DPS – MIS, DOHA- QATAR

Chemistry Lab Record

Chemistry Lab Record Index S No

Date

Experiment

1.

10/04/23 Crystallization of impure sample of copper sulphate.

2.

Determination of the strength of given NaOH solution with the help of standard solution of oxalic acid. Determination of the strength of given HCℓ solution with the help of standard solution of sodium carbonate. 16/04/23 Determination of the boiling point of an organic substance 16/04/23 Determination of the melting point of an organic substance

3.

4. 5.

Teacher’s Signature

CRYSTALLIZATION OF IMPURE SAMPLE OF COPPER SULPHATE

Aim: To crystallize impure sample of copper sulphate.

Materials Required: Beaker, China dish, Glass rod, Funnel, Tripod stand, Wire gauze, Filter paper, Mortar and pestle, Blue vitriol and Distilled water.

Theory: The chemical formula of blue vitriol is Cu2SO4.5H2O. This is also known as blue stone. This is of blue colour. The chemical name of this compound is copper sulphate. Crystals of blue vitriol can be obtained by the process of crystallization from the given impure sample. Use of blue vitriol: It is used as fungicide, herbicide and pesticide.

Procedure: Preparation of saturated solution of impure sample  Take about 10gm of given sample of copper sulphate.  Grind it to make powder.  Take a beaker and put copper sulphate powder in it.  Add about 50ml of distilled water and about 3 to 4ml of dilute    

sulphuric acid. (Addition of sulphuric acid prevents the hydrolysis of copper sulphate to cupric hydroxide). Stir the solution to mix blue vitriol and water. Now put the beaker on a tripod stand and start heating gently. Stir the solution continuously while heating. Heat the solution kept in beaker for about 2 to 3 minutes.

Filtration of hot solution:  Filter the solution with the help of filter paper and collect the       

filtrate in a china dish or a beaker. For this, take a filter paper and fold it into half; followed by another fold to make a quadrant. Open this quadrant to make a cone of filter paper. Insert the cone (of filter paper) inside a funnel. Using a wash bottle, wet the filter paper with water. By gently pressing the cone, fix the filter paper inside the funnel. Place the funnel over a china dish with the help of clamp and stand. Ensure that the stem of the funnel touches the rim of china dish. Transfer the solution from beaker into the funnel, with the help of a glass rod. Collect the filtrate in the china dish. Observe residual impurities in the filter paper.

Concentration of filtrate:

 Now put the china dish with filtrate over a tripod stand and start heating it.  Heat the filtrate up to the crystallization point.

Checking the crystallization point:  For this, dip a glass rod in the concentrate.  Take out the glass rod and cool it by blowing air from your mouth.  Deposition of solid crust on the glass rod indicates crystallization point.  Stop heating and allow the china dish to cool.

Cooling the hot concentrated solution:  After some time place the china dish on a water bath to cool it completely.

 After cooling, crystals are formed.  A seed can also be used for facilitating crystallization. For this, tie a small grain of blue vitriol crystal to a thread and suspend this in the concentrated solution. Seeding hastens the rate of crystallization.

Separation of crystals:  Separate the mother liquor from the crystals of blue vitriol. This is done by decantation of mother liquor from the china dish.  Press the crystals of blue vitriol between filter papers to soak excess liquid.  Weigh the crystals and observe its colour.

Result: Deep blue triclinic crystals of copper sulphate are formed.

Molar mass of oxalic acid =126 g To prepare 100mL of 0.05M i.e. (M/20) solution of oxalic acid

Molarity of oxalic acid x Volume of standard flask x Molar mass of oxalic acid 1000

Weight = 1/20 x 100 x 126 1000

= 0.63 g

DETERMINATION OF THE STRENGTH OF GIVEN NAOH SOLUTION WITH THE HELP OF STANDARD SOLUTION OF OXALIC ACID

Aim: To determine the strength of a given solution of sodium hydroxide by titrating it against standard solution of oxalic acid.

Materials Required: Burette, Burette stand, Pipette (10ml), Funnel, Titration flask, Phenolphthalein, distilled water, standard oxalic acid solution and NaOH.

Theory: When an acid is titrated against a base, the amount of acid and base becomes chemically equivalent at the end point. This reaction is called neutralization reaction. The pH of the solution shows sudden change near the end point. At this stage, addition of even a small amount of base or acid changes the solution to alkaline or acidic respectively. When oxalic acid reacts with NaOH neutralization reaction occurs as follows: (COOH)2(aq) + 2NaOH(aq) → (COONa)2(aq) + 2H2O The concentration of an unknown solution is calculated in terms of g/L. It can be calculated as follows: a1M1V1= a2M2V2 wherein a1 , M1, V1 are respectively basicity, molarity and volume of acid used and a2, M2 and V2 are acidity, molarity and volume respectively of base used in the titration. The strength of the unknown solution can be calculated in terms of molarity as follows;

Observation

S.No

Volume of Oxalic acid

Volume of NaOH Initial Reading Final Reading 0mL ….

1.

10mL

2.

10mL

0mL

….

3.

10mL

0mL

….

Volume of oxalic acid pipetted out = 10mL Molarity of oxalic acid = 1/20M or 0.05 M Volume of NaOH = x Number of moles of NaOH = 2 Number of moles of Oxalic acid = 1 MNaOH x VNaOH ─────────── aNaOH

=

MNaOH x X ─────────── 2

MOxalic acid x VOxalic acid ─────────── aOxalic acid

=

1/20 x 10 ─────────── 1

Indicator used: Phenolphthalein End point: pink to Colourless

Procedure: Preparation of 0.05 M standard solution of Oxalic acid: Weighing oxalic acid crystals:

 First take the weight of clean and dry watch glass.  Then put oxalic acid crystals in it and weigh them.  Take the difference between total weight and weight of the watch glass and this will give the weight of oxalic acid crystals.

Transferring oxalic acid

 Carefully transfer oxalic acid from watch glass to beaker.  Wash down the oxalic acid crystals from watch glass which have stuck there and dissolve it completely.  Weigh the empty watch glass to find the exact weight of oxalic acid transferred to the beaker. This will help in calculating the exact molarity of solution.

Making solution:

 Transfer the content of the beaker on a measuring flask using a funnel.  Wash the walls of the beaker with distilled water to transfer sticking remains of oxalic acid in measuring flask.  Now fill the measuring flask just below the 100ml mark.  With the help of pipette bring the level to exactly 100ml mark.  Close the mouth of measuring flask with stopper and shake well.  Put a label on flask showing the molarity of the solution.

Molarity of NaOH = _______ M Strength of NaOH = Molarity of NaOH x Molar mass of NaOH = Molarity of NaOH x 40 = __________ g/L

Filling the burette with Oxalic acid solution

 Clean and wash a burette thoroughly with distilled water. After that, rinse the burette with oxalic acid solution. (It is important to rinse the burette with the solution, which is to be filled in it).  Clamp the burette vertically with a burette stand.  Fill the burette with oxalic acid solution with the help of a funnel; above the zero mark.  Run the solution forcefully from the burette nozzle. This is necessary to remove any air gap.  Remove the funnel before noting the initial reading of the burette. While doing this, ensure that no drop of the liquid is suspended from the nozzle.  Keep your eye in line with the meniscus level; while taking the initial reading.

Titration of NaOH and Oxalic acid solution

 Thoroughly clean and dry a conical flask and a pipette with distilled water.  After that, rinse the pipette with NaOH solution.  10 mL NaOH solution is pipetted in a clean conical flask.  2 drops of phenolphthalein are added to NaOH.  Flask is placed below the burette containing oxalic acid solution.  Lower meniscus of oxalic acid is noted in the burette.  Oxalic acid is run slowly, drop wise in the flask, containing NaOH solution. This is done till pink colour is disappeared.  Final reading in burette is noted.  These steps are repeated for more set of data.

Result: The strength of NaOH solution is -------g/L.

Calculations: Exp 5 Molar mass of Na2CO3 = 106 g To prepare 100mL of 0.05M i.e. (M/20) solution of Na2CO3=

Molarity of Na2CO3 x Volume of standard flask x Molar mass of Na2CO3 1000

Weight = 1/20 x 100 x 106 1000

= ----- g

DETERMINATION OF THE STRENGTH OF GIVEN HCℓ SOLUTION WITH THE HELP OF STANDARD SOLUTION OF SODIUM CARBONATE

Aim: To determine the strength of a given solution of HCℓ (Hydrochloric acid) by titrating it against standard sodium carbonate solution.

Materials Required: Burette, Burette stand, Pipette(10ml), Funnel, Titration flask, Methyl orange, distilled water, M/20 sodium carbonate solution and HCℓ.

Theory: The strength of hydrochloric acid is determined by titrating it against sodium carbonate solution. When HCℓ reacts with sodium carbonate, it undergoes neutralization as per following reaction: Na2CO3 (aq) + 2HCl (aq) → 2NaCl (aq) + H2O + CO2 Methyl orange; being a weak base; is used in this titration. Methyl orange is yellow in unionized form. In this reaction when the entire solution of sodium carbonate becomes neutralized, the last drop of acid added produces the pinkish red colour. Appearance of this colour marks the end point of the reaction. The strength pf the unknown solution of acid is calculated in g/L. This is calculated by multiplying its molarity with its molecular mass which is 36.5 The following equation of molarity is used for this calculation. a1M1V1 = a2M2V2 Here, a1 is basicity, M1 is molarity and V1 is the volume of the acid being used. Similarly, a2 is the basicity, M2 is the molarity and V2 is the volume of the base used. Indicator used: Methyl orange End point: Yellow to red.

S. No 1.

Volume of Sodium Volume of HCl carbonate solution Initial Reading Final Reading 10mL 0mL ….

2.

10mL

0mL

….

3.

10mL

0mL

…..

Volume of sodium carbonate pipetted out = 10mL Molarity of sodium carbonate = 1/20M or 0.05 M Volume of HCl = x Number of moles of Na2CO3 = 1 Number of moles of HCl = 2 MNa2CO3 x V Na2CO3 ─────────── = a Na2CO3

1/20 x X ─────────── 1

MHCl x VHCl ─────────── aHCl

=

MHCl x 10 ─────────── 2

Procedure: Preparation of 0.05 M standard solution of sodium carbonate: Weighing sodium carbonate:

 First take the weight of clean and dry watch glass.  Then put sodium carbonate in it and weigh them.  Take the difference between total weight and weight of the watch glass and this will give the weight of sodium carbonate.

Making solution:

 Transfer sodium carbonate from watch glass to beaker.  Wash down the sodium carbonate from watch glass, which have stuck there and dissolve it completely.  Transfer the content of in a measuring flask and wash the walls of the beaker to transfer sticking remains of sodium carbonate in measuring flask.  Now fill the measuring flask just below the 100ml mark.  With the help of pipette bring the level to exactly 100ml mark.  Close the mouth of measuring flask with stopper and shake well.  Put a label on flask showing the molarity of the solution.

Filling the burette with HCl solution     

Clean a burette with distilled water. Rinse the burette with HCl solution. HCl is filled in a clean burette; above the zero mark. Run the HCl solution to remove any air gap. Note down the initial reading of the burette.

Titration of HCl by standard solution of Sodium carbonate

 10 mL of M/20 sodium carbonate solution is pipetted in a clean conical flask.

Molarity of HCl = _............__M Strength of HCl = Molarity of HCl x Molar mass of HCl = Molarity of HCl x 36.5 = _............. g/L

 2 to 3 drops of methyl orange are put in a conical flask and the flask is placed below the burette.  Initial reading of burette is noted.  HCℓ is run dropwise in the flask containing sodium carbonate solution. This is done till the solution becomes pink or red.  Final reading of burette is noted.  These steps are repeated for more set of data.

Result: The strength of given HCℓ solution is -------g/L.

DETERMINATION OF THE BOILING POINT OF AN ORGANIC SUBSTANCE Aim: Determining the boiling point of an organic compound. Materials Required: Distillation flask, Thermometer, Water condenser, Iron stand with clamp, conical flask, Tripod stand, Cork, Burner, given liquid, pumice stone. Theory: The temperature at which the vapour pressure of a liquid becomes equal to the atmospheric pressure is called its boiling point. Boiling point of a liquid is always fixed at a given pressure. Presence of impurities will alter the boiling point of a liquid. Procedure: Fixing the apparatus  Take a distillation flask, water condenser, conical flask,iron stand with clamp, tripod stand, cork, thermometer and burner.  Keep the distillation flask on top of a tripod. Fix the flask in its position with the help of iron stand and clamp.  Take the given liquid in the distillation flask.  Keep 2-3 pumice stones in the flask.  Insert a cork with one hole in the neck of the flask.  Insert a thermometer through the cork.  The thermometer should be at the level of side tube of the flask.  Connect the condenser with the outlet tube of distillation flask.  Connect another end of the condenser with the conical flask.  Make the apparatus airtight to get the correct reading. This can be done with the help of petroleum jelly. Observation Calculate the average of the temperature t1 + t2 + t3 + t4 + t5 °C 5

Heating the compound to find out the boiling point  Start heating the flask slowly and stir it gently  Wait till the liquid begins to boil (rapid and continuous stream of bubbles are seen).  Note down the temperature when it becomes constant, after rising.  Note the temperature five times after the interval of 30 seconds.

Result  Atmospheric pressure:_______ mm of Hg.  Boiling point of the given liquid:________°C. Precautions  Handle the apparatus gently.  Heat the flask smoothly.  Do not forget to put the pumice stones in the flask otherwise liquid may bump while heating.  Make the apparatus airtight to get the correct reading.  Level of thermometer should be along the level side tube of distillation flask.  Record the temperature only when the liquid starts to continuously produce bubbles.  Take at least five reading to ensure accuracy.

DETERMINATION OF THE MELTING POINT OF AN ORGANIC SUBSTANCE Aim: Determining the melting point of an organic compound Materials required: Beakers, glass capillary tubes, porous plate, thermometer, tripod stand, stirrer, spatula, heating medium, and given organic substance. Theory: The temperature at which a substance starts changing from solid state to liquid state is called its melting point. All pure substances have fixed melting and boiling points. Presence of impurities will alter the melting point of a substance. It is important to remember that compounds and elements are pure substances. On the other hand, mixtures are impure substances. Pure substances have fixed melting point. Notes:  Kjeldahl’s flask, which is especially designed, is used to determine the melting point.  Water and paraffin are usually used as heating medium to determine melting point for substances which has melting point less than 100° C.  For substances which has melting point between 100-250° C. Conc H2SO4 is used to determine their melting points. Procedure Sealing the capillary tube  Take a capillary tube and heat its one end on the burner for a few seconds. This will help in sealing the capillary tube. Powdering the substance  The given substance is placed on a dry and clean porous plate  The substance is powdered well with the help of spatula

Filling the capillary tube  One end of the capillary tube is pushed into the powdered substance. Some of the substance enters the capillary tube.  The closed end of the capillary tube is tapped gently so that the substance collects near the sealed end.  Repeat above steps to fill more of the given substance. Fixing the capillary tube  Apparatus is arranged as shown in the figure. Beaker is filled about half with water or paraffin oil.  Thermometer is suspended in the beaker so that bulb of the thermometer dips in the heating solution.  Capillary tube is made wet with heating medium and brought alongside the thermometer.  The capillary tube sticks to thermometer because of surface tension of water. Determining the melting point  Thermometer; along with the capillary tube is lowered down further in the beaker  The beaker is heated gently.  Rise in temperature is recorded when the solid starts melting. Liquid is stirred from time to time.  Repeat the experiment with at least 5 sets of capillary tube to collect more data of melting point. Using Thiele’s tube This experiment can also be done using Thiele’s tube. In this case, beaker is replaced with Thiele’s tube. The side arm of the Thiele’s tube is heated over a low flame. Temperature is recorded when the solid begins to melt. Using Kjeldahl’s flask This experiment can also be done by using Kjeldahl’s flask. In this case, beaker is replaced with Kjeldahl’s flask. Kjeldahl’s flask is uniformly heated. This is done by revolving the flame around the bottom of the flask. A sand bath is also used for this purpose. Temperature is recorded when the solid begins to melt.

Observation and Calculation

t1 + t2 + t3 + t4 + t5 °C 5

Result The melting point of the given substance = _____° C

Precautions  Keep the open end of capillary tube above liquid level to avoid the heating liquid from entering the capillary tube.  Keep the lower end of the capillary tube and the thermometer at the same level.  The solid must be made into fine powder.  Packing of the powder should be uniform; without any air gaps.  Wipe out the extra substance sticking on outer surface of capillary tube.  Do not use more heating medium as it would waste time.  Tap the capillary tube gently to avoid breakage.  Keep the side arm of Thiele’s tube over gentle heat.  The bulb of the thermometer should not touch the container.  There should be side groove in the cork; to allow escape of vapours.