Composition of Substances and Solutions 129
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Tutorial 2 FORMULAS, PERCENTAGE COMPOSITION
T-6 Tutorial 2 FORMULAS, PERCENTAGE COMPOSITION, AND THE MOLE FORMULAS: A chemical formula shows the elemental composition of a substance: the chemical symbols show what elements are present and the numerical subscripts show how many atoms of each element there are in a formula unit. Examples: NaCl: one sodium atom, one chlorine atom in a formula unit CaCl2: one calcium atom, two chlorine atoms in a formula unit Mg3N2: three magnesium atoms, two nitrogen atoms in a formula unit The presence of a metal in a chemical formula indicates an ionic compound, which is composed of positive ions (cations) and negative ions (anions). A formula with only nonmetals indicates a + molecular compound (unless it is an ammonium, NH4 , compound). Only ionic compounds are considered in this Tutorial. There are tables of common ions in your lecture text, p 56 (cations) and p 57 (anions). A combined table of these same ions can be found on the inside back cover of the lecture text. A similar list is on the next page; all formulas needed in this and subsequent Tutorial problems can be written with ions from this list. Writing formulas for ionic compounds is very straightforward: TOTAL POSITIVE CHARGES MUST BE THE SAME AS TOTAL NEGATIVE CHARGES. The formula must be neutral. The positive ion is written first in the formula and the name of the compound is the two ion names. EXAMPLE: Write the formula for potassium chloride. The name tells you there are potassium, K+, and chloride, Cl–, ions. Each potassium ion is +1 and each chloride ion is -1: one of each is needed, and the formula for potassium chloride is KCl. -
Determination of the Molar Mass of an Unknown Solid by Freezing Point Depression
Determination of the Molar Mass of an Unknown Solid by Freezing Point Depression GOAL AND OVERVIEW In the first part of the lab, a series of solutions will be made in order to determine the freezing point depression constant, Kf, for cyclohexane. The freezing points of these solutions, which will contain known amounts of p-dichlorobenzene dissolved in cyclohexane, will be measured. In the second part of the lab, the freezing point of a cyclohexane solution will be prepared that contains a known mass of an unknown organic solid. The measured freezing point change will be used to calculate the molar mass of the unknown solid. Objectives and Science Skills • Understand and explain colligative properties of solutions, including freezing point depression. • Measure the freezing point of a pure solvent and of a solution in that solvent containing an unknown solute. • Calculate the molar mass of the unknown solute and determine its probable identity from a set of choices. • Quantify the expected freezing point change in a solution of known molality. • Quantitatively and qualitatively compare experimental results with theoretical values. • Identify and discuss factors or effects that may contribute to the uncertainties in values determined from experimental data. SUGGESTED REVIEW AND EXTERNAL READING • Reference information on thermodynamics; data analysis; relevant textbook information BACKGROUND If a liquid is at a higher temperature than its surroundings, the liquid's temperature will fall as it gives up heat to the surroundings. When the liquid's temperature reaches its freezing point, the liquid's temperature will not fall as it continues to give up heat to the surroundings. -
Chemistry: Empirical & Molecular Formulas
Chemistry: Empirical & Molecular Formulas Name______________________ 1) What is the empirical formula for C15H30O5H5? 2) A compound has an empirical formula of C2H4O3N. Its molar mass is 359 g. What is the molecular formula? 3) A compound contains 12.7 g iron & 7.29 g oxygen. Its molar mass is 87.85 g. What is its empirical formula? What is its molecular formula? 4) A compound contains 65.6% carbon, 9.45% hydrogen & 25.0% oxygen. Its molar mass is 1922.85 g. What is its empirical formula? What is its molecular formula? 5) A compound contains 92.2% carbon & 7.75% hydrogen. It has a molar mass of 118 g. What is its empirical formula? What is its molecular formula? 6) A compound has an empirical formula of C2H5O3N. Its molar mass is 454 g. What is its molecular formula? 7) What is the empirical formula for C20H32O4N4? 8) A compound contains 69.6% carbon, 9.76% hydrogen & 20.6% oxygen. Its molar mass is 465.72 g. What is its empirical formula? What is its molecular formula? 9) A compound contains 42.044 g carbon & 7.956 g hydrogen. Its molar mass is 114.26 g. What is its empirical formula? What is its molecular formula? 10) A compound contains 30.79 g copper & 19.31 g oxygen. Its molar mass is 207 g. What is its empirical formula? What is its molecular formula? 11) A compound contains 40.9% carbon, 4.58% hydrogen & 54.5% oxygen. Its molar mass is 176.1 g. What is its empirical formula? What is its molecular formula? 12) A compound has an empirical formula of CH2O & a gram molecular mass of 180.16 g. -
About SI Units
Units SI units: International system of units (French: “SI” means “Système Internationale”) The seven SI base units are: Mass: kg Defined by the prototype “standard kilogram” located in Paris. The standard kilogram is made of Pt metal. Length: m Originally defined by the prototype “standard meter” located in Paris. Then defined as 1,650,763.73 wavelengths of the orange-red radiation of Krypton86 under certain specified conditions. (Official definition: The distance traveled by light in vacuum during a time interval of 1 / 299 792 458 of a second) Time: s The second is defined as the duration of a certain number of oscillations of radiation coming from Cs atoms. (Official definition: The second is the duration of 9,192,631,770 periods of the radiation of the hyperfine- level transition of the ground state of the Cs133 atom) Current: A Defined as the current that causes a certain force between two parallel wires. (Official definition: The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 × 10-7 Newton per meter of length. Temperature: K One percent of the temperature difference between boiling point and freezing point of water. (Official definition: The Kelvin, unit of thermodynamic temperature, is the fraction 1 / 273.16 of the thermodynamic temperature of the triple point of water. Amount of substance: mol The amount of a substance that contains Avogadro’s number NAvo = 6.0221 × 1023 of atoms or molecules. -
2•Stoichiometry: Chemical Arithmetic Formula Conventions (1 Of
Superscripts used to show the charges on ions Mg2+ the 2 means a 2+ charge (lost 2 electrons) Subscripts 2•Stoichiometry: Chemical Arithmetic used to show numbers of atoms in a formula unit Formula Conventions H2SO4 two H’s, one S, and 4 O’s (1 of 24) Coefficients used to show the number of formula units 2Br– the 2 means two individual bromide ions Hydrates CuSO4 • 5 H2O some compounds have water molecules included stoichiometry study of the quantitative relationships in chemical formulas and equations. atomic mass weighted average mass of an atom, found on the periodic table 2•Stoichiometry: Chemical Arithmetic formula mass sum of the atomic masses of the Stoichiometry Terms atoms in a formula molecular mass sum of the atomic masses of the (2 of 24) atoms in a molecular formula gram molecular mass molecular mass written in grams molar mass same as gram molecular mass empirical formula formula reduced to lowest terms Formula or molecular mass is found by simply summing the atomic masses (on the periodic table) of each atom in a formula. H2SO4 2•Stoichiometry: Chemical Arithmetic 1.01 + 1.01 + 32.06 + 16.0 + 16.0 + 16.0 + 16.0 = 98.08 u Calculating Formula Mass 2(1.01) + 32.06 + 4(16.0) = 98.06 u or 98.06 g/mole (3 of 24) Generally, round off your answers to the hundredths or tenths place. Don’t round off too much (98.06 g/mol or 98.1 g/mol is OK, but don’t round off to 98 g/mol) Units Use u or amu if you are referring to one atom or molecule A mole (abbreviated mol) is a certain number of things. -
WS 4.2: Empirical Formula Problems
Name: Answer Key Period: ______ Date: __________ Chem B odds for HW and evens for review WS 4.2: Empirical Formula Problems Directions: Determine the empirical formula for the following substances. If a molecular formula cannot be reduced, write “cannot be reduced in the box for empirical formula” Molecular Formula Empirical Formula Molecular Formula Empirical Formula 1) C6H6 CH 2) C10H18 C5H9 3) C8H18 C4H9 4) C7H15O2 Not reducible 5) WO2 Not reducible 6) N2H4 NH2 7) C2H6O2 CH3O 8) P3F6 PF2 9) X39Y13 X3Y 10) IF5 Not reducible 11) C4H10 C2H5 12) N2O5 Not reducible 13) C6H12O6 CH2O 14) N2O4 NO2 15) P2F4 PF2 16) SF6 Not reducible 17) SO3 Not reducible 18) N2Cl4 NCl2 19) N2Br4 NBr2 20) P2O5 Not reducible Directions: Solve the following problems. You may need to use a separate sheet of paper. 1) What is the empirical formula for a compound which 3) Barry Um has a sample of a compound which weighs 200 contains 0.0134 g of iron, 0.00769 g of sulfur and 0.0115 g of grams and contains only carbon, hydrogen, oxygen and oxygen? nitrogen. By analysis, he finds that it contains 97.56 grams of carbon, 4.878 g of hydrogen, 52.03 g of oxygen and 45.53 g of nitrogen. Find its empirical formula. 3 FeSO C5H3N2O2 2) A compound is found to contain 53.7 % iron and 46.27 % sulfur. Find its empirical formula. 4) What is the empirical formula for a compound which contains 80.3% zinc and the rest is oxygen? Fe2S3 ZnO 5) Rubbing alcohol was found to contain 60.0 % carbon, 13.4 9) Give the name and empirical formula of a compound % hydrogen, and the remaining mass was due to oxygen. -
Δtb = M × Kb, Δtf = M × Kf
8.1HW Colligative Properties.doc Colligative Properties of Solvents Use the Equations given in your notes to solve the Colligative Property Questions. ΔTb = m × Kb, ΔTf = m × Kf Freezing Boiling K K Solvent Formula Point f b Point (°C) (°C/m) (°C/m) (°C) Water H2O 0.000 100.000 1.858 0.521 Acetic acid HC2H3O2 16.60 118.5 3.59 3.08 Benzene C6H6 5.455 80.2 5.065 2.61 Camphor C10H16O 179.5 ... 40 ... Carbon disulfide CS2 ... 46.3 ... 2.40 Cyclohexane C6H12 6.55 80.74 20.0 2.79 Ethanol C2H5OH ... 78.3 ... 1.07 1. Which solvent’s freezing point is depressed the most by the addition of a solute? This is determined by the Freezing Point Depression constant, Kf. The substance with the highest value for Kf will be affected the most. This would be Camphor with a constant of 40. 2. Which solvent’s freezing point is depressed the least by the addition of a solute? By the same logic as above, the substance with the lowest value for Kf will be affected the least. This is water. Certainly the case could be made that Carbon disulfide and Ethanol are affected the least as they do not have a constant. 3. Which solvent’s boiling point is elevated the least by the addition of a solute? Water 4. Which solvent’s boiling point is elevated the most by the addition of a solute? Acetic Acid 5. How does Kf relate to Kb? Kf > Kb (fill in the blank) The freezing point constant is always greater. -
Guide for the Use of the International System of Units (SI)
Guide for the Use of the International System of Units (SI) m kg s cd SI mol K A NIST Special Publication 811 2008 Edition Ambler Thompson and Barry N. Taylor NIST Special Publication 811 2008 Edition Guide for the Use of the International System of Units (SI) Ambler Thompson Technology Services and Barry N. Taylor Physics Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899 (Supersedes NIST Special Publication 811, 1995 Edition, April 1995) March 2008 U.S. Department of Commerce Carlos M. Gutierrez, Secretary National Institute of Standards and Technology James M. Turner, Acting Director National Institute of Standards and Technology Special Publication 811, 2008 Edition (Supersedes NIST Special Publication 811, April 1995 Edition) Natl. Inst. Stand. Technol. Spec. Publ. 811, 2008 Ed., 85 pages (March 2008; 2nd printing November 2008) CODEN: NSPUE3 Note on 2nd printing: This 2nd printing dated November 2008 of NIST SP811 corrects a number of minor typographical errors present in the 1st printing dated March 2008. Guide for the Use of the International System of Units (SI) Preface The International System of Units, universally abbreviated SI (from the French Le Système International d’Unités), is the modern metric system of measurement. Long the dominant measurement system used in science, the SI is becoming the dominant measurement system used in international commerce. The Omnibus Trade and Competitiveness Act of August 1988 [Public Law (PL) 100-418] changed the name of the National Bureau of Standards (NBS) to the National Institute of Standards and Technology (NIST) and gave to NIST the added task of helping U.S. -
2.1.3 Amount of Substance the Mole Is the Key Concept for Chemical Calculations
2.1.3 Amount of substance The mole is the key concept for chemical calculations DEFINITION: The mole is the amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12. DEFINITION: Relative atomic mass is the average mass of one atom compared to one twelfth of the mass of one atom of carbon-12 DEFINITION: Molar Mass is the mass in grams of 1 mole of a substance and is given the unit of g mol-1 Molar Mass for a compound can be calculated by adding up the mass numbers(from the periodic table) of each element in the compound eg CaCO3 = 40.1 + 12.0 +16.0 x3 = 100.1 molar gas volume (gas volume per mole, units dm3 mol–1) . This is the volume of 1 mole of a gas at a given temperature and pressure. All gases have this same volume. At room pressure (1atm) and room temperature 25oC the molar gas volume is 24 dm3 mol–1 Avogadro's Constant There are 6.02 x 1023 atoms in 12 grams of carbon-12. Therefore explained in simpler terms 'One mole of any specified entity contains 6.02 x 1023 of that entity': 1 mole of copper atoms will contain 6.02 x 1023 atoms Avogadro's Constant can be 1 mole of carbon dioxide molecules will contain 6.02 x 1023 molecules used for atoms, molecules and 1 mole of sodium ions will contain 6.02 x 1023 ions ions For pure solids, liquids and gases Example 1: What is the amount, in mol, in 35.0g of CuSO4? amount = mass amount = mass/Mr Mr = 35/ (63.5 + 32 +16 x4) Unit of Mass: grams = 0.219 mol Unit of amount : mol Many questions will involve changes of units 1000 mg =1g 1000 g =1kg 1000kg = 1 tonne Significant Figures Give your answers to the same number of significant figures as the Example 2: What is the amount, in mol, in 75.0mg of number of significant figures for the CaSO4.2H2O? data you given in a question. -
TSCA Inventory Representation for Products Containing Two Or More
mixtures.txt TOXIC SUBSTANCES CONTROL ACT INVENTORY REPRESENTATION FOR PRODUCTS CONTAINING TWO OR MORE SUBSTANCES: FORMULATED AND STATUTORY MIXTURES I. Introduction This paper explains the conventions that are applied to listings of certain mixtures for the Chemical Substance Inventory that is maintained by the U.S. Environmental Protection Agency (EPA) under the Toxic Substances Control Act (TSCA). This paper discusses the Inventory representation of mixtures of substances that do not react together (i.e., formulated mixtures) as well as those combinations that are formed during certain manufacturing activities and are designated as mixtures by the Agency (i.e., statutory mixtures). Complex reaction products are covered in a separate paper. The Agency's goal in developing this paper is to make it easier for the users of the Inventory to interpret Inventory listings and to understand how new mixtures would be identified for Inventory inclusion. Fundamental to the Inventory as a whole is the principle that entries on the Inventory are identified as precisely as possible for the commercial chemical substance, as reported by the submitter. Substances that are chemically indistinguishable, or even identical, may be listed differently on the Inventory, depending on the degree of knowledge that the submitters possess and report about such substances, as well as how submitters intend to represent the chemical identities to the Agency and to customers. Although these chemically indistinguishable substances are named differently on the Inventory, this is not a "nomenclature" issue, but an issue of substance representation. Submitters should be aware that their choice for substance representation plays an important role in the Agency's determination of how the substance will be listed on the Inventory. -
Introduction to Chemistry
Introduction to Chemistry Author: Tracy Poulsen Digital Proofer Supported by CK-12 Foundation CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook Introduction to Chem... materials for the K-12 market both in the U.S. and worldwide. Using an open-content, web-based Authored by Tracy Poulsen collaborative model termed the “FlexBook,” CK-12 intends to pioneer the generation and 8.5" x 11.0" (21.59 x 27.94 cm) distribution of high-quality educational content that will serve both as core text as well as provide Black & White on White paper an adaptive environment for learning. 250 pages ISBN-13: 9781478298601 Copyright © 2010, CK-12 Foundation, www.ck12.org ISBN-10: 147829860X Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made Please carefully review your Digital Proof download for formatting, available to Users in accordance with the Creative Commons Attribution/Non-Commercial/Share grammar, and design issues that may need to be corrected. Alike 3.0 Unported (CC-by-NC-SA) License (http://creativecommons.org/licenses/by-nc- sa/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), We recommend that you review your book three times, with each time focusing on a different aspect. which is incorporated herein by this reference. Specific details can be found at http://about.ck12.org/terms. Check the format, including headers, footers, page 1 numbers, spacing, table of contents, and index. 2 Review any images or graphics and captions if applicable. -
Outline of Physical Science
Outline of physical science “Physical Science” redirects here. It is not to be confused • Astronomy – study of celestial objects (such as stars, with Physics. galaxies, planets, moons, asteroids, comets and neb- ulae), the physics, chemistry, and evolution of such Physical science is a branch of natural science that stud- objects, and phenomena that originate outside the atmosphere of Earth, including supernovae explo- ies non-living systems, in contrast to life science. It in turn has many branches, each referred to as a “physical sions, gamma ray bursts, and cosmic microwave background radiation. science”, together called the “physical sciences”. How- ever, the term “physical” creates an unintended, some- • Branches of astronomy what arbitrary distinction, since many branches of physi- cal science also study biological phenomena and branches • Chemistry – studies the composition, structure, of chemistry such as organic chemistry. properties and change of matter.[8][9] In this realm, chemistry deals with such topics as the properties of individual atoms, the manner in which atoms form 1 What is physical science? chemical bonds in the formation of compounds, the interactions of substances through intermolecular forces to give matter its general properties, and the Physical science can be described as all of the following: interactions between substances through chemical reactions to form different substances. • A branch of science (a systematic enterprise that builds and organizes knowledge in the form of • Branches of chemistry testable explanations and predictions about the • universe).[1][2][3] Earth science – all-embracing term referring to the fields of science dealing with planet Earth. Earth • A branch of natural science – natural science science is the study of how the natural environ- is a major branch of science that tries to ex- ment (ecosphere or Earth system) works and how it plain and predict nature’s phenomena, based evolved to its current state.