IPC 8C Investigate and identify the law of conservation of mass.

1. IPC 8C Investigate and identify the law of conservation of mass. The Law of conservation of massstates that matter cannot be created or destroyed in any chemical reaction The atoms in the reactants are rearranged to form new compounds, but none of the atoms disappear, and no new atoms are formed. H O H O H H Products Reactants

2. A chemical equation identifies the starting and ending chemicals as reactants and products: reactants products Formation of water 2H2 + O2 2H20 A chemical equation is balanced when it reflects the conservation of mass. Graphic: http://www.chemistry.ohio-state.edu/betha/nealChemBal/

3. O O O O O O O O Al Al O O Al Al O O The same number of each kind of atom must be on the left side of the arrow as are on the right side when an equation is balanced. Al Al Al Al

4. 2 H atoms 2 H atoms 2 O atoms 1 O atom 2 2 Balancing an equation: H2+ O2 H2O H H H O H O O Second: Determine which atoms are not equal and add coefficients to balance these atoms. First: Inventory the atoms on both sides of the yield arrow Hydogen atoms are = Hydogen atoms are = Hydogen atoms are ≠ 4 H atoms 2 O atoms 4 H atoms 2 O atoms Oxygen atoms are = Oxygen atoms are = Oxygen atoms are≠ When a coefficient is added you must multiply all atoms in the compound by this number. Redo the inventory After redoing the inventory, add coefficients to balanced other atoms. With each additional coefficient the inventory must be updated. Oxygen, as a product, must be multiplied by 2. A coefficient is placed in front of the compounds that contains O. This is now a balanced equation

5. So: Chemical equations are balanced, when the numbers and kinds of atoms on each side of the reaction arrow are equal. H H O H O O H O H H H H Products Reactants 4 Hydrogen 4 Hydrogen 2 Oxygen 2 Oxygen

6. F F F F H H H H Because atoms are conserved, the mass of the reactants in the chemical reaction is equal to the mass of the products. H2 + F2 2 HF 2g + 38g = 2( 20g) 40g = 40g Reactants Products 40 g 40 g

7. The Law of Conservation of Mass allows the calculation of the reactants or products. If 27.0 g of mercuric oxide (the red solid compound) is heated and completely decomposes to give the elements oxygen and mercury. 2.0 g of oxygen are produced. How many grams of mercury are produced? mercuric oxide  mercury + oxygenHgO  Hg + O2

8. 2.0 g O2 27.0 g HgO ? g Hg 27 g HgO = 2 g O2 + ? Hg = 25 g Hg Reactants Products

9. O O Ca O Ca Ca O Ca Which of the following chemical reactions indicate that mass in conserved? • Mg + Cl2 2 MgCl • 2 Ca + O2 2 CaO • Zn + S  2 ZnS • C + O2  2 CO Because atoms must be equal on each side of the equation: The correct answer is B

10. Mg + HCl → MgCl2 + H2 2 Mg + 2 HCl → MgCl2 + H2 • When the above equation is balanced, the coefficient for magnesium is — • A 0 • B 1 • C 2 • D 4 The correct answer is C

11. Suppose 100 g of iron metal rusts. We weigh the rust and find that the rust has a mass of 143 g. What mass of oxygen reacted with the iron?A. 243 g B. 57 g C. 100 gD 43 g Iron + Oxygen  Rust • 100 g + ?g  143g • What mass of oxygen is needed? 43 g Oxygen Choice D