Experiment Three

Separations in the Laboratory

FAQs

Introduction/Goals

Background

Pre-lab

Additional Questions

Supplies and Chemicals

Safety Precautions

Waste Disposal Instructions

In this lab you will use chromatography to separate components of a mixture and separate the components of a mixture using physical properties

Print a copy of the Grading Sheet for this lab.

Procedural Tips:

How to filter

Using the Bunsen Burner

Preparation of a Water Bath

Handle the chromatography paper as little as possible.

Don't overlap the edges of the chromatography paper when you are stapling it into a cylinder.

Make sure the solvent is not above your origin. If the solvent doesn't completely cover the bottom of the beaker, you may add a little more solvent mixture (using the same proportions).

FAQ:

Why do I need to wear safety goggles?

I'm in a hurry. Does it really matter how large my "spot" is/

Yes, keep the spots small as indicated in the laboratory manual. If necessary, put on additional solution on top of the spots after they have dried. It is better to have a small, concentrated spot rather that a large spot.

Introduction/Goals:

Introduction:

Mixtures are a part of our everyday life. One characteristic of a mixture is that its' components may be separated by physical means. In this experiment we will separate that components of a mixture by solubility and by using a technique called paper chromatography.

Separating components of mixtures has many applications in the real world. For example, chromatography is used to detect and identify the presence of drugs of abuse in urine and or blood samples. Urine and blood are both mixtures. If a person has used a drug of abuse, the drug (or one of its metabolites) will be found in the urine (or blood). By using the technique of chromatography, the drug can be separated from the urine (or blood) sample and identified by calculation of an R_f value.

Goals:

Background:

Matter may be classified as a pure substance or a mixture. A pure substance cannot be separated into two or more other substances by physical means. Pure substances also have the same intensive properties throughout. An intensive property is one that does not depend on the amount of matter being examined. Examples of intensive properties are color, odor, melting point, and density.

Pure substances are further subdivided into elements and compounds. An element is a pure substance that cannot be broken down into simpler substances. A compound can be broken down by chemical means into simpler substances (elements or other compounds).

A mixture is composed of two or more substances not combined in any fixed, definite proportion. It varies from a compound in that compounds are combined in fixed ratios. Mixtures may be homogeneous (uniform in composition) or heterogeneous (not uniform in composition).

Laboratory work often requires separating the components of a mixture. Several techniques have been developed to aid in the separation of one component from another. Some of these techniques are:

In this lab you will use the differences in solubility and the technique of filtration to separate the components of a mixture of NaCl and CaCO₃. 

You will also use paper chromatography to separate components based on the affinity, or attraction, the components in the mixture have for stationary phase (paper and water) and a mobile phase (acetone/acid solvent). Some substances will be more attracted to the stationary phase and others will have an affinity for the moving phase. The R_f value will be calculated. The R_f is calculated by dividing the distance the compound moved by the distance the mobile phase (solvent) moved.

Pre-lab:

Read the introductory material on the webpage.

Read Experiment Three in the laboratory manual.

Answer the pre-lab study questions on for Experiment Three.

You are encouraged to do the Application Questions at the end of  Experiment Two before coming to lab.

Additional Questions:

1. Why is the R_f value calculated with the solvent measured from the origin to the solvent front, rather than from the edge of the paper to the solvent front?

2. A component of a mixture has an R_f value of 0.63. If the solvent front traveled 35 cm, how far did the component move?

3. You and your lab partner calculate the R_f value of your unknown to be 1.3. Is this a reasonable answer? Why or why not?

4. Answer Question 1.59 on page 15 of your McMurray textbook.

Safety Precautions:

SAFETY GOGGLES MUST BE WORN AT ALL TIMES DURING THE LAB.

Acetone is flammable. Do not use around open flames.

HCl and HNO₃ are acids and may cause burns. If you get any on your skin, rinse thoroughly for 10 minutes.     

NH₄OH is very corrosive. If you get any on your skin, be sure to wash it off with water for 10 minutes.

          

 

Waste Disposal Instructions:

Solid wastes may be disposed of in the wastebasket.

Place the remaining solvent in the container marked “Used chromatography solvent – Acetone/HNO₃/HCl” found under the hood.