%Document Headings.
\begin{document}
\title{A Redox Titration to Determine the Ethanol Content of Wine (8A/RTE)}
-\author{Sam White Lab Partner: Mihkel Raidal}
+\author{Sam White (Author) and Mihkel Raidal}
\date{05/12/2017}
%\date{\vhCurrentDate\\\vhCurrentVersion}
\maketitle
}
%
\section{Titration Results and Calculation of \si{\percent} ABV of Wine}
-A \SI{7.7910}{\gram} of \ce{(NH4)2Fe(SO4)2.6H2O} was dissolved in \SI{60}{\centi\metre\cubed} of \ce{H2SO4} and made up to \SI{200.00}{\centi\metre\cubed} with deionised water in a volumetric flask. Each \ce{(NH4)2Fe(SO4)2.6H2O} molecule liberates one \ce{Fe^{2+}} ion in solution, thus their concentrations in the solution are equal. The molar mass of \ce{(NH4)2Fe(SO4)2.6H2O} is \SI{392.139}{\gram\per\mole}.\footcite[Physical Constants of Inorganic Compounds, 4-46]{crc-handbook}
+A mass of \SI{7.7910}{\gram} of \ce{(NH4)2Fe(SO4)2.6H2O} was dissolved in \SI{60}{\centi\metre\cubed} of \ce{H2SO4} and made up to \SI{200.00}{\centi\metre\cubed} with deionised water in a volumetric flask. Each \ce{(NH4)2Fe(SO4)2.6H2O} molecule liberates one \ce{Fe^{2+}} ion in solution, thus their concentrations in the solution are equal. The molar mass of \ce{(NH4)2Fe(SO4)2.6H2O} is \SI{392.139}{\gram\per\mole}.\footcite[Physical Constants of Inorganic Compounds, 4-46]{crc-handbook}
%
\begin{displaymath}
\text{Moles of \ce{Fe^{2+}} in \SI{200.00}{\centi\metre\cubed} standard solution} = \frac{\SI{7.7910}{\gram}}{\SI{392.139}{\gram\per\mole}} = \SI{0.019868}{\mole}
\begin{equation} \label{eq:ethanol-cr2o72-}
\ce{3CH3CH2OH + 2Cr2O7^{2-} + 16H+ -> 3CH3COOH + 4Cr^{3+} + 11H2O}
\end{equation}
-During this the solution changed colour from orange (due to the \ce{Cr2O7^{2-}}) to dark green (due to the liberation of \ce{Cr^{3+}}). A back titration was then performed with the standard solution of \ce{Fe^{2+}} ions. The volumes used for this were half of those stated in the method since when the stated volumes were used the initial titre was very large and a maximum of two more titrations would have possible before the reaction mixture was exhausted. This would have been problematic if these two titres were not concordant since the completion of additional titrations would have been impossible.
+During this the solution changed colour from orange (due to the \ce{Cr2O7^{2-}}) to dark green (due to the liberation of \ce{Cr^{3+}}). A back titration was then performed with the standard solution of \ce{Fe^{2+}} ions. The volumes used for this were half of those stated in the method since when the stated volumes were used the titre was very large and a maximum of two more titrations would have possible before the reaction mixture was exhausted. This would have been problematic if these titres were not concordant since the completion of additional titrations would have been impossible.
%
\begin{table}[h]
\centering
\hline
1 & 2.20 & 18.40 & 16.20 \\
\hline
- 2 & 18.90 & 39.75 & 16.35 \\
+ 2 & 18.90 & 35.25 & 16.35 \\
\hline
3 & 3.10 & 19.50 & 16.40 \\
\hline
Hence the \si{\percent} ABV of ethanol of the wine was found to be $11.9 \pm 0.2 \si{\percent}$.
%
\section{Analysis of Results}
-The reported \si{\percent} ABV value of the wine is greater than that determined by experiment, however the reported \si{\percent} ABV value of wine is required to be accurate within $\pm\SI{1}{\percent}$\footcite[Annex XII]{eur-32011R1169-en}, hence there is a slight overlap between the possible error in the reported value and that of the determined value from \SIrange{12.0}{12.1}{\percent}. Despite this systematic errors are likely to have influenced the \si{\percent} ABV determined since this is at the extreme end of the uncertainty in the reported value, hence it is unlikely that the true \si{\percent} ABV value lies within this range.
+The reported \si{\percent} ABV value of the wine is greater than that determined by experiment, however the reported \si{\percent} ABV value of wine is only required to be accurate within $\pm\SI{1}{\percent}$\footcite[Annex XII]{eur-32011R1169-en}, hence there is a slight overlap between the possible error in the reported value and that of the determined value from \SIrange{12.0}{12.1}{\percent}. Despite this systematic errors are likely to have influenced the \si{\percent} ABV determined since this is at the extreme end of the uncertainty in the reported value, hence it is unlikely that the true \si{\percent} ABV value lies within this range.
-A possible error is that the ethanol might not have been fully oxidised to acetic acid hence reducing the amount of \ce{Cr2O7^{2-}} reacted and thus the \si{\percent} ABV value determined. To minimise this the reaction mixture could be refluxed for a longer (e.g. 2 hours). There may have also been a loss of ethanol and ethanal vapour while the reactants were being transferred into the round bottomed flask. To minimise this the flask could have been cooled in an ice bath during this process, hence reducing losses due to evaporation. There was also uncertainty about the end point for the second titration since the indicator colour change was not very distinct. To reduce this an alternative indicator such as 1,10-phenanthroline ferrous sulphate solution which would have more distinct colour change from blue-green to brown at the end point.\footcite[pp.~3]{senior-chem}
-%
+A possible error is that the ethanol might not have been fully oxidised to acetic acid hence reducing the amount of \ce{Cr2O7^{2-}} which reacted and thus the \si{\percent} ABV value determined. To minimise this error the reaction mixture could be refluxed for longer (e.g. 2 hours). There may have also been a loss of ethanol and ethanal vapour while the reactants were being transferred into the round bottomed flask. To minimise this the flask could have been cooled in an ice bath until the condenser was added, hence reducing losses due to evaporation. There was also uncertainty about the end point for the second titration since the indicator colour change was not very distinct. To minimise this an alternative indicator such as 1,10-phenanthroline ferrous sulphate solution could be used which would have more distinct colour change from blue-green to brown at the end point.\footcite[pp.~3]{senior-chem}
\end{document}
projects / chemistry / university-chemistry-lab-reports.git / commitdiff