LAB 1. INTRODUCTION TO THE LABORATORY

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1 LAB 1. INTRODUCTION TO THE LABORATORY MEASURING AND MIXTURES PURPOSE: To become familiar with the function and use of common laboratory equipment. To learn techniques of measuring mass and volume To separate a mixture of salt and sand into its components. To calculate the % composition of an unknown mixture. BACKGROUND: LABORATORY TECHNIQUES: Measuring Volume: Graduated Cylinders are tools for accurately measuring the volume of liquids. They have more accurate markings than a beaker or Erlenmeyer flask, but have less accurate markings than a pipette, buret, or syringe. All types of volumetric glassware have a slender, cylindrical shape in the measuring region which causes the surface of most liquids to be curved downward. Take readings from the bottom of the curved surface (called the meniscus) with your eye at the same level. A: Read the bottom of a concave meniscus. B: Read the top of a convex meniscus. If the volumetric glassware that you are using has a number of graduations, estimate the volume as accurately as you can by noting the position of the meniscus between the graduations. See Figure Figure 2-5 The proper method of reading the meniscus. The reading is 85.5 ml. The scale divisions on a graduated cylinder are generally determined by its size. For example, the 50- ml graduated cylinder is divided into 1 ml increments. However, the scale of a 10-mL graduated cylinder is divided into 0.1 ml increments, and the scale of a 500-mL graduated cylinder is divided into 5 ml increments. The graduated cylinder scale is a ruled scale, and it is read like a ruler. Measuring Mass: When performing chemical reactions in the laboratory we often need to measure the mass of our ingredients. The techniques for measuring mass using an electronic balance will be explained and practiced in the experimental section of this lab. Our balances measure mass in grams. Lab 1:Intro to Measuring and Mixtures (F15) GS 105 7

2 Filtration: Filtration is the common process used to separate an insoluble solid from a liquid. Layers of rock and sand and algae are used to filter impurities from water to make it drinkable. Breweries use fine millipore filters to filter out harmful bacteria. In the laboratory the filtration process is carried out using a funnel and filter paper. The liquid that passes through the filter paper is called the filtrate, and the solid that remains on the filter paper is the precipitate or residue. Evaporation: Most substances that dissolve in a liquid (solutes) can be recovered from solution by evaporating the liquid portion (the solvent) over a direct flame, a hot plate, or a steam bath. The size of solid crystals often relates to the rate of evaporation of the solvent. Slowly formed crystals are usually larger than crystals formed rapidly. PROCEDURES: ACTIONS: I. MEASUREMENTS: A. MASS 1. Obtain a weighing boat or shiny weighing paper 1 and place it on the pan of an electronic balance. Press the Tare or Zero button on the face of your balance to set the mass of the paper to zero With your lab scoop or metal spatula, put enough salt/sand mixture on the weighing paper to measure about 3 2 grams. Record the exact mass on your report sheet (Box IA) to 3 places behind the decimal according to the accuracy of your balance. 3. Carefully remove the weighing paper with the salt/sand mixture from the balance and transfer it to a 125 ml Erlenmeyer flask. 4 B. VOLUME: 4. Measure 7 mls of water using a graduated cylinder 5. The bottom of the meniscus 6 should be right at the 7 ml line of the graduated cylinder. 5. In Box IB of your report sheet draw a picture of the meniscus in your graduated cylinder. Include a couple of graduation markings on your cylinder drawing above and below. NOTES: 1 Chemical powders and liquids should never be placed directly on the metal balance pan since they may cause corrosion. Shiny paper or boats are used so that powdered materials will slide off easily. If porous paper, like filter paper or paper towels, were used instead of shiny materials, then powders might get caught in the fibers and be lost. If you are using weighing paper then fold it into quarters by folding in half, opening, and then folding in half again the other direction. Open up the paper and place it on the balance pan. 2 The tare button will set the recorded weight of your paper to grams. Now when you add solid to the paper the balance will show only the added mass of the solid. If you do not tare the balance after the weighing paper is applied, then you would have to subtract the mass of the paper from your total mass to get the mass of your substance alone. 3 The mass does not have to be exactly grams but could be anywhere between and ( ); (for example or etc.) 4 The shape of an Erlenmeyer flask makes swirling/mixing materials less likely to splash or spill than if done in a beaker. 5 For fine control of your water level you can use an eye dropper for the last bit of water. Always hold eye droppers upright with the glass tip pointing down. Natural vacuum will keep the liquid from spilling. Do not tip the dropper back or the vacuum will be broken and the filling will run into the bulb and get contaminated, or air may enter the dropper and cause the contents to spill. 6 Water forms a meniscus in any glass tube or cylinder because water is attracted to glass and will try to climb the sides of a glass container. We measure the amount of water in a glass tube from the bottom of the meniscus. Lab 1:Intro to Measuring and Mixtures (F15) GS 105 8

3 II. SEPARATION OF SALT AND SAND: 6. Add the 7 mls of deionized water from the graduated cylinder to the Erlenmeyer flask of salt/sand mixture. Swirl to completely dissolve the salt to make a salt water solution Take a few minutes to talk with your partner and develop a procedure 8 to quantitatively identify how much salt and sand you have in solution. You need to develop a plan to measure the mass of each component not just the whole mass less one part. 8. Record your procedure on in II-A. 9. Show it to your instructor for approval 10. Execute your plan and record your progress in II-B 11. Determine the percent 9 of salt (II-C) and percent of sand (II-D) in your original mixture. 12. Describe the salt crystals formed. 13. Assess the quality of your results and make some conclusions about your data If the salt is not completely dissolved then it will remain solid and be filtered out of solution with the sand. Thus your results will show less salt and more sand than actually present. 8 For the procedure make it as detailed as possible. Think about it like a recipe, could you give your procedure away to your neighbor and have them complete the lab with little to no trouble? 9 Percent composition is the part divided by the whole X 100 or: part X 100 = % whole In this case the whole is the mass of the original salt and sand mixture. The part is the mass of the sand or the mass of the salt. 10 Do your percent compositions of salt and sand total 100? Why or why not? What might some of the errors be in your procedures or techniques? Lab 1:Intro to Measuring and Mixtures (F15) GS 105 9

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5 LAB 1 INTRO TO THE LABORATORY REPORT: I. MEASUREMENTS: A. Mass Unknown Salt/Sand Mixture g (report to the accuracy of the balance) B. Volume (Add labels & meniscus) NAME PARTNER DATE II. SEPARATION OF SALT AND SAND A. Proposed Procedure Instructor B. Actual Procedure C. % Composition of Salt in the mixture: (show the calculations) D. % Composition of Sand in the mixture: (show the calculations) ANALYSIS & CONCLUSIONS: salt and sand total 100 %.. Report the appearance of your separated salt and sand. Why doesn t your sum of Lab 1:Intro to Measuring and Mixtures (F15) GS

6 LAB 1. INTRO TO THE LABORATORY: LAB EXERCISES: NAME DATE The curve of the surface of a liquid when placed in a cylindrical tube is called the To set the mass of an object to zero on an electronic balance is called to The material that passes through a filter is called the The material that remains in the filter paper after a filtration is called the 5. Given the measuring devices above, and your experience in this lab, choose the right tool(s) to accurately measure: a) 5 ml of water b) 200g of sugar c) ml of vinegar d) 75 ml of water (D) 6. If the water was allowed to evaporate from your salt water solution at a slow rate rather than quickly over a hot plate would you expect the crystals to be larger or smaller? Lab 1:Intro to Measuring and Mixtures (F15) GS