Law of Conservation of Mass

1. Law of Conservation of Mass

2. Which of the following is an example of a physical change?   A. A solid and liquid react together to form bubbles and release a gas.  B. Metal left outside rusts. C. An ice cube melts. D. A cut apple turns brown. Bell Ringer

3. During this class, you will use the Law of Conservation of Mass to identify patterns in chemical equations. Objective

4. Video Clip on Law of Conservation of Mass Brainpop Video Clip

5. Think about the following question: If you burned a log in the fireplace, would the mass of the products (smoke, ashes, etc.) be the same as the reactants (the wood)? “What does it mean to conserve to you?” Law of Conservation of Mass

6. Yes! In a chemical reaction, the total mass of the reactants is always equal to the total mass of the products Matter is conserved  type of atoms does not change Nothing is created or destroyed Law of Conservation of Mass

7. Example: Burning of Methane Methane + Oxygen → Water + Carbon dioxide CH4 + O2 → H2O + CO2 Law of Conservation of Mass

8. CH4 + O2 → H2O + CO2 4 Hydrogen atoms on the left hand side (reactants); only 2 on the right side (products) Where did they go? Atoms cannot be created or destroyed, just rearranged in a chemical reaction NEED TO BALANCE THE EQUATION! Law of Conservation of Mass

9. CH4 + 2 O2 → 2 H2O + CO2 The 2means that there are 2 oxygen and water molecules Now there are equal numbers of atoms on both sides of the reaction Law of Conservation of Mass

10. If 50 grams of sodium reacts with chlorine to form 126 grams of salt. How many grams of chlorine reacted? 50g Sodium + ____Chlorine 126 g Salt Guided Practice Answer: 126g-50g= 76g of Chlorine

11. If 20 grams of aluminum reacts with 200 grams of bromide to form aluminum bromide, and no aluminum is left after the reaction, but 23 grams of bromine remained unreacted. How any grams of aluminum bromide were formed? 20g Aluminum + 177g Bromide ____g Aluminum Bromide Guided Practice • Answer: 177g+20g= 197 g of aluminum bromide

12. Determine if the equations are balanced or unbalanced. Justify. AgNO3 + H2S  Ag2S + 2HNO3 Al + N2 2AlN Fe2O3 + H2 2Fe + 3H2O Guided Practice

13. If 178.8 g of water is separated into hydrogen and oxygen gas, and the hydrogen gas has a mass of 20.0 g. What is the mass of the oxygen gas produced? Independent Practice

14. From a laboratory process, a student collects 28.0 g of hydrogen and 224.0 g of oxygen. How much water was originally involved in the process? Independent Practice

15. A student carefully placed 23.0 g of sodium in a reactor with an excess quantity of chlorine gas. When the reaction is complete, the student obtained 58 grams of salt. How many grams of chlorine gas reacted? Independent Practice

16. A 10 gram sample of iron reacts with oxygen to form 18.2 grams of ferric oxide. How many grams of oxygen reacted? Independent Practice

17. Determine if the equations are balanced or unbalanced. Write Yes or No. give a short justification for each answer. 3Zn(OH)2 + 2 H3PO4 Zn3(PO4)2 + 3 H2O Mg(ClO3)2 MgCl2 + O2 Independent Practice

18. Why is it important for a chemist to understand the law of conservation of mass? “If you burned a log in the fireplace, would the mass of the products (smoke, ashes, etc.) be the same as the reactants (the wood)?” Higher Level Thinking

19. During this class period, you used the law of conservation of mass to identify patterns in chemical equations. (DOK 1, 2a) What is the Law of Conservation of Mass? Explain the difference between a balanced and unbalanced equation. Tomorrow, you will (identify the properties of elements and describe the structure of the periodic table) identify unbalanced chemical equations and describe and apply steps to balance them. (DOK 1, 2a) Closure