LAB EXERCISE 1: SAFETY & TECHNIQUES

CHEMISTRY I - LABORATORY EXERCISE MANUAL

Laboratory Exercise No.1: Safety & Techniques

Welcome to the chemistry laboratory. It is here that we seek new discoveries -answers to questions both new and old, and empirical evidence for our theories and hypotheses.

As a chemistry student, you will learn to formulate a hypothesis for testing, create a procedure to use to that end, make observations throughout the course of your experiment, and then analyze that data to see if it supports your hypothesis. But before we can begin our experiments, there are several basic pieces of equipment and a few techniques we must become thoroughly familiar with.

1. ORGANIZATION

Good scientists are always neat and organized - they have to be to conduct error free experiments and collect reliable data. Before your experiment begins, make yourself familiar with its procedures, obtain and organize the equipment you'll need, discuss the experiment with your lab partner and decide who'll be responsible for what, and set up a note sheet so that you can get a head start in recording data. Poor organization results in more lab errors and unsatisfactory results than almost any other mistake.

2. SAFETY

Labs can be dangerous places - the chemistry lab especially so. Read and understand your safety contract, and practice safe lab technique! Be aware of the hazards involved in each experiment, clean up spills immediately, wear the proper safety clothing, and keep your eyes open for others to avoid spills and collisions. Know the locations and operating procedures for the eye wash and safety shower.

3. EQUIPMENT

There is a variety of common equipment that you will use in your laboratory work. while there will be some specialized equipment used in certain labs, the following items are used in nearly every lab.

Balances:

Balances are instruments used to determine the mass of objects and laboratory chemicals. There are two types of balances in our chemistry lab. The triple beam balance and the top-loading analytical balance. The instructor will demonstrate the correct use of these balances.

Procedure 1: Take the mass of two different items provided by the instructor on both the triple beam and the analytical balance. Record these masses on the data sheet. Record the accuracy, in decimal places, of each balance.

VOLUMETRIC GLASSWARE:

Many of the compounds you will use are in the form of aqueous solutions. You will therefore need to have several different kinds of volumetric glassware at your disposal.

Graduated cylinders:

Graduated cylinders are commonly used to measure larger volumes of liquid reagents, or to measure the volumes of solids by water displacement.

Procedure 2a: Look closely at a 10 mL and a 50 mL graduated cylinder. How accurately to the decimal place, can each be read? Record this data on your data sheet.

When using our volumetric glassware, we must be aware of the meniscus. The meniscus is the concave distortion of the surface of a liquid in a container (see illustration below). To properly read our volumes, we must read from the bottom of the meniscus.

Procedure 2b: Fill your 50 mL graduated cylinder to a volume of 20 mL with deionized water, paying special attention to the exact position of the meniscus.

Pipets:

Pipets are used to measure and deliver small volumes of liquid, generally 10 mL or less. Because of the variety of pipet volumes available, they are generally preferred to graduated cylinders. There are several different types of pipets used in the lab. Calibrated pipets come in many different volumes, and are usually labeled in one of two ways. "TD" pipets are labeled TD 20 ^oC. This means that they will deliver their labeled volume at 20 degrees Celsius. The liquid that is retained in the pipet tip is accounted for in that volume and need not be expelled. "TC" pipets are labeled TC 20 ^oC which means that they contain their labeled volume at 20 degrees C. The entire volume of liquid must be expelled from the pipet to get an accurate volume. It is fairly simple to remember - TD = "to deliver", TC = "to contain".

Beral pipets are small, uncalibrated plastic bulbs with long, slender tubes attached.

Pasteur pipets are small, slender glass tubes tapered at one end. To obtain accurate volumes for these instruments, they must be calibrated by filling them and then dispensing the liquid into a precalibrated instrument such as a graduated cylinder or pipet.

The instructor will demonstrate proper technique for each of these instruments.

Procedure 3: Obtain a precalibrated pipet and practice using it to dispense water. Obtain a Beral pipet and a Pasteur pipet. Calibrate and mark each pipet so that it delivers exactly 1 mL of water. Observe the number of drops each one delivers to make one mL, and calculate the volume per drop for each.

Beakers & Erlenmeyer Flasks:

Beakers are cylindrical glass containers that come in many different sizes, and are sometimes calibrated along the side. They are multi-purpose containers, but are not very accurate for volumetric measurements. Erlenmeyer flasks are conical glass containers that taper to a short neck at the top. These too are calibrated, but are also imprecise for volumetric uses.

Procedure 4: Obtain a 50 mL beaker and a 50 mL Erlenmeyer. flask. Using a precalibrated pipet, fill each of these to the very top marking with deionized water, and note how much water was delivered from the pipet to fill each. Calculate the percent error in the calibration of the flask and beaker. Percent error can in this instance be expressed as:

Net difference between dispensed volume and calibrated volume x 100
Calibrated volume

4. DENSITY

Density is an inherent property of all matter. It is the quotient of mass divided by volume, as expressed by the following equation -

D= m/V

When expressing density, and for that matter any numerical data, always be sure to include the appropriate units. For example, if we express density in metric terms, the answer would be expressed as grams (the unit of mass) per "mL (the unit of volume), e.g. 2.79 g/mL. Measurements and calculated values without the corresponding units included are meaningless.

Procedure 5a: Determine the mass of a 30 or 50 mL beaker. Fill a 10 mL pipet to the top mark with deionized water and dispense the water into the beaker. Record the new mass. Using this information, calculate the density of water at room temperature.

Procedure 5b: Obtain a 50 or 100 mL graduated cylinder and fill to the 20 mL mark with deionized water. Obtain a small object from the instructor and determine its mass. Now, tilting the cylinder, slide the object gently down into the water and then gently roll the object around to dislodge any air bubbles adhering to it. Right the cylinder and note the new volume. Using this information, calculate the density of the object.

5. DEIONIZED WATER

Deionized water is water that has been specially purified so that it contains no chemical impurities or free ions. It is the preferred medium for solutions and for washing glassware and equipment because it will not interfere with chemical reactions you may be experimenting with. Use deionized water exclusively in the lab. The only time using the tap is acceptable is for washing your hands after the lab.

Congratulations! You are now familiar with the basic techniques used in the Chemistry lab.

For this exercise, no formal lab report is needed. However, you need to fill out the attached data sheet and answer all of the following questions. Don't forget to turn in your signed safety contract,

Click here for DATA SHEET

Click here for QUESTIONS

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