GENERAL LABORATORY DIRECTIONS

Question 1

utilizes volumes of solutions ranging from 5 to 100 mL or more

Answer 1

ordinary or macro analysis

Question 2

the volumes used range from 1 drop to approximately 1 mL

Answer 2

semimicro procedures

Question 3

deals with quantities of materials which are less than one-tenth of those amounts handled in the other analysis

As a result of this reduced scale in volumes and also weights of materials, the apparatus of this analysis is designed to utilize the smaller quantities

Answer 3

semimicro analysis

Question 4

manipulations of semimicro analysis

Answer 4

1. precipitation
2. heating of solution
3. evaporation
4. centrifuge
5. removal of supernatant liquid
6. washing of precipitates
7. transferring of precipitates

Question 5

capacity of approximately 5mL and the ordinary 10-mL tube

tends to magnify the size of the precipitate, which it contains

have the decided disadvantage of being very difficult to clean

Answer 5

tapered test tube

Question 6

It is generally a good technique to carry out all precipitations in __________ except in those cases where the precipitates serve as confirmatory tests.

Answer 6

• ordinary test tubes

Question 7

A solution in a small test tube cannot be safely heated over a ___________, since bumping would cause the loss of part or all of the liquid.

The most satisfactory method for heating solutions contained
in small test tubes in a __________

The beaker should be kept ________ filled with water and heated to simmering during the entire time of an analysis.

Answer 7

• direct flame
• water bath
• 3/4

Question 8

It is frequently necessary to reduce the volume of a solution by __________

If care is exercised, this may be carried out satisfactorily by heating the solution in a ___________ (evaporating dish) over an ________.

When evaporating to dryness the casserole should be removed from the flame while a few drops of liquid remain.

The heat of the dish is sufficient to complete the evaporation

Answer 8

• evaporation
• small porcelain casserole
• open flame

Question 9

referred to as centrifugate

may be removed by means of micropipette using proper precautions not to disturb the precipitate

• The clear centrifugate is usually transferred to another test tube

Answer 9

supernatant liquid

Question 10

After removal of centrifugate, the precipitate remaining in the test tube is wet with the solution containing ions in the centrifugate.

These ions may cause interference in the analysis of the precipitate and are usually removed by __________

Answer 10

• washing

Question 11

The act of washing is accomplished by adding the required amount of distilled water (about _______) and mixing precipitate and wash water thoroughly with a stirring rod.

The mixture is then centrifuged, and the wash water removed by means of a ________.

Usually, ____ or ____ washings suffice.

Answer 11

• 5 drops
• micropipette
• one or two

Question 12

OCCASSIONALLY it is necessary to transfer a precipitate from a test tube to another receptacle.

This is often a difficult operation especially if the precipitate is _______ in nature.

Customarily such a transfer is accomplished with the use of a ___________

However, this instrument CANNOT be used on precipitate which is wet a solution that reacts with Ni

Answer 12

• gelatinous
• nickel microspatula

Question 13

Lead Ion (Pb++)

Answer 13

CR: 1F K2CrO4

expected positive result: yellow ppt

actual result: yellow ppt

interpretation: lead chemically reacts with 1F K2CrO4 forming PbCrO4 (a yellow ppt)