DENSITY. Presented by Dr / Osama Saher. Items to be discussed today:. Density. Definitions & Laws. Specific gravity. Specific volume. Exp.I. Determination of the density of a given liquid at a definite temperature using pycnometer. Experiments.
Presented by Dr / Osama Saher
Definitions & Laws
Exp.I. Determination of the density of a given liquid at a definite temperature using pycnometer
Exp.II. Determination of the density of solutions containing different concentrations of sodium chloride at room temperature
Units of Density:
1- In Metric (CGS) System:g/cm3 (g/ml)
2- In English System: gr/fl ℥ - lb/gal
Density (ρ) = Mass/Volume
It is the ratio of the weight of a substance to the weight of an equal volume of another substance chosen as a standard. Both substances having the same temperature.
Water Standard for liquids and solids
Hydrogen / Air Standard for gases
Specific gravity =Ws / Ww = ρs /ρw
e.g. for water: 1 g/ml, 455 gr/fl ℥ , 62.5 lb/ft3
e.g. for water: Sp. gravity = 1
It is the volume occupied by 1 g of a substance at a given temp. and pressure(reciprocal of density)
V = 1/ρ (cm3/g)
1. Clean the pycnometer by rinsing with water.
2. Weigh the stoppered dry pycnometer.
3. Fill the pycnometer with purified water and place the stopper.(Small amount of water comes out the capillary, wipe out the excess liquid outside the tube using tissue paper).
4. Weigh the pycnometer with water.
5. After removing the water, rinse the pycnometer with the test liquid (5 ml) and fill the liquid in the pycnometer in the same way.
6. Weigh the pycnometer with the test liquid.
7. Repeat each step at least three times and report the average.
Empty pycnometer definite temperature using pycnometer
Water filled pycnometer
Liquid filled pycnometer
(rinse with 5ml first)
Density of liquid definite temperature using pycnometer
accurate volume of pyc. is known
Weight of liquid (W3 – W1)
Ρ(liq) = ——————————
Volume of liquid (V)
accurate volume of pyc. is unknown
Weight of liquid (W3 – W1)
Ρ(liq) = —————————— X Ρ(water)
Weight of water (W2 – W1)
Example: definite temperature using pycnometer
A specific gravity bottle weighs 23.66 g. When filled with water it weighs 72.95 g; when filled with another liquid it weighs 73.56 g. What is the specific gravity of the liquid?
73.56 g - 23.66 g = 49.90 g of liquid
72.95 g - 23.66 g = 49.29 g of water
Specific gravity of liq. X Density of water
= 1.012 g/cm3
Procedure: definite temperature using pycnometer
1. Follow the procedure in experiment no.1.
2. Determine the density of the different sodium chloride solutions (1-10%) as described before.
3. Plot a graph between the concentration of sodium chloride solutions and density. Comment on the plot concerning the effect of concentration on density.
4. On the basis of the graph, determine the concentration of an unknown sodium chloride solution after determining its density.
1. Temperature (room temperature) = …… °C
2. Weight of pycnometer at room temperature (W1) = …… g
3. Weight of pycnometer + water (W2) = …… g 4. Weight of pycnometer + solutions of different concentrations of NaCl in water = (Wc).
(Use tableA to record your data).
5. Calculate the density of different NaCl solutions. Tabulate your results in table B.
Intercept at value 1
General Comment on Graphs definite temperature using pycnometer
What is drawn on Y-axis (dependant variable) and on X-axis (independant variable)
Shape of resulting curve
Slope and any special points
What to be concluded from this shape, slope, special points
So, Let’s apply this on our curve
Thank you definite temperature using pycnometer