Lab Report 2 Experiment 1: Density And Composition Of Solutions PDF

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Lab Report Experiment 1: Density and Composition of Solutions...

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9/8/17 Experiment 1: Density and Composition of Solutions

Purpose:

The purpose of this experiment is to learn that determining the density of sucrose solutions is the fastest and easiest way of finding its composition by two methods the direct method and indirect method (Archimedean). Theory/ Principles: When determining the density of sucrose solutions there are two methods of calculating it by the direct and indirect method. The simple direct method is by weighing an empty cylinder then weighing the mass of a cylinder + liquid and you get the equation of: density= mass cylinder + liquid – mass of empty cylinder / volume of liquid. The second/ indirect method is the Archimedean method which depends that when a solid is immersed in a fluid it loses weight and we also keep in mind that density is a function of temperature and in this experiment it remains constant. This method is given by the equation of: density= [mass of solid in air - apparent mass solid in liquid] 1.00 g/mL / mass of solid in air – apparent mass of solid in water. Another equation given to us once we start the procedure is to calculate the percent weight of sucrose in each solution given to us in: % by weight of sucrose= 100 x (mass of sucrose) / mass of sucrose + mass of water. In this experiment determining the density of solutions of both methods would lead to us creating a graph of composition vs. density which will hopefully help us determine of the unknown sugar solution and find its composition by using the graph. Experimental Procedures: The procedure for this experiment is broken down into four parts. Part A: In this part we prepare three standard sucrose solutions with the amounts given to us already. To start preparing we get three Erlenmeyer flask’s and label them A,B, and C to get the appropriate amounts of grams of sugar and volume of water already given to us already. To get

the right amount of sugar we get a weighing paper and place it on the triple beam balance and start transferring amounts of sugar to eventually get the correct grams of sugar given to us already which are 7.5g, 14.0g, and 30.0g. Once we gather the correct amounts of sugar for each we start transferring those amount to its designated flask and fill each with the amounts of water stated to us already which is 40.0mL, 36.0mL, and 30.0mL. From here we stir the mixture to make sure the sugar has dissolved and calculate the percent by weight of sucrose in each solution. Part B: In this part the data to be recorded is the mass of graduated cylinder, masses of graduated cylinder + solutions, and volumes of solutions. Once gathered we calculate the mass of each solution in the graduated cylinder and density of each solution by using the simple direct method. To start doing this we weigh a dry 10 mL graduated cylinder on the triple beam balance and once done we fill the cylinder with 10.0 mL first with solution A. Next we reweigh the cylinder containing solution A on the triple beam balance. We repeat this procedure for the next solutions B and C but we don’t reweigh the just the cylinder again and we make sure to rinse the cylinder with its own 2 mL solution portions before filling it in. Part C: The data to be record here is mass of sinker, apparent mass of sinker in water, apparent mass of sinker in the sucrose solutions. Once gathered we use the indirect method (Archimedean) to calculate the density of each of the sucrose solutions. We first start by suspending a metal sinker of a thread from the arm of the triple beam balance and determine its mass. Then we get a 100 mL beaker and put half full of water on the balance platform and raise the platform until our sinker is completely immersed in the water making sure it’s not touching the sides of the beaker or bottom. Then we determine its apparent mass. Next we remove the sinker from the water, empty out the beaker, and dry both of them. From here we full the beaker

with half full with solution A and suspend the sinker in it with same rules as before. We then just repeat this procedures for solutions B and C making sure to rinse and dry both sinker and beaker before weighing. Part D: The data to be recorded is the unknown solutions designating letter, mass of graduated cylinder + unknown sucrose solution, volume of unknown solution, and apparent mass of sinker in unknown solution. After we gain this we on a graph paper or on excel we plot the density vs. percent by weight of sucrose for the standard solutions of known composition. We include points from both methods of density determination and point of pure water on our graph. Then we connect the points with a smooth curve to locate the density of our unknown solution and record the percent by weight of sucrose in the unknown solution. To gain all this information we get a dry and clean 100 mL beaker and get 60 mL of our sucrose solution of unknown composition in our case it is unknown solution G. Next we just repeat the same procedures we did for part B and C for this unknown solution. Data Tables / Summary: -

Raw data of measurements for Part A, B, C, & D for each solution and unknown G

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cont. of raw signed data

Raw signed data from above formatted with my own measurements done already

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Table 1: including all calculations done for each solution by using the % by weight of sucrose equation, direct method, indirect method, and % uncertainties for each measurement in parts B & C and densities found in these parts as well

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Graph 1 (Direct Method): Here I graphed my % weight of sucrose on the x- axis and my density using the direct method on the y- axis in order to find out the % weight of sucrose of my unknown (G) which ended up being 25.0 %

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Graph 2 (Indirect Method): Here I once again graphed the % weight of sucrose on the xaxis and density using the indirect method on the y-axis in order to find out the % weight of sucrose for my unknown (G) which ended up being 23.0%

Results and Discussions: Sample calculations:

Logical Explanation: By collecting our measurements for each solution and unknown solution through each procedure we were able to find out the percent weight of sucrose for our unknown (G) through the use of both direct and indirect methods. Finding the percent weight of sucrose for our solutions A, B, and C assisted in plotting both of the graphs along with finding the densities through direct/ indirect methods for each solution including our unknown (G). By plotting two graphs it helped us accurately pin point our percent weight of sucrose unknown (G) when using direct and indirect methods. Finishing my calculations I was able to calculate their percent uncertainties for each measurements in parts B and C. As well as calculate their percent uncertainties in their densities in parts B and C. For both percent uncertainties I noticed them mainly to be near the 0.05 %. I believe the second method of determining percent uncertainty is more precise just because it involved gaining their volumes and masses to which lead to more of an accurate percentage. Through this experiment I was able to learn how to use some of these equations and apply them to problems. By using d=m/v I was able to determine the density of the sinker I was

used which ended up being 0.108 g/mL. I was also able to determine the density of molten potassium tungstate at 925 Celsius using the indirect method which ended up being 3.10 g/mL. Conclusions: The use of both direct and indirect methods to determine the densities of sucrose solutions were the fastest and easiest methods as it assisted in gaining the percent weight of our unknown solution G. Both methods were able to show us the compositions of the solutions and realize how not so far off these calculations are from one another. References: Goldwhite, H.; Tikkanen, W. Experiment 1. Density and Composition of Solution, Experiments in General Chemistry, 4th ed.; The McGraw Hill Companies. (21-24)...