YOU WERE LOOKING FOR: 7.1 The Mole A Measurement Of Matter Section Review Answers
Presentation on theme: "Unit 6 Review The Mole. Which of the following sets of empirical formula, molar mass, and molecular formula is correct A. CH, 78 g, C13H13 B. NO3, g, N3O9 3 A. Kelvin 2. What SI unit is used to measure the number of...
A moles B moles C moles D moles 8 7. How many moles are in Empirical formula B. Molecular formula C. Mole formula 9. Mole formula D. None of the above 11 How many hydrogen atoms are in 5 molecules of isopropyl alcohol, C3H7O? Which of the...
Chemistry Chapter 10 The Mole Study Guide Answers Each contestant creates a beautiful work of art out of millions of tiny grains of sand. It also teaches you how to calculate the mass of a mole of any substance. Look at Figure Avogadro's number of representative particles, or 6. Then add the masses of the elements in the compound. Chemistry Chapter Each element has an atomic mass that can be found in the periodic table. What is the molar mass of each of the following compounds? Calculate the molar mass of each of the following ionic compounds: a. What is the percent composition of a compound? A Measurement of Matter Describe how Avogadro's number is related to a mole of any substance Solve problems involving mass in grams, amount in moles 1. Convert the given amount of atoms to the amount of moles by dividing by Avogadro's number.
Answer: 1. The amount in The number of representative 2. To find the mass of a mole of a compound, scientists add 4. It measures the amount of substance of a system containing as many elementary entities equal to number of atoms. A mole is a unit of measurement used in chemistry to express the amounts of molecules within a substance. Describe the relationship between Avogadro's number and one mole of any substance. The percent composition of a compound is the Copyright 4. Search Results I really can't understand why is the mole a unit of measurement and not just a constant.
I mean, we use units to express things that we can measure but that are not Mole is a unit that has become the way of scientist and those who are interested in the filed to count the number of substances or atoms. A mole is defined as the amount of substance that contains Avogardro number of the substance. Avogadro's number is given by.
The number 6. The concept of the mole can be used to convert between mass and number of particles. A mole of a substance or a mole of particles is defined as exactly 6. Translation: "Each compound has a definite, unchanging chemical formula. What is a Mole? A mole is defined as the amount of a substance that contains the number of carbon atoms in exactly 12 g of isotopically The definition of a mole—that is, the decision to base it on 12 g of carbon—is arbitrary but one arrived at after some discussion between This is sometimes known as the 'molar gas volume' as it contains the Avogadro Number of particles.
In more general terms, Avogadro's Law states that equal volumes of all gases at the same temperature and pressure contain the same number of particles. Download Report. The density of a gaseous compound containing carbon and oxygen is 1. Determine the molar mass of the compound. Slide All of the digits in a measurement, including the Scientists typically make repeated measurements of a quantity to ensure the quality of their findings and to know both the precision and the accuracy of It is defined as the amount of a substance that contains as many elementary It is measured in units of cubic centimeters in metric.
Yahoo Answers 2. Calculate the mole fraction of KCl in the solution. Source s : Mastering Chemistry: the measurements in the question changed. How do you think about the answers? You can sign in to vote the answer.
Chapter 3. Composition of Substances and Solutions 3. Given the chemical formula of the substance, we were able to determine the amount of the substance moles from its mass, and vice versa. But what if the chemical formula of a substance is unknown? In this section, we will explore how to apply these very same principles in order to derive the chemical formulas of unknown substances from experimental mass measurements. Percent Composition The elemental makeup of a compound defines its chemical identity, and chemical formulas are the most succinct way of representing this elemental makeup.
For example, consider a gaseous compound composed solely of carbon and hydrogen. What is the percent composition of this compound? Check Your Learning A Answer: The element nitrogen is the active ingredient for agricultural purposes, so the mass percentage of nitrogen in the compound is a practical and economic concern for consumers choosing among these fertilizers. For these sorts of applications, the percent composition of a compound is easily derived from its formula mass and the atomic masses of its constituent elements. A molecule of NH3 contains one N atom weighing The formula mass of ammonia is therefore The latter amount is most convenient and would simply involve the use of molar masses instead of atomic and formula masses, as demonstrated Example 2.
As long as we know the chemical formula of the substance in question, we can easily derive percent composition from the formula mass or molar mass. What is its percent composition? It is convenient to consider 1 mol of C9H8O4 and use its molar mass Check Your Learning To three significant digits, what is the mass percentage of iron in the compound Fe2O3? However, we must keep in mind that chemical formulas represent the relative numbers, not masses, of atoms in the substance. Therefore, any experimentally derived data involving mass must be used to derive the corresponding numbers of atoms in the compound. To accomplish this, we can use molar masses to convert the mass of each element to a number of moles. We then consider the moles of each element relative to each other, converting these numbers into a whole-number ratio that can be used to derive the empirical formula of the substance.
Consider a sample of compound determined to contain 1. The corresponding numbers of atoms in moles are: [latex]1. The empirical formula for this compound is thus CH2. Consider as another example a sample of compound determined to contain 5. To convert this into a whole number, we must multiply each of the subscripts by two, retaining the same atom ratio and yielding Cl2O7 as the final empirical formula. Figure 1. The empirical formula of a compound can be derived from the masses of all elements in the sample.
What is the empirical formula of hematite? Figure 2. Hematite is an iron oxide that is used in jewelry. Check Your Learning What is the empirical formula of a compound if a sample contains 0. Answer: For additional worked examples illustrating the derivation of empirical formulas, watch the brief video clip. In such cases, the percent composition can be used to calculate the masses of elements present in any convenient mass of compound; these masses can then be used to derive the empirical formula in the usual fashion. Determining an Empirical Formula from Percent Composition Example 4 The bacterial fermentation of grain to produce ethanol forms a gas with a percent composition of What is the empirical formula for this gas? Figure 3. An oxide of carbon is removed from these fermentation tanks through the large copper pipes at the top. Check Your Learning What is the empirical formula of a compound containing Determining the absolute numbers of atoms that compose a single molecule of a covalent compound requires knowledge of both its empirical formula and its molecular mass or molar mass.
These quantities may be determined experimentally by various measurement techniques. Molecular mass, for example, is often derived from the mass spectrum of the compound see discussion of this technique in the previous chapter on atoms and molecules. Molar mass can be measured by a number of experimental methods, many of which will be introduced in later chapters of this text. As the name suggests, an empirical formula mass is the sum of the average atomic masses of all the atoms represented in an empirical formula. The empirical formula mass for this compound is approximately 30 amu the sum of 12 amu for one C atom, 2 amu for two H atoms, and 16 amu for one O atom. In this case, we are merely considering one mole of empirical formula units and molecules, as opposed to single units and molecules. Example 5 Determination of the Molecular Formula for Nicotine Nicotine, an alkaloid in the nightshade family of plants that is mainly responsible for the addictive nature of cigarettes, contains If The empirical formula mass for this compound is therefore Answer: C8H10N4O2 Key Concepts and Summary The chemical identity of a substance is defined by the types and relative numbers of atoms composing its fundamental entities molecules in the case of covalent compounds, ions in the case of ionic compounds.
Determine the empirical formulas for compounds with the following percent compositions: a What is its molecular formula? Dichloroethane, a compound that is often used for dry cleaning, contains carbon, hydrogen, and chlorine. Analysis of a sample shows that it contains Determine the empirical and molecular formula for chrysotile asbestos. Chrysotile has the following percent composition: The molar mass for chrysotile is Polymers are large molecules composed of simple units repeated many times. Thus, they often have relatively simple empirical formulas. Calculate the empirical formulas of the following polymers: a Lucite Plexiglas ; The dye has a percent composition of Determine the molecular formula of the dye. Glossary sum of average atomic masses for all atoms represented in an empirical formula percent composition percentage by mass of the various elements in a compound Solutions Answers to Chemistry End of Chapter Exercises 2.
This section is a review of Chapter 1 Section 1. In the rest of Chapter 7 we will use the mole to calculate the outcomes of reactions, how much of one substance reacts with another, how many molecules a mass of a substance contains, what are chemical reactions and how do we account for the number of molecules of one kind that react with another and how many different products molecules the reaction produces. The name that chemists use for such things is stoichiometry.
We have been using the mole concept in previous chapters to do problems, you have been using it in ALeKs problems and you have been also using it in General Chemistry Laboratory. What follows is a bare bones review. More problems and a more thorough review can be found in Section 1. The mass number is the sum of the numbers of protons and neutrons present in the nucleus of an atom.
The mass number is an integer that is approximately equal to the numerical value of the atomic mass with the difference being accounted for by binding energy. Although the mass number is unitless, it is assigned units called atomic mass units amu. Because a molecule or a polyatomic ion is an assembly of atoms whose identities are given in its molecular or ionic formula, we can calculate the average atomic mass of any molecule or polyatomic ion from its composition by adding together the masses of the constituent atoms. The average mass of a monatomic ion is the same as the average mass of an atom of the element because the mass of electrons is so small that it is insignificant in most calculations. We must differentiate between the mass in amu of a single isotope and the atomic weight of an element given in the periodic table chart.
The latter is an average over the naturally occuring isotopes accounting for the mass percentage of each as they occur in nature. Molecular and Formula Masses - Review The molecular massThe sum of the average masses of the atoms in one molecule of a substance, each multiplied by its subscript. It is calculated by adding together the atomic masses of the elements in the substance, each multiplied by its subscript written or implied in the molecular formula. Because the units of atomic mass are atomic mass units, the units of molecular mass are also atomic mass units. The procedure for calculating molecular masses is illustrated in Example 1. Among its many uses, ethanol is a fuel for internal combustion engines. Given: molecule Strategy: A Determine the number of atoms of each element in the molecule.
B Obtain the atomic masses of each element from the periodic table and multiply the atomic mass of each element by the number of atoms of that element. C Add together the masses to give the molecular mass. So for ionic compounds we use the formula mass also called the empirical formula massAnother name for formula mass. The formula massThe sum of the atomic masses of all the elements in the empirical formula, each multiplied by its subscript. It is directly analogous to the molecular mass of a covalent compound. Once again, the units are atomic mass units. Example 2 Calculate the formula mass of Ca3 PO4 2, commonly called calcium phosphate. This compound is the principal source of calcium found in bovine milk. Given: ionic compound Strategy: A Determine the number of atoms of each element in the empirical formula. C Add together the masses to give the formula mass.
The formula mass of this molecular unit is calculated by adding together the atomic masses of three calcium atoms, two phosphorus atoms, and eight oxygen atoms. Chemists need a way of simply determining how many molecules they have in a beaker. The mole concept bridges that gap by relating the mass of a single atom or molecule in amu to the mass of a collection of a large number of such molecules in grams. Grams rather than kilograms are used, because the mole concept was introduced at a time when the base units of the measuring system were centimeters, grams and seconds, rather than today's SI units of meters, kilograms and seconds.
Also, because, well a kilogram of a compound is a rather large amount of stuff. A mole is defined as the amount of a substance that contains the number of carbon atoms in exactly 12 g of isotopically pure carbon According to the most recent experimental measurements, this mass of carbon contains 6. Since gas in a volume can be weighted on a sensitive balance, we can determine the mass in grams g of a number of molecules.
This, indeed, up until the beginning of the 20th century, was the most accurate way of determining the molecular weight of a molecule that could be voltatized. You will do an experiment in General Chemistry Laboratory that uses this method. The definition of a mole—that is, the decision to base it on 12 g of carbon—is also arbitrary. The important point is that 1 mol of carbon—or of anything else, whether atoms, compact discs, or houses—always has the same number of objects: 6. Note the Pattern One mole always has the same number of objects: 6. The concept of the mole allows us to count a specific number of individual atoms and molecules by weighing measurable quantities of elements and compounds. To obtain 1 mol of carbon atoms, we would weigh out 12 g of isotopically pure carbon Because each element has a different atomic mass, however, a mole of each element has a different mass, even though it contains the same number of atoms 6.
Because of the way in which the mole is defined, for every element the number of grams in a mole is the same as the number of atomic mass units in the atomic mass of the element. Because the atomic mass of magnesium For example, 1 mol of water H2O has 2 mol of hydrogen atoms and 1 mol of oxygen atoms. Molar Mass The molar massThe mass in grams of 1 mol of a substance. One mole of isotopically pure carbon has a mass of 12 g. For an element, the molar mass is the mass of 1 mol of atoms of that element; for a covalent molecular compound, it is the mass of 1 mol of molecules of that compound; for an ionic compound, it is the mass of 1 mol of formula units.
That is, the molar mass of a substance is the mass in grams per mole of 6. In each case, the number of grams in 1 mol is the same as the number of atomic mass units that describe the atomic mass, the molecular mass, or the formula mass, respectively. The periodic table lists the atomic mass of carbon as
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