Safety
Powder extinguishers available in lab are suitable to extinguish fires from flammable
liquids and energized electrical equipment T F
What should be done if your fellow student faints in class:
a) rise students’ shoulder (put a bag under head and shoulders) and call TA
b) make artificial breathing
c) flap the cheeks, until student conscious
During hot summer, there is no need to wear long pants in chemistry lab T F
Being in lab, it’s OK to take off goggles for a moment, just to wipe moisture T F
Being in lab, it’s OK to take off goggles after you completed an experiment T F
What chemical/solution is not hazardous?
a) silver nitrate
b) H2SO4 conc
c) chlorine in water
d) NaCl
If chemical spilled all over your body, you should:
a) take off coat and goggles and use shower b) take off coat and use shower
In the case of fire in lab, you should:
a) run
b) call TA
c) extinguish fire
Broken glass should be disposed to:
b) special container
a) trash
To remove an acid from eyes wash eyes first with:
a) water
b) base
Close-toe shoes are required in the chemistry lab T F
Unused chemicals should be collected and returned to their containers, if they look pure
TF
When diluting acids, concentrated acid is added to water, to avoid overheating and
spillage T F
Concentrated HCl should be used in a hood, because HCl is:
a) corrosive b) volatile
c) light-sensitive
Exp 1&2 questions
Mass and volume are the examples of intensive property T F
Mass 5.4321 g was obtained on a balance reading 4 decimals. Indicate amount of
significant figures:
a) 4 b) 5 c) 4 or 5
How many decimals in volume reading 2.1 mL?
a) 0 b)1
c) 2
Match the columns (write a letter only, in a space provided):
e pump
____
a. measures mass
b graduated cylinder
____
b. measures volume
a
____ balance
c. holds test tube
d Bunsen burner
____
d. heat source
e b. attached to a pipet
c clamp
____
Match the columns (write a letter only, in a space provided):
a balance
____
a. milligrams
c
____ thermometer
b. milliliter
b buret
____
c. degrees
Reaction of sodium metal with an unknown should be done in a hood T F
Keeping balances clean helps to avoid errors in weighting T F
Is it Physical (P) or Chemical (C) property?
Ethanol boils at 79 oC
P C
NaCl dissolves in water
P C
Metal conducts electricity
P C
Compounds A and B reacts with each other P C
Product of reaction has a density 0.95 g/mL P C
Given the following experimental data for volume and mass of ethanol:
Volume: 5.0 mL
Mass: 3.935 g d= 3.935g/5.0mL =0.787 g/mL, round up to 0.79
Volume: 6.2 mL
Mass: 4.713 g d= 4.713g/6.2mL =0.76 g/mL
Volume: 8.1 mL
Mass: 6.320 g d= 6.320g/8.1mL =0.78 g/mL
Calculate average density of ethanol:
a) 0.778
b) 0.8
c) 0.78 average d = (0.79+0.76+0.78)/3=0.776,
round to 2 sig fig, to 0.78
A liquid fills a container (200 mL). Density of liquid is 1000 g/L. What is the weight of a
liquid?
a) 1000 g
b) 200 g
c) 100 g
Measurement is the process of obtaining:
a) quantities
b) qualities
To weight solid on balances, one needs to put solid: first on
a) weighting pan
b) weighting paper c) filter paper
mL vs. cm3:
a) mL > cm3
b) mL < cm3
Meniscus is:
a) glassware
b) curved shape of water layer
c) mL = cm3
Intensive properties depend on the size of sample
c) solid
T
F
Describe briefly the correct technique to smell chemical
Density units are:
a) mL/g
b) g/mL
c) moles
To heat unknown chemical the following is used:
a) hot plate
b) Bunsen burner
c) water bath heated with Bunsen burner
Bunsen burner flame color is adjusted by regulation gas : air ratio on Bunsen burner.
Correct color of natural gas flame is:
a) red
b) yellow
c) pale blue
Water bath is used for:
a) cleaning
b) heating
Sodium metal is cleaned (wiped) from oil before the reaction with unknown, because oil
will:
a) make beaker cleaning difficult
b) delay or prevent reaction
c) boil
Sodium is not stored in open air, because it reacts with air components
T F
Exp 3 questions
Group of elements in the periodic table, reacting vigorously with water:
a) period
b) halogens c) alkali metals
d) base
Color of litmus indicator in a base is:
a) red b) blue
Color of litmus indicator in an acid is:
a) red b) blue
Solid lead waste is disposed in:
a) sink
b) trash
c) waste bottle in hood
d) special waste can in hood
For the reaction CuSO4*5H2O Æ CuSO4 + 5 H2O calculate theoretical amount of CuSO4
produced from 1.00 g of pentahydrate (Cu = 64, S = 32, O = 16, H = 1)
a)b)c) MWCuSO4x5H2O = 64+32+4x16+5x18=250 g/mol; MWH2O=18 g/mol
Theor. g CuSO4=(1.00g/250g mol-1)*160g mol-1 = 0.64g
For the reaction CuSO4*5H2O Æ CuSO4 + 5 H2O calculate theoretical amount of water
produced from 1.00 g of pentahydrate (Cu = 64, S = 32, O = 16, H = 1)
a)b)c)MWCuSO4x5H2O = 64+32+4x16+5x18=250 g/mol; MWCuSO4=160g/mol
Theor. g H2O=(1.00g/250g mol-1)x5x18 g mol-1 = 0.36 g
For the reaction 2 Mg + O2 Æ 2 MgO calculate the theoretical mass of product, if 2.4 g
magnesium was burnt in the oxygen (Mg=24, O=16):
a)b)c) AW Mg=24g/mol; mols Mg=2.4g/24g*mol-1=0.10mol, same as mols MgO
MW MgO=24+16=40g/mol; g MgO=mols MgO*MW MgO=0.10x40=4.0 g
Hydrate CaSO4 * x H2O (3.44 g) was heated in a crucible to the constant mass (2.72 g).
Ca=40, S=32, O=16, H=1. Calculate x: Product is CaSO4. Calculate mols of CaSO4.
a) 1 b) 2 c) 3 d) 4
Calculate grams and mols of H2O. Divide
Classify the reaction Zn + HNO3 = Zn(NO3)2 + H2O + NO2 according to the type:
a) methathesis b) redox or reduction/oxidation
c) acid-base d) decomposition
Classify the reaction Zn(NO3)2 + Na2CO3 + H2O = ZnCO3 + CO2 + NaNO3 according to
the type:
a) methathesis b) redox,, or reduction/oxidation
c) acid-base d) decomposition
What law or principle you will try to prove in today’s experiment?
a) 1st law of thermodynamics
b) Dalton’s law
c) Principle of mass conservation
When doing experiment with combustion of magnesium, why do you need to lift the lid
occasionally?
a) to release vapors b) to allow air come into
c) to cool down the reaction
Balance the reaction Mg + O2 Æ MgO and calculate mass of MgO in grams that you
could get from 1.00 g of Mg (Mg=24, O=16):
a) 1.70
b) 1.67
c) 1.20
Balance the reaction Mg + O2 Æ MgO and calculate mass of O2 in grams used in reaction
with 1.00 g of Mg (Mg=24, O=16):
a) 0.70
b) 0.67
c) 1.20
If reactants are solids and products are gases, the Principle of Conservation of Mass is:
a) valid
b) not valid
For sodium metal, physical properties are:
Dissolving in mercury to form an alloy T F
Dissolving in water to form sodium hydroxide T F
Principle of conservation of mass is not valid in vacuum T
F
Principle of conservation of mass is not valid if reagents are solids and products are gases
T F
Reaction Pb(NO3)2 + 2KI Æ PbI2 + 2KNO3 is an example of:
a) metathesis
b) acid-base
c) decomposition
Pb2+ (lead) in the salt Pb(NO3)2 is:
a) cation
b) anion
c) base
Mass of the product after combustion of magnesium in air is higher than starting mass of
magnesium, because of:
a) oxygen
b) water
c) contamination
Combustion of 1.0 g magnesium produces 1.6 g magnesium oxide. Calculate amount of
oxygen consumed, when 0.20 g of magnesium was burned in air.
(1.6/1.0)x0.20 = 0.32 g
Mass of the product after heating of copper sulfate pentahydrate is lower than starting
mass of solid, because of losing of:
a) oxygen
b) water
c) due to contamination
Heating of 2.5 g copper sulfate pentahydrate CuSO4*5H2O produces 1.6 g of anhydrous
copper sulfate CuSO4 and water. Calculate amount of water, in grams and moles DO NOT USE HINT
produced, if 1.0 g of CuSO4*5H2O was used for the heating experiment (Hint - atomic
weights are: Cu=64, S=32, O=16, H=1) 2.5g CuSO4*5H2O produces 2.5-1.6=0.9g H2O
Neutralization reaction is:
a) acid-base
1.0 g --"--"---- will give 1.0*0.9/2.5=0.36g
H2O
b) decomposition
c) metathesis
Lead salts are toxic
T F
Copper sulfate could exist as pentahydrate T F
Decomposition reaction leads to more then one product T F
Crucible cleaning procedure includes:
a) washing with water
b) heating in flame
Magnesium metal could evaporate, if it burning violently T F
Ammonia vapors are:
a) safe for health
b) dangerous to inhale
Sodium hydroxide is:
a) caustic
b) corrosive
-
c) both
Exp 4 questions
After the completion of the reaction sequence:
Cu Æ Cu(NO3)2 Æ CuCO3*Cu(OH)2 Æ CuO Æ CuSO4 Æ Cu,
mass of the product is higher than mass of starting material. Does it mean that Principle
of Conservation of Mass is not valid? Explain your answer. No. All the reactions are
giving <100% yield
CuSO4 + Mg Æ MgSO4 + Cu is a metathesis reaction T F
H2SO4 + Mg Æ MgSO4 + H2 is a redox (reduction-oxidation) reaction T F
Why the reaction Zn + HNO3 Æ Zn(NO3)2 + H2O + NO2 should be performed in
a hood? Balance the reaction. NO2 is toxic gas
Heating of CuCO3*Cu(OH)2 produces toxic gas T F
Filtrate is:
a) solution that passed filter
b) residue on filter
c) solution poured on filter
The purpose of washing the solid on filter is:
a) to remove impurities
b) to dissolve the solid
Dissolving the solid copper oxide CuO on filter is an example of:
a) washing
b) reaction
The purpose of adding Mg to copper sulfate solution is:
a) producing copper metal from salt
b) consuming of excess sulfuric acid
c) dissolving of magnesium
The purpose of adding sulfuric acid to the precipitate, copper + excess of magnesium, is:
a) dissolving copper
b) dissolving magnesium
c) both
Reaction of magnesium and sulfuric acid H2SO4 produces flammable gas T F
Reaction of CuO and sulfuric acid produces toxic gas T F
Reaction of copper nitrate Cu(NO3)2 and sodium carbonate Na2CO3 produces CO2 T F
Exp 5 questions
To prepare diluted acid:
a) add acid to water b) add water to acid
c) either a. or b. will work
Hot glassware after glassblowing work looks the same as the cold one T F
HCl gas could be prepared on the bench T F. Explain your answer HClgas is toxic
Ammonia gas NH3 is collected by air substitution. Explain why. NH3 (MW=17g/mol) lighter
than air (ave. MW=29g/mol)
Calculate amount of hydrogen gas formed in the reaction:
Zn + HCl Æ ZnCl2 + H2, if 2 mL of 1M HCl (limiting reagent) was used.
(Hints: balance the reaction; 1M = 1 mole per 1 liter, or 0.001 mol per 1 mL)
2mL 1MHCl gives 0.002 mol HCl, or 0.001 mol H2 (because 2mol HCL produces 1molH2)
Complete and balance the equation:
CaCO3 + HCl Æ
CaCO3 + 2HCl --> CaCl2 + H2O + CO2
Complete and balance the equation:
NH4Cl + NaOH Æ
NH4Cl + NaOH --> NH3 + H2O + NaCl
Exp 6 questions
What temperature units are used for calculations related to the Charles’ Law:
a) oC
b) oF
c) K?
Name at least 3 gas laws you will study in today’s experiment
See answer in manual
Sketch Boyle’s Law graph, which is #books vs. 1/V. Could the graph cross x-axis, i.e.,
could 1/V=0? Why? NO, because it's true only for V=infinity
See answer in manual
For Boyle’s Law calculations, #books vs. 1/V, why the mass of the book is not important?
We only need to prove linearity of changing volume vs #books
Avogadro’s Law describes relationship volume of gas produced vs. mass of reagent T F
vs. #mols, not vs. mass
Complete and balance the equation, and calculate the theoretical volume of gas produced
from 0.10 g Zn (atomic weight, Zn=65):
Zn + HCl Æ Zn + 2HCl --> ZnCl2 + H2;
mols Zn=0.10g/65g mol-1=0.0015; mols H2=mols Zn =0.0015;
Liters H2=0.0015mols*22.4Lmol-1=0.034L
Calculate number of moles in 0.10 g Zn (atomic weight, Zn=65).
See above
Calculate volume of 3M HCl needed to completely dissolve 0.1 g Zn (Zn=65, H=1,
Cl=35.5)
See above: mols Zn=0.0015. One mol Zn reacts with 2 mols HCl.
mols HCl needed=0.0030. 3MHCl means 3 mols/1L or 0.003 per mL
Complete and balance the equation, and calculate mols of gas produced from 0.65 g Zn
(atomic weights: Zn=65, H=1, Cl=35.5):
Zn + HCl Æ
Same as above, but easier
Charles’ Law concerns relationship between volume and temperature T F
What coolant is used in exp 6, to get temperature below oC:
a) ice-salt
b) Freon
c) dry ice – isopropanol?
What thermometer would you choose to measure temperature below −40 oC:
a) mercury-filled
b) alcohol-filled
Exp 6 questions
rate
Graham’s Law of diffusion states that diffusion is inversely proportional to the molecular
weight of gas T F
Gas occupies all the volume available T F
Calculate the final pressure formed after the containers 1 and 2 were connected:
Total volume= 1L+2L=3L; total amount of gas
Container 1, 1L under 2 atm of gas
Container 2, 2L under 1 atm of gas
at normal pressure= 4L*atm
(2 L in Container 1 and 2 L in Container 2)
Final pressure=4L*atm/3L=1.33atm
Graham’s Law experiment allows to calculate:
a) the molecular weight of any gas
b) ratio of molecular weights of gases involved
c) volume of gas vs. temperature
Exp 7 questions
For the Ideal Gas Law equation PV=nRT, what are the units for P, V, n and T (hint: units
for R=atm*L/mole*K)? See in manual
For the Ideal Law Equation PV=nRT, define “n” = number of mols
For the Ideal Law Equation PV=nRT, what parameter in not measurable in exp 7?
R
Calculate the volume of 1.6 g natural gas (mostly CH4, MW=16 g/mol) at standard
temperature and pressure. V=(mass/mols)*22.4 L/mol = (1.6/16)*22.4 =2.24L
Units for molar mass are:
a) g/mol
b) mol/g
c) mol/L
d) L/mol
For molecular mass measurement, manual instructs you to take about 3 mL of unknown
liquid. How molecular mass will change if 10 mL of liquid will be used in the
experiment? Will not change: excess of vapors will escape from flask
Derive formula for molecular mass determination from the 2 equations: PV=nRT and
n=g/MM. Calculate the molecular mass of unknown, if P=1.0 atm, V=145 mL, R= 0.082
L*atm*K-1 *mol-1, T=300K, m = 0.50 g
MM=(m in g * RT)/PV = 85 g/mol. [Use V in liters]
at
Given that 0.77g of certain gas occupies volume 140 mL at 970C and 1.0 atm, what is the
molecular mass of gas?
MM gas = 167 g/mol, or ~ 170 g/mol after rounding up to 2 sig figs
Gaussian distribution is:
a) distribution of molecules
b) distribution of numbers
Why the real scientist does not bases any conclusion on just one result?
Try to answer yourself. Hint: statistics
Exp 8 questions
What the First law of Thermodynamic states? Energy may be transferred
but never created or destroyed
Where goes the energy gained by a process in thermochemistry lab experiment?
It is consumed by surrounding
Define specific heat. What are the units for specific heat? cal/g*0C
See in manual
Express the heat change in terms of mass, specific heat and temperature change.
What is the surrounding in thermochemistry experiment? Water
Express heat change of process in terms of heat change of water and heat change of
calorimeter
Heat change Qprocess = -(Qwater + heat absorbed by calorimeter)
What is used as calorimeter for experiment 8
For calorimeter heat capacity, why mass of calorimeter is not measured?
Using m x c is OK for the purpose, we don't need to know "c" for calorimeter
Describe briefly the procedure how to measure specific heat capacity of metal.
Calculate heat change of metal, if:
mass of metal = 25 g
temperature of metal before transferring to calorimeter = 95 oC
temperature of cold water = 20 oC
maximum temperature of mixture = 30 oC
specific heat of metal = 0.2 cal/g* oC
See example of calculations
in manual or use link:
Calculate heat change of cold water, if:
http://www.chem.uh.edu/Freshman/Labs/
mass of cold water = 25 g
Chem111x/calculations/Exp%208%
temperature of cold water = 20 oC
20calculations.xls
temperature of mixture = 40 oC
2.8 g of NaOH produces 1800 cal when dissolved in water. Calculate the molar heat of
solution (atomic weight Na=13, H=1, O=16), if heat capacity of calorimeter = 0 cal.
Molar heat = 1800 cal/(2.8g/40g mol-1)= 25714 cal/mol or ~26 kcal/mol
Calculate the energy of reaction KOH (1.1 mol) + HNO3 (1.0 mol) Æ KNO3 + H2O, if:
temperature change ΔT= 30o
Calculate as above, for limiting reagent
mass of solution = 1000 g
heat capacity of calorimeter = 10 cal/oC
Heat capacity of colorimeters: A, 50 cal/oC; B, 100 cal/oC. Which one is better one? Why?
A, because it consumes less heat
Exp 9 questions
- Practice yourself to answer
those questions
Device you will use to study light (emission spectrum):
a)b)c)
Planck’s equation gives relationship of frequency of photon and:
a)b)c)
What property of light is measured in terms of Hz:
a)b)c)
Calculate what wavelength is expected for light of photons produced due to n = 4 to n = 2
transition in a hydrogen atom (R = 3.25x1015 Hz, c = 3.00x1010 cm/sec):
a)b)c)
What wavelength is expected for light composed of photons due to n=5 to n=2 transition
in hydrogen atom? (ν = R(1/n1-1/n2), R = 3.25 x 1015 Hz, c= 3.00x1010 cm/sec):
a)b)c)
What device will you use today to study electron excitation from ground state:
a) spectrometer
b) Bunsen burner
What is the relationship between the energy of light and its frequency?
a)b)c)
What spectroscope is used for?
a)b)c)
When transferring from ground state to excited state, electron:
a) absorbs energy
b) emits energy
When transferring from excited state to ground state, electron:
a) emits photon
b) absorbs photon
What the relationship between photon energy (E) and its frequency (ν)?
a) E = hν
b) E = νmc2 c) E = λν
A green line of wavelength λ = 4.86 x 10-7 m is observed in the emission spectra of
hydrogen. Calculate the energy for this line. (c = 3 x 108 m/sec, h = 6.63 x 10-34 J x sec)
a)b)c)
What energy level is higher:
a) -6 x 10-19 J
b) -5 x 10-19 J?
Exp 10 questions
How elements are organized in the Periodic Table? (Check one)
a) mass
b) electronic structure
c) melting points
d) size of nucleus
Lithium, Sodium and Potassium metals react vigorously with water T F
Blue litmus paper in acid:
a) change color
b) does not change color
Elemental halogens are toxic. It is dangerous:
a) to breathe them
b) to handle them with bare hands
c) both
The most electronegative element in whole periodic system is:
a) hydrogen b) fluorine
c) lithium
d) helium
Atomic size of elements across the period from left to right generally:
a) increases
b) decreases
c) stays the same
Atomic size of elements across the group from top to bottom generally:
a) increases
b) decreases
c) stays the same
If 2Br- + Cl2 Æ Br2 + 2Cl-, and 2Cl- + Br2 Æ no reaction, what is more reactive?
a) chlorine
b) bromine
Dry ice should be taken with:
a) tongs
b) paper towel
c) hand
Exp 12 questions
Define: solvent. Define: solute -minor component of solution
- major component of solution
Physical properties of solution, which are dependent only on the number of solute
particles, are called …colligative
Solution of the ionic compound sodium chloride freezes at lower temperature than
solution of non-ionic naphthalene of the same molality. Explain, why. Ionic NaCl dissociates
giving twice more
Molality is the concentration in terms of:
particles than napht-ene
a) moles of solute/kg of solvent
gives
b) moles of solute/g of solvent
c) moles of solute/L of solution
Calculate the freezing point constant of the solvent, if freezing temperature of camphor
solvent dropped by 15.5 oC after 5.1 mg of non-ionic organic compound (MW=207) was
dissolved in 63.5 mg of camphor solvent. Kf=15.5/((51.5*10-3/207)/63.5*10-6)=0.206
Kf=deltaT/m; m=(mass solute/MM solute)/kg of solv.
Give at least 2 examples of colligative properties.
Vapor pressure, boiling point
Sketch the graph for experiment 12, freezing of cyclohexane solvent
Calculate molality of solution, 2.0 g of naphthalene (MW=128) in 100 g of cyclohexane.
m=(2.0g/128g*mol-1)/0.100kg=0.156 mol/kg
Cyclohexane is:
a) flammable
b) toxic
c) both
Solution of the unknown compound (1.0 g) freezes at higher temperature than solution of
naphthalene (1.0 g). Compare molecular weights of the unknown and naphthalene.
delta T unkn<delta T naphth, so MM unknown> MM naphtalene, because: delta T~1/MM
Explain how sodium chloride works when used to melt ice on pavement in northern part
of USA. What will work better for the purpose: 1 g of NaCl or 1 g of Na2SO4 (atomic
weights are Na=23, Cl=35.5, S=32, O=16)?
In the presence of salt, water freezing point depression occurs
MM NaCl=23+35.5=58.5g/mol; moles NaCl=(1/58.5)=0.017, or 0.134 "moles" of
particles, because NaCl dissociates giving 2 particles: Na+ and ClMM Na2SO4=23*2+32+16*4=152g/mol; moles Na2SO4=(1/152)=0.0066, or
0.0066*3= 0.0198 "moles" of particles,
because Na2SO4 = 2Na+ + SO42- (3 particles per each Na2SO4)
"Moles" of particles NaCl < "moles" of particles Na2SO4, so Na2SO4 works
better
Exp 13 questions
Define: amphiphilic compound. Give an example of the one
having affinity to both water and organic substances; soap
What is used as the starting material to prepare soap in exp 13?
Lard
Define: polymer - large compound made up of repeating units
Describe/sketch the correct smelling procedure
Why glacial acetic acid is dangerous?
It is very corrosive
Glacial acetic acid is:
a) concentrated
b) diluted acid
Why the container for solid NaOH should be kept closed all the time?
Solid NaOH is hygroscopic (attracts water)
Exp 14 questions
In A = εbc, what is ε:
a) absorptivity
b) molar absorptivity
c) path length
For the reaction S2O82-(aq) + 3I-(aq) Æ 2SO42-(aq) + I3-(aq) decrease in transmittance of
solution was recorded. What are the colored species?
b) I-(aq)
c) SO42-(aq)
d) I3-(aq)
a) S2O82-(aq)
For the reaction S2O82-(aq) + 3I-(aq) Æ 2SO42-(aq) + I3-(aq) 86 % transmittance was
recorded. Assuming εl = 45, calculate concentration of I3-(aq):
a)b)c)
A=log(100/%Trans); A=epsilon x l x c, so c=(log(100/%Trans)/epsilon x l =0.001456, or 1.5E-3
In calculations for the completed reaction S2O82-(aq) + 3I-(aq) Æ 2SO42-(aq) + I3-(aq) we
use the fact that concentration of product triiodide ion is equal to:
a) initial concentration of S2O82-(aq) b) initial concentration of I-(aq) c) both
For the reaction H2 (g) + I2 (g) Æ 2HI (g) the rate constant k1 = 2.7 x 10-4 L/(mol*sec) at
600 K and 3.5 x 10-3 L/(mol*sec) at 650 K. Find the activation energy Ea (R = 8.31
J/mol*K): ln(k2/k1)=-Ea*(1/T2-1/T1)/R; Ea=-ln(k2/k1)*R/(1/T2-1/T1)=
a)b)c)
=-ln(3.5E-3/2.7E-4)*8.31/(1/650-1/600)=166070 J, or 170kJ
Find the concentration of the stock solution of (NH4)2S2O8, if 0.016 M (NH4)2S2O8
solution was obtained immediately after mixing the stock solution (3 mL), KI solution (6
mL) and water (1 mL): Final volume = 3+6+1=10 mL; Initial vol = 3 mL
a)b)c)
Final conc = 0.016M x 3mL/10mL = 0.0048M
Find the concentration of (NH4)2S2O8 immediately after addition of KI solution (6 mL)
and water (1 mL) to 0.020 M (NH4)2S2O8 (3 mL):
Final volume = 6+1+3=10 mL; Initial vol = 3 mL
a)b)c)
Final conc = 0.020M x 3mL/10mL = 0.0060M
2For the reaction S2O8 (aq) + 3 I-(aq) Æ 2 SO42-(aq) + I3-(aq), calculate the rate constant
given the following: rate = 0.005 M/min, [S2O82-] = 0.01 M, [I-] = 0.15 M, rate = k
[S2O82-]a [I-]:
a)b)c)
a=1; k=rate/[S2O82-][I-] =0.005M*min-1/(0.01M x 0.15M)=3 M-1*min-1
The following affects the rate of reaction S2O82-(aq) + 3 I-(aq) Æ 2 SO42-(aq) + I3-(aq):
a) temperature
b) humidity
c) light
The rate constant for reaction S2O82-(aq) + 3 I-(aq) Æ 2 SO42-(aq) + I3-(aq) depends on:
a) temperature
b) humidity
c) light
The following does not affect the rate of reaction S2O82-(aq) + 3 I-(aq) Æ 2SO42-(aq) + I3a) concentration
b) catalyst
c) time from start
d) water solvent
The following does affect the rate constant, S2O82-(aq) + 3 I-(aq) Æ 2 SO42-(aq) + I3a) concentration
b) catalyst
c) time from start
d) water solvent
Exp 15 questions
Which of the following relationships between %absorbance and % transmittance is not
correct?
b) A = 2- log10(%T)
c) A = log10(1/%T)
a) A = log10(100/%T)
At equilibrium (select correct answer):
a) forward and reverse reactions continue to occur
b) forward reaction is fast
c) reverse reaction is fast
d) forward and reverse reactions do not proceed
e) none of the above
For the reaction 2A + B = C, initial concentrations [A]ini = 0.020 M and [B]ini = 0.005 M.
At equilibrium, [C]eq = 0.001 M. Calculated equilibrium concentration [A]eq is:
a)b)c) [A]eq=[A]ini-[A]consumed; to get 1 mole of C, 2 mols of A is needed,
so [A]eq=0.020M-0.001M*2=0.018M
For the reaction 2A + B = C, initial concentrations [A]ini = 0.020 M and [B]ini = 0.005 M.
At equilibrium, [C]eq = 0.001 M. Calculated equilibrium concentration [B]eq is:
a)b)c) [B]eq = [B]ini-[B]consumed=0.005-0.001=0.004M
Studying the reaction Fe3+ + SCN- Æ Fe(SCN)2+ we record:
a) transmission
b) absorption
c) color changes
d) temperature
calculate
Studying the reaction Fe3+ + SCN- Æ Fe(SCN)2+ we record absorbance of:
a) Fe3+
b) SCNc) Fe(SCN)2+
For the reaction 2A + B = C, where [A] = 0.3 M, [B] = 0.1 M, [C] = 0.2 M calculate Kc:
a)b)c)d)f)
Kc=[C]/[A]^2[B]=0.2/(0.3^2*0.1)=20 M-2
Calculate the equilibrium constant Kc for reaction CO (g ) + 3H2 (g) = CH4 (g) + H2O(g),
if [CO] = 0.2 M, [H2] = 0.3 M, [CH4] = 0.1 M, [H2O] = 0.1 M
Kc=[H2O][CH4]/[CO][H2]^3=0.1*0.1/(0.2*0.3^3)= 1.85, or ~2 M-2
The equilibrium constant Kc = 400 for Fe3+ + SCN- = Fe(SCN)2+. Calculate
concentration [Fe(SCN)2+], if [Fe3+] = 9.45 x 10-4 M and [SCN-] = 1.45 x 10-4 M:
a)b)c)
Kc=[FeSCN]/[Fe][SCN]; [FeSCN2+]=Kc*[Fe3+][SCN-]=400*9.45E-4*1.45E-4=5.48E-05 M
An equilibrium constant is independent on the temperature: T F
Transmittance of solution is 72%. Calculate the absorbance.
a)b)c)
A=log(100/%Trans)=log(100/72)=0.14
Exp 16 questions
Diluted acid and bases are disposed in:
a) waste bottle in hood
b) sink
After addition of 0.1 M HCl (10 mL) to 0.2 M NaOH (6 mL) solution becomes:
a) basic
b) acidic
c) neutral
After addition of 0.2 M NaOH (4 mL) to 0.1 M HCl (10 mL) to solution becomes:
a) basic
b) acidic
c) neutral
Exp 19 questions
Why we used a paper bridge soaked with KNO3 to connect solutions in Carrou cell:
a) ? to balance charge of the system
If Eo > 0 reaction is (hint: ΔGo = -n*F*ΔEo):
a) spontaneous
b) non-spontaneous
Calculate half-reaction potential for I-/I3-:
S2O82-(aq) + 2e Æ 2SO42-(aq)
E= +2.010 V
3I (aq) Æ I3 (aq) + 2 e
E=______ V
E=2.010-1.475=0.535 V
______________________________
S2O82-(aq) + 3I-(aq) Æ 2SO42-(aq) + I3-(aq) Ereaction= +1.475 V
Solutions from Carrou cell could be disposed in sink T F
Species gaining electrons are reduced T F
Species losing electrons are oxidized T F
Species at anode lose electrons T F
Species at cathode gaining electrons T F
In redox reaction species gaining electrons are oxidized T F
Oxidation takes place at anode while reduction takes place at cathode T F
Reaction Cl2(g) + 2e Æ 2Cl-(aq) represent reduction of chlorine T F
Redox potential (Eo) is expressed in Joules T F
Acid and base conduct an electric current T F
moles of
For the half-reaction BrO3- Æ Br2 number of electrons transferred per mole of Br2 is:
a) 1 b) 2 c) 3 d) 5 e) 10
Zn metal dissolves in Cu2+ solution. What of the following is not true?
a) Cu is easier to oxidize than Zn
b) Cu2+ is easier to reduce than Zn2+
c) Zn is better reducing agent than Cu
d) Cu2+ is better oxidizing agent than Zn2+
Cathode is an electrode where oxidation occurs T F
Anode is an electrode where oxidation occurs T F
The following is an example of a reduction reaction?
Yes
Ni2+(aq) + 2e
-
Æ Ni(s)
The ampere is the unit of measure used to quantify potential T F
The potentials measured in Experiment #19 are standard potentials T F
Standard potentials are to be measured at standard state: 1M at 25oC
In a galvanic cell, reduction occurs at the anode T F
The standard potential can be used to predict the spontaneity of a redox reaction T F
The more positive the potential of a half-reaction for a particular element (compound) the
T F
more likely that element (compound) will accept electrons
The more negative the potential of a half-reaction for a particular element (compound),
the more likely that element (compound) will accept electrons
T F
The more positive the potential of a half-reaction for a particular element (compound),
the more likely that element (compound) will act as a reducing agent in a reaction T F
The more negative the potential of a half-reaction for a particular element (compound),
the more likely that element (compound) will act as a reducing agent in a reaction T F
K+ has a standard reduction potential of -2.92, so it is a reducing agent T F
The element with the highest reduction potential is most easily reduced T F
For reduction to take place, the following process should also proceed:
a) dilution
b) oxidation
c) evaporation