Common Laboratory Operation (Principles of Chemistry Lab)

Question 1

In reading the volume, of the graduated cylinder, why does the eye must be at level with the lower meniscus?

Answer 1

The meniscus of most liquids is concave-up, with the lowest point in the center that
is used to determine the meniscus reading. Your eye must be on the same level as the
bottom of the meniscus to read the volume correctly.

Question 2

What is the procedure in measuring volume of colored liquids using a graduated cylinder?

Answer 2

Upper meniscus at eye level. Since colored liquids are opaque, lower meniscus would be hard to locate, thus upper meniscus at eye level should be utilized.

Question 3

What is a curved surface in a graduated cylinder called?

Answer 3

The liquid’s curved surface in a graduated cylinder is called the meniscus.

Question 4

Why should one use a glass rod or piece of glass tubing in transferring liquids from one vessel to another?

Answer 4

The glass stirring rod is used in liquid transfer in order to prevent spillage and facilitate the maximum amount of liquid transferred from one vessel to the next. The liquid’s surface tension, or the fact that like molecules will tend to “stick” to each other make the liquid transfer virtually seamless from the lip of one vessel, to the stirring rod, and into the receiving vessel.

Question 5

Why should one heat the upper portion of the liquid rather than the bottom?

Answer 5

If you heat the test tube from the bottom, any liquid can turn into a gas. The gas will rapidly expand shooting heated liquid out of the test tube like a cannon.
1.1. Heating the test tube at the top allows any gases formed to escape without forcing liquids on top of the gas out of the tube.
1.2. Heating the tube at an angle reduces the pressure on the heated substances again allowing the gases to escape harmless into the air.
2. To boil and distribute heat evenly and concentrate the boiling near the surface of the liquid
3. To prevent vapors from recondensing

Question 6

How to read the graduated cylinder?

Answer 6

Graduated Cylinder must be on equilibrium (flat surface)

Eye level of the meniscus:
Concave (downward) = Lower Meniscus
Convex (upward) = Upper Meniscus

Question 7

How to heat a test tube?

Answer 7

Using a test tube holder:

1. Hold test tube at 45° angle
2. Pass the tube slowly back and forth through the flame (top of the flame is near the top of the liquid and does not touch the empty part of the glass)

Question 8

The cone on the filter paper should always be smaller than that of the funnel, that is, no part of the filter
paper should protrude above the edge of the funnel. Why?

Answer 8

1. support strength of the filter paper in the immersion state will be further reduced, which is likely to cause liquid spillage;
2. the other is to facilitate the liquid level control in the filtration process.

Question 9

When heating liquid never point the opening of the test tube towards another person. Why?

Answer 9

Accidents happen even heating the test tube gently at an angle can result in heating liquid being shot out of the test tube. This is why the test tube must be pointed away from any other person

Question 10

Why do we need to moisten filter paper?

Answer 10

1. Wetting the filter paper with the solvent or liquid being filtered helps it adhere to the funnel’s surface and minimizes air bubbles or gaps that may interfere with the filtration process.
2. The moistened filter paper should help keep the paper in place for the filtration.
3. It helps to reduce the formation of gaps or cracks between the paper fibers.

Question 11

Why do we need to tear the filter paper?

Answer 11

to enable a closed seal to be made across the folded portion of the paper.