Summary
Overview
When discussing material properties, most of us usually think of solid materials and material properties such as hardness, flexibility, or strength. However, liquids are characterized by distinct properties, too. Some of these properties overlap with those of solids, like density or transparency, but others are more specific to liquids. Viscosity—the resistance of a fluid to flow—and surface tension, are two examples of properties that are specifically used to characterize liquids. In this lesson plan, students will investigate the properties of different liquids by pouring them, smelling them, and investigating their densities by stacking them on top of each other.
Learning Objectives
- Explain, with evidence, that different liquids have their own unique properties.
- Plan and conduct an investigation to identify the properties of a liquid.
- Use appropriate vocabulary to describe the properties of liquids.
NGSS Alignment
This lesson helps students prepare for these Next Generation Science Standards Performance Expectations:- 2-PS1-1. Plan and conduct an investigation to describe and classify different kinds of materials by their observable properties.
| Science & Engineering Practices | Disciplinary Core Ideas | Crosscutting Concepts | |||
| Science & Engineering Practices | Planning and Carrying Out Investigations. Plan and conduct an investigation collaboratively to produce data to serve as the basis for evidence to answer a question. |
Disciplinary Core Ideas | PS1.A: Structure and Properties of Matter. Different kinds of matter exist and many of them can be either solid or liquid, depending on temperature. Matter can be described and classified by its observable properties. |
Crosscutting Concepts | Patterns. Patterns in the natural and human designed world can be observed. |
Materials
Materials for each group of 2-3 students:
- Dark corn syrup, 1 Tbsp.
- Dish soap, 1 Tbsp.
- Water, 1 Tbsp.
- Vegetable oil, 1 Tbsp.
- Plastic cup, 16-oz
- Liquid food coloring (green)
- Mini plastic cups with lids, 2-oz (10)
- Paper towels
Materials for teacher:
- Mini plastic cups with lids, 2-oz (4); put 1 Tbsp. of each liquid in its own mini cup
- Tablespoon
- One extra mini cup with lid, 2-oz
- Apple cider vinegar, 1 Tbsp.
Background Information for Teachers
This section contains a quick review for teachers of the science and concepts covered in this lesson.Different materials are characterized by different properties. This is not only true for solids but also for liquids. Liquids and solids share many properties. Among them are, for example, the transmittance, which measures how much light is able to pass through a material, and the density. The density is different for each individual compound and defined as the mass of a compound divided by its volume. In other words, the more matter there is in a certain amount of volume, the denser a substance is. All types of matter—solids, as well as liquids—are made up of many different atoms. Depending on the mass of these atoms, their size, and the way they are arranged, different substances will have different densities. One cubic centimeter (1 cm³) of rock, for example, is much heavier than 1 cm³ of wood. This is because there is much more matter in the same volume of rock compared to the wood. Liquids can also have different densities. Freshwater, for example, has a density of about 1 gram per cubic centimeter (g/cm³) at room temperature. The density of an object will determine whether it sinks or floats in water. Any substance—either liquid or solid—that has a higher density than water will sink, whereas substances with a lower density than that will float (Figure 1).
Figure 1. Objects with a density higher than water will sink (left) and objects with a lower density than water will float (right).
There are also some properties that are used to specifically characterize a liquid. Surface tension or viscosity are two examples. The viscosity of a liquid is a measure of its resistance to deformation or flow. It is also often referred to as the "thickness" of a liquid. The thicker a liquid is, the higher is its velocity. Corn syrup, for example, has a higher viscosity than water. An easy way to measure viscosity is to measure how long it takes for a liquid to pour out of a cup into another container, and how long it takes until it takes the shape of the receiving container. Water will do that almost instantly, whereas corn syrup will take some time to pour out and settle.
Liquids also experience surface tension. The molecules a liquid is made of pull on each other or exert a force. As shown for water in Figure 2, a water molecule in the middle of a droplet gets pulled equally in all directions by the neighboring molecules. However, a molecule at the surface of the droplet gets pulled mostly inward by the molecules below it. This means that all the molecules at the surface help "hold together" the droplet of water, which is called surface tension. The surface tension of different liquids can be determined by measuring how much volume of each liquid fits on a penny before it spills over the edge of the penny.
Figure 2. A diagram showing the forces on water molecules that create surface tension. Note that the diagram is not to-scale—there are quintillions of water molecules in a single drop!
In this lesson plan, students will investigate the properties of different liquids. By pouring, smelling, or stacking them on top of each other, they will realize that not all liquids have the same properties. They can vary in color (transmittance), smell, viscosity, or density (mass per volume).
