ENVE-2110EXAM I Help Session

DCC337 9-17-13 4-5 pm

AbbreviationsLook through lecture notes, book and

assignments

Examples: (sample test Q1)V, w, M, L, N, n, ppm, ppb, T, p, Z, Ca, Mg, CO3

2-, C, HB, HA, CaCl2, acid, base, pH, pKa, KH, Creactants, k, C0, t, A, Ea, alkalinity, acidity, HCO3

-, S.S., C.V., Qi, Qo, influent, effluent, r,v, MW etc.

UNITSFollowing units are considered:

mg/LppmppbMNMolalitymg/m3

Expressed as CaCO3, P, N or S

EXAMPLESSee your notes, book and homework

assignments 1 and 2:

EXAMPLE: (sample test Qs 5,6, and 7)

Q5: The concentration of trichloroethylene (TCE) is 10 ppm and the molecular weight of TCE is 131.5 g/mole. Convert this to units of

[a] mg/L

SOLUTION:

[b]molarity

SOLUTION:

€

10ppm =10mg

L

⎛

⎝ ⎜

⎞

⎠ ⎟x

1000μg

mg

⎛

⎝ ⎜

⎞

⎠ ⎟=10,000

μg

L

€

10mg

L

⎛

⎝ ⎜

⎞

⎠ ⎟x

g

1,000mg

⎛

⎝ ⎜

⎞

⎠ ⎟x

mole

131.5g

⎛

⎝ ⎜

⎞

⎠ ⎟= 7.60x10−5 M

IDEAL GAS LAWNotes and book:

Understand the equationBe able to label all the variables and give

appropriate unitsUse the conversion equation between ppm and

mg/m3

€

pV = nRT

€

mg

m3 =ppmv xMW

22.4x

273KoT

xpatm

1atm

EXAMPLE: (sample test Q6)

What is the carbon monoxide concentration expressed in mg/m3 of a 10 L gas mixture that contains 10-6 mole of carbon monoxide?

SOLUTION:

€

CO[ ] =10−6 mole

10L= 10−7 mole( )x

1000L

m3

⎛

⎝ ⎜

⎞

⎠ ⎟x

28g

mole

⎛

⎝ ⎜

⎞

⎠ ⎟x

106 μg

g

⎛

⎝ ⎜

⎞

⎠ ⎟= 2,800

μg

m3

CHEMISTRYBe able to understand

Matter – solid, gas, liquidElements – see Periodic TableCompounds – substances made of two or more

elementsMixturePeriodic Table

AtomNeuton Proton Electrons

Atomic number – Z Number of protons in nucleus

Atomic weight or molecular weight Be able to calculate by utilizing the Periodic Table

Isotopes Understanding what isotopes are

Be able to calculate atomic weight by utilizing isotopic mass and fractional abundance

Chemical bonds Covalent bonds Ionic bonds

Chemical reactions Stoichiometry Balancing equations/reactions

Types of reactions Precipitation Acid-base

ACID-BASE REACTIONSAcid – proton donor

Base – proton acceptor

Understand terminologyAcid, base, pH, conjugate acid, conjugate base, H+,

OH-, amphoteric substance, zwitter ion, pKa or Ka

ACID-BASE EQUILIBRIASee lecture notes and book:

Understand difference between Kw and Ka

Be able to define the equation for Ka

€

HA ↔ H + + A−

€

Ka =H +

[ ] A−[ ]

HA[ ]

EXAMPE: (sample test Qs ,11, and 12)

Define the following compounds as acids or bases:HCl – acidNH3 – base

CH3OH – acid

NO3- - base

pHBe able to solve simple pH calculations or solve

for concentrations when pH is given (see lecture notes, HW assignments and book)

Scale 0-14

Acidic: <7

Basic: >7

Neutral: 7

€

pH = −log H +[ ]( )

€

pH + pOH = pKw

EXAMPLE: (sample test Qs 11 and 12)

Hydrochloric acid, HCl, completely ionizes when dissolved in water. Calculate the pH of the solution containing 40 mg HCl/L.

€

HCl ↔ H + + Cl−

Calculate MW: 1+35.5=36.5 g/mole

Convert 40 mg HCl/L to moles HCl/L:

Since HCl dissociates completely in the ratio of 1 mole HCl produces 1 mole of H+, there must be 0.001M H+

€

40mgHCl

L

⎛

⎝ ⎜

⎞

⎠ ⎟x

mol

36.5gHCl

⎛

⎝ ⎜

⎞

⎠ ⎟x

g

1,000mg

⎛

⎝ ⎜

⎞

⎠ ⎟= 0.001

molesHCl

L= 0.001M

€

pH = −log H +[ ]( )

pH = −log 0.001[ ]

pH = 3

What if the acid produces more than one H+?

You’ll have to multiply the concentration of acid by the number of moles H+ produced.

EXAMPLE: (book, HW assignment)

If 100 mg H2SO4 (MW=98 g/mole) is added to 1L of water, what is the final pH?

€

H2SO4 ↔ 2H + + SO42−

€

100mg

L

⎛

⎝ ⎜

⎞

⎠ ⎟x

mole

98g

⎛

⎝ ⎜

⎞

⎠ ⎟x

g

1,000mg

⎛

⎝ ⎜

⎞

⎠ ⎟=1.02x10−3 M

pH = −log 2x1.02x10−3( ) = 2.69

REACTION KINETICSBe able to define zero-, first-, and second-order

reaction kinetics

Understand what pseudo-first order mean

Understand the + and – sign usage:+ produced-consumed, decay

Be able to define the overall reaction orderSum of orders

Arrhenius EquationKnow the equation, be able to define all the

terms

€

k = Aexp−Ea

RT

⎡ ⎣ ⎢

⎤ ⎦ ⎥

BUFFERSUnderstand buffers and buffer capacity

Alkalinity – water’s ability to resist changes in pH on the addition of acid = acid-neutralizing capacity

Acidity – water’s ability to resist changes in pH due to addition of a base = base-neutralizing capacity

ALKALINITY pH < 4.5

Only carbonic acid present [HO-] negligible

pH 7-8 [HCO3

-] predominates over [CO3-]

[H+]=[HO-] but small compared to HCO3-

Alkalinity = [HCO3-]

pH >12.3 [H+] is negligible [HO-] is not negligible

Alkalinity = 2[CO32-]+[HO-]

Expressed typically in (see hardness example in your notes) mg CaCO3/L

N (eq/L)

MATERIAL BALANCESUnderstand the mass balance on mass and flow

At S.S. accumulation is zero

Understand the general mass balance equation with terms and units

See sample exam Q 10

€

dM j

dt= φ j,i − φ j ,o ± r V

BATCH REACTORAssumptions:

Well-mixedUniform composition

Constant volumeNoting in or out

1-st order

2-nd order

See sample exam Q9 Be able to recognize, draw and label

€

C = C0 exp −kt[ ]

€

C =C0

1+ C0kt

CSTRAssumptions:

Completely mixedUniform concentration throughout the reactorWater enters and leaves the reactor at a given

volumetric flow rate of Q (volume/time)Mass or quantity = CiV

Average r = rAble to define terms with units

Be able to recognize, draw and label

€

dM j

dt= QiCi − QoCo ± r V

During S.S. conditions:

See examples from sample exam – Q 2

€

Ci − Co

θ± r = 0

PFRAssumptions:

Uniform longitudinal velocity profileMixing is rapid enough that X-sec. can be considered

well-mixedNo interaction between adjacent fluid elements in

the direction of flow

Equation:

Be able to recognize, draw and label€

∂C j

∂t= −v

∂C j

∂x± r

€

C = C0 − kt