To learn how to prepare a standard solution.
To learn how to standardize a solution.
The process of determining the concentration or molarity of a solution with high accuracy is called standardization (Ernest, 2014). To standardize HCl acid solution, we react the solution with another solution whose has high accuracy concentration which is sodium carbonate solution of 0.060M (Ernest, 2014; Chemistry 104, 2005). Titration is often used in standardizing a solution (Chemistry 104, 2005). By adding a few drops of methyl orange indicator in the standard solution, we can determine how much of HCl solution is needed to change the colour from yellow to orange-pink, where the point of completion in titration is called end-point. (Chemistry 104, 2005)
A 100 mL beaker is used to accurately weigh about 1.3 g of the anhydrous solid sodium carbonate. The mass is recorded accurately.
A funnel (solid short stemmed funnel) is used to carefully transfer the sodium carbonate, a little at a time, into a 250 mL volumetric flask.
A wash bottle of de-ionised water is used to ensure complete transfer of sodium carbonate. De-ionised water is added to the flask until it is half full. The contents of the flask are stoppered and swirled to dissolve the sodium carbonate.
More water is carefully added until the bottom of the meniscus of the solution is exactly level with the calibration line on the neck of the bottle. The flask is stoppered and mixed well.
This standard solution is used to standardize a solution of hydrochloric acid.
A 20.00 mL pipette is rinsed with the standard carbonate solution, discarding the rinsings. 25.00 mL samples of the solution are transferred into each of three 100 ml conical flasks. 2 or 3 drops of methyl orange indicator are added to each flask.
A burette is rinsed and filled with the hydrochloric acid solution to be standardized.
The initial burette reading is recorded on the table below.
The sodium carbonate solution is titrated with the acid until the indicator shows the first permanent change from yellow to orange-pink. The final burette reading and the volume of the titre are recorded on the table below.
The titration is repeated until three concordant titres are obtained. All titration runs are recorded below.
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Goggles must be worn when pouring HCl (acid) into the burette to avoid splashes to get in our eyes.
Clamp the burette gently and carefully to avoid cracking of glass.
Disposable gloves must be worn when handling HCl (acid) because acid is corrosive.
Titration Initial Burette Reading Final Burette Reading Titre (mL)
1 0 25.80 25.80
2 0 26.00 26.00
3 0 25.80 25.80
Average of 3 concordant titres: 25.90 mL
Relative formula mass of Na2CO3 = 14(2)+12+16(3)
Molar mass of Na2CO3 = 88 g/molNo. of mole of Na2CO3 = mMr = 1.388 = 0.015 molConcentration of standard solution of sodium carbonate = nV = 0.0150.25 = 0.060 M
The equation for the titration reaction is
Na2CO3 + 2HCl 2NaCl + H2O + CO2
From the equation above,
1mol of Na2CO3 reacts with 2mol of HCl, hence
0.015 mol of Na2CO3 reacts with 0.030 mol of HCl.
Concentration of the HCl acid solution = nV = 0.0300.259 = 0.12 M
Firstly, we can use a pH meter instead of methyl orange indicator. This is to reduce the uncertainty when determine the colour change of the solution, where the point is called end-point. Second, we can shake the solution well to make sure the HCl acid solution is evenly added to the standard solution of sodium carbonate.
First, we make sure we did not take too much of HCl to prevent wastage because excess HCl cannot be poured back into the container. We also make sure that the final product and the leftovers in the burette are discarded properly to avoid environment pollution.
The concentration of standard solution of Na2CO3 is 0.060 M. The concentration of the HCl is 0.12 M.
Chemistry 104 (2005). Standardization of Acid and Base Solutions. Retrieved from http://www.chem.latech.edu/~deddy/chem104/104Standard.htmChik (2003). Chemistry Experiment Lab Report 1. Retrieved from http://vincentchik.tripod.com/sitebuildercontent/sitebuilderfiles/chem_lab_report.pdf
Ernest (2014). Preparation of standard acid solution. Retrieved from https://www.slideshare.net/Ernest13/experiment-on-the-standardization-of-acid-solutionAppendix