent solutions are also very common. These solutions are indicated by w/v % & are defined as the grams of solute per 100 mL of solution. Example: 1 g of phenolphthalein in 100 mL of 95% ethyl alcohol is a 1 w/v % solution. 19
  • 19. 20
  • 20. 5. PPM and PPB ppm: The number of parts of solute per 1 million parts of total solution. ppb: The number of parts of solute per billion parts of solution. Example 5 ppm chlorine = 5 g of chlorine in 1 million g of solution, Or 5 mg chlorine in 1 million mg of solution, Or 5 pounds of chlorine in 1 million pounds of solution 21
  • 21. CONVERSIONS To convert ppm or ppb to simple weight per volume expressions: 5 ppm chlorine = 5 g chlorine = 106 g water 5 g chlorine 106 mL water = 5 mg/1 L water = 5 X 10-6 g chlorine/ 1 mL water = 5 micrograms/mL
  • 22. A COMPARISON OF METHODS OF EXPRESSING THE CONCENTRATION OF A SOLUTE CONCENTRATION OF SOLUTE (Na2 SO4 ) 2 4 AMOUNT OF SOLUTE AMOUNT OF WATER 1M 142.04 g Na2SO4 BTV 1 L with water 1m 142.04 g Na2SO4 Add 1.00 kg of water 1N 71.02 g Na2SO4 BTV 1 L with water 1% 10 g Na2SO4 BTV 1 L with water 1 ppm 1 mg BTV 1 L 23
  • 23. PREPARING DILUTE SOLUTIONS FROM CONCENTRATED ONES • Concentrated solution = stock solution • Use this equation to decide how much stock solution you will need: C1V1=C2V2 Where, C1 = concentration of stock solution C2 = concentration you want your dilute solution to be V1 = how much stock solution you will need V2 = how much of the dilute solution you want to make 24
  • 24. EXAMPLE • How would you prepare 1000 mL of a 1 M solution of Tris buffer from a 3 M stock of Tris buffer? – The concentrated solution is 3 M, and is C1. – The volume of stock needed is unknown, ?, and is V1. – The final concentration required is 1 M, and is C2. SUBSTITUTING INTO THE EQUATION: C1 V1 = C2 V2 3 M (?) 1 M (1000 mL) ? = 333.33 mL So, take 333.33 mL of the concentrated stock solution and BTV 1 L. – The final volume required is 1000 mL and is V2. 25
  • 25. Preparation of exact 1N HCL • Dilute 100 ml of HCl with water to 1 L. Mix well. • Prepare exact 1N sol. Of Na2CO3 by dissolving 5.30g anhydrous Na2CO3 in 100 ml H2O. • Phenolphthalein indicator – Dissolve 250 mg indicator in 50 ml of 50% alcohol. • Titration – Take 10ml of acid sol & 10ml H2O in a small beaker – Add 2-3 drops of indicator – Titrate with Na2CO3 sol from a 25ml burette till a faint red colour is obtained – Note the vol.(x ml) of base consumed at the end point 26
  • 26. Contd.. • Calculate the exact normality of the acid by formula – Normality of base X vol. of base = normality of acid X vol. of acid – So, the normality of HCl = 1x X/10 – Normality of base is 1 vol of base is x ml. • After calculating the exact normality of the acid, it is proportionately diluted with water to obtain to exact 1 normal sol. 27
  • 27. Exact 1N NaOH solution • Eq. Wt. Of NaOH is 40g So 40g dissolved in 1L of H2O fo approx. 1N sol. & used. • But for exact normality it is titrated against Oxalic acid sol.(6.3g in 100ml water) • Take 10ml oxalic acid + 10ml water in a beaker, add 2-3 drops of phenolpthalein indicator. Titrate against the NaOH from a burette till a faint red colour is obtained. • Calculate exact normality of sodium hydroxide sol as in case of acid & dilute proportionately with water to obtain exact 1N sol. 28
  • 28. • Do not use chemicals from unlabeled containers • Do not place labels on top of one another. • Label chemicals clearly and permanently. 29
  • 29. You make it- you label it 1. identity of contents 2. concentration 3. your name 4. date of preparation 5.Hazard alert (if applicable) An unlabeled container will become tomorrow’s 30
  • 30. Do NOT × eat, drink or smoke in the laboratory . × pipette by mouth × leave equipment using water, gas or electricity on overnight × Never add water to conc. Sulphuric acid 31
  • 31. ALWAYS  Keep your working area clean and tidy.  wear a lab coat & appropriate eye protection  Open bottles near window where ventilation is available.  wash hands after using any substances hazardous to health, on leaving the laboratory.  Handle conc. Acids & liquor Ammonia with care.  label containers & solutions.  keep broken glassware & sharps separate from other waste & dispose of in the appropriate containers  secure the tops of reagent bottles immediately after use 32
  • 32. Know the solutions & different conc. to represent them. Documentation, labeling & recording what was done Traceability SOPs & SPs Maintenance and calibration of instruments Stability and expiration date recorded Proper storage 33
  • 33. References Gallagher Sean R.; A.Wiley Emily; Current protocols, essential laboratory techniques; 2nd Ed. ; Wiley-Blackwell a John Wiley & sons, Inc. 34
  • 34. 35
  • 35. Your Question s 36