Density
In this article we are going to learn about density, describe an experiment to determine the density of a liquid and of a regularly shaped solid, and make the necessary calculation describe the determination of the density of an irregularly shaped solid by the method of displacement.
Definition of terms:
Density: In everyday language, lead is said to be ‘heavier’ than wood. By this it is meant that a certain volume of lead is heavier than the same volume of wood. In science such comparisons are made by using the term density. This is the mass per unit volume of a substanc and the SI unit of density is kilogram per cubic metre (kg/m3).
Calculations of density:
We can calculate density with the help of this equation ρ = m/V.
WHERE:
ρ is density.
m is the mass.
V is the volume.
Worked example:
Question: A student researched that density of pure water is 1 g/cm3 and poured 0.02 litres of pure water in the measuring cylinder. Calculate the mass of the pure water.
Solution: first step; We should list our known and unknown variables so that we can see what we have and what we do not have.
ρ = 1 g/cm3
m = ?
V = 0.02L
Second step; We should write our equation and place the variables, but we must convert 0.02 L to cm3. So, 1L = 1 000 cm3 and 0.02L = 20 cm3. Now we can place our variables and calculate.
Our Formula: ρ = m/V
1 g/cm3 = m/20 cm3
m = ρ x V
m = 1 g/cm3 x 20cm3
m = 20 g
The mass of 20 cm3 pure water is 20 g.
Experiment to determine the density of a liquid:
We can find the density of a liquid by doing the following steps:
Materials: pure water, measuring cylinder, triple beam balance, and a beaker.
Step 1: Measure the volume of the pure water with the measuring cylinder.
Step 2: Place the beaker on the triple beam balance to measure its mass, name this mass m1.
Step 3: Pour the pure water from measuring cylinder in the beaker.
Step 4: Place the beaker with the pure water on the triple beam balance to measure the mass of the beaker and the pure water, name this mass m2.
Step 5: Subtract m1 from m2 to get the mass of the pure water, name this mass m.
Step 6: Use ρ = m/V to calculate the density of the pure water.
Experiment to determine the density of a regularly shaped solid:
We can find the density of a regularly shaped solid by doing the following steps:
Materials: ruler, cuboid and triple beam balance.
Step 1: Measure the length, width and the height of the cuboid with the ruler.
Step 2: Use V = lwh to calculate the volume of the cuboid.
WHERE: V is the volume, l is the length, w is the width, h is the height.
Step 3: Place the cuboid on the triple beam balance to measure its mass.
Step 4: Use ρ = m/V to calculate the density of the cuboid.
Experiment to determine the density of an irregularly shaped solid by the method of displacement:
We can find the density of an irregularly shaped solid by the method of displacement with the following steps:
Materials: stone, triple beam balance, water, measuring cylinder and string.
Step 1: Place the stone on the triple beam balance to measure its mass.
Step 2: Pour half water in the measuring cylinder to measure the volume of the water, name this volume V1.
Step 3: Hold the stone with the string and immerse the stone in the measuring cylinder that you poured the water to measure the volume of the water and the stone, name this volume V2.
Step 4: Subtract V1 from V2 to find the volume of the stone, name this volume V.
Step 5: Use ρ = m/V to calculate the density of the stone.