Density of a liquid

The density of a liquid can be calculated by knowing its mass and volume. To determine the density, follow these steps:

Steps for measuring the density of a liquid

1. Weigh the empty beaker. First, measure the mass of the empty beaker and record it as $m_0$.

2. Measure the volume of liquid. Using a burette, transfer a known volume ($V$) of the liquid into the beaker. Measure the mass of the beaker containing the liquid and record it as $m_1$.

3. Calculate the mass of the liquid. Subtract the mass of the empty beaker ($m_0$) from the total mass ($m_1$) to find the mass of the liquid:

   $\text{Mass of liquid} = m_1 - m_0$

4. Calculate the density of the liquid. The density of the liquid is calculated by dividing the mass of the liquid by the known volume of liquid:

   $\rho = \frac{m_1 - m_0}{V} \quad (\text{in g/cm}^3)$

Example calculation: density of liquid Y

In an experiment to determine the density of liquid Y, the following measurements were recorded:

• Mass of empty beaker ($m_0$) = 500 g
• Mass of beaker + liquid Y (25 cm³) = 600 g

Step 1: calculate the mass of the liquid

$\text{Mass of liquid Y} = 600 \, \text{g} - 500 \, \text{g} = 100 \, \text{g}$

Step 2: calculate the density of liquid Y

The volume of liquid Y is 25 cm³, so the density of liquid Y is:

$\rho = \frac{100 \, \text{g}}{25 \, \text{cm}^3} = 4 \, \text{g/cm}^3$

Therefore, the density of liquid Y is 4 g/cm³.

Activity: determining the densities of kerosene and milk

Aim: to determine the densities of kerosene and milk.

Materials:

1. Beakers
2. Pipettes
3. Beam balance
4. Kerosene
5. Milk

Procedure:

1. Weigh the empty beaker. Weigh the dry, empty beaker using a weighing balance and record the mass as $m_0$.
2. Measure the kerosene. Use a pipette to accurately measure 20 ml of kerosene and transfer it into the weighed beaker.
3. Weigh the beaker with kerosene. Measure the mass of the beaker containing kerosene and record it as $m_1$.
4. Repeat for milk. Repeat steps 1–3 for milk, using the same method.

Questions

(a) Calculate the mass of the 20 ml of kerosene and milk.

The mass of the liquid can be calculated by subtracting the mass of the empty beaker ($m_0$) from the mass of the beaker containing the liquid ($m_1$):

$\text{Mass of liquid} = m_1 - m_0$

(b) Calculate the density of kerosene and milk.

The density is calculated by dividing the mass of the liquid by the volume of the liquid:

$\rho = \frac{\text{Mass of liquid}}{\text{Volume of liquid}} \quad (\text{in g/cm}^3)$

(c) Why is it necessary to measure the mass of the empty beaker?

Measuring the mass of the empty beaker is necessary because it serves as a baseline. This ensures that the mass recorded for the liquid is accurate and excludes the mass of the container itself.