Presentation on theme: "Rachel Jarrett Matt Marthaler. In this experiment, we will determine the concentration of carbonate and bicarbonate species in different sodas using."— Presentation transcript:
Rachel Jarrett Matt Marthaler
In this experiment, we will determine the concentration of carbonate and bicarbonate species in different sodas using the technique of titration. A primary standard used in this experiment is NaOH for the direct titration of the diprotic acid. Color indicators which utilize changes in pH will be used to determine the presence of the different species of the acid.
Approximately 2 g of NaOH(s) pellets were placed in a 500mL volumetric flask and diluted to the mark with distilled water to make an approximate 0.1M solution. Approximately 0.51g of KHP was weighed for three different samples for standardization of the base. The KHP was dissolved in 25 mL of water, phenolphthalein was added and the solution was titrated with NaOH. The mL required to reach the endpoint were used to determine the concentration of the base; the individual calculations were averaged to determine molarity.
25 mL of each cold, fresh soda was measured in a graduated cylinder. The sample was then placed in a beaker Methyl orange indicator was added to the solution The solution was titrated with NaOH until an approximate endpoint was reached
Color of this indicator changes from yellow to orange to red at pH between 3.1 and 4.4 At a strong orange, all carbonic acid has turned into bicarbonate and indicates a pH around 3.7 This color difference was difficult to determine
25 mL of each cold, fresh soda was measured in a graduated cylinder. These samples were separate from the previous samples. The sample was then placed in a beaker Phenolphthalein indicator was added to the solution The solution was titrated with NaOH until an endpoint was reached
Color of this indicator changes from colorless in an acidic solution to pink/purple in a basic solution At pink/purple, all bicarbonate has turned into carbonate
Amount of NaOH Pellets 0.1 moles NaOH x 0.5 L x 39.997 g NaOH 1 L NaOH1 mole NaOH = 1.999 g Mass KHP 25mL x 1L x 0.1mole NaOH x 1 mole KHP x 204.221g KHP 1000mL 1L 1 mole NaOH 1 mole KHP =0.5106 g Molarity NaOH 0.5106g KHP x 1 mole KHP x 1mole NaOH x 1 x 1000mL 204.221g 1mole KHP 26.64mL 1L =0.09345 M
Bicarbonate (Sprite): 0.0888 moles NaOH x 0.67 mL x 1 L x 1 mole HCO 3 - x x 1,000 mL L 1,000 mL 1mole NaOH 25 mL L = 0.002380 moles HCO 3 - / L Carbonate (Sprite): 0.0888 moles NaOH x 17.41 mL x 2 moles CO 3 2- x _ L 1 mole NaOH 25 mL = 0.1237 moles CO 3 2- / L
Bicarbonate (Sprite): average moles x 61 g bicarbonate x 591 mL mole 25 mL = 0.0823854 g bicarbonate x 100 591 g Sprite = 0.01394% Carbonate (Sprite): average moles x 60 g carbonate x 591 mL mole 25 mL = 4.244562 g carbonate x 100 591 g Sprite = 0.7318%
Our experiment can not be considered entirely accurate, but it was not a failure. Some of the inaccuracies come from: Re-standardization of more NaOH due to a short supply of the solution in the middle of the experiment Inconsistencies due to the gradual color change of methyl orange. We did not know when to stop the titration since the color of orange is difficult to read consistently. Due to the carbonation in soda, a graduated cylinder was used to measure the volume of soda since the bubbles made it impossible to use a pipet. The density of water was used to calculate the percent carbonate and bicarbonate since there are not published values for the density of the different sodas When measuring the acidity of these beverages, other acids present in the soda such as citric acid can distort the perception of carbonic acid and change results. Regardless of the possible reasons for error, the standard deviations of this experiment were reasonable, so precision was achieved within the calculations. The amount of carbonate and bicarbonate were determined, therefore, the experiment was successful and error can be acknowledged.