quantitative composition of compounds
DESCRIPTION
Quantitative Composition of Compounds. Define the MOLE Determine molar mass of compounds Calculate percent composition of compounds Distinguish the differences between (and be able to calculate) empirical formulas and molecular formulas. Composition of Compounds. - PowerPoint PPT PresentationTRANSCRIPT
•DEFINE THE MOLE•DETERMINE MOLAR MASS OF COMPOUNDS•CALCULATE PERCENT COMPOSITION OF COMPOUNDS•DISTINGUISH THE DIFFERENCES BETWEEN (AND BE ABLE TO CALCULATE) EMPIRICAL FORMULAS AND MOLECULAR FORMULAS
Quantitative Quantitative Composition of Composition of
CompoundsCompounds
Composition of CompoundsComposition of Compounds
Ratios of ingredients determines end result
Ratios in chemical compounds Determine identity of the substance Changing changes the entire compound Example
Chemical Measurements
How can we measure masses of atoms?
Counting by weighing
Chemical Measurements
Atomic mass:
Mole (mol):
Chemical Measurements
Avogadro’s number:
Molar mass:
The Mole
Mole – unit for counting atoms
The Mole
Molar Mass Grams of element (or compound) that contain
Avogadro’s number of atoms
The Mole
The atomic mass expressed in grams is the molar mass of an element
One mole of any element contains Avagadro’s number of atoms
The Mole
Can now convert between:
25.0 g of iron is how many moles?
mass moles molecules
The Mole
How many grams of Na are in 2.55 moles?
How many atoms of Carbon are in 2.35 grams?
Molar Mass of Compounds
One mole of a compound contains 6.022 x 10-
23 formula units of that compound
Molar Mass of Compounds
Molar mass – add molar masses of all atoms What is the molar mass of H2O?
What is the molar mass of Ca(OH)2?
Molar Mass of Compounds
How many molecules are there in a 3.46 g sample of HCl?
= 5.71 x 1022 molecules
Molar Mass of Compounds
If you burned 6.10 x 1024 molecules of ethane (C2H6) what mass of ethane did you burn?
= 304.7 g C2H6
Moles and Gases
At the same temperature and pressure, equal volumes of gases contain the same number of gas particles
STP = Standard Temperature (00 C) and Pressure (1 atmosphere)
Moles and Gases
A student fills a 1.0 L flask with CO2 at STP. How many molecules of gas are in the flask?
Moles and Gases
A container with a volume of 893 L contains how many moles of air at STP?
A chemical reaction produces 0.37 moles of N2 gas. What volume will that gas occupy at STP?
Percentage Composition of Compounds
Mass of one element in a compound compared to the total mass of the whole compound
Two ways to determine…
Percentage Composition of Compounds – from Formula
1) Calculate the molar mass2) Divide the total mass of each element in the
formula by the molar mass and multiply by 100.
Total mass of element x 100 = % of element molar mass
Percentage Composition of Compounds – from Formula
What is the percent composition of each element in table salt (NaCl)?
Should equal 100%
Percentage Composition of Compounds – from Experimental Data
1) Calculate the mass of the compound formed
2) Divide the mass of each element by the total mass of the compound and multiply by 100
Percentage Composition of Compounds
A sample of 2.45 g of aluminum oxide decomposes into 1.30 g of aluminum and 1.15 g of oxygen. What is the percent composition of each element?
Percentage Composition of Compounds
Find the percentage composition of a compound that contains 1.94 g of carbon, 0.480 g of hydrogen, and 2.58 g of sulfur in a 5.00 g sample of that compound.
Empirical Formula
A formula that gives the SIMPLEST whole-number ratio of elements in that compound
Ratio of masses (percent composition)
Ratio of atoms (formula)
Empirical Formula
What is the empirical formula of a compound containing 40% carbon, 53.3% oxygen, and 6.7% hydrogen?
Divide by smallest number
= 1
= 1
= 2
Empirical Formula
Determine the empirical formula of a compound containing 5.75 g Na, 3.5 g N, and 12.0 g O
Empirical Formula
Determine the empirical formula of a compound containing 2.644g of gold and 0.476 g of chlorine.
Molecular Formula
Formula that gives the actual number of atoms in a given compound
Some compounds may have same empirical formula but actually be very different
Sometimes empirical formula and molecular formula are the same
Compare molar mass with empirical formula mass
Molecular Formula
Ribose has a molar mass of 150 g/mol and a chemical composition of 40.0% carbon, 6.67% hydrogen, and 53.3% oxygen. What is the molecular formula for ribose?
Molecular Formula
Find the molecular formula of a compound that contains 42.56 g of palladium and 0.80 g of hydrogen. The molar mass of the compound is 216.8 g/mol.
Octane, a compound of hydrogen and carbon, has a molar mass of 114.26 g/mol. If the compound contains 18.17 g/mol hydrogen, what is its molecular formula?
Homework
Questions #1, 6-10Paired Exercises #11-31 odd (a, b, c only);
33; 37-41 oddAdditional Exercises #43, 47, 50 & 51NO CLASS TUESDAY – Study help???
Morning, afternoon, evening?
TEST THURSDAY – Chapters 11, 6 & 7TEST THURSDAY – Chapters 11, 6 & 7