Unit 7 Notes Page 1 of 16
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CRHS Academic Chemistry
Unit 7 - Chemical Quantities
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7.1 INTRODUCTION TO THE “MOLE”
What is a MOLE?
A mole is __6.02x1023______particles______of a pure substance. This is called _____Advogadro’s______number. We use Avogadro’s number and “mole” the same way we use 12 and “dozen”. Mole is abbreviated as ___mol______(this does _not______mean __molecule______).
What is Molar Mass? How do I calculate it?
Molar mass is the ___mass______of 1 __mol______of a compound. Its units are __g/mol______.
To calculate molar massof an element or compound:
1)Make a __chart______of the elements present and how many atoms of each there are.
2)Use the periodic table to determine the ____atomic______mass______of each element (round to the hundredths).
3)_____Multiply______across the chart.
4)___Add______up the totals.
Example: Na2SO4
Na: 2 x22.99 = 45.98
S:1 x32.07 = 32.07
O:4 x16.00 = 64.00
142.04 g/mol
Practice:
1)Calculate the molar mass of zinc.
2)What is the molar mass of barium nitrate? Ba(NO3)2
Ba: x137.33 = 137.328
N:2 x14.007 = 28.014
O:6 x15.999 = 95.994
261.34 g/mol
3)You decide to electroplate your old rims on your 1977 Cadillac Eldorado with a bright silver finish and find a nickel color to be your favorite. The substance used for nickel electroplating is called nickel (II) phosphate. Determine the molar mass of nickel (II) phosphate.
Ni3(PO4)2
Ni: 3 x58.693 = 176.079
P:2 x30.974 = 61.948
O:8 x15.999 = 127.992
366.019 g/mol
7.2 MOLE TO MASS AND MASS TO MOLE CONVERSIONS
How do I convert from MOLES to mass?
1)Calculate the ____molar mass______of the compound.
2)Use the conversion factor created in step 1 in dimensional analysis to find the number of moles.
Example:
What is the mass of 2.50 mol of NaCl? 22.999 (Na) + 35.453 (Cl) = 58.443 g/mol NaCl
Practice:
1)What is the mass of 2.32 mol of dicarbon hexahydride?
C2H6
C = 2 x 12.011 = 24.022
H = 6 x 1.008 = 6.048
30.070 g/mol
2)You need 1.70 moles of calcium hydroxide to make your magic “potion” for the traveling carnival in which you portray a magician. You have 86 grams of the powder in your apothecary’s chest. Do you have enough to make your potion?
Ca(OH)2
Ca = 1 x 40.078 = 40.078
O = 2 x 15.999 = 31.998NO
H = 2 x 1.008 = 2.016
74.092 g/mol
How do I convert from mass to MOLES?
1)Calculate the _____molar mass______of the compound.
2)Use the conversion factor created in step 1 in dimensional analysis to find the number of moles.
Example:
How many moles are in 74 g of potassium sulfide?
K2S
K = 2 x 39.098 = 78.196
S = 1 x 32.066 = 32.066
110.26 g/mol
Practice:
1)How many moles are in 39 g of barium hydroxide?
Ba(OH)2
Ba = 1 x 137.328 = 137.328
O = 2 x 15.999 = 31.998
H = 2 x 1.008 = 2.016
171.342 g/mol
2)Heading into your last lap around campus, Coach Beasley yells, “You can have 1 mole of water when you finish this lap!” However, you finish and chug 100 g of water. How many moles are in 100 g of water?
H2O
H = 2 x 1.008 = 2.016
O = 1 x 15.999 = 15.999
18.015 g/mol
7.3 REPRESENTATIVE PARTICLES
What are representative particles?
A representative particle is the __smallest______unit of a pure substance that still holds the ____properties______of that substance!
Example / Symbol / Pure Substance / Representative Particlepotassium / K / element / Atoms
magnesium chloride / MgCl2 / Ionic compound / Formula unit
diphosphorous pentoxide / P2O5 / Covalent compound / Molecules
fluorine* / F2 / *Diatomic Molecule / Molecules
*Diatomic Molecules are ___elements______that only exist in nature in their “pure” form bonded to another identical atom. For example, fluorine ONLY exists “by itself” in nature bonded to another atom of fluorine. It is still called fluorine, but is written F2.
The Diatomic Molecules are:
H2N2O2F2Cl2Br2I2
You can use the mnemonic “Dr.___HOFBrINCl______”
How do I convert from MOLES to particles?
1)Remember : 1 mole of anything = 6.02 x 1023 __particles______
2)Use the above __conversion______factor______in dimensional analysis to calculate the number of representative particles.
3)End with the correct _unit______for the compound type.
Example:
How many representative particles are in 0.72 mol of Zn?
Practice:
1)How many representative particles are in 7.5 mol of sulfur dioxide?
What are the representative particles for SO2 called?molecules
2)How many representativeparticles are in 0.4 mol of potassium chloride?
What are the representative particles called? Formula Units
How do I convert from particles to MOLES?
1)Use _Advogadro’s _____ number in dimensional analysis to calculate the number of moles present
Example:
How many moles are in 8.34 x 1024 molecules of bromine?
Practice:
1)How many moles are in 4.81 x 1024 atoms ofrubidium?
2)To fill a 4 liter tank with nitrogen dioxide you need 16 moles of the gas. If you have 3.4 x 1026 molecules of nitrogen dioxide, will the tank fill?
Yes it will fill the tank.
7.4 MIXED MOLE CONVERSIONS
Mixed mole questions ask you to convert between_mass______and ___particles______. To do these conversions you MUST convert to _moles______before converting from particles to mass or mass to particles.
How do I solve a mixed mole problem?
1)Use dimensional analysis and start with the __given______.
2)Find the ___molar mass______of substances when necessary.
Example
How many formula units in 20.0 g of CaCl2? Molar Mass = 40.08 + (2 x 35.45) = 110.98 g/mol CaCl2
Practice:
1)How many atoms of sodium are you eating when you consume 1.09 g of sodium (the amount in a sausage McGriddle)?
2)How many grams in 4.29 x 1039formula units of sodium sulfate? Na2SO4
Na – 2 x 22.99 = 45.980
S – 1 x32.066= 32.066
O – 4 x 15.999= 53.996
142.042 g/mol
3)You just inhaled 57 grams of the toxic gas carbon tetrachloride. A lethal dose is 2.26 x 1024 molecules of the gas. Are you going to die from this dose?
CCl4
C = 1 x 12.011 = 12.011
Cl = 4 x 35.45) = 141.812
______
153.823 g/mol
7.5 PERCENT COMPOSITION
Percent composition is the ____percent______, by __mass______, of each element in a compound.
% composition of an element = x 100%
1)Calculate the __Molar Mass of the compound.
Example: CO2(C) 1 x 12.011 = 12.011
(O) 2 x 15.999 = 31.998 +
44.009 g/mol
2)Look at the calculations above. For each element, we have already calculated the ______in the compound.
(C) 1 x 12.011 = 12.011 g/mol mass of C in CO2
(O) 2 x 15.999 = 31.998 g/mol mass of O in CO2
3)Using the formula, solve for % composition for each element.
C O
Practice:
1)Find the % composition of each element in ammonium chloride.
NH4Cl Molar mass = 14.007+4(1.008)+35.453 = 53.492 g/mol
N:
2)What is the % composition of each element in mercury (IV) oxide?
HgO2 Molar Mass = 200.59 + 2(15.999) = 232.588 g/mol = 232.59 g/mol
7.6 EMPIRICAL FORMULA
Empirical Formula
The empirical formulaof a compoundis the formula with the ____lowest______whole number ___ratio______of elements.
How do I calculate it?…
Youwill be given either:
- The actual __mass______of the elements in the compound or
- The_%______compositions. The ___ratio______of elements in a compound is preserved in a percentage, so we can just change the ___given___ from ___percent(%)______to ____grams (g_____!
1)Use ___the mass______of each element to determine the number of ___moles______of each element.
2)Divide all ____moles______by the ____lowest______mole number.
3)If whole numbers, apply these numbers as ___subscripts______to their corresponding elements in the compound.
4)IF NOT WHOLE NUMBERS, Convert to ____lowest______whole number ratio. To do this: multiply results by a common number. Apply these numbers as subscripts.
For example:
Phosphorus = 1x 2 = 2Nitrogen = 1x 3 = 3
Oxygen = 2.5x 2 = 5Chlorine = 1.33x 3= 4
P1O2.5 P2O5N3Cl4
Example:
Determine the empirical formula for a compound that contains 40.05 g sulfur and 59.95 g oxygen.
Practice:
1)What is the empirical formula of a compound that contains 5.90 g hydrogen and 94.1 g oxygen?
2)Determine the empirical formula for a compound that contains 48.64% carbon, 8.16% hydrogen, and 43.20% oxygen.
x 2 = 3 C
x 2 = 6 H
x 2 = 2 O
3)While an undergraduate assistant in food chemistry, you discover a new non-nutritive sugar substitute that tastes better than maple syrup. After evaluating the substance’s properties you find the substance contains12.12% carbon, 71.72% chlorine, and 16.16% oxygen? From your learning, you know that a substance with more chlorine than carbon tends to cause cancer. Is your sugar substitute safe to eat?
7.7 MOLECULAR FORMULA
The molecular formula is the ___number______of atoms ofeach element in a compound. In order to find the molecular formula you need to compare the ______mass______of the compound with the mass of the ____ermpirical______formula.
How do I find the molecular formula?
1)Determine the _____mass______of the ______empirical______formula.
2)Find the scale.
Round the Scale to the nearest whole number.
3)“_____Scale up______” empirical formula. ____Multiply______# atoms of each element by the scale from ___#2 above______.
Example:
Find the molecular formula for a compound with a molar mass of 78.12 g/mol and an empirical formula of CH.
1)Molar Mass of CH = 1(C) x 12.011 + 1(H) x 1.008 = 13.019 g/mol
Scale = 6 x (CH) = C6H6
2)Practice:
1)Find the molecular formula for a compound with 43.64% phosphorus and 56.36% oxygen and a molar mass of 283.88 g/mol.
A. Determine empirical formula
x 2 = 2 P
x 2 = 5 O
B. Determine Mass of P2O5C. Determine ScaleD. Multiply empirical formula
P – 2x30.974 = 61.946283.88/141.943 = 2by scale to get molecular formula
O – 5 x 15.999 = 79.995
141.943 g/mol2 x P2O5 = P4O10
2)As a medical bioengineer, you encounter a compound capable of curing seasonal allergies. You know one mole has a mass of 90.04 grams. You have used mass spectrometry to surmise the substance has an empirical formula of CHO2. Find the molecular formula of the compound.
A. Mass of CHO2B. Determine Scale
C – 12.01190.04/45.02 = 2
H – 1.008
O – 2 x 16.00 = 32.00C. Multiply empirical formula by scale
Sum = 45.02 gCH02 x 2 = C2H2O4
3)Find the molecular formula for a compound with 46.68% nitrogen and 53.32% oxygen and a molar mass of 60.01 g/mol.
A. Determine empirical formula
N - 46.68/14.007 = 3.333 3.333/3.333 = 1
O – 53.32/16.00 = 3.333 3.333/3.333 = 1
Empirical Formula = NO
B. Mass of NO = 14.007 + 16.00 = 30.01
C. Scale = 60.01/30.01 = 2
D. Multiply empirical formula by 2 -> 2 x NO -> N2O2
Common Polyatomic Ions List
Name / Ion / Name / Ionacetate / C2H3O2–or CH3COO– / hypochlorite / ClO–
ammonium / NH4+ / nitrate / NO3–
carbonate / CO32– / nitrite / NO2–
chlorate / ClO3– / perchlorate / ClO4–
chlorite / ClO2– / permanganate / MnO4–
chromate / CrO42– / phosphate / PO43–
cyanide / CN– / phosphite / PO33–
dichromate / Cr2O72– / silicate / SiO32–
hydrogen carbonate / HCO3– / sulfate / SO42–
hydroxide / OH– / sulfite / SO32–
How to key scientific notation into a TI calculator:
Type in 6.02 x 1023:
Should display:
How to key molar mass into a TI calculator in ONE STEP!:
Example: Na2SO4