Viscosity

viscosity of Liquids Part I scummy Viscosities Mona Kanj Harakeh 1 Objectives To measure and analyze the viscosities of ideal (methylbenzene/p-Xylene) and nonideal ( wood spirit/water system) binary solutions and their components. To determine the Activation Energy to viscous black learnet. The put together of temperature change on the viscousness will be studied. Method The viscosities of lucids are determined by metre the extend era for various fluidnesss in an Ostwald viscosimeter. 2 Ostwald viscometer 3 Viscosity The resistance of a luculent to issue is called its viscousness Viscosity is a property of melteds that is important in applications ranging from oil flow in engines to blood flow by arteries and veins. Measuring viscousness How long a liquid takes to flow out of a pipette infra the force of gravity. How fast an object (steel ball) sinks through the liquid under gravitational force. 4 Molecular properties contributing to viscosity Viscosity arises from the directed motion of molecules past distributively other, it is a measure of the ease with which molecules move past one another. It is affected by many factors such(prenominal) as Molecular size. Molecular shape. Intermolecular interactions ( fetching force between the molecules). Structure of the liquid itself. Temperature(Viscosity decreases with increase temperature the increasing kinetic energy overcomes the attractive forces and molecules can more easily move past individually other). 5 Viscosity ? The IUPAC symbol of viscosity is the greek symbol eta ? . ? Viscosity ? of a fluid is its resistance to flow. ? When a Liquid flows, whether through a tube or as the result of pouring from a container. Layers of liquid slide over each other. The force (f) required is directly proportional to the Area (A) and velocity (v) of the layers and mutually proportional to the distance (d) between 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 Poiseuille Jean Louis Marie. It is most commonly expressed in terms of centipoise cP. The centipoise is commonly apply because pissing 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 between the units 1 P = 0. 1 Pa. s For many liquids at room temperature the viscosity is very small 7 (0. 002-0. 04) wherefore (10-2 P), centiP is often utilize. Ostwald Method Time for fixed the great unwashed V of liquid to fall through a capillary into a reservoir Upper Fiducial recognise Depends on density. Depends on viscosity. Reference liquid is used. This type can be used for liquids of viscosity up to 100 poise. Lower Fiducial mark 8 Ostwald Method The drift of flow R (cm3/sec) of a liquid through a rounded tube of radius r and length l under a pressure head P is given 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 comparing it with another liquid of know viscosity. Since P = ? gh Equ. 4 The viscosity of a solution can be determined relative to a quotation liquid (de-ionized water supply). 9Oswald viscometer The Oswald viscometer is a simple device for comparing the flow generation of two liquids of known density. If the viscosity of one liquid is known, the other can be calculated. Ostwald viscometer is used to measure the low viscosities liquid. subsequently the reservoir is filled with a liquid, it is pulled by suction higher up the upper mark. The time required for the liquid to fall from mark 1 to mark 2 is recorded. Then the time required for the same volume of a l iquid of known viscosity to flow under identical conditions is recorded, and the viscosity is calculated with comparability ? ? ? k? Equ. 5 ? ? ( r ) ? t ? r tr Where r refers to the viscosity, density and flow time for a reference liquid, usually irrigate. Therefore it is important to do set of measurements of known liquid and at controlled temperature. 10 liquid state Equ. 6 The reciprocal of viscosity is fluidity, F ? ? The concept of fluidity can be used to determine the viscosity of an ideal solution. One particular advantage for fluidity is that the fluidities of mixed binary solutions of liquids a and b are approximately additive. So if each thin liquid has fluidities Fa and Fb, the fluidity of a compartmentalisation is given by where ? a and ? b is the mole subdivision of component a and b respectively, liquidity equation is only slightly simpler than the equivalent equation in terms of viscosity = ? Equ. 8 where ? a and ? b is the mole share of component a an d b respectively, and ? a and ? b are the components of virginal viscosities. The viscosity of the florilegium is not linear 11 Kendall proposed another approach 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 plain viscosities. The above equation is valid for the Ideal Solutions such as Toluene/p-Xylene in which the interaction energies between the components are the same as those between the pure components. The failure of component fluidities to be additive in the mixed state arises, then, either from the formation of tie-up 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. Under 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 wide te mperature range, the viscosity of a pure liquid increases exponentially with inverse absolute temperature. This relation 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 order to overcome intermolecular attractive forces. RT ) Equ. 10 A plot of ln ? against 1/T (Arrhenius plot) should be linear and have a position equal to E? R. E ln ? ? ln A ? ? Equ. 9 RT 13 Experimental 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 exactly. Ostwald viscometer should be set with a reference liquid therefore the radius and Length of the viscometer can be known precisely. Operationally, the experiment is make by measuring the time required for a given volume of liquid to f low through the viscometer capillary. The driving force is the gravity. Ostwald viscometer is designed to keep the height of the separation of the upper and glare 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 pcts of liquids will be measured using Ostwald method. Chemicals Molar Mass(g/mol) Molecular Formula 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 liquid then measure the viscosity 20%, 40%, 60% and 80% percentages by volume. 4 7 8 8 10 2 15 Procedure Suspend the viscometer into a self-aggrandizing beaker (2-L) of water that is placed on a hot plate, that is as close to 25 C as possible. Make 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 pipette lightbulb to push or pull the liquid level up above the upper fiducial mark on the viscometer. Allow the water to run back down and start the timer exactly as the meniscus passes the upper mark. Stop the timer just as the meniscus passes the lower mark. Repeat at least twice. Your flow times should agree to in spite of appearance well-nigh 0. 4 seconds. 2. Clean and dry the viscometer by running a few milliliters of acetone through it. Drain the acetone and aspirate for about a minute to evaporate all the acetone. 3. Determine 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 agr ee to within about 0. 4 seconds. 5. Clean and dry the viscometer as before. 6. Determine the flow times of each toluene/p-xylene solution as in step 3. End the determinations with the pure p-xylene. 7. For our temperature work heat 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 Table Data 1 The flow times of each of ( methyl alcohol/water) and (toluene/p-xylene) solutions at 25oC %by volume 100% water 20% methanol 40% methanol 60% methanol 80% methanol 100% methanol run away time (1) (s) Flow time (2) (s) Flow time (3) (s) Average Flow time (s) 100% p-xylene 20% toluene 40% toluene 60% toluene 80% toluene 100% toluene 18 The flow times of methanol at different temperature Table Data 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 , weight % 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 fraction 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 Vis cosity 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. Determine the viscosity coefficient for t he methanol/water solutions and toluene/p-xylene solutions using equation ? ? k?. t Calculate Fluidity using 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. Compare 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 dependence of viscosity of p-Xylene on temperature. Plot ln ? vs. 1/T and determine the activation energy and the wrongdoing in the activation energy. (Use Excel to get the error in the slope and use it in a simple propagated error analysis) 25