Questions and Answers
What do the questions 'how much?' and 'how many?' have in common?
They are questions about the amount of a substance and are similar to questions scientists ask.
List two or three ways to measure matter.
Count the matter, measure the mass or weight, measure the volume.
What is the term of an SI unit for measuring the amount of a substance?
Mole.
What is Avogadro's number?
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What is the letter of the term that is NOT a representative particle of a substance?
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Representative particle for molecular compounds?
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Representative particle for ionic compounds?
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Representative particle for elements?
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To determine the number of representative particles in a compound, you count the molecules by viewing them under a microscope.
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How can you determine the number of atoms in a mole of a molecular compound?
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What is the atomic mass of an element?
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The atomic masses of all elements are based on the mass of the carbon isotope C-12.
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How do you determine the mass of a mole of a compound?
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What is the molar mass of a compound?
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What is the molar mass of KI (potassium iodide)?
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The volumes of one mole of different solid and liquid substances are the same.
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What is the temperature that is defined as standard temperature?
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Standard pressure is 101.3 kPa or 1 atmosphere (atm).
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What is the molar volume of a gas at standard temperature and pressure (STP)?
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What units do you normally use to describe the density of a gas?
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What is Avogadro's Hypothesis?
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Why is Avogadro's hypothesis reasonable?
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How many gas particles occupy a volume of 22.4 L at standard temperature and pressure?
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How do you express relative amounts of each element in a compound?
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The number of percent values in the percent composition of a compound is?
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What is the formula for the percent by mass of an element in a compound?
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In the diagram below, which compound has a greater percent composition of chromium?
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To calculate the percent composition of a known compound, start with the chemical formula of the compound and calculate the?
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You can use percent composition to calculate the number of grams of an element in a given amount of a compound.
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How do you calculate the grams of an element in a specific amount of a compound?
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An empirical formula of a compound gives the?
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The empirical formula of a compound is always the same as the molecular formula.
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Name three compounds that have an empirical formula of CH.
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What is the formula for the molar mass of sodium chloride (NaCl)?
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What is the molar mass of barium nitrate (Ba(NO3)2)?
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What is the percentage composition formula?
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What is the percent composition of pure chalcocite, Cu2S?
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How can you determine the last percentage in a percent composition calculation?
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How do you approach determining the formula of a compound based on percent composition?
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Study Notes
Chemical Quantities
- Questions about "how much?" and "how many?" relate to measuring the quantity of substances, significant in scientific inquiry.
- Matter can be quantified by counting particles, measuring mass or weight, and assessing volume.
SI Unit and Mole Concept
- The mole is the standard SI unit for quantifying the amount of a substance.
- Avogadro's number, approximately (6.02 \times 10^{23}), represents the number of atoms or molecules in one mole of any substance.
Representative Particles
- Different substances have unique representative particles:
- Molecular compounds: Formula unit
- Ionic compounds: Molecule
- Elements: Atoms
- "Grain" is not recognized as a representative particle.
Molecular Composition and Atomic Mass
- The number of atoms in a mole of molecular compound can be determined via its chemical formula multiplied by Avogadro's number.
- Atomic mass in atomic mass units signifies the mass of a single atom.
- Atomic masses of elements rely on the mass of the carbon isotope C-12.
Calculating Molar Mass
- Molar mass is the weight of one mole of a substance measured in grams.
- Calculated by summing the atomic masses of each atom in the compound's formula (e.g., SO3 = 80.1 amu combines 32.1 and 48.0 amu).
- The molar mass for potassium iodide (KI) is 166.0 g.
Molar Volume and Gas Laws
- Molar volume at standard temperature and pressure (STP) is 22.4 L.
- Volume of a gas changes with temperature, container size, and pressure.
- Standard temperature is defined as 0 degrees Celsius, while standard pressure is 101.3 kPa or 1 atm.
Percent Composition
- Percent composition indicates the relative amounts of each element in a compound:
- Expressed using the formula: % mass of an element = (grams of element / grams of compound) x 100%
- The number of values corresponds to the number of different elements in the compound.
Empirical and Molecular Formulas
- An empirical formula represents the simplest whole-number ratio of atoms in a compound, while it may differ from the molecular formula.
- Compounds like ethyne, styrene, and benzene share the empirical formula CH.
Mole Calculations and Applications
- 1 mole of any substance contains (6.02 \times 10^{23}) particles, a concept pivotal in stoichiometry.
- Molar mass calculations involve summing individual atomic masses (e.g., for sodium chloride, NaCl mass totals 58.5 g/mole).
Examples and Problem Solving
- To determine percent composition from a given compound, calculate the total molar mass and the mass of each element.
- A specific example provided explains the composition of copper(I) sulfide (Cu2S) showing copper at 79.87% and sulfur at 20.13%.
- In calculating grams of an element from a compound, utilize the mass of the compound and the conversion factor based on percent composition.
Final Points
- Knowing percent composition aids in formulating compound formulas and establishing their elemental ratios.
- The connection between atomic and molar mass allows for a deeper understanding of chemical quantities and reactions in chemistry.
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Description
Explore the fundamental concepts of chemical quantities in Chapter 10 of your chemistry studies. This quiz focuses on measuring matter, including mass, volume, and the SI unit for substance amount. Test your knowledge and enhance your understanding of these essential principles in chemistry.
