Download Percent composition of Hydrogen Peroxide
and more Lecture notes Chemistry in PDF only on Docsity! Percent composition (mass percent, percent composition by mass) Mass % = mass of component in substance (grams) x 100 mass of substance (grams) What is the mass % composition of water? MM (H2O) = 18.0152 g/mol MM (H) = 1.0079 g/mol MM (O) = 15.9994 g/mol %H in water = 11.21% H %O in water = 88.79% O We went from chemical formula (H2O) to percent composition. We can also go from percent composition to the chemical formula. Chemistry 101 Fall 2009 2 Mass % composition of: 75.7% C, 8.8% H, and 15.5% O. yielded these molar ratios … 6.30 mol C : 8.7 mol H : 0.969 mol O, which is the same as saying … 6.30 atoms C : 8.7 atoms H : 0.969 atoms O. Atoms do not combine as fractions or pieces (0.30, 0.7, 0.969), so we must scale up to reach whole atoms (whole numbers). Divide by the smallest number to reach 1 for at least one element: 0.969 = 1 atom O => 1 mol O 0.969 6.30 = 6.50 atoms C => 6.5 mol C 0.969 8.7 = 9.0 atoms H => 9.0 mol H 0.969 Chemistry 101 Fall 2009 5 Naming substances (Chapter 3.1 – 3.6) Writing formulas and names 1. Recognize compound as molecular or ionic. Watch out for polyatomic ions. 2. Molecular compounds (Chapter 3.2) N2O5 H2O carbon monoxide 3. Ionic binary compounds (Chapter 3.5 & 3.6) Ca(OH)2 CuO copper(I) nitrate iron (III) oxide Chemistry 101 Fall 2009 6 Oxyanions (Chapter 3.6) -ite vs. –ate (higher in the alphabet = more oxygens). Hypo = “low” = even less oxygens than –ite. Per = “super” = even more oxygens than – ate. Must memorize at least one –ite or –ate. Examples: SO4 2-, ClO2 - Chemistry 101 Fall 2009 7 Conservation of Matter Example: H2 + Cl2 HCl The starting atoms must equal the final atoms! A balanced chemical equation is similar to a recipe: = ratio of ingredients to products (ratio of inputs to outputs). = can have leftover ingredients (inputs). Bread example: 2 cups water + 2/3 cup sugar + 1 1/2 tablespoons yeast + 1 1/2 teaspoons salt + 1/4 cup butter + 6 cups bread flour 2 loaves of bread. Car example: 4 tires + 1 engine + 2 side mirrors + lots of other parts 1 car. Chemistry 101 Fall 2009 10 Practice: Ca(OH)2 + H3PO4 H2O + Ca3(PO4)2 (hint: what is the most complicated formula?) Chemistry 101 Fall 2009 11 Problem-solving example Reaction of iodine (I2) and chlorine (Cl2) produces IXClY. Reaction of 0.678 g of iodine with excess chlorine produces 1.246 g of IXClY. What is the empirical formula of IXClY? 1. What exactly are you asked to find? (unknown) 2. Search what you are given. (your knowns) 3. Think about how you can connect your knowns to your unknown, in light of what you are studying. 4. Find or obtain additional information to make the connection. 5. Often it helps to draw a picture or diagram. Often it helps to write a chemical equation. 6. Work through your solution. 7. Consider if your answer is reasonable.
