Practical Exam Flashcards
Density def:
Property indicating how much substance is in unit of volume
Density formula:
p = m/V (mass, volume) kg/m^3
Density SI
Kg/m^3
Density depends on
Temperature, mass, crystalline form
If T goes up p goes down, exception for water
Density of heterogenous
p(r) = dm(r)/dV(r)
Relative density of liquid
p = p(liquid)/p(solution)
Measuring density of liquids (material)
- scale
- pipette
- pycnometer
- distilled water
- solution sample
Density of liquids procedure
- weigh empty pycnometer
- fill with water and weigh
- fill with sample and weigh
- find pycnometer volume
- calculate density
Density of solids material
- scale
- pycnometer
- solid
- distilled water
Density of solids procedure
- weight solid in air
- fill pycnometer with water znd weigh
- fill water pycnometer with solids and weigh
- calculate
What is measurement of density of solids by immersion technique based on
Archimeds law: a solid is lighter in water than in air
Buoyant force formula
Fb = mH2O x g
Density of solids by immersion material
- scale
- beaker
- water
- sample
Density of solids by immersion procedure
- weight sample in air
- weight sample immersed in water
- calculate
Order of magnitude
Approximating answer
Fluids definition
Substance that can flow, given by velocity of particles per time
Flaw rate through pipe
Quantity of fluid passing through cross section of pipe in unite time
Volumetric flow rate
Qv = delta V /delta t
SI = m^3/s
Mass flow rate
Qm = delta m / delta t
SI: kg/s
Relation btw mass flow rate and voluletric flow rate
Qm = p x Qv
Laminar or streamline flow
- liquid flows smooth
- parallel layers to direction of flow
- low energy consume
Turbulent flow
- molecular flow irregulzr
- generate currents
- high energy consumption for flow rate
Viscosity def
Resistance to flow
Viscosity determinced by
- internal frictions btw layers of fluid
- determined by size of molecules
- more temperature leads to lower viscosity
Motion of liquid newtonian law
F = nxAx(delta Vx / delta y)
Constant of proportionality n
- represents dynamic viscosity of liquid
- SI: (N x s)/m^2 = Pa x s
Newtonian fluids
If dynamic viscosity of fluid depends on velocity, liquids are non newtonian like blood
Flow rate through cylindrr formula
Qv = delta (p . pi . r^4)/(8.n.L)
What does the nature of flow depend on
Reynold’s number
Re = (p.v.r).n
Re < 2000 -> laminer
Re > 4000 -> turbulent
Also there is in between
Buoyancy force
Weight of didplaced Volume of liquid
Fb = (4.pi.r^2)/3 .p.g
Instrument for viscosity
Ostwald viscosmeter
n(solution) = n(h20).(ps/ph2o).(ts/th2o)
Hoppler viscometer
- fill with water
- put solide in tube
- wait for it to go from line 1 to line 2 and record time
- do the same with other liquids
- calculate
What keeps molecules packed together
Intermoleculzr interactions, cohesive forces
What is internal pressure
The molecules at surface in contact with air are attracted inwars creating pressure
Potential energy of surface layer
Ep = surface tension x A
Surface tension
Represents the surface energy per unit area
SI: J/m^2 = N/m
Tensioactive substance
Substance that are absorbed in surface layer and reduce surface tension
Stalagmometer, drop counting method
- fill stalafmometer with water, count drops, use a solution with diff concentration after, determine surface tension for solution
Enthalpy formula
H = U + pV
U = internl energy
P = pressure
V = volume
Enthalpy variation formula
delta H = delta U + p x delta V
Enthalpy variation def
Heat released or absorbed by the system in isobaric process
Why use calorimeter
So the energy will be conserved
deltaQ…
Determination of dissolution enthalpy procedure
Fill calorimeter with some water, measure temperature, put kcl in tube and put tube in calorimeter, meadure temp, put tube contents in calorimeter, measure temp
Determination of enthalpy formula
delta Q = delta H = -(m.c+C).delta T
Heat definition
Form of energy describing energetic exchange between a thermodynamic system and surrounding environment
Heat capacity
Amount of heat necessary to change temperature of substance by 1°C
C = deltaQ/deltaT
Specific heat capacity
Quantity of heat necessary for unit mass of substance to change by 1°C
c = 1/m . deltaQ/deltaT
Molar heat capacity
Quantity of heat necessary for mole of substance to change temperature by 1 degree
Cmolar = 1/n . deltaQ/deltaT
delta Q is heat exchanges with surrounding
Delta T is température variation
Heat in SI
Joules J
Calorie def
Amount of heat required to rise teperzture of one gram of water
C (Heat capacity) SI
C = deltaQ/deltaT
1.J/K
c (specific heat) SI
c = 1/m. deltaQ/deltaT
J/(kg.K)
Cmolar (molar heat) SI
Cmolar = deltaQ/(n.deltaT)
J/mole.K
Latent heat
Specific heat at phase transition, heat exchange with no temperature change
J/kg
Determination of specific heat of solids
- weight metals, fill water in cup and heat to 100 degrees with metals inside, put water in calorimeter and record temp, put metal in calorimeter and record temperature when equilibrium, use formulas
Refractive index
Ratio between speed of light in vacuum and in material
n = c/v
Shows how much the speed of light is reduced when passing through optical transparent
Reflection of light
Partial or total return of light
Refraction of light
Abrupt change in direction of propagation as it passes from one optical medium to another
Snell’s law
Sin i /sin r =n2/n1 =n21
n21 = relative reftractive index
Optical lenses
Refracting devices
Focal point of lens
Point where parallel rays incident upon the lens converge
How many focal points does lens have
2, object and image
Convergence power
Reciprocal of focal length, C=1/f
SI: diopter = 1m^-1
Magnification of a lens
B =y2/y1
Optical aberration
Distortion of optical images, caused by shape of lens and wave of light
Types of aberration
Spherical,coma,chromatic,distortion
Focal distance
1/x2-1/x1=1/f
Optical microscope
Optical instrument, objective,eyepiece,condenser
Magnification
Ratio between tangent of angle under which one can see image thru instrument and tangent of zngle once can see when looked at with naked eye
G = tg a’/tg a
Resolution
Shortest distance between two points of specimen
d = (0,61 . lambda)/NA
NA = numerical aparture