6-the mole concept

8/17/2019 6-The Mole Concept

1/26

The Mole ConceptMole Concept | Stoichiometry Calculations


2/26

The Concept of the Mole

•

Impossible to count all the atoms• Mole (mol): is defined as the amount of substance tha

contains the same number of elementary entities as thatoms in exactly 12 g of pure carbon-12.

1 mol = 6.02214179 × 1023 elementary entities

NA = 6.02214179 × 1023 elementary entities/mo


3/26



4/26


•

Mass of one mole of a substance = mass of an atom osubstance

1 u = 1.66 × 10−24 g


5/26

Molar Mass

•

Molar Mass: mass of one mole of atom, in g × mol

−1

AB

C

D

One mole of each element


6/26

Dimensional Analysis

•

Given unit cancels leaving the desired unitGiven Unit × Desired Unit/Given Unit = Desired U

• CF = Desired Unit/Given Unit

• For example:

1.50 cm ×

1 m/100 cm = 1.50×

10

−3

m95 USD × 46.70 Php/1 USD = 4.4365 × 103 Php


7/26

Mole Calculations

•

The conversion factor is NA1 mol = 6.02214179 × 1023 elementary entities

• Follow proper cancellation of units

mass (in grams) = mols × g/mol

amount of substance (in mols) = g × mol/g

number of entities = mols × entities/mols

amount of substance (in mols) = entities × mol/en


8/26

Mole Calculations: Dimensional Ana

•

How many atoms of sulfur are present in 4.07 g?atoms S = (4.07 g S) × (1 mol S/32.065 g S) ×

(6.022 × 1023 atoms S/1 mol S) = 7.64 × 1022 atom


9/26


•

What is the mass of 2.35×

1024

atoms of Cu?mass Cu = (2.35 × 1024 atoms Cu) × (1 mol Cu/6.022

atoms Cu) × (63.546 g Cu/1 mol Cu) = 247.98 g


10/26


•

Potassium-40 is one of the few naturally occurring radisotopes of elements of low atomic number. Its percenabundance among K isotopes is 0.012 %. How many 4atoms are present in 225 mL of whole milk containingK/mL?

mL milk → mg K → g K → mol K → atoms K → atom

225 mL milk × (1.65 mg K/mL milk) × (1 g K/1000 m

(1 mol K/39.10 g K) × (6.022 × 10−23 atom K/1 mol

(0.012 atoms 40K/100 atoms K) = 6.9 × 1017 atoms


11/26


•

A stainless steel ball bearing has a radius of 6.35 mm density of 7.75 g/cm3. Iron is the principal element in Carbon is a key minor element. The ball bearing conta% carbon, by mass. Given that the percent natural abuof 13C is 1.108%, how many 13C atoms are present in thbearing.

g/cm3 steel → g steel → g C → mol C → atoms C → a

atoms 13C = 1.2 × 1019 13C atoms


12/26


•

Medical experts generally believe a level of 30 μg Pb pdeciliter of blood poses a significant health risk (1 dL =Express this level in the unit mol Pb/L blood.

30 μg Pb/dL blood × (1 × 10−6 g Pb/1 μg) ×

(1 mol Pb/207.20 g Pb) × (1 dL blood/1 × 10−1 L blo

1.448 × 10−

6 mol Pb/L blood = 1.448 × 10−

6 M P


13/26


•

Medical experts generally believe a level of 30 μg Pb pdeciliter of blood poses a significant health risk (1 dL =Express this level in the unit mol Pb/L blood.

30 μg Pb/dL blood × (1 × 10−6 g Pb/1 μg) ×

(1 mol Pb/207.20 g Pb) × (1 dL blood/1 × 10−1 L blo

1.448 × 10−

6 mol Pb/L blood = 1.448 × 10−

6 M P


14/26


•

Monel metal is a corrosion-resistant copper nickel allothe electronics industry. A particular alloy with a densig/cm3 and containing 0.022% Si by mass is used to mrectangular plate 15.0 cm long, 12.5 cm wide, 3.00 mmand has a 2.50 cm diameter hole drilled through its ceHow many silicon-30 atoms are found in this plate? Th

of a silicon atom is 29.97376 u, and the percent naturaabundance of silicon-30 is 3.10%.


15/26


•

An analytical balance can detect a mass of 0.1 mg. Hoions are present in this minimally detectable quantity o


16/26


•

How many moles of F atoms are in a 75.0 mL sample halothane (composed of C, H, Br, F, Cl; d = 1.871 g/mL

Halothane


17/26


•

The volatile liquid ethyl mercaptan, is one of the mostodoriferous substances known. It is sometimes addednatural gas to make gas leaks detectable. How manymolecules are contained in a sample? The density of lethyl mercaptan is 0.84 g/mL.

Mercaptan (C, H and S


18/26


•

How many molecules of Ag2CO3 are decomposed to g Ag in this reaction?

Silver Carbonate → Silver + Carbon Dioxide + Oxy


19/26

Mass Percent

•

Determine the molar mass of the compound.Molar MassABC= MMA + MMB + MMC• Determine the contribution of the given element to th

mass.

Formula Subscript × Molar Mass of the Elemen

• Take the ratio and multiply by 100.Mass Percent = (Formula Subscript × MMelem)/(MMcom


20/26

Mass Percent

•

What is the mass percent composition of halothane,C2HBrClF3?


21/26

Determining the Formula

•

Given the mass percentages, assume 100 g of the samcalculate the mass of each element.

• Convert to moles.

• Divide all of the results by the smallest mole calculated

• Apply multipliers if calculated ratios are not in whole n

• Determine EF and MF.


22/26


•

Dibutyl succinate is an insect repellant used against hoants and roaches. Its composition is 62.58% C, 9.63% 27.79% O. Its experimentally determined molecular m230 u. What are the empirical and molecular formulasdibutyl succinate?


23/26


•

Determine the formula of the compound 2-deoxyribosugar that is the basic constituent of DNA (deoxyribonacid) with the following mass percent compositions: 47.52 % H and 47.71 % O.


24/26

Combustion Analysis

Combustion Analy


25/26

Combustion Analysis

• Vitamin C is essential for the prevention of scurvy. Comof 0.2000 g sample of this carbon-hydrogen-oxygencompound yields 0.2998 g CO2 and 0.0819 g H2O. Whempirical formula of vitamin C?


26/26

Combustion Analysis

• Combustion of a 1.505 g sample of thiophene, a carbohydrogen sulfur compound, yields 3.149 g 0.645 g andas the only products of the combustion. What is the eformula of thiophene?

6-the mole concept

Documents