Chemistry: Understanding Chemical Formulas, Composition, and Ionic Compounds - Prof. Marti, Study notes of Chemistry

Download Chemistry: Understanding Chemical Formulas, Composition, and Ionic Compounds - Prof. Marti and more Study notes Chemistry in PDF only on Docsity! Chapter 2 Chemical formulas and composition stoichiometry Chemical formula: shows chemical composition and the ratio in which atoms of the elements occur. Organic compounds: contain C-C or C-H bonds Inorganic compounds: do not contain C-H bonds Law of Constant Composition (Law of Definite Proportions) Different pure samples of a compound always contain the same elements in the same proportion by mass; this corresponds to atoms of these elements combined in fixed numerical ratios. I Table 2-1 Names and Formulas of Some Common Molecular Compounds Name Formula Name water H,0 sulfur dioxide hydrogen peroxide HO; sulfur trioxide hydrogen chloride* HC carbon monoxide sulfuric acid H,S0, carbon dioxide nitric acid HNO, methane acetic acid CH,COOH ethane ammonia NH; propane *Called hydrochloric acid if dissolved in water. Memorize these. Formula 50; 50; C0 C0, CH, CH GH Name butane pentane benzene methanol (methyl aleohol) ethanol (ethyl aleohol) acetone diethyl ether (ether) Formula CH Cu, CH, CH,OH CH,CH,OH CH,COCH, CH,CH,OCH,CH, Table 2-1, p. 50 Ions and ionic compounds Ion: is an atom or group of atoms that carries an electric charge. Ions are formed when neutral atoms lose or gain electrons. Cation: ions that possess a positive charge, e.g. Na+ lost an e- Anion: ions that possess a negative charge, Cl- gained an e- NaCl crystal Each Na+ is surrounded at equal distances by 6 Cl- ions and each Cl- ion is similarly surrounded by 6 Na+ ions. Any compound whether ionic or molecular is electrically neutral (has not net charge). Names and Formulas of some ionic compounds Examples Clicker Q: Name Li2S Common Cations (positive ions) Formula Charge Name lithium i fluoride sodium : chloride potassium bromide ammonium ; iodide silver ) hydroxide acetate magnesium NO; | nitrate calcium zinc = oxide copper(I) iS sulfide copper(II) £ sulfate iron(II) sulfite carbonate iron(II) aluminum i 3 phosphate  Atomic weights (atomic mass) Atomic mass unit (amu): defined as exactly 1/12 of the mass of an atom of a particular kind of carbon atom, called carbon-12 Periodic table has amu. Units: g/mole The Mole Defined as the amount of substance that contains as many entities (atoms, molecules, or other particles) as there are atoms in exactly 0.012 kg of pure carbon-12 atoms. 1 mole = 6.022 x 1023 particles Avogadro’s number Mole derived from the Latin word moles which means “a mass”. “molecule” is the diminutive form of this word and means a small mass. A note: anything/mole goes for Avogadro’s #, so snowflakes/mole, marbles/mole, ions/mole, m&m/mole etc. 1 mole of whatever atoms = atomic mass of whatever element So 1 mole of Na is how many grams? 2 moles of Be is how many grams? 2 moles of O2 is how many grams? Clicker Q: How many grams in 3 moles of C? How many atoms are contained in 1.245 moles of Na? Calculate the number of atoms of Li in 37.6 g of Li The density of K is 0.86 g/mL. The density of N2 is 1.3 x 10-3 g/mL. In the following responses compare 1.0 mole of K to 1.0 mole of N2. Mass of 1 mole of K to 1 mole of N2. The volume of 1 mole of K to 1 mole of N2. The density of K is 0.86 g/mL. The density of N2 is 1.3 x 10 - 3 g/mL. In the following responses compare 1.0 mole of K to 1.0 mole of N2. # of atoms in 1 mole of K to # of atoms in 1 mole of N2 # of molecule in 1 mole of K to # of molecules in 1 mole of N2 Write the formula for aluminum sulfate. What is its formula weight? How many g are in 1.2 moles? How many atoms of Al are there in the formula? O atoms Clicker Q: How many moles are in 50.0 g of sodium hydroxide? Clicker Q: Write the formula for Fe(III) phosphate. Clicker Q: What is its formula weight? Enter that into clicker. In 3.0 moles of Na2CO3 there are _______ Na atoms. Clicker Q: Determine the formula weight of this compound in g/mol. Mg (NO3)2 Clicker Q: How many moles of Mg(NO3)2 are present in 89.6 g of Mg(NO3)2? Clicker Q: How many N atoms are present in 89.6 g of Mg(NO3)2? A sample of propane, C3H8, has the same mass as 4.38 million molecules of methane, CH4. How many propane molecules does the sample contain? What mass of KMnO4 (in grams) would contain 17.07 g of manganese? Percent composition and formulas of compounds Percent composition of water Derivation of formulas from elemental composition Empirical (simplest) formula: is the smallest whole-number ratio of atoms present Example: benzene (molecular formula C6H6), so empirical formula is ? Molecular formula indicates the actual numbers of atoms present in a molecule of the compound The analysis of a salt shows that it contains 56.58% potassium; 8.68% carbon; and 34.78% oxygen. Calculate the empirical formula for this substance. 41 A sample of a compound contains 6.541g of Co and 2.368g of O. What is the empirical formula for this compound? Problem solving tip in book page 69 What do you need to multiply a fraction (or decimal pt) by to get a whole # 0.5 multiply by 0.33 multiply by 0.25 multiply by 0.67 multiply by 0.75 multiply by 0.20 multiply by Clicker Q: Calculate the % composition of carbon monoxide. Enter only the %O into the clicker to one decimal place. Determination of Molecular formulas A compound is found to contain 85.63% C and 14.37% H by mass. In another experiment its molar mass is found to be 56.1 g/mol. What is its molecular formula? Short cut to previous problem 50 Purity of Samples • The percent purity of a sample of a substance is always represented as impurities includes sample of mass %100 sample of mass substance pure of mass =purity %  A bottle of sodium phosphate, Na3PO4, is 98.3% pure Na3PO4. What is the mass of Na3PO4 in 250.0 g of this sample of Na3PO4? Clicker questions 1. Sodium sulfate 2. Aluminum phosphate 3. CaS 4. Iron (II) nitrate 5. Silver hydroxide 6. Fe2(SO3)3