Viscosity

honiedness of Liquids Part I Low Viscosities Mona Kanj Harakeh 1 Objectives To measure and analyze the viscosities of ideal (methylbenzene/p-Xylene) and nonideal (Methanol/ pee) binary star solutions and their comp desirousshotnts. To study the Activation Energy to viscous range. The effect of temperature change on the viscousness will be studied. Method The viscosities of quiets atomic number 18 positiond by measuring the rise condemnation for various swimmings in an Ostwald viscometer. 2 Ostwald viscometer 3 viscousness The fortress of a tranquilness to work is called its viscousness viscousness is a property of unstables that is definitive in applications ranging from oil flow in engines to blood flow with arteries and veins. bill viscousness How long a fluidness takes to flow out of a pipet under the office of gravity. How fast an design (steel ball) sinks through the politic under gravitative force. 4 molecular properties contributing to viscosity Viscosity arises from the directed motion of gram moleculecules former(prenominal) from each one separate, it is a measure of the rest period with which molecules prompt past one other. It is change by many a(prenominal) factors such as molcular size. Molecular shape. Intermolecular interactions ( mesmerizing force mingled with the molecules). Structure of the liquid itself. Temperature(Viscosity decreases with change magnitude temperature the increasing kinetic free energy crosss the attractive forces and molecules passel more easily move past each other). 5 Viscosity ? The IUPAC symbolization of viscosity is the greek symbol eta ? . ? Viscosity ? of a fluid is its enemy to flow. ? When a Liquid flows, whether through a electron thermionic vacuum tube or as the number of pouring from a container. Layers of liquid drop off over each other. The force (f) compulsory is directly proportional to the Area (A) and swiftness (v) of the layers and inve rsely proportional to the distance (d) amongst them. Av Equ. 1 f ?? fd gcms cm ? ? gcm ? 1 s ? 1 ? 1 piose ? 1P Av cm 2 cms ? 2 ?2 d unit of viscosity 6 Viscosity Units The unit of viscosity is the poise named after equilibriseuille Jean Louis Marie. It is more or less commonly expressed in legal injury of centipoise cP. The centipoise is commonly utilize because peeing has a viscosity of 1. 0020 cP at 20oC the closeness to one is a convenient coincidence. The SI unit of viscosity is Pascal-second (Pas) = Ns m2 or Kg m-1 s-1. In cgs unit 1 Poise P = 1 g. cm-1. s-1 (dyne . s) 10-2 Poise P= 1 centipoise cP 1 Pa. s = 103 cP 10 P = 1 Kgm? 1s? 1 = 1 Pa. s 1 cP = 0. 001 Pa. s = 1 mPa. s The conversion amid the units 1 P = 0. 1 Pa. s For many liquids at room temperature the viscosity is very small 7 (0. 002-0. 04) therefore (10-2 P), centiP is a lot used. Ostwald Method Time for fixed lot V of liquid to fall through a capillary into a rootage Upper fiduciary mark Depends o n engrossment. Depends on viscosity. Reference liquid is used. This instance can be used for liquids of viscosity up to degree centigrade poise. Lower Fiducial mark 8 Ostwald Method The rank of flow R (cm3/sec) of a liquid through a cylindrical tube of radius r and length l under a pressure brainpower P is give by the Pousille equating. Equ. 2 Measurement of P, r, t, V, and l permits the calculation of the viscosity Equ. 3 It is easier to measure the viscosity of a liquid by comparison it with a nonher liquid of know viscosity. Since P = ? gh Equ. 4 The viscosity of a solution can be determined relative to a lineament liquid (de-ionized weewee). 9Oswald viscometer The Oswald viscometer is a straightforward device for comparing the flow periods of ii liquids of cognize denseness. If the viscosity of one liquid is known, the other can be cipher. Ostwald viscometer is used to measure the low viscosities liquid. After the source is filled with a liquid, it is breaked by suction supra the f number mark. The cartridge holder unavoidable for the liquid to fall from mark 1 to mark 2 is recorded. Then the eon required for the same great deal of a liquid of known viscosity to flow under identical conditions is recorded, and the viscosity is calculated with Equation ? ? ? k? Equ. 5 ? ? ( r ) ? t ? r tr Where r refers to the viscosity, compactness and flow time for a reference liquid, usually water. Therefore it is grand to do set of measurements of known liquid and at controlled temperature. 10 runniness Equ. 6 The mutual of viscosity is liquidity, F ? ? The concept of fluidity can be used to determine the viscosity of an ideal solution. One crabby advantage for fluidity is that the fluidities of merge binary solutions of liquids a and b be approximately additive. So if each clean liquid has fluidities Fa and Fb, the fluidity of a mixture is given by where ? a and ? b is the mole fraction of component a and b respectively, Fluidity equation is only middling simpler than the equivalent equation in name of viscosity = ? Equ. 8 where ? a and ? b is the mole fraction of component a and b respectively, and ? a and ? b ar the components of pure viscosities. The viscosity of the mixture is not linear 11 Kendall proposed another get for expressing the viscosity of a mixture ln? ? ? A ln? A ? ? B ln? B Equ. 9 Where xA and xB are the mole fractions of component A and B respectively, and ? A and ?B are the components as pure viscosities. The above equation is valid for the Ideal Solutions such as methylbenzene/p-Xylene in which the interaction energies amongst the components are the same as those between the pure components. The failure of component fluidities to be additive in the mixed evidence arises, whence, either from the formation of association complexes between the components or from the destruction of such complexes that may be present in the pure components after the pure components are mixed. i nfra this circumstance the following equations would not be valid and ln? ? ? A ln?A ? ? B ln? B 12 Temperature Dependence of Viscosity Over a reasonably gigantic temperature range, the viscosity of a pure liquid increases exponentially with inverse absolute temperature. This sexual intercourse was first expressed quantitatively by Arrhenius E? (1912). ? ? A exp( Where A is a constant for a given liquid and E? is the activation energy of viscosity. The transported molecules should overcome the activation energy in erect to overcome intermolecular attractive forces. RT ) Equ. 10 A plot of ln ? against 1/T (Arrhenius plot) should be linear and have a incline equal to E? R. E ln ? ? ln A ? ? Equ. 9 RT 13 experimentational To measure the viscosity by Ostwald method, A liquid is allowed to flow through a thin-bore tube (< 1 mm) then the flow rate is determined and the physical dimensions for the tube should be known on the button. Ostwald viscometer should be calibrated w ith a reference liquid therefore the radius and Length of the viscometer can be known precisely. Operationally, the experiment is done by measuring the time required for a given masses of liquid to flow through the viscometer capillary. The driving force is the gravity. Ostwald viscometer is intentional to keep the height of the separation of the upper and lower levels of the flowing liquid as constant as possible. 14 calibration of the Ostwald Viscometer Ostwald viscometer is calibrated victimization 10 mL of purified water. The flow rate, density and known viscosity of purified water are used to calculate k. Measurement of viscosity of different solutions The viscosity of two mixed solutions with different percentages of liquids will be heedful development Ostwald method. Chemicals Molar Mass(g/mol) Molecular principle Methanol 32. 04 CH O Toluene 92. 4 CH A- Toluene/p-xylene p-Xylene 106. 16 CH Water 18. 02 HO B- Methanol/Water Measure the viscosity for each pure liqui d then measure the viscosity 20%, 40%, 60% and 80% percentages by wad. 4 7 8 8 10 2 15 Procedure forfend the viscometer into a large beaker (2-L) of water that is placed on a hot plate, that is as close to 25 C as possible. get along sure the viscometer is fully immersed in the water. 1. Pipette 10 ml of de-ionized water of known density into the Ostwald viscometer and allow time for the liquid to equilibrate to the temperature of the bath.Then use a pipet bulb to push or pull the liquid level up above the upper fiducial mark on the viscometer. Allow the water to run hazard down and start the timer exactly as the meniscus passes the upper mark. decimal point the timer just as the meniscus passes the lower mark. Repeat at least twice. Your flow times should comply to indoors intimately 0. 4 seconds. 2. sporting and change the viscometer by running a few milliliters of acetone through it. course the acetone and aspirate for about a minute to evaporate all the acetone. 3. g et wind the flow times of each of your wood alcohol/water 16 solutions at 25 C. Procedure contd . Complete the series by measuring the flow time for pure Methanol. Repeat each at least twice. Your flow times should agree to within about 0. 4 seconds. 5. Clean and dry the viscometer as before. 6. retrieve the flow times of each methylbenzene/p-xylene solution as in spirit 3. End the determinations with the pure p-xylene. 7. For our temperature work lovingness the water bath in roughly 5 to 10 degree increments and determine the flow time of the pure pxylene as before at each temperature. Make sure that the temperature is constant. The exact temperature is not important as long as it is known to 0. C, and that the viscometer has had time to equilibrate to a new temperature. Stop at about 60 C. 17 shelve info 1 The flow times of each of ( wood alcohol/water) and (methylbenzene/p-xylene) solutions at 25oC %by tidy sum atomic number 6% water 20% wood alcohol 40% wood alcohol 60% wood spirit 80% methanol cytosine% methanol menstruate time (1) (s) full point time (2) (s) run for time (3) (s) Average Flow time (s) blow% p-xylene 20% methylbenzene 40% toluene 60% toluene 80% toluene c% toluene 18 The flow times of methanol at different temperature Table selective information 2 The flow times of p-xylene at different temperature.Temperature Flow time (1) (s) Flow time (2) (s) (C) 25 30 35 40 45 50 55 60 65 Flow time (3) (s) Average Flow time (s) 19 Viscosity Table of Results 1 Methanol, volume % 0% Methanol Methanol , tip % The flow times of a series of Water/Methanol solutions that are 0,20,40,60, 80, and 100% by volume. Average Flow time, t (sec) viscosity, ? (cP) ? ? k? t Fluidity F ? Density, ? (g/mL) ? 1 100% Water 20 40 0 density of H2O 0. 99704 0. 971 0. 944 ? of H2O 0. 8904 16. 54 34. 57 60 80 100 54. 33 76. 02 100 0. 909 0. 859 0. 788 20 Density of Methanol/Water Mixtures at 25 0CViscosity Table of Results 1 Contd %by volume Densi Mole fra ction ln? ? ? ln? ? ? ln? A A B B ty (g/ml ) 0. 997 0. 971 0. 944 0. 909 0. 859 0. 788 Xwater =1 Xwater= Xmethanol= Xwater= Xmethanol= Xwater= Xmethanol= Xwater= Xmethanol= Xmethanol=1 viscosity ? (cP) Fluidity F ? ? A FA ? ? B FB 100% water 20% methanol 40% methanol 60% methanol 80% methanol 100% methanol 21 Viscosity Table of Results 2 The flow times of a series of toluene/p-xylene solutions that are 0,20,40,60, 80, and 100% by volume. Density, ? (g/mL) Average Flow time, t (sec) Viscosity, ? (cP) ? k? t Toluene, volume % Fluidity F ? ? 1 0%Toluene (100% pxylene) 20% Toluene 40 60 80 100 0. 857 0. 858 0. 859 0. 859 0. 960 0. 861 Density of Toluene/p-Xylene Mixtures at 25C 22 Viscosity Table of Results 2 Contd %by volume 100% pxylene 20% toluene 40% toluene 60% toluene 80% toluene 100% toluene Densit y (g/ml ) 0. 857 0. 858 0. 859 0. 859 0. 960 0. 861 Mole fraction ln? ? ? A ln? A ? ? B ln? B viscosity ? (cP) Fluidity F ? ? A FA ? ? B FB Xp-xylene =1 Xtoluene = Xp-xylene = Xtoluene = Xp-xylene = Xtoluene = Xp-xylene = Xtoluene = Xp-xylene = Xtoluene =1 3 Table of Results 3 T(oC) 20 25 D (g mL-1) 0. 879 0. 857 ln ? vs. 1/T ln ? T(K) 1/T Average ? Flow time, ? ? k? t t (sec) 30 35 0. 852 0. 848 40 45 0. 943 0. 839 50 55 0. 834 0. 830 60 0. 825 24 1. jell the viscosity coefficient for the methanol/water solutions and toluene/p-xylene solutions exploitation equation ? ? k?. t Calculate Fluidity apply equation ? 2. Calculate viscosity ? for the above solutions using equation ln? ? ? A ln? A ? ? B ln? B Calculate Fluidity using equation for all above solutions using equation F ? ? A FA ? ? B FBData Analysis F ? 1 3. equate the viscosity of the methanol/water mixtures to the toluene/pxylene mixtures by graphing the value of the viscosity coefficient (? ) versus the volume percentage of each mixture. Comment on the shape of the graphs. Comment on the ideality of the two solutions. 4. Next look at the dependance of viscosity of p-Xylene on temperature. Plot ln ? vs. 1/T and determine the activation energy and the error in the activation energy. (Use outgo to get the error in the slope and use it in a simple propagated error analysis) 25