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Physical Chemistry (lab) > Viscosity and Surface Tension > Flashcards

Viscosity and Surface Tension Flashcards

1
Q

State the three van der Waals forces

A

Dispersion forces: all molecules, temporary dipoles
Dipole-dipole attraction: polar molecules permanent dipoles
Hydrogen bonding: O–H, N–H, F–H molecules

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2
Q

Differentiate cohesive and adhesive forces

A

Cohesive forces are attraction between same type of molecule (bonds water molecules)
Adhesive forces are attraction between different type of molecules (droplet to surface)

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3
Q

Define viscosity

A

Resistance of fluid to flow due to internal friction

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4
Q

Usual unit of dynamic viscosity

A

mPa s or cP (centipoise)

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5
Q

Force required to flow is equal to?

A
  • (dynamic viscosity)(surface area)(velocity gradient, dvy/dx)
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6
Q

A fluid that obeys Newton’s Law

A

Newtonian fluid

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7
Q

What is dynamic viscosity?

A

The resistance to shear flow. When force is applied, does it flow?

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8
Q

Poiseuille’s Law

A

describes flowing liquids under laminar (smooth) flow which allows calculation of volume flowrate V/t which depends on radius and length.

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9
Q

Volume flowrate is equal to?

A

(pie r^4)/[8(dynamic visc)] x (dP)/L

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10
Q

Viscosity of water at 25 deg C

A

0.890 mPa s

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11
Q

Types of flow and differentiate the two

A

Laminar (streamline) flow: smooth flow, one direction
Turbulent flow: chaotic flow

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12
Q

What is critical Re?

A

The transition from laminar to turbulent flow.

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13
Q

Reynold’s number formula

A

Re=[(density)(velocity)(diameter)]/(dynamic viscosity)

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14
Q

Define kinematic viscosity and its formula

A

It is the resistance to transfer of momentum; when fluid layer flows against another, does the other layer flow?

kinematic viscosity = dynamic viscosity/density

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15
Q

Dynamic viscosity and temperature relationship (liquid)

A

Inverse. Increase in thermal energy, IMF overcome

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16
Q

Dynamic viscosity and pressure relationship (liquid)

A

Direct. Due to fluid compression

17
Q

Dynamic viscosity and temperature relationship (gas)

A

Direct. Due to increased collision leading to mentum transfer

18
Q

Dynamic viscosity and pressure relationship (gas)

A

Direct. Due to fluid compression

19
Q

Five ways to measure of viscosity

A

Flow rate thru capillary tube w/ known diameter
Ostwald viscometer (relative visc.)
Falling ball viscometry
Orifice viscometry

20
Q

Viscosity formula using Ostwald viscometer

A

dynamic: nb/na = (pb tb)/ (pa ta)
kinematic: Vb = Va tb/ta

21
Q

Define surface tension

A

Energy (work) required to extend a surface by a unit area
Force required to increase the length of a surface

22
Q

Unit for Surface Area

A

1 N/m = 1J/m^2

23
Q

IMF and surface tension relationship

A

Direct. Dispersion<Dipole-dipole<H-bonding<ionic

24
Q

Surface tension and temperature relationship

A

Inverse. Increased KE, IMF overcomes

25
Q

Surface tension and pressure realtionship

A

Surface tension of liquid decreases with pressure of gas above
At higher pressure, surface tension increases

26
Q

Measurements of surface tension

A

Drop-weight method (stalagmometer)
Ring-pull method (Du Nouy tensiometer)
Wilhelmy plate method
Capillary rise method
Contact angle goniometry

27
Q

Relationship of surface tension with weight of drop formed (drop-weight method)

A

Direct. st=mg/2 pie r

28
Q

Surface tension depends on ___ in Du Nuoy/ ring-pull method

A

Force required to lift the ring. st=F/2 pie D

29
Q

Surface tension depends on ___ in Wilhelmy plate method

A

Force required to lift the plate.
st=F-m of plate/2 pie D

30
Q

Surface tension depends on ___ in Capillary rise method

A

height of liquid. st = rhpg/2costheta

31
Q

Surface tension depends on ___ in contact angle goniometry

A

contact angle

32
Q

T/F: Concave meniscus has higher surface tension than convex

A

False.

33
Q

In convex meniscus: cohesive force ___ adhesive force

A

greater than (>)

34
Q

In concave meniscus: cohesive force ___ adhesive force

A

less than (<)

35
Q

Average mass of droplets formula

A

total mass of droplets/ number of drops

36
Q

Surface tension formula as respect to reference liquid

A

st sample=st reference (m sample / m reference)

37
Q

Alcohol-water concentration and surface tension relationship.

A

higher the concentration of alcohol in a mixture the lower the surface tension of that mixture

Physical Chemistry (lab) (4 decks)

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