Chem 142 Lab 1

Weigh the empty vial and cap and record the mass. Be sure to use the same balance for all of your measurements.

When you measure liquid in the glassware you are using in this lab, you will see that the surface of the liquid is slightly bowl-shaped. This curvature is called the meniscus and appears black in this picture because it is reflecting the black countertop. In order to correctly read the volume of the liquid, keep your eye level with the meniscus and read the volume at the point where the bottom of the meniscus falls on the scale markings.

Fill the graduated cylinder to 10 mL with deionized water, making sure that you are reading the volume while eye level with the meniscus.

Pour the water into the pre-weighed vial, cap the vial, and weigh the water, vial and cap. Record the mass in your notebook. Empty the vial and repeat all of your steps 4 more times.

Using a squirt bottle provided in lab, and making sure the stopcock is closed, fill the buret with deionized water. (You will not use a beaker, as shown here, because the opening of your buret will be smaller than the one on the larger buret shown in the picture.)

Make sure there are not any bubbles in the tip of your buret. If you see any, hold the buret over the sink (a beaker is not necessary), open the stopcock, and give the buret one careful but swift shake to dislodge the bubble while the water is flowing out. Then close the stopcock and add more deionized water to make sure that the meniscus is exactly on the 0 mL mark at the top of the buret. It's probably easiest to over fill it a little and then let some drip out slowly by slightly opening the stopcock.

Once the meniscus is exactly at the 0 mL mark, deliver 10 mL of water to the pre-weighed vial.

Make sure that you slow down the water delivery as you get close to the 10 mL mark and stop exactly at 10 mL. If there is a drop of water left on the tip of the buret, touch the tip on the inside of the vial to transfer the drop to the vial. The volume markings on the buret only count what is in the buret, not anything hanging onto the tip. Weigh the water, vial and cap and record the mass in your notebook. Empty the vial and repeat all of your steps 4 more times.

Place the tapered tip of the pipet into a beaker containing deionized water. Squeeze the pipet bulb to remove the air, hold the pipet bulb firmly on the top of the pipet, and slowly release the bulb, using the suction to pull water into the pipet. You will probably need to re-empty the bulb a second time in order to fill the pipet. To do this, once the bulb has filled with air, quickly remove it, placing your finger tightly over the top of the pipet to prevent all the water from draining out, squeeze the bulb, and replace it on the top of the pipet to continue suctioning water into the pipet.

Once you have filled the large bubble in the middle of the pipet, the water will travel up the neck of the pipet. Try not to get any liquid in the bulb, but bring the level above the calibration marking. Then, quickly remove the bulb and again cover the pipet opening tightly with your finger. With the calibration marking at eye level, relax your finger and allow the water to slowly drain until the bottom of the meniscus is touching the calibration mark. (This will take practice and patience!)

Once you are confident that the pipet is correctly filled, place the tip of the pipet in the pre-weighed vial and release your finger to let the 10 mL of water drain into the vial. Weigh the water, vial and cap and record the mass in your notebook. Empty the vial and repeat all of your steps 4 more times.

Weigh the empty, dry beaker on the balance and record the mass in your notebook.

Add the 3 level spoons of sucrose to the beaker and weigh the beaker containing the sucrose. Record the mass in your notebook.

Determine the volume of water to add to the sucrose (see "Intro" in the online Prelab section). Using the 100 mL graduated cylinder, add that amount of water to the sucrose and stir until dissolved. Based on the data you recorded for the water measurements, determine which piece of glassware provides the best precision. Use that piece of glassware and the same steps used in those measurements to determine the mass of 10 mL of your sucrose solution. Repeat this mass measurement at least two times.

Fill the 10 mL graduated cylinder two-thirds full with deionized water and read the volume as precisely as possible. Record the volume in your notebook.

Weigh the unknown metal you received from your TA and record the mass in your notebook. Then carefully add the piece of metal to the graduated cylinder, making sure not to splash any water or break the cylinder.

Read the new volume of water in the cylinder and record it in your notebook. Repeat these steps for a second trial, being sure to dry the metal completely before re-weighing it.