Chemists use the mole to count atoms, molecules, ions and formula units. A mole always contains the same number of particles, however, moles of different substances have different masses. The molar mass of a compound can be calculated from its chemical formula and can be used to convert from mass to moles of that compound. A molecular formula of a compound is a whole- number multiple of its empirical formula
Explain how a mole is used to indirectly count the number of particles of matter. Relate the mole to a common everyday counting unit. Convert between moles and number of representative particles.
The mole is the SI base unit for measure of amount of a substance: 6.0221367 x 1023 The number of carbon atoms in exactly 12 g of pure carbon-12. Called Avogadro’s number – Italian physicist who in 1811, determined the volume of 1 mol of gas. By mass, we can determine the number of particles (atoms, molecules) in a sample. We typically round to 3 sig figs – 6.02 x 1023
The mole is a number. What other unit is usedin a similar manner?A dozen flowers, doughnuts or eggs. A baker’s dozen of cookies or bagels. A pair of socks or friendsIf you have a dozen flowers and a dozeneggs, do they weigh the same?
In order to convert between moles and number of particles we need to use this ratio of equivalent values (conversion factor) to express the same quantity in different units.
How many particles are in 3.5 mols?How many moles of atoms are in 9.63 x 1026 atoms?
What does the mole measure?A. mass of a substanceB. amount of a substanceC. volume of a gasD. density of a gas
What is the conversion factor for determining the number of moles of a substance from a known number of particles?A.B.C. 1 particle 6.02 1023D. 1 mol 6.02 1023 particles
Recognize the mole relationships shown by a chemical formula Calculate the molar mass of a compound. Convert between number of moles and mass of a compound. Apply conversion factors to determine the number of atoms or ions in a known mass of a compound
Steps to calculate molar mass:1. Count the number of atoms in each molecule.2. Find the molar mass of each atom.3. Multiply the molar mass of each atom to the number of atoms in a compound.4. Add the total molar masses together.
Find the molar mass of the followingcompounds/molecules. H2 O NaCl H2SO4
Explain what is meant by the percent composition of a compound. Determine the empirical and molecular formulas for a compound from percent and actual mass data. Explain what a hydrate is and relate the name of the hydrate to its composition. Determine the formula of a hydrate from laboratory data.
The percent composition is a percent by mass of each element in a compound.Steps to determine percent composition of a compound:1. Assume 1 mole of a compound.2. Calculate molar mass of each element in the compound.3. Use each element’s molar mass to calculate percent by mass.
Percent by mass is a description of the amount of an element in a compound. Percent by mass = æ mass of 1 mole of element ö %mass = ç è molar mass of compound ÷ ø
What is the percent by mass of each elementin NaHCO3?
The empirical formula is the smallest whole number ratio of elements in a compound This ratio provides the subscripts for the elements. May or may not be the same as the actual molecular formula. If they are different the molecular formula will be a simple multiple of the empirical formula. Hydrogen peroxide: HO- empirical formula H2O2 – actual formula (molecular formula)
Steps to figure empirical formula from percent composition:1. Assume an overall 100g sample of the compound.2. Each element’s percentage can be used as mass in calculations.3. Use this ‘mass’ to convert to moles. This provides a ‘mole ratio’ for the compound.
Sincethese mole ratios are not whole numbers, we convert them to whole numbers what can be used as subscripts by dividing them all by the smallest ratio. (We assume the smallest mole ratio is a 1 in the compound)
A compound has the following mass percentages: C – 48.64%, H – 8.16%, O – 43.20%What is the empirical formula for this molecule?
The molecular formula specifies the actual number of atoms of each element in one molecule/formula unit of the substance.
Steps to determine the molecular formula:1. Determine the molar mass of the empirical formula.2. Determine the molar mass of the actual compound. (might be given to you)3. Divide the molar mass of the actual compound by the molar mass of the empirical formula4. Multiply all subscripts of the empirical formula by this molar mass ratio.
The mass of benzene has been experimentally determined to be 78.12 g. We know that benzene is 92 % C by mass and 8 % H by mass. What is the molecular formula of benzene?
Hydrates are solid ionic compounds in which water molecules are trapped. Hydrates are formed when water molecules adhere to the ions as the solid forms. Water molecules become a part of the crystal solid structure. The number of water molecules associated with each molecule is written following a dot after the molecular formula: Na2CO310H2O
Names of these compounds are named with a prefix representing the number of water molecules and the word hydrate. Na2CO3 10H2O – sodium carbonate decahydrate Prefixes are the same as the ones used in naming covalent molecules
An anhydrous is a compound without water. When a hydrate is heated, water molecules are driven off leaving the compound.
Steps to determining the formula of a hydrate:1. Determine the initial mass of the compound prior to heating.2. Determine the final mass of the compound after heating.3. The final mass is used to determine the number of moles of the anhydrous compound. Grams to moles
4. Calculate the difference of the initial mass and the final mass and use this mass to determine number of moles of water, grams to moles5. Number of hydrates per compound molecule (molar ratio – hydrate: anhydrous) = moles of H2O/moles of compound moles of H2O # H 2O = moles of compound
A mass of 2.50 g of blue, hydrated copper sulfate (CuSO4) ?H2O) is place in a crucible and heated. After heating, 1.59g of white anhydrous copper sulfate (CuSO4) remains. What is the formula for the hydrate? Name the hydrate.
What is the empirical formula for the compound C6H12O6?A. CHOB. C2H3O2C. CH2OD. CH3O
Which is the empirical formula for hydrogen peroxide?A. H2O2B. H2OC. HOD. none of the above
Heating a hydrate causes what to happen?A. Water is driven from the hydrate.B. The hydrate melts.C. The hydrate conducts electricity.D. There is no change in the hydrate.
A hydrate that has been heated and the water driven off is called:A. dehydrated compoundB. antihydrated compoundC. anhydrous compoundD. hydrous compound
Howdoes the mole apply to balanced equations?
How many grams of each reactant are neededto run the following reaction? How manygrams of each product are produced? (Hint:complete, balance, convert) CuSO45H2O(aq) + CaCl2(aq)
From the reaction above, how much is needed ofeach reactant in the net ionic equation toproduce the balanced amount of the precipitate?How much precipitate is produced?
The mole is a unit used to count particles of matter indirectly. One mole of a pure substance contains Avogadro’s number of particles. Representative particles include atoms, ions, molecules, formula units, electrons, and other similar particles.
One mole of carbon-12 atoms has a mass of exactly 12 g. Conversion factors written from Avogadro’s relationship can be used to convert between moles and number of representative particles. The mass in grams of 1 mol of any pure substance is called its molar mass.
The molar mass of an element is numerically equal to its atomic mass. The molar mass of any substance is the mass in grams of Avogadro’s number of representative particles of the substance. Molar mass is used to convert from moles to mass. The inverse of molar mass is used to convert from mass to moles.
Subscripts in a chemical formula indicate how many moles of each element are present in 1 mol of the compound. The molar mass of a compound is calculated from the molar masses of all of the elements in the compound. Conversion factors based on a compound’s molar mass are used to convert between moles and mass of a compound.
The percent by mass of an element in a compound gives the percentage of the compound’s total mass due to that element. The subscripts in an empirical formula give the smallest whole-number ratio of moles of elements in the compound. The molecular formula gives the actual number of atoms of each element in a molecule or formula unit of a substance. The molecular formula is a whole-number multiple of the empirical formula.
The formula of a hydrate consists of the formula of the ionic compound and the number of water molecules associated with one formula unit. The name of a hydrate consists of the compound name and the word hydrate with a prefix indicating the number of water molecules in 1 mol of the compound. Anhydrous compounds are formed when hydrates are heated.
What does Avogadro’s number represent?A. the number of atoms in 1 mol of an elementB. the number of molecules in 1 mol of a compoundC. the number of Na+ ions in 1 mol of NaCl (aq)D. all of the above
The molar mass of an element is numerically equivalent to what?A. 1 amuB. 1 moleC. its atomic massD. its atomic number
How many moles of hydrogen atoms are in one mole of H2O2?A. 1B. 2C. 3D. 0.5
What is the empirical formula of Al2Br3?A. AlBrB. AlBr3C. Al2BrD. Al2Br3
What is an ionic solid with trapped water molecules called?A. aqueous solutionB. anhydrous compoundC. hydrateD. solute
How many water molecules are associated with 3.0 mol of CoCl2 • 6H2O?A. 18B. 1.1 1025C. 3.6 1024D. 1.8 1024
How many moles of Al are in 2.0 mol of Al2Br3?A. 2B. 4C. 6D. 1
How many atoms of hydrogen are in 3.5 mol of H2S?A. 7.0 1023B. 2.1 1023C. 6.0 1023D. 4.2 1024
Which is not the correct formula for an ionic compound?A. CO2B. NaClC. Na2SO4D. LiBr2
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