Lab Report Acid Base Lab Determination of CaCO3 in Toothpaste Chawalnrath Wongdeshanan(Kat) 11 1 Pitchaya Areekarnlert (Petch) 11 1 Karnsinee Yotsakulsate(Jenny) 11 1 Pukjira Ittarut(Pim) 11 1 Date: 27 February 2015 Introduction Titration is a method to analyze the precise end point of a reaction and the precise quantity of reactant in the titration flask. A buret is used to dispense the second reactant to the titration flask. A ph meter is used to detect the endpoint of the reaction. 1 There are four types of titration. Acid base titration determines the content of a particular acid or base. 2 Oxidation reduction(redox) titration which depends upon the gain or loss of electron. Precipitation titration determines the concentration of chloride ion in a specific solution. 3 Complexometric titration is similar to the precipitation titration but it is superior. Since it makes no error owing to co precipitations. 4 The titration of a strong acid with a strong base is the most common type because it involves a strong acid and strong base which completely dissociate in water, it resulting in a strong acid strong base neutralization reaction. 5 In this experiment, it s not easy to determine the amount of CaCO 3 using acid to dilute and calculate the exact amount of CaCO 3 reacted with acid. Instead, the back titration method is the proper method to calculate how much of CaCO 3 in the solution by adding excess amount of acid then diluted the acid with water to certain volume and lastly titrate it with the known concentration of base. Purpose The purpose of this experiment is to find out the unknown concentration of CaCO 3 in the toothpaste by using acid base titration. Hypothesis As see in this reaction, 2HCl (aq) + CaCO 3 (s) > Ca 2+ (aq) + CO 2 (g) + H 2 O + 2Cl (aq)
2 mole of hydrochloric acid will react against 1 mole of calcium carbonate and then form CaCl 2, water and carbon dioxide. The prediction will be that the amount of calcium carbonate in the toothpaste will be half of the amount of the hydrochloric acid reacted in the solution. Materials 3 x 125 ml Erlenmeyer Flasks (Conical Flask) 1 x spatula 1 x stand w/ double buret holder 1 x buret 1 x stir bar 1 x ph meter 1 x graduated cylinder Methods 1. Put 125 ml Erlenmeyer on zero scale. 2. Weigh out about 0.5 g of toothpaste into Erlenmeyer flask. 3. Add 10 ml of water into Erlenmeyer flask by using graduated cylinder. 4. Add exactly 10.00 ml HCl into the solution by using volumetric pipette. 5. Heat and stir for 5 mins at the temperature 95 105 c and let it cool. 6. Add a Phenolphthalein indicator. 7. Slowly add 0.10 M NaOH in buret. Then record volume and initial ph with ph meter. 8. Add the titrant slower when the solution starts to turn pink but not return to transparent. Then record the final ph and final volume. 9. Continue adding an additional 4 ml of titrant and record ph and volume each time. 10. Continue doing the experiment for 2 more times and you will get a total 3 separate titrations. Data/Results Sample 1 Sample 2 Sample 3 Weight toothpaste (g) 0.52 g 0.49 g 0.52 g Initial Vol. (ml) 25.21 ml 3.29 ml 40.21 ml Initial ph 1.94 1.37 1.46 Final Vol. (ml) 31.29 ml 40.21 ml 46.19 ml
Final ph 8.07 10.99 8.38 Total vol. (ml) 6.08 8.92 5.98 Vol HCl reacted with toothpaste 3.92 1.08 4.02 Moles HCl reacted 3.92*10^ 4 mol 1.08*10^ 4 mol 4.02*10^ 4 mol HCl Moles CaCO 3 9.8*10^ 5 5.4*10^ 5 2.01*10^ 4 mol CaCO3 Amount CaCO 3 (mg) 9.36 mg. 5.157*10^ 3 0.02 mg Amount CaCO 3 (mg/g) 18 mg/g 5.16 mg/g 20 mg/g Average CaCO 3 (mg/g) *milligram of CaCo3 per gram of toothpaste. Standard deviation = 8.05286 Relative standard deviation = 55.97% 14.39 14.39 14.39 Discussion 1. What was the purpose of heating the solution? The purpose of heating the solution is to eliminate the carbon dioxide in the solution because carbon dioxide will evaporate from the solution as it is heating up. 2. Why was the acid added in excess? The acid was added in excess because at last the excess will be subtracted out by the remainder acid to determine amount of acid that reacted with CaCO 3 during the experiment and calculate how much CaCO 3 in the toothpaste. 3. What is an end point? What is an equivalence point? An end point is the point where the indicator or phenolphthalein changes its colour. An equivalent point is the point where the mol or quantity of acid and base is equal. 4. Why did the solutions turn pink around a ph of 8 9? The solution turned pink around a ph of 8 9 because phenolphthalein will change color from colorless to pink when the ph changes 8.3 to 10. The pink color appears from
phenolphthalein loses its electron then it allows electron to move freely within the molecule causing color changes in the solution. 5. Why were 3 replicates performed? 3 replicates were performed to rule out any mistakes that can happen during these 3 experiments because we can see the trend of each experiment and then compare it together to check if there are any mistakes happened. References (1) ChemLab Titration. http://www.dartmouth.edu/~chemlab/techniques/titration.html [ Sunday 08 Mar 2015 22:28:50 EST ] (2) Types of titration. http://classroom.synonym.com/types titration 14630.html [Sunday 08 Mar 2015 22:30:10 EST] (3) Introductory University Chemistry I precipitation titration. http://dwb.unl.edu/teacher/nsf/c14/c14links/www.chem.ualberta.ca/courses/plambeck/p1 01/p01194.htm [Sunday 08 Mar 2015 22:32:40 EST ] (4) Types of titrations. https://shailendrakrchemistry.files.wordpress.com/2009/11/types of titration.pdf. [Sunday 08 Mar 2015 22:34:01 EST ] (5) Chemwiki Titration of a strong acid with a strong base. http://chemwiki.ucdavis.edu/analytical_chemistry/quantitative_analysis/titration/titration _Of_A_Strong_Acid_With_A_Strong_Base [ Sunday 08 Mar 2015 22:36:55 EST ] (6) Toothpaste :Sparkle White Fresh. Kuron Co.,Ltd. 193,195,197 Krungthep Kreetha Rd., Sapansoong, district Bkk 10250 Conclusion After careful considerations of all the results and all the possible of concentration, it is concluded that the average concentration of NaOH was and average concentration of CaCO3 was 14.39 mg/g There were some mistakes that occurred because our error. The first mistake was that we opened the valve of the buret which contained sodium hydroxide(naoh), too loose, then the NaOH flowed into the flask too much. Resulting in the solution in the flask turned dark pink very quickly. The second mistake was, at the first time we didn t wash the ph meter before put it
into the flask to measure the ph, then we realized that we must wash before using it. To improve, we will be more careful when we open the valve of buret and think carefully before using any equipments.