Understanding Percent Composition and Empirical Formulas in Chemistry, Lecture notes of Chemistry

Download Understanding Percent Composition and Empirical Formulas in Chemistry 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 10 g 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 If you have 18.015 g of water, what is the mass % composition of water? Does mass % composition of a substance depend on the amount of substance you have? Why? Chemistry 101 Fall 2010 2 We went from chemical formula (H2O) to percent composition. We can also go from percent composition to the chemical formula. You have 100 grams of a compound, and you find out it has a mass % composition of: 75.7% C 8.8% H 15.5% O. How many moles of C, H, and O do you have? Chemistry 101 Fall 2010 5 Practice: Nicotine has a percent composition of 74.0% C, 8.65% H, and 17.35% N and has a molar mass of 162 g/mol. Determine the (a) empirical and (b) molecular formulas of nicotine. Chemistry 101 Fall 2010 6 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 2010 7 Practice: H2 + N2  NH3 Practice: Titanium (Ti) combines with oxygen (O2) to form titanium (IV) oxide. Write the balanced equation for this process.