A. Identification of Apparatus

The first part of the experiment will have sketch pieces of equipment you find in your drawer. This can be completed outside of lab. Images of all equipment can be found in the data sheet page (link).

B. Balance Use

This part of the experiment will have introduce the use of balances to measure mass. You will measure the mass of a substance using two methods. The “subtraction method” will have you place weighing paper on the balance and record the mass. Some substance is then transferred to the weighing paper and weighed again giving the mass of the substance and the weighing paper. The mass of the substance will then be determined by subtraction.

The “tare method” will have you place the weighing paper on the balance. The tare button on the balance will then be used to zero the balance and disregard the mass of the weighing paper. A substance is then transferred to the paper and the new mass will be recorded.

c. Dispensing liquids

The last part of the experiment will have you compare the precision and accuracy of a graduated cylinder, pipet, and buret. This is done by using each of the instruments to transfer a specific volume of water to a beaker. You will then use the balance measurement techniques of the first part to obtain the mass of each transfer. The most accurate will be the one closest to the expected mass given the density of water is 1 gram/mL.

CALCULATOR (LINK)

A scientific calculator is needed for calculations on quizzes. Some labs have calculations that need to be turned in before leaving.

LAB GOGGLES (LINK)

Required eye protection. Must be worn at the start of the experiment and until leaving

COMBINATION LOCK (LINK)

A combination lock is required to lock your equipment drawer for the semester.

LAB COAT (LINK)

A lab coat is required and must be worn once lab begins.

LAB MANUAL (LINK)

Specifically, General Chemistry Laboratories A Freshman Workbook. The lab manual will have all the experiment procedures you will be performing during the semester including their respective datasheet and postlab questions

bottlenecks

All groups must use the balance multiple times to obtain values for calculations, but there are limited balances available. This may present you with a bottleneck with multiple groups waiting to use the balance. Some suggestion to mitigate this are given below.

Group Tasks

You will be weighing many dry empty beakers. Count how many beakers you need and weigh them all at once instead of one at a time with each part of the experiment procedure.

Split Tasks

Instead of the group waiting for the balance, break out the tasks. That is, one person can line-up waiting for the balance while others can move ahead and set up the other instruments (graduated cylinder, pipet, and buret) for volume transfer.

Balances

The balance will be used to measure the mass of substances used in lab. Generally, there are two types of balances you may see, analytical balances and top loading balances. The analytical balance has greater precision but can be more cumbersome to use while the top loading balances are more convenient but have less precision.  When using balances to measure susbstances, you will put the substance on weighing paper, weigh boat, or some other container. Do not put substance directly on the balance.

The experiment will have you measure the mass using two methods. The “subtraction” method will have you weigh the container, record its mass, transfer the substance into the container, record the new mass and use subtraction of the container from the container+substance to get the mass of the substance. The “tare” method will have you put the container on the balance, press tare which will zero the balance, transfer the substance into the container, and record the new mass.

Beaker

The beaker is often used for liquid substances. You will have a variety of beakers with different volumes available to you. Though they have volume markings, these are almost never used for measurements. Rather, beakers are usually used to hold large amounts of substances for other purposes like as a water bath or holding larger quantities of a substance for convenience

Graduated Cylinder

Like the beaker, the graduated cylinder is used for liquids. However, graduated cylinders can be used to measure and transfer. You will probably have two types of graduated cylinders available to you, 100 mL and 10 mL. Keep in mind what you are measuring when using a graduated cylinder. Some substances, like water, will cling to the sides and create a meniscus that require you to read the volume level at its center point.

Pipet and pump

The pipet is another instrument used with liquids. These instruments can be very precise in delivering their indicated volume and other smaller volumes. To use a pipet, attached it to a pipet pump. The pump will have a dial in which you can turn with your thumb to either collect or deliver liquid. Often times you will need to “prime” or “rinse” your pipet with the liquid you will be collecting to address any residual impurities or water that may alter or dilute the solution you are collecting. As you collect liquid use the dial, the plunger ontop of the pump will elevate. This plunger will enable you to expel liquid much quicker. The area on the pump at your fingers can be depressed to also release the liquid more quickly. When using the pipet and pump, remember not to draw in more liquid than the pipet can hold. This may result in the liquid going up the pump and contaminating the liquid sample you obtained.

Buret

The buret or burette is the final instrument used to deliver liquids and is often used in titration. Like the pipet, this instrument can deliver very precise volumes and can give you greater control over the amount delivered. Moreover, it may also be necessary to “prime” or “rinse” your pipet with the liquid you will be collecting to address any residual impurities or water that may alter or dilute the solution you are collecting. The buret is used in conjunction with a stand and buret clamp. When using to deliver liquid, transfer the liquid to a convenient level and note the volume. This will be your initial volume. To find where to stop in delivering the amount you want, you need to add it to the initial volume. This will give you the final volume and thus the amount you dispense to before stopping.

Calculations

Density is a physical property that involves mass and volume. It is calculated by taking the mass of a substance divided by its volume. Having 2 of the 3 values will enable you to calculate the third value. Since the density of water is known and we measure the mass of the balance, the volume can be calculated. Keep in mind that we are assuming the mass from the balance is accurate.

Density = Mass ÷ Volume

In this experiment, you will be using the density of water which is 1 gram/mL. This means every 1 mL of water will be 1 gram and vice versa. Using the mass and the density of water, you will see which instrument gave you the closest transfer to 6 mL (thus 6 grams) to determine the accuracy. Remember your significant figures. This is often an area where points are deducted for incorrect number of significant figures.