Chemistry for Engineering Students, 4Th Edition Lawrence S
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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. -
Chapter 20 Electrochemistry
Chapter 20 Electrochemistry Learning goals and key skills: Identify oxidation, reduction, oxidizing agent, and reducing agent in a chemical equation Complete and balance redox equations using the method of half-reactions. Sketch a voltaic cell and identify its cathode, anode, and the directions in which electrons and ions move. o Calculate standard emfs (cell potentials), E cell, from standard reduction potentials. Use reduction potentials to predict whether a redox reaction is spontaneous. o o Relate E cell to DG and equilibrium constants. Calculate emf under nonstandard conditions. Identify the components of common batteries. Describe the construction of a lithium-ion battery and explain how it works. Describe the construction of a fuel cell and explain how it generates electrical energy. Explain how corrosion occurs and how it is prevented by cathodic protection. Describe the reactions in electrolytic cells. Relate the amounts of products and reactants in redox reactions to electrical charge. Electrochemistry Electrochemistry is the study of the relationships between electricity and chemical reactions. • It includes the study of both spontaneous and nonspontaneous processes. 1 Redox reactions: assigning oxidation numbers Oxidation numbers help keep track of what species loses electrons and what species gains them. • An element is oxidized when the oxidation number increases • An element is reduced when the oxidation number decreases • an oxidizing agent causes another element to be oxidized • a reducing agent causes another element to be reduced. Assigning oxidation numbers (sect. 4.4) 1. Elemental form, each atom has ox. # = 0. Zn O2 O3 I2 S8 P4 2. Simple ions, = charge on ion. -1 for Cl-, +2 for Mg2+ 3. -
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. -
Find the Molar Mass of Sodium Carbonate, Na 2CO3. Na 2 X
Moles and Molar Mass The mole is the "counting unit" used by chemists to indicate the number of atoms, ions, molecules, or formula units present in a particular chemical sample. The mole is similar to other counting units that you've used before....pair (2), dozen (12), and gross (144). One mole of a compound contains Avogadro's number (6.022 x 1023) of molecules (molecular compound) or formula units (ionic compound). The molar mass of a compound tells you the mass of 1 mole of that substance. In other words, it tells you the number of grams per mole of a compound. The units for molar mass are, therefore, grams/mole. To find the molar mass of a compound: 1. Use the chemical formula to determine the number of each type of atom present in the compound. 2. Multiply the atomic weight (from the periodic table) of each element by the number of atoms of that element present in the compound. 3. Add it all together and put units of grams/mole after the number. Example: Find the molar mass of sodium carbonate, Na2CO3. Na 2 x 23.0 = 46.0 C 1 x 12.0 = 12.0 O 3 x 16.0 = 48.0 molar = 106.0 g/mole mass For many (but not all) problems, you can simply round the atomic weights and the molar mass to the nearest 0.1 g/mole. HOWEVER, make sure that you use at least as many significant figures in your molar mass as the measurement with the fewest significant figures. -
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. -
Battle of the Acids Weak Acids and Bases SCIENTIFIC
Battle of the Acids Weak Acids and Bases SCIENTIFIC Introduction Not all acids are created equal. This demonstration compares the “frothing and foaming” activity of different acids with calcium carbonate and examines their behavior in the presence of their conjugate bases to distinguish strong versus weak acids. The use of a “rainbow acid” universal indicator produces a rainbow spectrum of color changes as the mixtures react. Concepts • Strong acid • Weak acid • Conjugate base • pH Materials (for each demonstration) Acetic acid, CH3COOH, 1 M, 400 mL Water, distilled or deionized Calcium carbonate, CaCO3, 40 g Demonstration tray, large Hydrochloric acid, HCl, 1 M, 400 mL Graduated cylinder, 250-mL “Rainbow acid” universal indicator, 5 mL Hydrometer cylinders, 600-mL, 4 (includes accompanying color chart) Pipet, Beral-type Sodium acetate, NaCH3CO2, 16 g Weighing dishes or small beakers, 6 Sodium chloride, NaCl, 12 g Safety Precautions Hydrochloric acid and acetic acid solutions are toxic and corrosive. Avoid contact with skin and eyes. “Rainbow-acid” universal indicator solution is an alcohol-based solution and is flammable. Avoid contact with flames or other ignition sources. Wear chemical splash goggles, chemical-resistant gloves, and a chemical-resistant apron. Please review current Material Safety Data Sheets for additional safety, handling, and disposal information. Preparation To save time in the presentation, pre-measure the amounts of solids needed for the demonstration. Weigh out 12 g of sodium chloride, 16 g of sodium acetate, and 4 × 10-g samples of calcium carbonate in separate, labeled weighing dishes or small beakers. Procedure 1. Obtain 4 large hydrometer cylinders or tall-form beakers and place them on a large demonstration tray. -
2.1 Relative Atomic and Molecular Masses, the Avogadro Constant, and the Mole Calculations AQA Chemistry
2.1 Relative atomic and molecular AQA Chemistry masses, the Avogadro constant, and the mole Calculations The Avogadro constant Specification reference 3.1.2.2 MS 0.1 Recognise and use expressions in decimal and ordinary form MS 0.4 Use calculators to find and use power, exponential, and logarithmic functions MS 1.1Use an appropriate number of significant figures. Learning objectives After completing the worksheet you should be able to: carry out calculations using the Avogadro constant carry out calculations using numbers in standard and ordinary form substitute numerical values into algebraic equations, and change the subject of equations report calculations to an appropriate number of significant figures. Introduction One mole of any substance contains the same number of particles as the number of atoms in 12 g of carbon-12. This number of particles is a huge number and is called the Avogadro constant. It has a value of 6.02 1023 and is given the units of mol−1 (per mole). The relative atomic mass of an element in grams contains 6.02 1023 atoms or one mole of that element. The relative formula mass of a compound in grams contains 6.02 1023 particles (molecules or ions) or one mole of that compound. Therefore we use the term molar mass to describe the relative atomic or formula mass of a substance in grams and give it the unit g mol−1. To calculate the number of particles in a certain mass of a substance we can use the following equation. mass m (g) Number of particles = ´ 6.02 ´ 1023(mol-1) molar mass M (g mol-1) Worked example Question 1 How many molecules are there in 42.5 g of ammonia, NH3? Answer © Oxford University Press 2015 www.oxfordsecondary.co.uk/acknowledgements This resource sheet may have been changed from the original 1 2.1 Relative atomic and molecular AQA Chemistry masses, the Avogadro constant, and the mole Calculations Step 1 Calculate the molar mass of ammonia using the relative atomic masses of nitrogen and hydrogen from the periodic table. -
Stoichiometry of Chemical Reactions 175
Chapter 4 Stoichiometry of Chemical Reactions 175 Chapter 4 Stoichiometry of Chemical Reactions Figure 4.1 Many modern rocket fuels are solid mixtures of substances combined in carefully measured amounts and ignited to yield a thrust-generating chemical reaction. (credit: modification of work by NASA) Chapter Outline 4.1 Writing and Balancing Chemical Equations 4.2 Classifying Chemical Reactions 4.3 Reaction Stoichiometry 4.4 Reaction Yields 4.5 Quantitative Chemical Analysis Introduction Solid-fuel rockets are a central feature in the world’s space exploration programs, including the new Space Launch System being developed by the National Aeronautics and Space Administration (NASA) to replace the retired Space Shuttle fleet (Figure 4.1). The engines of these rockets rely on carefully prepared solid mixtures of chemicals combined in precisely measured amounts. Igniting the mixture initiates a vigorous chemical reaction that rapidly generates large amounts of gaseous products. These gases are ejected from the rocket engine through its nozzle, providing the thrust needed to propel heavy payloads into space. Both the nature of this chemical reaction and the relationships between the amounts of the substances being consumed and produced by the reaction are critically important considerations that determine the success of the technology. This chapter will describe how to symbolize chemical reactions using chemical equations, how to classify some common chemical reactions by identifying patterns of reactivity, and how to determine the quantitative relations between the amounts of substances involved in chemical reactions—that is, the reaction stoichiometry. 176 Chapter 4 Stoichiometry of Chemical Reactions 4.1 Writing and Balancing Chemical Equations By the end of this section, you will be able to: • Derive chemical equations from narrative descriptions of chemical reactions. -
Answer Key Chapter 6: Standard Review Worksheet 1
Answer Key Chapter 6: Standard Review Worksheet 1. 1 amu = 1.66 _ 10–24 g. For example, the average atomic mass of sodium is 22.99 amu, which represents the average mass of all the sodium atoms in the world (including all the various isotopes and their relative abundances). So that we will be able to use the mass of a sample of sodium to count the number of atoms of sodium present in the sample, we consider that every sodium atom in a sample has exactly the same mass (the average atomic mass). The average atomic mass of an element is typically not a whole number of amu’s because of the presence of the different isotopes of the element, each with its own relative abundance. Since the relative abundance of an element can be any number, when the weighted average atomic mass of the element is calculated, the average is unlikely to be a whole number. 2. On a microscopic basis, one mole of a substance represents Avogadro’s number (6.022 _ 1023) of individual units (atoms or molecules) of the substance. On a macroscopic basis, one mole of a substance represents the amount of substance present when the molar mass of the substance in grams is taken (for example, 12.01 g of carbon will be one mole of carbon). 3. The molar mass of a compound is the mass in grams of one mole of the compound (6.022 _ 1023 molecules of the compound) and is calculated by summing the average atomic masses of all the atoms present in a molecule of the compound. -
15-1 SECTION 15 ELECTROCHEMISTRY Electrochemistry: the Branch of Chemistry That Covers the Relative Strengths of Oxidants and R
15-1 SECTION 15 ELECTROCHEMISTRY Some systems involving redox reactions can be designed so that the reactants (and products) are partially separated from each other, and the reaction leads to an electric current being produced in an external circuit, and which can be used for many useful purposes. Batteries and their many uses are the obvious examples. Electrical energy can also be used to drive non-spontaneous chemical reactions to produce desired products in processes known as electrolysis. This section introduces the language and concepts of these processes collectively known as electrochemistry. Electrochemistry: The branch of chemistry that covers the relative strengths of oxidants and reductants, the production of electric current from chemical reactions, and the use of electricity to produce chemical change. Electrochemical cell: A system made up of two electrodes in contact with an electrolyte. Electrode: A conductor of electricity, commonly a metal or graphite in contact with an electrolyte in an electrochemical cell. Electrolyte: A medium (phase) which conducts electricity by the movement of ions [e.g. a molten salt] or a substance which dissolves in a solvent to give a conducting solution [e.g. aqueous sodium chloride, NaCl or any other soluble ionic compound]. Electrode reaction: A chemical reaction occurring at an electrode involving gain or loss of electrons. It is called a half-reaction. [e.g. Cu2++ 2e– → Cu; Zn → Zn2+ + 2e– ] (See page 12-4.) Redox couple: The two species of a half- reaction involving oxidation or reduction. (See 2+ – page 12-3.) Represented as oxidised species/reduced species [e.g. Cu /Cu; Cl2/Cl ; Fe3+/Fe2+]. -
Chemical Reactions Name C2H4O2 + Nahco3
Chemical Reactions Name ________________________ 1. Look at the chemical equation for the reaction between vinegar and baking soda to answer the following questions. C2H4O2 + NaHCO3 → NaC2H3O2 + H2O +CO2 acetic acid + sodium bicarbonate → Sodium acetate + Water + carbon dioxide What are the reactants in this chemical reaction? What are the products in this chemical reaction? C2H4O2 + NaHCO3 → NaC2H3O2 + H2O +CO2 Atom Reactant side Product side Carbon Hydrogen Oxygen Sodium 2. How many of each type of atom appears on each side of the chemical equation? 3. What does the statement “Mass is conserved during a chemical reaction” mean? Activity Question to investigate How can you make just the right amount of foam that rises to the top of the graduated cylinder without overflowing? Materials for each group • Vinegar in a cup • Baking soda in a cup • Detergent solution in a cup • Dropper • Graduated cylinder (50 mL) • Measuring spoons • Plastic overflow container Procedure 1. Decide on how much vinegar and baking soda you will use and write these amounts in the chart on the activity sheet. 2. Use a graduated cylinder to measure the amount of vinegar your group agreed on. 3. Pour the vinegar in a small cup and add 1 drop of detergent. Swirl gently to mix. 4. Add the amount of baking soda your group agreed on to the empty graduated cylinder. 5. Place the graduated cylinder in a plastic overflow container. 6. Pour the vinegar and detergent from the cup into the graduated cylinder. Observe the level of foam in the graduated cylinder 7. Rinse the graduated cylinder over the waste container. -
Experiment 9
Experiment Molar Mass by Vapor Density 7 Vapor is the term for a gas produced from the vaporization of a liquid. If it is assumed that the resulting vapor is an ideal gas, then we can use the ideal gas law: By substituting moles for mass and molar mass the following equation is derived after some simple rearrangements: The molar mass of the compound is represented by Mm and d is the vapor density in g per liter. Another way to calculate the molar mass of the sample is to determine the moles of the gas produced. The number of moles can be determined from the measured volume, pressure, ad temperature of the gas. From the mass of the liquid sample used and the moles calculated from experimental measurements, the molar mass of the sample can be determined. Many organic compounds are liquids that vaporized below the boiling point of water. A boiling water bath will be used as a constant temperature (100 C or 373 K) heat source to convert your unknown liquid to a gas. The pressure of the gas will be the barometric pressure of the room and the volume is the volume of the gas inside the container (flask). In this experiment, you will be given an unknown liquid and you will determine the molar mass of the liquid. Equipment and Reagents Analytical balance unknown liquid high capacity balance 200 mL flask tap water thermometer Aluminum foil stand w/ iron ring barometer Pin wire gauze 600 mL beaker buret clamp 1 Procedure 1. On an analytical balance weigh a 200 mL Erlenmeyer flask with a piece of aluminum foil large enough to cover the mouth of the flask.