Basic Technologies of Handling Chemicals and Laboratory Apparatus

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Basic Technologies of Handling Chemicals and Laboratory Apparatus

INTRODUCTION
Density is defined as mass per unit volume. The commonly used unit to indicate the density of water is (g/cm3). Water never has an absolute density because its density varies with temperature. Water has its maximum density of 1 g/cm3 at 4oC. When the temperature changes from either greater or less than 4oC, the density will become less than 1g/cm3 only when it is pure water. Other factors that can affect water’s density whether it is tap water, fresh water or salt water. These variations of water change its density because what is in the water has its own density.

A measuring cylinder is used to accurately measure the volume of liquids. Measuring cylinder is generally more accurate and precise for this purpose than flasks and beakers. It is meant to be read with the surface of the liquid at eye level, where the centre of the meniscus shows the measurement line. Usually, the surface of the solution will form a curve known as meniscus. Typically the accuracy of the measuring cylinder is +/- 0.05mL.

A burette is a vertical cylindrical piece of laboratory glassware with a volumetric graduation on its full length and a precision is necessary. It is accurate and has a tolerance of 0.1cm3.
A pipette is used to transport a measured volume of liquid. Its accuracy is 0.5mL.

OBJECTIVE
1. To practice correct method of handling laboratory apparatus.
2. To determine the density of water.

CHEMICAL/APPARATUS
250mL beaker, pipette, burette, top loading balance, 50mL measuring cylinder, filter funnel, pipette bulb/pipette filler

METHODS
A) Determining the density of water by using a burette.
1. The mass of the empty beaker is weighed by using a top loading balance in unit grams. 2. The burette is washed with tap water.
3. The burette is clamped vertically to the retort stand.
4. 30mL of tap water is poured into the burette by using a filter funnel. 5. The stopcock of the burette is turned to allow 10mL of tap water to flow into the beaker placed below the burette tip. 6. The beaker containing the 10mL of tap water is weighed again by using the top loading balance. 7. The mass of water transferred is determined by subtracting the mass of the beaker containing the 10 mL of distilled water with the mass of the empty beaker. 8. The density of the water is calculated by using the formula, mass (g) / volume (mL).

9. The results are recorded in a table.

B) Determining the density of water by using a pipette.
1. The mass of the empty beaker was measured by using a top loading balance in unit grams. 2. The pipette is washed with tap water.
3. The pipette tip is dipped well below the surface solution. By using a pipette bulb, the pipette is filled with tap water. 4. The symbol ‘E’ on the pipette bulb is pressed to allow 10mL of tap water to flow out of the pipette into the beaker placed below the tip of the pipette. 5. The beaker containing the 10mL of tap water is weighed again by using the top loading balance. 6. The mass of water transferred is determined by subtracting the mass of the beaker containing the 10mL of tap water with the mass of the empty beaker. 7. The density of the water is calculated by using the formula, mass (g) / volume (mL).

8. The results are recorded and tabulated.

C) Determining the density of water by using a measuring cylinder. 1. The mass of the empty beaker is weighed by using top loading balance in unit grams. 2. The measuring cylinder is washed with tap water.

3. The measuring cylinder was filled with 10mL of tap water. 4. The 10mL of distilled water contained in the measuring cylinder is poured into the empty beaker. 5. The beaker containing the 10mL of tap water is weighed again by using the top loading balance. 6. The mass of water transferred is determined by subtracting the mass of the...
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