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Unformatted text preview: Chapter 10
Chemical Quantities Chemical
or How you measure how much? How
You can measure mass, You s or volume, s or you can count pieces. s We measure mass in grams. s We measure volume in liters.
s s We count pieces in MOLES. We MOLES. Moles Moles
s Defined as the number of carbon Defined atoms in exactly 12 grams of carbonatoms 12. 1 mole is 6.02 x 1023 particles. s Treat it like a very large dozen
s s 6.02 x 1023 is called Avogadro's number. number. Representative particles Representative
The smallest pieces of a substance. s For an element it is an atom. For atom – Unless it is diatomic s For a molecular compound it is a For molecule. molecule s For an ionic compound it is a For formula unit. formula
s Conversion factors Conversion
Used to change units. s Three questions – What unit do you want to get rid of? – Where does it go to cancel out? – What can you change it into?
s Calculation question Calculation
s How many molecules of CO2 are the in 4.56 moles of CO2 ? 4.56 Calculation question Calculation
s How many moles of water is 5.87 x 1022 molecules? molecules? Calculation question Calculation
s How many atoms of carbon are there in How 1.23 moles of C6H12O6 ? 1.23 Measuring Moles Measuring
The amu was one twelfth the mass of a The carbon 12 atom. carbon s Since the mole is the number of atoms Since in 12 grams of carbon-12, in s the decimal number on the periodic the table is table – The mass of the average atom in The amu amu – the mass of 1 mole of those atoms in the grams. grams.
s Gram Atomic Mass Gram
The mass of 1 mole of an element in The grams. grams. s 12.01 grams of carbon has the same 12.01 number of atoms as 1.01 grams of hydrogen and 55.85 grams of iron. hydrogen s We can write this as We 12.01 g C = 1 mole s We can count things by weighing We them. them.
s Examples Examples
s How much would 2.34 moles of How carbon weigh? carbon Examples Examples
s How many moles of magnesium in How 4.61 g of Mg? 4.61 Examples
s How many atoms of lithium in 1.00 g How of Li? of Examples
s How much would 3.45 x 1022 atoms of U weigh? of What about compounds? What
in 1 mole of H2O molecules there are molecules two moles of H atoms and 1 mole of O atoms atoms s To find the mass of one mole of a To compound – determine the moles of the determine elements they have elements – Find out how much they would Find weigh weigh – add them up
s What about compounds? What
s s What is the mass of one mole of CH4? 1 mole of C = 12.01 g s 4 mole of H x 1.01 g = 4.04g
s 1 mole CH4 = 12.01 + 4.04 = 16.05g Molar Mass Molar
s s s The mass of 1 mole What is the molar mass of Fe2O3? 2 moles of Fe x 55.85 g = 111.70 g s 3 moles of O x 16.00 g = 48.00 g s The GFM = 111.70 g + 48.00 g = 159.70g Calculate the molar mass of the following following
s s C6H12O6 (NH4)3PO4 Using Molar Mass Using
Finding moles of compounds Counting pieces by weighing Molar Mass Molar
The number of grams in 1 mole of The atoms, formula units, or molecules. atoms, s We can make conversion factors We from these. from s To change grams of a compound to To moles of a compound. moles s Or moles to grams
s For example For
s How many moles is 5.69 g of NaOH? 1 mole 40.00 g q need to change grams to moles q for NaOH q 1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g q 1 mole NaOH = 40.00 g 5.69 g For example For
s How many moles is 5.69 g of NaOH? 1 mole 5.69 g = 0.142 mol NaOH 40.00 g need to change grams to moles q for NaOH q 1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g q 1 mole NaOH = 40.00 g
q Gases and the Mole Gases s Many Many of the chemicals we deal with are gases. are s They are difficult to weigh, so we’ll They measure volume measure s Need to know how many moles of gas Need we have. we s Two things affect the volume of a gas s Temperature and pressure s Compare at the same temp. and Compare pressure. pressure. Gases Gases Standard Temperature and Pressure Pressure
s Avogadro's Hypothesis - at the same temperature and pressure equal volumes of gas have the same number of particles. of s 0ºC and 1 atmosphere pressure 0ºC s Abbreviated atm s 273 K and 101.3 kPa s kPa is kiloPascal At Standard Temperature and At and Pressure
s abbreviated STP s At STP 1 mole of gas occupies 22.4 L s Called the molar volume Called molar s Used for conversion factors s Moles to Liter and L to mol Examples Examples
sWhat What is the volume of 4.59 mole of CO2 gas at STP? mole Density of a gas Density
D = m /V /V s for a gas the units will be g / L s We can determine the density of any We gas at STP if we know its formula. gas s To find the density we need the mass To and the volume. and s If you assume you have 1 mole than If the mass is the molar mass (PT) the s At STP the volume is 22.4 L.
s Examples Examples
s Find the density of CO2 at STP. at Quizdom
s Find the density of CH4 at STP. The other way The
s Given Given the density, we can find the molar mass of the gas. molar s Again, pretend you have a mole at Again, STP, so V = 22.4 L. STP, sm = D x V s m is the mass of 1 mole, since you is have 22.4 L of the stuff. have s What is the molar mass of a gas with a What density of 1.964 g/L? density All the things we can change All Volume 22.4 L PT Mass Moles 6.02 x 1023 Representative Particles Atoms Count Ions Percent Composition Percent
Like all percents s Part x 100 % Part whole whole s Find the mass of each component, s divide by the total mass.
s Example Example
s Calculate the percent composition of Calculate a compound that is 29.0 g of Ag with 4.30 g of S. 4.30 Getting it from the formula Getting
If we know the formula, assume you If have 1 mole. have s Then you know the pieces and the Then whole. whole.
s Examples Examples
s Calculate the percent composition of Calculate C2H4? Examples Examples
s What is the percent composition of What Aluminum carbonate. Aluminum Percent to Mass Percent
Multiply % by the total mass to find Multiply the mass of that component. the s How much aluminum in 450 g of How aluminum carbonate?
s Empirical Formula Empirical
From percentage to formula The Empirical Formula The
s The The lowest whole number ratio of elements in a compound. elements s The molecular formula the actual The ratio of elements in a compound. ratio s The two can be the same. The s CH empirical formula 2
sC H 24 sC H 36 s H 2O molecular formula molecular formula both Finding Empirical Formulas Finding
s Just find the lowest whole number ratio sC H O 6 12 6 s CH N 42 s It It is not just the ratio of atoms, it is also the ratio of moles of atoms. the Calculating Empirical Formulas Calculating
s Means Means we can get ratio from percent composition. composition. s Assume you have a 100 g. s The percentages become grams. s Turn grams to moles. Turn s Find lowest whole number ratio by Find dividing everything by the smallest moles. moles. s Calculate Calculate the empirical formula of a compound composed of 38.67 % C, 16.22 % H, and 45.11 %N. 16.22 s Assume 100 g so s 38.67 g C x 1mol C = 3.220 mole C 38.67 12.01 gC s 16.22 g H x 1mol H = 16.1 mole H 16.22 1.01 gH 1.01 s 45.11 g N x 1mol N = 3.220 mole N 45.11 14.01 gN 14.01 Example Example Example Example
s The ratio is 3.220 mol C = 1 mol C 3.220 molN 1 mol N s The ratio is 16.1 mol H = 5 mol H 3.220 molN 1 mol N
sC H N 151 s Caffeine Caffeine is 49.48% C, 5.15% H, 28.87% N and 16.49% O. What is its empirical formula? empirical Empirical to molecular Empirical
s Caffeine Caffeine is 49.48% C, 5.15% H, 28.87% N and 16.49% O. What is its empirical formula? formula? s Since the empirical formula is the lowest Since ratio the actual molecule would weigh the same or more. same s By a whole number multiple. s Divide the actual molar mass by the the Divide mass of one mole of the empirical formula. mass s You will get a whole number. s Multiply the empirical formula by this. Example Example
s A compound has an empirical formula of ClCH2 and a molar mass of 98.96 g/mol. What is its molecular formula? A compound has an empirical formula of CH2O and a molar mass of 180.0 g/mol. What is its molecular formula? s Percent to molecular Percent
s Take the percent x the molar mass –This gives you mass in one mole of This the compound the s Change this to moles –You will get whole numbers –These are the subscripts s Caffeine is 49.48% C, 5.15% H, 28.87% N Caffeine and 16.49% O. It has a molar mass of 194 g. What is its molecular formula? 194 Example Example
s Ibuprofen is 75.69 % C, 8.80 % H, 15.51 % O, and has a molar mass of about 207 g/mol. What is its molecular formula? ...
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- Spring '08