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Sponge science and math lab workshop – absorption density and mass

c. Donald Reinhardt, September 25, 2012

Household sponges are either real (natural) or artificial (manufactured) sponges. Anyone can do simple, easy, virtual or real science experiments to understand absorption, buoyancy, density, volume and mass. So let’s do some sponge science here and now.
True sponges absorb water. Here one sponge absorbs well and three polyfoams do not.                                                                    
Photo credit and copyright: Donald Reinhardt

Sponge science workshop – definitions

Sponge – an air-laden complex of manufactured cellulose or synthetic material or a true, natural sponge which was harvested, processed and dried for use.
Please note: Some sponges are made of polyfoam or other synthetic materials and do not work as true sponges. The photo own above proves that point.

Absorption – the process of water entrance and retention or holding by a material substance such as a sponge, paper towel, handkerchief or any similar absorbent material.

Buoyancy – the upward force that is created by a gas or fluid when any object displaces a defined amount or portion of fluid or gas.
When any object creates an upward force that is greater than the downward force of gravity, then the object rises.
If the object creates less upward force (after the displacement of a gas or fluid), then the downward force of gravity causes the object to sink.  

Density – is the mass/volume (m/V) relationship of any object. Density varies dramatically among different objects and materials and is dependent on the shape and type of material.

Sponge Science: Materials and Methods

This sponge experiment can be done as a virtual experiment using the pictures and data supplied here. If you do not have these materials, then a virtual experiment will work.
If you can get your own simple materials and do the experiments, that will be good. Either way you will learn and have fun. So, let’s start.

Sponge Science Experiment: Materials

·        Sponge – one absorbent sponge. Use a few sponges, if they are available.

·        Water to add to the sponges and also water to float the sponges in.

·        Measuring cup or cylinder to help determine and estimate how much water a sponge can hold.

·        Scale or Balance to determine the mass (weight) of the sponge and the mass (weight) of the water and its volume.

·        Clear plastic containers to hold, weigh or float sponges as needed
 *   Ruler to measure the dimensions of the sponge. Rectangular or square sponges are preferred to amorphous or irregular-sized sponges for this purpose.

Sponge Science Experiment: Methods, Procedure and Results

Sponge Experiment 1. Measure the area and volume of your sponges.  

Use a ruler with centimeter and millimeter markings to measure the sponge dimensions. The sponge pictured below is a small rectangular sponge of this size:  length = 9.5 cm, a width = 8.0 cm and a depth or height of 2.0 cm. The volume of the sponge is the length x width x depth.  Determine the volume of the sponge as follows 9.5 x 8.0 x 2.0 = 150 cubic centimeters or cc.

Sponge Experiment 2. How much does a dry sponge weigh? Weighing dry sponges.

Sponges are fairly light when dry. The dry weight of the sponge pictured here below is 14.4 grams. Record the sponge weight as given above and any sponge you may have.

Sponge Experiment 3. How much water can a sponge hold?

·        Place the sponge over a dry, clear plastic cup or container. See photo below.

·        Next, fill a measuring cup carefully with water to the 150 or 200 ml mark. (Note that 100 ml = 100 cc for purposes of this simple experiment.)

·        Slowly pour the water from the measuring cup onto the sponge. Start in the middle of the sponge and slowly add water in a spiral motion outward toward the edges. Watch and notice how the sponge expands as water is added and air is displaced.

·        Keep watching the catch cup or container and look for the first drop of water to appear. When this occurs stop adding water because this means the sponge has absorbed all the water it can.

·        Carefully remove the sponge from the catch cup and place the wet sponge on a pan balance or scale.

·        Weigh the sponge and record its weight accurately in a lab book or paper.

·        The wetted sponge in this experiment weighed 118.7 grams. The dry sponge weighed 14.4 grams. Therefore, the total amount of water held by the sponge is: 118.7 – 14.4 = 104.3 grams (gm). Since 1.0 ml or 1 cc of water weighs 1 gram the sponge actually absorbed 104.3 cc or ml or 104.3 grams of water.

Sponge Experiment 4. What is the density of a dry and the same wet sponge?

The density of any object is mass/volume (m/V). For simplicity consider that weight = mass. Here the dry sponge density is: 14.4 grams (mass)/150 cc (volume) = 0.096 = 0.1 rounded off. The sponge has a density of 0.1 and relative to water (density of 1.0) – it should float since its density is 1/10 the density of water.

What happens with the same sponge when wet? Will a wet sponge float? 
Remember these facts:
  • The weight of the dry sponge measured by us at the sciencesuperschool lab was 14.4 grams.
  • That sponge can displace 150 cc of water based on its volume 150 cc or 150 mls or 150 gms of water when immersed in water.
  • The total weight or mass of the sponge in water will the weight of the sponge alone plus the weight of the water it absorbs which is 118.7 grams.
  • Therefore: What is the density of this wet sponge in water? 118.7 = wet sponge mass (weight) for the sponge volume = 150 cc. Therefore, wet-sponge density = 118.7/150 = 0.79. That density value means the wet sponge will float because the sponge density is less than that of the water in which the sponge floats. Remember that water has a density of 1.0 and the fully wet sponge here has a density of 0.79.Therefore, the sponge floats even though it is soaked in water. 

Sponge Science Experiment Conclusions and Discussion

In summary, sponges are water-hungry structures which are useful for absorbing water from surfaces on floors, tables, countertops or anywhere water spills need to dealt with.  A good sponge absorbs well. A poor sponge absorbs hardly at all.
In this experiment a dry sponge weighing 14.4 grams absorbed 104.3 grams of water. How many times its own weight was this sponge absorbing? Therefore, 104.3/14.4 = 7.2/1. This means that a good-absorbing sponge, such as this one, can hold an amount of water about 7 times its own weight.
 If you compare a natural sponge with manufactured cellulose and polyfoam sponges you will note sometimes big differences in absorbency. Again, check and ee the photo at the top. Compare the colorful polyfoam manufactured sponges and note how poorly they absorb water compared to a natural sponge.
Ohaus triple beam balance with sponge to be weighed and water for wettting the dry sponge (see methods).
Photo credit and copyright: Donald Reinhardt
Photogrphed here is a sponge which was wetted slowly and almost completely over a catch cup to determine when the sponge was saturated with water (i.e., when the first drop of water falls as one drop at a time of water is slowly added). Note that the very edge of the sponge was still dry. Fives drops of water later the edge of the sponge was wet and the sponge was fully saturated with water. 
Photo credit and copyright: Donald Reinhardt 
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Donald Reinhardt is a Consultant in Medical and Industrial Microbiology and a Freelance Science writer. He is available for specific assignments for those who are interested – by contacting