Lab 2-Investigating the Law of Conservation of Mass

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1 Name: Period: Lab 2-Investigating the Law of Conservation of Mass Objective: To corroborate the law of conservation of mass through laboratory experimentation. Background: When wood burns or water evaporates, some or all of it appears to disappear but does it? A pile of ash is a lot smaller than the wood it originally started as and a dry empty cup seems a lot lighter if all of the water is allowed to evaporate. When you pop open a soda can, the fizz is really carbon dioxide, tiny gas bubbles that rise out of the soda and mix back with the atmosphere. To the naked eye, it seems like these materials just vanish. However, does matter ever really disappear? According to the law of conservation of mass, mass is always conserved. In many situations, the end products appear to have decreased but when all the products are captured and their mass measured, it was discovered that the mass of the reactants is equal to the mass of the products. In other words, matter can neither be created nor destroyed. This is called the law of conservation of mass. All atoms present in the reactants are also present in the products. The "Law of Conservation of Mass" states that when matter goes through a physical or chemical change, the amount of matter stays the same before and after the changes occur. In other words, matter cannot be created or destroyed. According to this principle, matter cannot just appear or disappear, but matter can change its nature. When atoms chemically combine with or split away from other atoms the chemical and physical properties of that substance can be completely altered. Take table salt, for example. The chemical formula for salt is NaCl, or sodium chloride. Sodium by itself is an element an unstable and poisonous metal. Chlorine by itself is also an element, which at room

2 temperature is a poisonous gas. However, combine these two atoms together with a chemical bond and they are completely transformed into a very stable substance that is edible crystalline solid at room temperature. Materials: Sodium bicarbonate, NaHCO 3 scoopula Funnel Acetic acid, CH 3 COOH 250 ml Erlenmeyer flask Balloon Triple beam balance Graduated cylinder Masking tape Procedure: 1. Observe the physical properties of acetic acid and sodium bicarbonate and record your observations in data table Put your funnel inside the balloon. Make sure the neck of the funnel is deep inside the balloon, so you do not get any sodium bicarbonate stuck in the neck of the balloon. 3. Put 4 scoops of sodium bicarbonate in the funnel. 4. Measure out 50 ml of acetic acid. Pour the acetic acid into the Erlenmeyer flask. 5. Stretch the balloon over the mouth of the flask, with the balloon hanging to the side of the flask. (DO NOT let the reactants mix). Use masking tape to seal the balloon to the neck of the flask. 6. Record the combined mass of the ENTIRE SETUP in data table 2 7. Lift the balloon so that the sodium bicarbonate now drops into the Erlenmeyer flask. 8. Observe for 5 minutes. 9. Observe the physical properties of the products and record your observations in data table Record the mass of the ENTIRE SETUP again data table 2.

3 Data: Table 1: reactants Acetic Acid, CH 3 COOH (aq) Substance Physical Properties Sodium Bicarbonate, NaHCO 3(s) products NaCH 2 COOH (aq) H 2 O (l) +CO 2(g) Table 2: Total Mass Before Reaction (grams) Total Mass After Reaction (grams) Results: 1. What evidence that a chemical reaction took place did you observe when the sodium bicarbonate and acetic acid were mixed? 2. Calculate the change in mass that you measured between the initial reactants and final products of the reaction.

4 3. Calculate the percent error between your measured final mass and the final mass predicted by the law of conservation of mass. 4. Why was it necessary to do this experiment in a sealed container (closed system) in order to accurately illustrate the principle of conservation of mass? Conclusion: 1. The reaction between sodium bicarbonate and acetic acid is represented by the balanced equation below. NaHCO 3(S) +CH 3 COOH (aq) CH 3 COONa (aq) +H 2 O (l) +CO 2(g) Determine the total mass of CO 2(g) produced when grams of NaHCO 3(S) reacts completely with grams CH 3 COOH (aq) to produce grams NaCH 2 COOH (aq) and grams H 2 O (l). 2. Which chemical equation best illustrates the Law of Conservation of Mass? Explain your choice. 1. 2H 2 0 H 2 + O 2 2. Zn + HCl ZnCl 2 + H 2 3. Al 4 C 3 + 3H 2 O CH 4 + 4Al(OH) 3 4. CH 4 + 2O 2 CO 2 + 2H 2 O

5 3. Base your answer to the following question on the information below. The particle diagrams below represent the reaction between two nonmetals, A2 and Q2. Compare the total mass of the reactants to the total mass of the product. 4. Base your answer to the following question on the information below. A 4.86-gram sample of calcium reacted completely with oxygen to form 6.80 grams of calcium oxide. This reaction is represented by the balanced equation below. 2Ca(s) + O2(g) 2CaO(s) Determine the total mass of oxygen that reacted.

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