Unit 2 Learning aim D: Review personal development of scientific skills for
laboratory work.
During this unit, I have partook in many procedures and techniques involving titration,
colorimetry, calorimetry and chromatography.
In learning aim A I undertook titration which is the process of determining the concentration of
an unknown solution using a solution of known concentration. In my case, I slowly added a
standardised solution of sodium carbonate (of known concentration) to a known volume of
hydrochloric acid with an unknown concentration until the reaction reached a neutralisation
point, (which was indicated through a colour change). I was then able to find out the
concentration of hydrochloric acid using the mass balance formula C1V1=C2V2, where C1 was
the concentration of the stock solution sodium carbonate, V1 is the volume of the sodium
carbonate, V2 is the volume of the hydrochloric acid dilution and C2 is the concentration of the
hydrochloric acid dilution. I also carried out another titration experiment to determine the
concentration of sodium hydroxide by volumetric pH titration of the hydrochloric acid (which was
standardised from the first experiment) using a calibrated pH meter. This involved me having to
draw a graph of change in pH with change in volume of acid to determine the equivalence point
(which is the point at which the solutions have been mixed in exactly the right proportions
relating to the chemical equation). Once I determined the equivalence point, I was able to
calculate the concentration of sodium hydroxide using the same mass balance formula of
C1V1=C2V2. I also undertook colorimetry, which is the process of determining an unknown
concentration of coloured compounds in a solution. In the experiment I conducted, I recorded
the measured absorbance of a series of sample solutions of known concentrations and plotted
them against their corresponding concentrations. From this, I produced a calibration graph
whereby the plot of absorbance versus concentration was linear (showing that Beer-Lambert
law was obeyed) and from this I calculated the concentration from the absorbance/ slope of the
best-fit line. In learning aim B I undertook calorimetry, which is the process of measuring the
amount of heat released or absorbed in a chemical reaction, change of state, or formation of a
solution, (1). I conducted two calorimetry experiments; the first experiment was to determine the
melting/freezing point of candle wax by collecting temperature data and producing a cooling
curve graph which could be analysed; the second experiment was to determine the rate of
cooling from a produced cooling curve graph of stearic acid. Finally, in learning aim C I
undertook chromatography, which is the technique of separating components within a mixture. I
undertook three individual experiments using two of the chromatography techniques, paper
chromatography of amino acids as well as paper chromatography of extracted plant pigments
and thin-layer chromatography of extracted plant pigments. I used the paper and thin-layer
chromatography techniques to separate said mixtures, which enabled me to identify the
components within these mixtures. In the first experiment and second experiments, identified all
the components within spinach leaves by observing the colours/pigments that were present in
spinach leaves (extracted plant pigments) and calculating their Rf value (with the first
experiment I used paper chromatography, and the second experiment I used thin layer
chromatography). In the third experiment, using paper chromatography, I identified the amino
acids present in the mixture by measuring the Rf values of the spots present and comparing
values of known standards.
laboratory work.
During this unit, I have partook in many procedures and techniques involving titration,
colorimetry, calorimetry and chromatography.
In learning aim A I undertook titration which is the process of determining the concentration of
an unknown solution using a solution of known concentration. In my case, I slowly added a
standardised solution of sodium carbonate (of known concentration) to a known volume of
hydrochloric acid with an unknown concentration until the reaction reached a neutralisation
point, (which was indicated through a colour change). I was then able to find out the
concentration of hydrochloric acid using the mass balance formula C1V1=C2V2, where C1 was
the concentration of the stock solution sodium carbonate, V1 is the volume of the sodium
carbonate, V2 is the volume of the hydrochloric acid dilution and C2 is the concentration of the
hydrochloric acid dilution. I also carried out another titration experiment to determine the
concentration of sodium hydroxide by volumetric pH titration of the hydrochloric acid (which was
standardised from the first experiment) using a calibrated pH meter. This involved me having to
draw a graph of change in pH with change in volume of acid to determine the equivalence point
(which is the point at which the solutions have been mixed in exactly the right proportions
relating to the chemical equation). Once I determined the equivalence point, I was able to
calculate the concentration of sodium hydroxide using the same mass balance formula of
C1V1=C2V2. I also undertook colorimetry, which is the process of determining an unknown
concentration of coloured compounds in a solution. In the experiment I conducted, I recorded
the measured absorbance of a series of sample solutions of known concentrations and plotted
them against their corresponding concentrations. From this, I produced a calibration graph
whereby the plot of absorbance versus concentration was linear (showing that Beer-Lambert
law was obeyed) and from this I calculated the concentration from the absorbance/ slope of the
best-fit line. In learning aim B I undertook calorimetry, which is the process of measuring the
amount of heat released or absorbed in a chemical reaction, change of state, or formation of a
solution, (1). I conducted two calorimetry experiments; the first experiment was to determine the
melting/freezing point of candle wax by collecting temperature data and producing a cooling
curve graph which could be analysed; the second experiment was to determine the rate of
cooling from a produced cooling curve graph of stearic acid. Finally, in learning aim C I
undertook chromatography, which is the technique of separating components within a mixture. I
undertook three individual experiments using two of the chromatography techniques, paper
chromatography of amino acids as well as paper chromatography of extracted plant pigments
and thin-layer chromatography of extracted plant pigments. I used the paper and thin-layer
chromatography techniques to separate said mixtures, which enabled me to identify the
components within these mixtures. In the first experiment and second experiments, identified all
the components within spinach leaves by observing the colours/pigments that were present in
spinach leaves (extracted plant pigments) and calculating their Rf value (with the first
experiment I used paper chromatography, and the second experiment I used thin layer
chromatography). In the third experiment, using paper chromatography, I identified the amino
acids present in the mixture by measuring the Rf values of the spots present and comparing
values of known standards.
