Introduction
The purpose of this experiment is to assist one to learn how different equipment in the laboratory is being use when carrying out the experiment. It tests the level of accuracy required when using different apparatus for measuring the volume. For very approximate result of volume, a beaker or conical flask is preferred when measuring volumes of liquids.
Accurate methods of measurement
This is done by the use of burette, conical flask and pipette. These measuring apparatus are discussed below.
When a much more accurate measurement is required, always measuring cylinders are preferred Measuring cylinders, which are much more accurate than beakers and conical.
Also volumetric pipettes and volumetric flask the mostly used apparatus used when measuring accurate volume.
There is achieved by ensuring that the bottom of the meniscus is exactly marked by the liquid to be measured. To confirm that the meniscus has been reached, a piece of a white paper is the place behind the flask and sees the line at the eye-level. To be much more accurate, the flask should be filled with a small Pasteur pipette drop by drop till the correct mark is attained.
Exercise 1
In the exercise on water was used
Procedures to be followed:
- Fill the volumetric flask with distilled water.
- Fill the pipette by using the pipette filler. Never suck the solution up.
Part – B
Apart from using the volumetric flask to measure the accuracy of liquid, also the burette measures the accuracy. It is mainly used when the liquid to be measured, its volume is not known in advance. Always note the burette’s reading at the initial and at the final reading and the lower meniscus must be read correctly.
Results obtained
Exercise 3
Also only water was used in this experiment.
Procedures:
- Fill a 50 cm3 burette with distilled water. (start with 0.05 cm3)
- Read the start and end volume of the burette. Calculate the volume added.
Exercise 2
Now using the burette, the measured equal volumes are added into different beakers. Once the desired volume is closer, the solution is added slowly to reach at the mark.
Part – C Error analysis
In every measurement carried out, there is an error with created by various ways. We can do away with error since perfection is not guaranteed. Since errors are present, the only thing to be done is the estimation to arrive at the accuracy of the result. To determine the density of a liquid, it is done through weighing and then the following formula is applied.
Density =massvolume
Exercise 1
A sample tube is weighed on the analytical balance. The 5 cm3 of the water is pipetted using the volumetric pipette. Re-weighing is done and finally result recorded down in the table provide.
Since the density of water is known to be 1g/cm3 therefore the volume of the liquid can be easily calculated.
* The density of pure water = 1 g/cm3
Errors
It was stated above that determining the volume from its mass was more accurate than by measuring the volume directly, but how do we know this? The accuracy of a volumetric pipette, which is often written on the bulb of the pipette is typically within about ± 0.03 – 0.05 cm3. Larger pipettes are generally more accurate than smaller pipettes.
Since, in the above exercise you used only a 5 cm3 pipette, let us assume the error is
0.05 cm.
The percentage error of your pipette is given by:
percentage error=errorvolume*10
=0.05 cm3*100%5 cm3= 1%
A four figure balance has an error of ± 0.00005 g. Again, the percentage error is given by the equation:
Percentage error =
Error ×100%
Mass
=1g/cm3 * 50cm3
=50 g
Therefore % error =0.00005g50g*100%
=0.0004%
.
It is evidently that the percentage error in the mass of water is 1.5 times greater than the calculated one. This is because the mass of water is different when using different weighings and the weighing error is 650 times smaller. It is much accurate when measuring the volume than when weighing.
Experiment-2:
Qualitative Analysis
Introduction
This experiment helps to identify the chemical species present in a substance and find out how much of the substance is present. Therefore qualitative analysis is the only process that can be used to identify these materials present while quantitative analysis is the measurement on how much the substance is present.
This experiment helps to identify ten unknown aqueous solutions which are in their various chemicals behaviour while its objectives are to understand qualitative analysis, making detailed and accurate observation and know how to interpret the observations.
Materials:
- Ten test tubes
- Ten colourless aqueous solutions. (Na2CO3, H2O, HNO3, NH3, NaOH, AgNO3, KI. KIO3, Pb(NO3)2, KCl )
Procedure
- Mix the solutions together in a pair-wise fashion (i.e. 1 and 2, 1 and 3, 1 and 4, and so on) until you have mixed all possible pairs.
- Watch what happens very carefully and write your observations down in the grid provided (on the next page).
- Allow the mixed solutions to stand for a while, because some changes may occur over a period of time (i.e. not all reactions are instantaneous!).
- Carefully note down any changes that do happen.
- Repeat the above procedures until you have mixed all possible pair-wise combinations.
Result analysis
- Reactions of silver(I) ions with
Reactions of lead(II) ions with
Reaction of carbonates ions
When the carbonate ion reacts with acid, it liberates carbon dioxide gas:
Equation
CO32- + 2H+→CO2 + H2O
Reaction of iodid
Reactions of iodate ions
In addition to the above reactions, iodate ions react slowly with iodide ions to give a brown coloured solution of triodide ions. The rate of the reaction is
increased by adding acid.
Chemical equation: IO3- + 8I- + 6H+→3I3- + H20
Observation
A white precipitate of AgCl forms immediately on mixing solutions containing Ag+ and Cl− ions. Later the white precipitate of AgCl turns pink. On mixing, gave a white solid that turned pink on standing.
Experiment-3: Gravimetric Analysis.
Introduction
This method of quantitative analysis is used to determine the amount of substances present in a material after weighing. This method is very easy as it is always straight forward procedure.
Procedures
- Dissolve the pre-weighed sample.
- Dissolve the sample.
- Add an excess of precipitating agent
- Filter, dry and weigh the precipitate formed.
Aim
Objectives
- Accuracy in measurement.
- Using gravimetric analysis to determine the amount of a material.
Experiment
This experiment is to determine the amount of barium in a mixture of barium chloride, NaCl and barium chloride, BaCl2. This is achieved by precipitating barium from the solution the amount of barium (chemical symbol Ba) in a mixture of barium chloride, BaCl2 and sodium chloride (NaCl, common salt). Barium carbonate, BaCO3 which is insoluble in water is formed by adding potassium carbonate to the solution. Since barium carbonate, BaCO3 formed is completely insoluble in water; therefore barium can be easily precipitated, then drying it and finally weighed to determine the amount of barium.
Procedure
- Weight the sample of sodium chloride/barium chloride.
- Dissolve the sample in 20cm3 of distilled water.
- Dissolve 1.5g of potassium carbonate, K2CO3 in a separate beaker.
- Mix the two mixtures, by slowly adding the solution of potassium carbonate to the solution of the mixture.
- Stir the mixture for about 5 minutes till a white solid of BaCO3 is formed
- Filter to isolate the solid
- Wash the residue with 50 cm3 of distilled water then followed with 50 cm3 of alcohol.
- Allow the solid to settle for about 20 minute and the weigh it on an analytical balance.
Weighing result
Mass of barium carbonate
Interpreting the result;
=0.5g208.23g/mol
=0.0024 moles
- Reaction of barium chloride with potassium carbonate
BaCl2·2H2O + K2CO3 → BaCO3↓ + 2KCl + 2H2O.
Moles of Ba= atomic mass of Baatomic mass of BaCl2 *no. of moles
=137.34208.23*0.0024
=0.00158 moles
- mass of Ba =number of moles*RAM
=0.00158 * 137.34
=0.217g
Conclusion
During the experiment, excess of the precipitating agent is used in order to allow complete reaction to take place.
Volumetric analysis
Introduction
Volumetric analysis is used to determine the concentration of a solution. This is done by reacting a known volume of solution of unknown concentration with the unknown volume of known concentration. This technique is known as titration.
Materials
- Beaker
- 250 cm3 conical flask
- 5 cm3 pipette
- burette
Reagents
- acetic acid, CH3COOH
- Sodium hydroxide, NaoH.
- phenolphthalein indicator
- Titrate acetic acid with sodium hydroxide.
Equation
CH3COOH + NaOH → CH3COONa + H2O
Aim
Determine the amount of acetic acid in vinegar.
Procedure
- Wash a beaker with 5 cm3 of vinegar.
- Wash a volumetric pipette with vinegar
- Decant 20 cm3 of vinegar into a beaker.
- Pipette 5 cm3 of vinegar into a clean 250 cm3 conical flask
- Add 25 cm3 of distilled water into a conical flask
- Add 5 drops of phenolphthalein indicator
- Wash a 50 cm3 burette with 5 cm3 of the 0.1 mol dm-3 NaOH and discard it.
- Top up the burette with NaOH solution
- Then do titration with NaOH solution till the solution changes to pale pink colour.
Average volume of NaOH .
Average volume =titration 1+titration 2+titration 3+titration 44
=17.6+17.2+18.1+17.34
=17.55 cm3
Interpreting the results
=17.55 cm3*0.11000
=0.001755 moles
Equation
CH3COOH + NaOH → CH3COONa + H2O
=0.0017555*1000
=0.351 mol dm-3
Conclusion
Indicator in titration is used to show the neutral point of the reaction
Experiment-5: Titration with Iodine
Aim
Determine the concentration of iodine solution by volumetric analysis method.
Introduction
This purpose of this experiment is to determine the concentration of iodine solution by preparing a solution of sodium thiosulfate and by adding it to iodine solution which has unknown concentration.
Procedure
- Weigh 2.5 g of sodium thiosulfate using an analytical balance.
- Dissolve it in distilled water to make a solution and add it into a 250 cm3 volumetric flask.
- Invert the flask severally to ensure a homogeneous solution.
- Add sodium thiosulfate solution into a 50 cm3 burette.
- Pipette 10 cm3 of standard iodine solution into a conical flask.
- Titrate the iodine solution with sodium thiosulfate solution till the end-end point is reached where the colour changes to colourless. Add few drops of starch indicator to have a sharper colour change.
Result:
- Average volume of sodium thiosulfate use:
=titration 1+titration 2+titration 3+titration 44
=15.77 cm3
Interpreting the results
=2.5g248.5g/mol
=0.01006 moles
Concentration of sodium thiosulfate solution
Chemical equation
2Na2S2O3 + I2 → Na2S4O6
N o moles = volume (cm3 ) × concentration (mol dm )
1000
Mole ratio = 1:2
=0.01006*100015.77
=0.638 M
(iii) Number of moles of sodium thiosulfate added to the iodine solution
N o moles = volume (cm3 ) × concentration (mol dm )
1000
250*0.6381000
= 0.1595
=0.1595-0.01006
=0.14944 moles
- It is indicated from the balanced equation that the mole ration between sodium thiosulfate and iodine is 1:2, therefore basing on this ratio, the number of moles of iodione present in 10 cm3 can be calculated as follows. Mole ratio =1:2
=0.01006 * 0.5
=0.00503 moles
- Concentration of iodine can be calculated using the number of moles and the volume by this equation
Molarity =moles*100010
=0.00503*100010
=0.5 M
Conclusion
The experiment carried out the volumetric analysis to determine the concentration of iodine through titration method.
The reaction of thiosulphate with iodine during titration gives a pale colour which is not easy to determine the end-point of the reaction. Therefore the use of starch indicator clearly indicates the end-point by changing to deep blue in the presence of iodine.
Experiment-6: Complexometric Titration
Introduction
Complexometric Titration is a method that is used to quantify the amount of calcium in milk also can be used to determine the hardness of water which is caused by the presence of calcium carbonate compound.
The calcium ions react with ethylenediaminetetraacetic acid to form a calcium-EDTA complex. This complex compound formed stops further reaction to occur.
M = Ca
Chemical equation: Ca2+ + EDTA4− [Ca-EDTA] 2−
These Ca2+ ions are detected by the use of Calconcarboxylic acid which changes to blue from pink-red when the Ca2+ ions are detected.
Reagents used:
- Milk
- EDTA
Procedure
- Weigh 4.65 g of disodium EDTA
- Dissolve EDTA in 500 cm3 of distilled water in a volumetric flask.
- Pipette 10 cm3 of milk into a 250 cm3 conical flask
- Dissolve 3.2 g of NaOH in 50 cm3 water and add this solution into a conical flask containing milk.
- Swirl the solution for 5 minutes
- Add 0.001g of Calconcarboxylic acid indicator while swirling to ensure complete dissolving
- Do milk tittration with EDTA solution till the colour changes from pink to red.
- Repeat the titration for two more time.
Result
Average volume used =17.6+17.2+18.1+17.34
=17.6 cm3
- Molarity of EDTA =massRMM
=4.65g292.24g/mol
=0.0159 M
No. moles=volume*molarity1000
17.6 cm3*0.01591000=0.000279 moles
- Molarity of Ca2+ ions in milk. This can be calculated by the use of mole ration from the chemical equation of the reaction.
Chemical equation: Ca2+ + EDTA4− [Ca-EDTA] 2−
Mole ratio = 1:1
Therefore the number of moles of calcium ions in milk is 0.000279 moles
Molarity of ca2+ =no. moles*1000volume
=0.000279*100010=0.0279 M
Experiment-7: Precipitation Titration
Introduction
This experiment shows how to yield a compound of limited solubility by using a silver nitrate as precipitating reagent. The method is also used to determine the ions of bromine, chlorine and cyanide.
The indicator to be used is potassium chromate. During the reaction, chromate ions react with silver ions forming a red-brown precipitate of silver chromate at the end-point.
Chemical equation
2Ag+ + CrO42− Ag2CrO4 (s)
Procedure
- Prepare a 5% solution of potassium chromate of 1.0 g.
- Dissolve it in 20 cm3 of distilled water.
- Prepare 250 cm3 of a 0.1 mol dm-3 of silver nitrate.
- Weigh ca. 0.2 g solid chloride and then place it in a 250 cm3 conical flask.
- Dissolve the weighed solid in 100 cm3 of distilled water then add sodium carbonate till the PH is 8. Use the PH paper to test it.
- Add 2 cm3 of K2CrO4 indicator.
- Do titration till first permanent appearance of silver chromate is observed
- Repeat the above steps for two time and record the results
Results
Result analysis
Average volume used=8.6+8.6+8.53=8.57 cm3
Silver ions react with chloride ions in a 1:1 ratio:
Ag+ + Cl− AgCl(s)
- no. moles of silver nitrate=vol. *molarity 1000
=8.57*0.1 1000=0.000857 moles
Using the mole ration from the above equation, the ratio is 1:1; therefore to get the number of chloride = 0.000857 moles
Experiment-8: Protein colour tests
Introduction
This experiment carried out was to investigate how to isolate a protein in milk (Casein) and carry out qualitative test to identify the presence of proteins through colour test.
- Isolation of casein.
Material:
Beaker, hot plate, weighing machine
Reagents
Skimmed milk, acetric acid, distilled water
Procedure
(i) Weigh a beaker and add 20 cm3 of skimmed milk.
(ii) Reweigh the beaker and determine the mass of milk added.
- Warm the milk on a hot plate about 50 oC.
- Add 10% acetric acid drop wise while stirring after removing the beaker from the heat.
- Stop stirring once all the casein precipitates.
- Filter off the casein with distilled water (30 cm3) and allow the solid to dry for one hour
- Weigh the casein.
- Protein colour tests
Material: test tubes,
Reagents: solution of glycine, tyrosine, gelatin, egg albumin, casein
Procedure
- Add 2cm3 of 10% sodium hydroxide to each test tube
- Add 5 drops of biuret reagent (5% copper sulphate CuSO4 solution)
- Record the observations.
Observation
A pink-violet colour was formed indicating the presence of a protein with at least two peptide bonds.
- Put 2 cm3 solutions of glycine, tyrosine, gelatin, egg albumin and casein into the first five test tubes.
- Add to each test tube 1 cm3 of 0.2% ninhydrin solution.
- Place the tubes in a beaker of water and heat to boil and note the observations
Observation
Ninhydrin turns a blue-violet colour indicating the presence of proteins
- Carefully add 10 drops of concentrated nitric acid.
- Place the test tube in a bath of boiling water and heat for 5 minutes
- Remove the test tubes from the bath and allow them to cool.
- Slowly add 10% of sodium hydroxide solution drop by drop till the solution becomes alkaline. Observe the colour changes.
Observation
The solution turned to yellow-orange in colour indicating the presence of tyrosine or tryptophan in the proteins. This test is known as xanthoproteic test.
Experiment-9: Extraction of DNA
Introduction
This experiment was to show how to extract the DNA which is a blueprint of life of each living thing. In this experiment, the DNA is isolated from vegetation (onion)
Reagents: buffer solution, sodium lauryl sulfate, sodium chloride, sodium cutrate and 0.3 g EDTA in 1 litre of deionised water
Procedure
Discussion
Sodium lauryl sulfate is used in the DNA extraction as it is a strong detergent that lowers surface tension of the liquid used, thus acting as an agent.
Sodium chloride it is used to provide sodium ion which will assist in blocking negative charges from phosphate of DNA. These ions neutralize the negative charges to allow the DNA molecules to be together for easy isolation.
Sodium citrate provides the sodium ions that neutralize negative charges produced by the DNA enabling it to be less soluble in the solution.
Procedure
- Cut a 50 g sample from the onion
- Cut small pieces of the onion sample and place them in a beaker.
- Add 50 cm3 of the extraction buffer, warm the beaker in a bath to 60 0C for 15 minutes.
- Remove it from the bath and cool it for 10 minutes.
- Filter and collect the liquid.
- Slowly add an equal volume of ice-cold isopropanol onto the liquid and allow the solution to sit for 5 minutes
- Draw the strands out of the solution by using the glass rod.
- Put the strand on the glass slide and let it dry and observe it through a microscope.
Observation
A white viscose strand of DNA will be formed between the two layers since the DNA is insoluble in isopropanol solution.
