Introduction to the Chemistry Lab

Introduction This experiment is designed to introduce you to the chemistry laboratory and introduce techniques you will need in order to work efficiently and effectively. Specific objectives for this laboratory period are: 1. to become proficient in the use of significant figures; 2. to become familiar with the physical layout of the laboratory; 3. to light and properly adjust a Bunsen burner; 4. and to develop skills in using and reading a beam balance, graduated cylinder, and

buret. There is no report sheet to complete for this lab. You are to fill in the blanks in the lab manual pages. Complete the pre-laboratory problems before

you come to the lab, tear out that page, and place it in the appropriately labeled bin prior to performing lab activities.

Otherwise, it will be late and will cost you 10% of the grade (per week late). Turn in the remaining pages at the beginning of the next lab period.

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Name Lab Partner(s)

Section Date

Introduction to the Chemistry Lab

Pre Lab Problems Read the section on “Significant Figures,” then solve the following problems. Hand this page in before

performing the lab activities.

1. Write the correct number of significant figures for each of the following readings. If the number of significant figures is unclear (ambiguous), say so.

(a) 70,503 kg

(b) 67,000,000 m

(c) 0.00847 g

(d) 4.826 x 10-5 sec 2. Perform the following operations, reporting the answers with the correct number

of significant figures.

(a) 38.904 + 196.63 + 48 + 1.0648 =

(b) 34.068 – 12.8 =

(c) 41.8 x 2.1 =

(d) (1.412 x 103) x (2.60 x 10−4) =

(e) 42.31 / 0.040 =

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Name Lab Partner(s)

Section Date

Introduction to the Chemistry Lab

Lab Activities Do the following activities in the laboratory, fill in the blanks, and submit all pages and calculations at the beginning of the next

lab period.

Laboratory Information Draw a simple lab floor plan in the space below. Indicate the locations (using their numbers) of each of the following items (some will be used more than once):

1. First aid kit 5. Large sinks 2. Safety shower 6. Fume hood 3. Eye wash fountain 7. Beam balance table 4. Fire extinguisher

Floor Plan: Briefly describe the following:

Location of fire alarm

Location of emergency phone

Location of stockroom

Your clean-up assignment

Fire evacuation route

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Basic Laboratory Techniques

Handling liquid reagent bottles

1. Read the label twice. (Why? To be sure you have the right stuff?) 2. Loosen the stopper. 3. Remove the stopper from the bottle with the back of your hand as shown. Touch

the stopper to the inside of the neck of the bottle to remove any liquid drops.

4. Take care never to set the stopper down, and never place a dropper pipet

directly in a bottle. □ Obtain an acid or base bottle and practice removing the stopper properly. Place a

check in the box when you have done this task.

The Bunsen burner

Identify the following parts of the Bunsen burner and enter the appropriate numbers in the circles on the diagram located on the following page: 1. Air inlet 2. Gas needle valve 3. Gas supply valve 4. Hottest part of the flame To light the burner: 1. Partially open the air inlet. 2. Open the gas needle valve as far as possible, and be sure that the burner sits

evenly on the lab bench. 3. Turn on the gas supply valve and bring a striker to the top of the barrel.

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To adjust: 1. After you have a flame, try adjusting the air

inlet open and shut, and notice the effect on the flame. A hot, well-adjusted flame has an inner blue cone about one inch high.

2. Slowly close the gas needle valve and notice

the effect on the flame. □ Obtain a Bunsen burner, light it properly, and

adjust it for a cool flame and for a hot flame. Check the box when you have completed this task.

The graduated cylinder

The graduated cylinder is used to measure volumes of liquid with an uncertainty of about ± 0.1 mL. To read the volume, be sure the graduated cylinder is vertical and your eye is at the level of the meniscus; then read the position of the bottom of the meniscus, reading between the lines to estimate the last digit. (Note that if you are going to be reading a buret, you should see Appendix A.) This meniscus reads approximately 82.8 mL. The correct reading of this volume is mL .

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□ Cross out the incorrect diagram:

The beam balance

Enter the appropriate numbers in the circles to identify the parts of the balance. 1. Zero adjustment screw 2. Balance pointer 3. Index line 4. Slide weights 5. Weighing pan Directions for weighing with the beam balance: 1. Place the slide weights in their zero

notches. If the balance pointer is more than 2 millimeters off-line, use the zero adjustment screw to bring it into alignment.

2. Place the sample in the

middle of the pan. Always use a container or piece of weighing paper for the sample; never

place a chemical directly on the pan.

3. Move the slide weights one at a time, starting with the heaviest (giving 100-gram divisions) and then going on to the 10-gram, 1-gram, and 1/100-gram divisions. Move each of the weights in turn from higher to lower positions (200, 100, etc.), stopping at the notch where the pointer moves above the index line. Then position the smallest slide weight to align the pointer with the index line. The mass reading is the sum of the positions of all four slide weights. Estimate to the nearest 0.001 gram.

4. After recording the reading, return the slide weights to their zero positions and

be sure the balance is clean for the next user.

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Practice Activities NOTE: You must show all of your work for full credit. Every

calculation should be shown neatly, be properly labeled, and should not be crammed into the margins of your lab notebook. It may be necessary to attach a separate page of calculations.

Determining the Mass of an Object

Obtain from your lab assistant a metal object which will also be used for your density determination. Determine the mass, and keep the object at your lab station. Mass of object g Obtain a crucible and its cover. Find their individual masses. Mass of crucible g Mass of cover g Add the mass you obtained for the crucible and the mass you obtained for the cover. Sum of masses g Place the cover on the crucible, and find the mass of the crucible and cover together. Mass of crucible and cover g Compare the calculated value (sum) of the crucible and cover with the actual mass obtained on the balance. Are they the same value? Why or why not?

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Determining the Density of an Object

Obtain a metric ruler or meter stick. Use the same metal object you’ve already weighed; place one edge of your metal object on the zero mark (as precisely as possible) and estimate the reading of the other edge. Use the correct number of significant figures for your readings. If you have a cylinder, find the diameter and height. If you have a cube or a rectangle, find length, width, and height.

Cube (or rectangle) Cylinder

Length cm

Height cm

Width cm Diameter cm

Height cm

Calculate the volume of the object by using one of the following formulas:

For a cube or rectangle, use: HeightWidthLengthVolume ××= For a cylinder, use: HeightrVolume ×= 2π (r = diameter / 2)

Volume of object cm3

Mass of object (from previous page) g Now that you have the mass and the volume of the object, calculate the density using the equation:

VolumeMassDensity =

Density of object g/cm3

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Determining the Density of Water - The Graduated Cylinder Method

Your instructor will demonstrate the use of a wash bottle for rinsing glassware with distilled water. 1. Wash a 50 or 100 mL graduated cylinder with soap solution and rinse at least

three times with tap water. Shake out excess water. Rinse with two separate 5 mL portions of distilled water using a wash bottle.

2. Pour a small portion of distilled water from your wash bottle into a small beaker.

Use a thermometer to measure the temperature of the distilled water to the nearest 0.1°C, and record the reading in Data Table 1 (located on the following page).

3. Record the density of water at the temperature you recorded. You can locate this

value in Table 1 on page 25. You will most likely need to interpolate, which is better than just rounding off your temperature to get a density from Table 1.

4. Dispense about 50 mL of distilled water from your wash bottle into the graduated

cylinder. Read the volume of water in the graduated cylinder to the nearest 0.1 mL. Record the value in Data Table 1 as “Volume: At Start.”

5. Obtain and weigh a dry 50 mL beaker. Use the same balance for the remainder of

your mass determinations. Record the mass (with the number of significant figures appropriate for the uncertainty of the reading) in Data Table 1 as “Mass: At Start.”

6. Pour 10-15 mL (must be at least 10 mL

) of water from the graduated cylinder into the beaker.

(a) Measure the volume of distilled water that remains in the cylinder. Record this value as “Volume: After Pour #1.”

(b) Weigh the beaker (which now contains at least 10 mL of distilled water).

Record the value as “Mass: After Pour #1.” Do not discard the water in the beaker.

7. Repeat Steps 7(a) and 7(b) two more times. (You will end up with at least 30 mL

of water in the beaker.) Record these volumes and masses in Data Table 1. The “ΔVolume” column and “ΔMass” column of your Data Table should still be blank.

8. Subtract the volume “After Pour #1” from the volume “At Start” and record the

difference in the “ΔVolume” column of Data Table 1. (This difference is the volume of the water poured out; the sign “Δ” means “change in.”) Do the same

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subtractions between Pour #2 and Pour #1, and between Pour #3 and Pour #2, recording the values in your Data Table. Show all work for full credit!

9. Subtract the mass “At Start” from the mass “After Pour #1,” and record in the

“ΔMass” column. (This is the mass of the water that was poured into the beaker.) Do the same subtractions between Pour #2 and Pour #1, and between Pour #3 and Pour #2, recording the values in your Data Table. Show all work for full credit!

Data Table 1 – The Graduated Cylinder Method

Temperature of water °C

Density of water (see Table 1) g/mL

Volume ΔVolume Mass ΔMass

At Start mL g

After Pour #1 mL mL g g

After Pour #2 mL mL g g

After Pour #3 mL mL g g Calculate the density of water for each pour, and the average density of water. Show all work for full credit! Use the formula:

VolumeMassDensity

∆∆

= .

Density for Pour #1 g/mL

Density for Pour #2 g/mL

Density for Pour #3 g/mL

Average Density g/mL

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Determining the Density of Water - The Buret Method

1. Carefully wash a buret with soap solution and a long buret brush. (CAUTION:

Handle the buret gently and be especially careful not to hit it against the faucet.) (See Appendix A.) Rinse the buret three times with tap water and a final time with distilled water. If water does not “bead” as the buret drains, the buret is ready to use.

2. Attach a buret clamp to a ring stand, and carefully secure the buret in the clamp.

Close the stopcock by turning the handle until it is perpendicular to the length of the buret tube. Pour a small amount of water from your wash bottle into the buret. Open the stopcock slowly, and allow a small portion of water to run out of the tip. Stop the flow a couple of times (by closing the stopcock) to ensure that there are no air bubbles in the tip or stopcock. If air is present, tap the tip lightly while water is flowing. If this does not remove the air, consult your instructor.

3. Close the stopcock and use a funnel to fill the buret with distilled water to slightly

below the top graduation. (Note: You will notice that the buret is graduated differently from the graduated cylinder. At the 0.00 mL graduation the buret will contain 50.00 mL of distilled water, however the values you record in your “Volume” column will be increasing, not decreasing.) Estimate the position of the bottom of the meniscus to the nearest 0.01 mL and record the value in Data Table 2 (on the following page) as “Volume: At Start.”

4. Measure the temperature of the distilled water in your wash bottle (to the nearest

0.1 °C) by pouring a little water into a beaker and measuring the temperature of the water in the beaker. Do not attempt to measure the temperature of the water that is inside the buret, as you may drop the thermometer and break it. Record this value in Data Table 2.

5. Record the density of water at the temperature you recorded. You can locate this

value in Table 1 on page 25. You will most likely need to interpolate, which is better than just rounding off your temperature to get a density from Table 1.

6. Weigh a dry 50 mL beaker and record the mass in Data Table 2 as “Mass: At

Start.” Use the same balance for the remainder of your mass determinations. (Be sure to use number of significant figures appropriate for the uncertainty of the reading).

7. Open the stopcock slowly, and let 10-15 mL (at least 10 mL

) of water run from the buret into the beaker.

(a) Again, read the location of the meniscus in the buret. Record this value as “Volume: After Pour #1.”

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(b) Weigh the beaker (which now contains at least 10 mL of distilled water).

Record the value as “Mass: After Pour #1.” Do not discard the water in the beaker.

8. Repeat Steps 7(a) and 7(b) two more times. (You will end up with at least 30 mL

of water in the beaker.) Record these volumes and masses in Data Table 2. The “ΔVolume” column and “ΔMass” column of your Data Table should still be blank.

9. Subtract the volume “At Start” from the volume “After Pour #1” and record the

difference in the “ΔVolume” column of Data Table 1. (This difference is the volume of the water poured out; the sign “Δ” means “change in.”) Do the same subtractions between Pour #1 and Pour #2, and between Pour #2 and Pour #3, recording the values in your Data Table. Show all work for full credit!

10. Subtract the mass “At Start” from the mass “After Pour #1,” and record in the

“ΔMass” column. (This is the mass of the water that was poured into the beaker.) Do the same subtractions between Pour #2 and Pour #1, and between Pour #3 and Pour #2, recording the values in your Data Table. Show all work for full credit!

Data Table 2 – The Buret Method

Temperature of water °C Density of water (see Table 1) g/mL Volume ΔVolume Mass ΔMass

At Start mL g

After Pour #1 mL mL g g

After Pour #2 mL mL g g

After Pour #3 mL mL g g

Density for Pour #1 g/mL

Density for Pour #2 g/mL

Density for Pour #3 g/mL

Average Density g/mL

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Compare the average density by the graduated cylinder method with the average density by the buret method.

Compare both average densities with the accepted value (from Table 1).

Explain, with reasons, which method is expected to give better results.

Table 1 Density of distilled water at different temperatures

Temperature (°C) Density (g/mL)

18 0.9986 19 0.9984 20 0.9982 21 0.9980 22 0.9978 23 0.9975 24 0.9973 25 0.9970 26 0.9968 27 0.9965 28 0.9962 29 0.9959 30 0.9957 31 0.9953 32 0.9950 33 0.9947 34 0.9944 35 0.9940

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Calculations: