Transcript Slide 1
Quantitative Chemistry
• matter • units • significant figures • atomic structure, isotopes, periodic table • basic nomenclature (ions, molecular &inorganic compounds) • stoichiometry and balancing equations by inspection • moles and Avogadro’s number • empirical and molecular formulae • limiting reagents 1
PRACTICE EXAMPLE A nugget of gold with a mass of 521 g is added to 50.0 mL of water. The water level rises to a volume of 77.0 mL. What is the density of the gold?
2
PRACTICE EXAMPLE
Naturally occurring Mg has three isotopes:
24 Mg (78.90 %) 23.9850 u 25 Mg (10.00 % )24.9858 u 26 Mg (11.10 %) 25.9826 u
AAM=?
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NAME:
NaCl K 2 SO 4 Ba(OH) 2 cobalt(II) nitrate silver sulfide ferric chloride
PRACTICE EXAMPLE
4
Anion
Cl -
S 2-
ClO 4 ClO 3 ClO 2 ClO -
PRACTICE EXAMPLE Corresponding acid
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NAME:
SO 2 PCl 5 N 2 O 3 NF 3 P 4 S 10 silicon tetrabromide
PRACTICE EXAMPLE
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BALANCE:
C 2 H 6 + O 2 → CO 2 + H 2 O
PRACTICE EXAMPLE
Al + HCl → AlCl 3 + H 2 7
PRACTICE EXAMPLE
How many oxygen atoms are in 1.50 mol of sodium carbonate?
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PRACTICE EXAMPLE
Determine the empirical formula of a compound with 10.4% C, 27.8% S and 61.8% Cl.
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PRACTICE EXAMPLE
Eucalyptol has an empirical formula of C 10 H 18 O. The experimentally determined molecular mass of this substance is 152 u. What is its molecular formula?
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PRACTICE EXAMPLE
Determine (i) which reactant is the limiting reactant and (ii) how much excess reactant is leftover in the following reaction: 3NH 4 NO 3 + Na 3 PO 4 → (NH 4 ) 3 PO 4 + 3NaNO 3
30.0 g 50.0 g
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PRACTICE EXAMPLE
Determine the theoretical yield and the % yield of NaNO 3 is formed when the reaction is carried out.
if 15.0 g of sodium nitrate 3NH 4 NO 3 + Na 3 PO 4 → (NH 4 ) 3 PO 4 + 3NaNO 3
30.0 g 50.0 g
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TYPES OF REACTIONS
• • • • • • • • Electrolytes Acid- base reactions Solubility rules Precipitation reactions Writing ionic equations Oxidation numbers Redox reactions Concentration 13
PRACTICE EXAMPLE BALANCE AND SHOW PHASES:
BaCl 2 + H 2 SO 4 → BaSO 4 + HCl 14
PRACTICE EXAMPLE
BALANCE: H 2 SO 4(aq) + NaOH (aq) → 15
PRACTICE EXAMPLES
OXIDATION No OF BOLD:
S
2 O 3 2 FeO 4 2 Na 2 SO 3
S
8 NH 4 + 16
PRACTICE EXAMPLE BALANCE IN ACIDIC:
Fe 2+ (aq) + MnO 4 ¯ Fe 3+ (aq) + Mn 2+ (aq) 17
BALANCE IN BASIC:
S (s) + ClO ¯ (aq) SO 3 2 (aq) + Cl¯ (aq)
PRACTICE EXAMPLE
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PRACTICE EXAMPLE
Calculate the molarity of a solution made by dissolving 5.00 g of glucose, C 6 H 12 O 6 , in sufficient water to form exactly 100
.
mL of solution.
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PRACTICE EXAMPLE
** How many grams of NaOH are needed to neutralise 20.0 cm 3 H 2 SO 4 solution?
of 0.150 M 20
PRACTICE EXAMPLE
How many millilitres of 5.00 M K 2 Cr 2 O 7 cm 3 of 0.100 M solution?
solution must be diluted to prepare 250
.
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PRACTICE EXAMPLE
What mass of Ag 2 CrO 4 (331.8 g mol
-1
) will precipitate if excess K 2 CrO 4(aq) is added to 514.6 mL of 0.1683 M AgNO 3 . The unbalanced equation for the reaction is: AgNO 3(aq) + K 2 CrO 4(aq) → Ag 2 CrO 4(s) + KNO 3(aq) 22
BALANCE AND SHOW PHASES:
Ba(NO 3 ) 2 (aq) + Li 2 SO 4 (aq) →
PRACTICE EXAMPLE
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GASES
• • • • Properties of gases Gas Laws Gas equations – General gas equation – Ideal gas equation (density & molar mass derivation) – Partial pressures – Gas collected over water – Van der Waal’s real gas equation Kinetic molecular theory of gases 24
Convert: 253 Torr → atm 326 Pa → atm 51 atm → mmHg 65 atm → bar
PRACTICE EXAMPLES
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PRACTICE EXAMPLE
A gas bubble with a volume of 1.00 mm 3 originates at the bottom of the lake where the pressure is 3.00 atm and the temperature is 12.5 0 C. Calculate its volume (in mm 3 ) when the bubble reaches the surface of the lake where the pressure is 695 Torr and the temperature is 15 0 C.
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PRACTICE EXAMPLE
Determine the molar mass and identity of a 0.134 g sample of gas with a volume 75.0 mL at STP?
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PRACTICE EXAMPLE
What is the density (in g dm -3 ) of a sample of Cl 2 gas at 1124 Torr and 24 0 C?
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PRACTICE EXAMPLE
A gaseous mixture made from 6.00 g O 2 and 9.00 g CH 4 is placed in a 15.0 L vessel at 0 °C. Calculate the partial pressure of each gas and the total pressure in the vessel (in Pa).
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PRACTICE EXAMPLE
A 31.46 mL sample of gas was collected over water at 296.9 K and at a pressure of 706.4 mmHg. Consider the gas sample to be a mixture of water vapour and N mmHg) 2 gas. What mass of nitrogen was collected? (Vapour pressure of water at 296.9 K is 22.3 30
PRACTICE EXAMPLE
Calculate the pressure of 1.00 mol Cl 2(g) confined to a volume of 3.00 dm 3 using the van der Waals equation. at 0.0 C (Note a= 3.64 kPa dm 6 mol -2 , b = 0.0427 dm 3 mol -1 , R = 8.314 kPa dm 3 mol -1 K -1 ) 31
ELECTRONIC STRUCTURE OF ATOMS
• • • • • Wave nature of light Quantum theory Line spectra (Bohr model) Quantum numbers and atomic orbitals Electron configuration 32
PRACTICE EXAMPLE For radiation of wavelength 242.4 nm, what is the energy of one photon of light?
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PRACTICE EXAMPLE Calculate the wavelength (in nm) associated with an electronic transition in the hydrogen atom from n=4 to n=1.
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PRACTICE EXAMPLE Determine
E for the transition of an electron from n=5 to n=2 in a hydrogen atom.
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PRACTICE EXAMPLES Give the numerical values of n and l and m l corresponding to each of the following designations: i) 3p ii) iii) 2s 4f
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PRACTICE EXAMPLE Write the expanded and condensed electron configuration of the following: i) N ii) Si iii) Cu
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PRACTICE EXAMPLE Draw the electron “block” diagram of carbon and aluminium
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BASICS OF BONDING
• • • • • • • •
Octet rule Ionic bonds and compounds Covalent bonds and compounds Polarity and Electronegativity Lewis symbols and structures Formal Charge Resonance structures Exceptions to Lewis Rules
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PRACTICE EXAMPLES
Draw Lewis symbols or structures for Calcium
,
silicon
,
neon
,
PCl 3
,
CH 3 OH
,
N 2
,
NH 4 +
,
OH 40
PRACTICE EXAMPLE
Draw three structures of CNS
-
with N as the central atom and decide with formal charge which is the best structure.
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PRACTICE EXAMPLE
Draw the resonance structures of O 3 and NO 3
-
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ELECTRON & MOLECULAR GEOMETRY
• • •
VSEPR Electron geometries Molecular geometries
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PRACTICE EXAMPLES DETERMINE ELECTRON AND MOLECULAR GEOMETRY AND BOND ANGLE: PF 4 + , AlCl 6 3 , ICl 3 , CH 3 +
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INTERMOLECULAR FORCES
• • • •
Physical state
Inter- vs Intra-
Types of IM forces
– –
Dipole-dipole forces Hydrogen bonding
– –
Ion-ion forces Ion-dipole forces
–
Van der Waal’s forces Liquid properties
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PRACTICE EXAMPLES
Why does NH 3 have a higher boiling point than CH 4 ?
Why does KCl have a higher melting point than I 2 ?
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PRACTICE EXAMPLE
Arrange the following in order of increasing boiling points and identify the IM forces present in each compound:
CH 3 OH , CO 2 , RbF , CH 3 Br
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PRACTICE EXAMPLES
INTERMOLECULARE FORCES PRESENT=?
i. H 2 O ii. N 2 iii. C 6 H 5 Cl iv. C 6 H 6
•
THERMOCHEMISTRY
Energy – Heat – Heat capacity – Calorimetry • Enthalpy – Heat of formation – Heat of reaction – Bond energies
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PRACTICE EXAMPLES
A piece of titanium metal with a mass of 20.8 g is heated in boiling water to 99.5 °C and then dropped into a coffee-cup calorimeter containing 75.0 g of water at 21.7 °C. When thermal equilibrium is reached, the final temperature is 24.3 °C.
Calculate the specific heat capacity of titanium. (Specific heat of water is 4.184 J g -1 K -1 )
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PRACTICE EXAMPLES
A 50.0 g sample of water at 100 °C is poured into a 75.0 g sample of water at 25 °C.
What will be the final temperature of the water? Specific heat capacity of water = 4.184 J g -1 °C -1
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PRACTICE EXAMPLES
A 0.1375 g piece of magnesium was burned in a bomb-calorimeter containing 300 .g of water. The temperature increased by 1.126 C. The heat capacity of the calorimeter is 1769 J C -1 and the specific heat capacity of water is 4.184 J g -1 C -1 . Calculate the heat given off by the magnesium in J g
-1
.
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PRACTICE EXAMPLES
When 50.0 mL of 1.00 M NaOH is added to 100.0 mL of 0.500 M HCl in a coffee cup calorimeter at 25.8 C, the temperature rises to 34.8 C. Assume that the density of the solution is 1.00 g mL -1 and that its specific heat capacity is 4.184 J g -1 C -1 . The equation for the reaction is:
NaOH (aq) + HCl (aq) → NaCl (aq) + H 2 O (l)
Calculate the enthalpy of the reaction in kJ mol -1 .
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PRACTICE EXAMPLES
Calculate H rxn for the combustion of 1 mol of benzene (C 6 H 6(l) ) given that H f C 6 H 6(l) , CO 2(g) and H 2 O (l) for are 49.0 kJ/mol, -393.5 kJ/mol and -285.8 kJ/mol respectively.
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PRACTICE EXAMPLES
Find H rxn ½N 2 (g) + ½O 2 (g) 2NO 2 (g) for ½ N
2 (g) + O 2 (g)
NO(g) 2NO(g) + O 2 (g) H
NO 2
(g) given that: = 90.25 kJ H = 114.14 kJ
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PRACTICE EXAMPLES
Use the table of bond energies shown below to calculate H rxn
C 2 H 4(g) + HCl (g)
C 2 H 5 Cl (g)
for:
Bond Bond energy/kJ mol -1
C C 348 C=C 614 C H 413 H Cl 431 C Cl 328
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REACTION KINETICS
• • • • • • • Reaction rates Reaction order Reaction mechanisms Collision frequency Energy profile diagrams Arrhenius equation Catalysts 57
PRACTICE EXAMPLES
(a)N 2 Rate = + 3H 2 2NH 3 (b) H 2 O 2 + 2H + + 3I¯ Rate = I 3 ¯ + 2H 2 O 58
PRACTICE EXAMPLE
A + B products rate = k[A] m [B] n initial conc/mol dm –3 [A] 0.10 0.20 0.30 0.30 0.30 [B] 0.10 0.10 0.10 0.20 0.30 initial rate/mol dm –3 s –1 0.20 0.40 0.60 2.40 5.40 1 2 3 4 5
CALCULATE m, n and k
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PRACTICE EXAMPLE
For the reaction: NO 2 (g) + CO(g) NO(g) + CO 2 (g) the variation of the initial rate with the initial concentration of NO 2 (the initial concentration of CO kept constant), was found to be as follows:
Experiment
1 2 3 4
[NO 2 ]/mol dm -3
0.150
0.300
0.600
0.900
Initial rate/mol dm -3 s -1
0.010
0.040
0.160
0.360
Deduce the order of the reaction with respect to NO 2
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PRACTICE EXAMPLE
For the alkaline hydrolysis of ethyl nitrobenzoate (A) the following data were obtained at 25 C.
Time/s
0 500 800 1500
[A]/mol dm -3
0.0500
0.0167
0.0119
0.0071
2000 0.0056
Evaluate the order of the reaction and calculate k
t
0 500 800 1500 2000
[A]
0.05
0.0167
0.0119
0.0071
0.0056
t
0 500 800 1500 2000
ln[A]
-2.99573
-4.09235
-4.43122
-4.94766
-5.18499
t
0 500 800 1500 2000
1/[A]
20 59.88024
84.03361
140.8451
178.5714
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SOLUTION
0.06
0.05
0.04
0.03
0.02
0.01
0 0 500 1000
t/s
1500 2000 2500 -4 -5 -6 0 -1 0 -2 -3 500 1000 1500 2000 2500
t/s
200 180 160 140 120 100 80 60 40 20 0 0 500 1000
t/s
1500 2000 2500 62
PRACTICE EXAMPLE
For the reaction A products, the following data is given in the table below:
[A]/M
0.600
0.497
0.413
0.344
0.285
0.198
0.094
Time/s
0 100 200 300 400 600 1000 A) Show that the reaction is first order by plotting the appropriate graph for first order reactions.
B) What is the value of the rate constant, k?
C) What is [A] at t = 750 s?
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SOLUTION
0 0 -0,5 -1
ln[A]
-1,5 200 400
time/s
600 800 1000 1200 -2 -2,5 y/ x = (-2.36-(-0.51))/(1000-0) s= 1.85 x 10 -3 s -1
time/s ln[A]
0 100 -0.51
-0.699
200 300 400 600 1000 -0.884
-1.07
-1.26
-1.62
-2.36
PRACTICE EXAMPLE
A single step reversible reaction has an activation energy for the forward reaction (E a,f ) of 28.9 kJ and 41.8 kJ for the reverse reaction (E a,r ) Draw a potential energy level diagram and indicate H
PRACTICE EXAMPLE
The rate constant for the reaction:
H 2(g) + I 2(g)
2HI (g)
has been determined at the following temperatures:
k/M -1 s -1 T/K
5.4 x 10 -4 599 2.8 x 10 -2 683 Calculate the activation energy, E a , for the reaction in J mol -1 .
CHEMICAL EQUILIBRIUM
• • Dynamic Equilibrium • Equilibrium constant expression – K c – K p – Q c Le Chatelier’s principle
EXPRESS K C a) 2 H 2 S (g)
⇌
2 H 2(g) + S 2(g) PRACTICE EXAMPLES b) PCl 3(g) + 3 NH 3(g)
⇌
P(NH 2 ) 3(g) + 3 HCl (g) c) Na 2 CO 3(s) + SO 2(g) + ½ O 2(g)
⇌
Na 2 SO 4(s) + CO 2(g)
PRACTICE EXAMPLE N 2 O (g) + ½ O 2(g)
⇌
2 NO (g)
K c = ?
N 2(g) + ½ O 2(g) ⇌ N 2 O (g)
K c
= 2.7 x 10 -18 N 2(g) + O 2(g) ⇌ 2NO (g)
K c
= 4.7 x 10 -31
PRACTICE EXAMPLE
A 5.00 L flask is filled with 1.86 mol NOBr. At equilibrium there is 0.082 mol Br 2 present. Determine K c for the reaction at 25 C.
2 NOBr (g)
⇌
2 NO (g) + Br 2(g)
PRACTICE EXAMPLE
A 0.0240 mol sample of N 2 O 4(g) L flask at 25 C. is allowed to come to equilibrium with NO 2(g) in a 0.372 Calculate the amount of N 2 O 4(g) at equilibrium.
N 2 O 4(g)
⇌
2 NO 2(g)
K c =
4.61 x 10 -3
at 25 C
PRACTICE EXAMPLE 2 NH 3(g)
⇌
N 2(g) + 3 H
2(g)
K c
= 2.8 x 10 -9 at 298K
K p = ?
PRACTICE EXAMPLE
Is a mixture of 0.0205 mol NO 2(g) and 0.750 mol N 2 O 4(g) in a 5.25 L flask at 25 equilibrium? If not, in which direction will the reaction proceed?
C at
N 2 O 4(g)
⇌
2 NO 2(g)
K c = 4.61 x 10 -3 at 25
C
A mixture consisting of 0.150 mol H 2
PRACTICE EXAMPLE
and 0.150 mol I 2 is brought to equilibrium at 445 3.25 L flask. What are the equilibrium amounts of H 2 , I 2 C in a and HI? The equilibrium reaction is given below.
H 2(g) + I 2(g)
⇌
2HI (g)
K c
= 50.2 at 445 C
(a)
PRACTICE EXAMPLE 4 HCl (g) + O 2(g)
⇌
2 H 2 O (g) + 2 Cl 2(g)
Effect on equilibrium and K
c
?
Addition of oxygen gas
ΔH = 28 kJ
(b) An increase in temperature (c) Reduction of the volume of the reaction container (d) Addition of a catalyst (e) Removal of HCl(g) from the reaction vessel.
ACID-BASE EQUILIBRIA
• • • • •
Definition of acids and bases
–
Arrhenius
–
Brønsted-Lowry Strong vs weak acids and bases Self-ionization of water (K w ) Ionisation constants (K a , K b ) pH, pOH
PRACTICE EXAMPLES
LABEL CONJUGATE ACID-BASE PAIRS:
(a) HPO 4 2 + NH 4 + ⇌ NH 3 + H 2 PO 4 ¯ (b) SO 4 2 + H 2 O ⇌ HSO 4 ¯ + OH ¯
PRACTICE EXAMPLE
Calculate the pH of a 0.050 M nitrous acid (HNO 2 ) solution. K
a
= 4.5 x 10 -4
PRACTICE EXAMPLE
What is the pH of a 0.10 M solution of NH 3 ? What is the % ionisation for this solution?
K b
= 1.8 x 10 5
PRACTICE EXAMPLE
Quinine is a naturally occurring base used to treat malaria. A 0.0015 mol dm -3 solution of quinine has a pH of 9.84. The basicity of quinine is due to the nitrogen atom that picks up a proton from water in the same manner as ammonia.
a) Calculate Kb for quinine. b) Determine the degree of ionisation.