For Honors
Initial Lab: Avogadro and All ThatExperiment 1
Objective
- The purpose of this laboratory exercise is to help you familiarize yourself with the layout of the laboratory including safety aids and the equipment that you will be using this year.
- Then, to make an order-of-magnitude estimate of the size of a carbon atom and of the number of atoms in a mole of carbon based on simple assumptions about the spreading of a thin film of stearic acid on a water surface
Grading
- Pre-lab – not required for the first lab
- Lab Report (90%)
- TA points (10%)
Before coming to lab……
- Read the following:
- Lab instructions
- Background Information
- Concepts of the experiment
- Print out the lab instructions and report form.
- You may fill out the lab survey, due at the beginning of the lab, for extra credit if you wish.
- Read and sign the equipment responsibility form and the safety rules, email Ms Duval at
nduval@rice.edu to confirm completing this requirement by noon on August 31st
Introduction
Since chemistry is an empirical (experimental) quantitative science, most of the experiments you will do involve measurement. Over the two semesters, you will measure many different types of quantities – temperature, pH, absorbance, etc. – but the most common quantity you will measure will be the amount of a substance. The amount may be measured by (1) weight or mass (grams), (2) volume (milliliters or liters), or (3) determining the number of moles. In this experiment we will review the methods of measuring mass and volume and the calculations whereby number of moles are determined.
Experimental Procedure
We will start in the amphitheater of DBH (above DBH 180) for demonstrations: oxygen, hydrogen and a mixture of the two in balloons and more besides.
Mandatory Safety talk by Kathryn Cavender, Director of Environmental Health and Safety at Rice.
1. Identification of Apparatus
On your benches, there are a number of different pieces of common equipment. With your TA's help, identify each and sketch - I know this may sound a trivial exercise but it is necessary so that we are all on the same page.
- beaker
- erlenmeyer flask
- graduated (measuring) cylinder
- pipette
- burette
- Bunsen burner
- test tube
- boiling tube
- watch glass
2. Balance Use
In these general chemistry laboratories, we only use easy-to-read electronic balances – saving you a lot of time and the TA’s a lot of headaches. However, it is important that you become adept at the use of them.
Three aspects of a balance are important:
- The on/off switch. This is either on the front of the balance or on the back.
- The "Zero" or "Tare" button. This resets the reading to zero.
- CLEANLINESS. Before and after using a balance, ensure that the entire assembly is spotless. Dirt on the weighing pan can cause erroneous measurements, and chemicals inside the machine can damage it.
- Turn the balance on.
- After the display reads zero, place a piece of weighing paper on the pan.
- Read and record the mass. (2)
- With a spatula, weigh approximately 0.2 g of a solid, common salt NaCl, the excess salt is discarded, since returning the excess salt may contaminate the rest of the salt - in this exercise, this is not a big deal but in strict analytical procedures it is.
- Record the mass (1). To determine how much solid you actually have, simply subtract the mass of the weighing paper(2) from the mass of the weighing paper and solid (1). Record this mass (3).You have just determined the mass of an "unknown amount of solid."
- Now place another piece of weighing paper on the balance and press the Zero or Tare button then weigh out approximately 0.2 g of the salt (4). Thus, the zero/tare button eliminates the need for subtraction.
