Experiment One: Techniques and Measurements
Objectives
You will be able to properly select and operate a balance and analytical glassware such as pipet, buret and graduate cylinder. As a practice, you will be determining the density of a selected solid and liquid.
Introduction
The use of laboratory equipment requires a knowledge and understanding of the scope of and limits of the equipment that is being used. Thus, a large scale balance is sufficient to measure the student, while, it is not suitable to measure the mass of gold ring. Once, the appropriate laboratory apparatus has been selected for the experiment, the next step is to use it properly to obtain reliable data.
The laboratory balance is perhaps the most common equipment in any laboratory. Balances are of different sizes, ranges and sensitivities. The selection of the appropriate balance depends upon the degree of accuracy and precision required from the analysis.
Most glassware in your laboratory has been marked by the manufacturer to indicate the volume and accuracy. For example, beakers and Erlenmeyer flasks are marked with approximate volumes and could not be used for accurate measurements. However, burets, pipets and graduate cylinders are used for accurate and precise measurements.
In this experiment you will use some of the laboratory equipment to determine the density of a liquid sample and the density of solid substance. Density is an intensive property (its value is independent on mass or volume of substance). Its value is expressed as the ratio between mass and volume.
Density= Mass / Volume
For most solid and liquid samples, it is reported in g/cm3. In this experiment the density of a liquid is determined by measuring the mass of a known volume of the liquid. The density of a water-insoluble solid is determined by measuring its mass and then the volume of water it displaces.
Examples
Example 1: Determine the density of water.
massgraduated cylinder 37.288 g mass cylinder and water 42.290 g
mass of water 5.002 gvolume of water 5.00 mL
density of water
Example 2: Determine the density of mineral.
mass graduated cylinder 37.249 gmass cylinder and mineral oil 41.720 g
mass mineral oil4.471 gvolume of mineral oil 5.00 mL
density of mineral oil
Example 3: Determine the density of the sodium chloride solution.
Unknown Number 1355
mass graduated cylinder 37.222 g mass cylinder + salt solution42.455 g
mass salt solution5.233 gvolume of salt solution5.00 mL
density of salt solution
Example 4: Determination of the densities of the regularly shaped objects.
cuberectangular solid
dimensions 3.65 cm per sidedimensions7.52 cm 3.76 cm 1.29 cm
volume(3.65 cm)3 = 48.6 cm3volume 36.5 cm3
mass19.565 gmass24.034 g
spherecylinder
dimensions 15.88 circumferencedimensions 1.15 cm dia. 7.60 cm length
volumevolume V = (3.1416)(0.575 cm)2(7.60 cm)
V = 7.89 cm3
mass4.400 gmass6.029 g
Example 5: Determination the density of the unknown, irregularly shaped metal.
Unknown number 5000 metal identity aluminum
mass of metal15.058 g
volume of water20.0 mL
volume of water plus metal26.0mL
density of metal
Experimental
Apparatus / Reagents Required
Graduated cylinder (50, 100 mL), pipet (10, 25 mL), pipet filler, sodium chloride, water-soluble liquids, small pieces of metal materials.
Procedures
Record your data and observations directly on the data sheet. Perform at least two trials.
A. Determination of the density of pure liquid
1. Clean and wipe dry a 50-mL beaker to the nearest 0.01 g.
2. Obtain about 50 mL distilled water in a clean 100-mL Erlenmeyer flask. Measure and record the temperature of the water.
3. obtain a 10-mL pipet and a pipet bulb. Clean the pipet with soap and water. Rinse the pipetwith tab water followed by distilled water.
4. Pipet 10.0 mL of the distilled water from the flask into the clean beaker.
5. Calculate the density of the water.
6. Obtain an unknown liquid and record its identification number.
7. Determine the density of of the unknown liquid following steps 1 to 5.
B. Density of Solutions
1. Prepare approximately 50 mL of 10 % mass/volume sodium chloride solution by dissolving 5.00 g NaCl in 50 mL distilled water.
2. Follow steps 1 to 4 in section A.
3. Calculate the density of sodium chloride solution.
C. Density of solids
1. Obtain a sample of the solid substance and record its identification number.
2. Weigh an empty 50-mL beaker to the nearest 0.01 g. Weigh about 50 g of solid material and record the total mass to the nearest 0.01 g.
3. Add water to your 50-mL graduated cylinder to approximately the 25-mL mark. Record the exact volume of water in the cylinder to the nearest 0.1 mL.
4. Pour the solid sample into the graduated cylinder, making sure that none of the pieces sticks to the walls of the cylinder above the water level. Shake the cylinder gently to make certain that no air bubbles have been trapped among the pieces of the solid.
5.Read the level of the water in the graduated cylinder to nearest 0.1 mL.
6. Calculate the density of solid substance.
Experiment One: Techniques and Measurements
Pre-Laboratory Questions
Student name:ID:
Section:Instructor:
Q1. A piece of metal weighing 9.48 g is added to 21.27 mL water in a graduated cylinder. The water level rises to 24.78 mL. Calculate the density of the metal.
Q2. An empty beaker weighs 32.4257 g. A 10.00 mL sample of unknown liquid is transferred to the beaker. The total mass of the beaker and the sample was 39.4507 g. Calculate the density of unknown liquid.
Q3. Fill the space with higher or lower or no effect in all the following statements:
1. In section B, part of liquid was left in pipet, measured density will be ------.
2. In section B, the level in liquid in pipet was above the mark, measured density will be ------.
3. In section B, a 20-mL pipet was used instead of 10-mL pipet, measured density will be ------.
4. In section C, part of the solid substance was above the level of water, measured density will be ------.
5. In section C, Air bubbles were not removed before measuring final volume, measured density will be ------.
6. In section C, a 100-mL graduated cylinder was used instead of 50-mL graduated cylinder, measured density will be ------.
Experiment One: Techniques and Measurements
Results and Calculations
Student name:ID:
Section:Instructor:
A. Determination of the density of pure liquid
Pure water / Trial 1 / Trial 2Mass of beaker (empty) / g / g
Mass of beaker and water / g / g
Mass of water / g / g
Volume of water / mL / mL
Temperature of water / oC / oC
Density / g/mL / g/mL
Average density / g/mL
Unknown liquid
Unknown number
Mass of beaker (empty) / g / g
Mass of beaker and liquid / g / g
Mass of liquid / g / g
Volume of liquid / mL / mL
Temperature of liquid / oC / oC
Density / g/mL / g/mL
Average density / g/mL
B. Density of Solutions
Solution / Trial 1 / Trial 2Mass of beaker (empty) / g / g
Mass of beaker and solution / g / g
Mass of solution / g / g
Volume of solution / mL / mL
Temperature of solution / oC / oC
Density / g/mL / g/mL
Average density / g/mL
C. Density of Solids
Solid / Trial 1 / Trial 2Mass of beaker (empty) / g / g
Mass of beaker and solid pieces / g / g
Initial water level in graduated cylinder / mL / mL
Final water level in graduated cylinder / mL / mL
Volume of solid particles / mL / mL
Temperature of water / oC / oC
Density / g/mL / g/mL
Average density / g/mL
Calculations:
Conclusions