The concept of density was developed in Greek antiquity, with the well-known principle of Archimedes, or hydrostatics, which says that if a body is immersed in a fluid, such as water, it will have an upward vertical force equivalent to the weight of the volume of fluid that is displaced, as happens when someone gets into a bathtub and the water level rises.
In this way, if two objects are introduced into a fluid, such as water, for example, the denser one will sink faster, regardless of their size.
According to the account of the Roman architect, Archimedes discovered his principle when the tyrant Hiero II of Syracuse asked him to find out if a goldsmith had deceived him by making a gold crown, mixing it with silver, a less valuable metal, but without melting the crown. to compare it with another object. The solution occurred to him while he was taking a bath, observing that the water rose as it entered the tub. It seems that the discovery filled him with such joy that he went out into the street naked, shouting ” Eureka !” (“I’ve found it”).
However, to calculate the density of liquids, such as water , alternative methods are needed, for which various devices can be used that will allow knowing that density.
Therefore, we show you how to calculate the density of water in a simple way, since it is a small experiment that you can do in class, if you are a student, or at home, if you are a fan of physics and chemistry.
What do you need to calculate density?
- Water
- A measuring cylinder or graduated tube
- A scale that gives the weight in grams
- Pencil and paper
Instructions for calculating density
- What is density. Density is defined as the amount of mass there is with respect to the volume of a specific body, that is, the space it occupies. It is usually transcribed in grams per milliliter, and for this reason, to find out the density, the formula is used, put in simple terms, that density is equal to the mass divided by the volume, once these data are known.
- How can density be measured? Density can be measured directly or indirectly. The indirect way is to know the parameters of mass and volume, measuring them separately, with the measurements of the body in question and by displacement in a fluid. In addition, several devices have been created to measure the density, both of liquids such as water, and of gases.
- Measuring instruments. The most common devices for measuring density in liquids and fluids are the densimeter, a device with digital components and with which the density of a liquid such as water and others can be measured immediately, and which is based on the technique of oscillating U-tube, and the frequency with which resonance occurs in the fluids being analyzed; the pycnometer, which is a bottle specially designed for the precise measurement of the density of both liquids and solids and gases; the hydrostatic balance, used mainly for the calculation of densities in solids; Mohr’s balance, which is a derivative of the hydrostatic balance, and with which the density of liquids can be measured quite accurately.
- Practical demonstration. To practically demonstrate the calculation of the density of water, you need few things and it is quite simple to perform. You have to get a graduated cylinder or cylinder, with lines indicating the units of density, a scale to weigh and, of course, tap water.
- Cylinder weight. Take the empty cylinder and weigh it on the scale. Record your weight on a piece of paper. As we have indicated before, to find out the density of water, we must know its mass and volume. It is necessary to measure the mass of the water with the graduated cylinder, but, obviously, the cylinder is not water and its weight must be subtracted. You have to write down the weight of the empty measuring cylinder in grams. Let’s say that the test tube in these conditions has weighed 15 grams. That is the mass of the test tube or cylinder.
- The volume. When you load the test tube with water, before you weigh it, you must write down the amount of volume that the test tube contains, observing the height that the introduced water reaches and at what measurement number or line it is located. To have an exact measurement of the volume of the water, you must place the test tube at the level of your eyes, or find a position where you can observe it at that level. Specifically, you should look at the height of the so-called meniscus in physics, which is the highest or lowest point of the water level in the test tube, since it makes a bit of a curve. Let’s say, for example, that the volume reaches 40 milliliters. Write it down.
- Water weight. Now is when you have to proceed to put the measuring tube on the scale and weigh it, after zeroing the scale, well adjusted. It doesn’t matter much how much you put in it, but write down the weight in grams. As an example, let’s assume that the filled cylinder weighs 40 grams. Write down this number. Take into account an important condition: be careful not to spill even a drop of water when supporting the test tube or cylinder on the scale, if you have already taken note of the volume, because if you write down one amount of volume and then it is another, because a little, and you have already written down the weight of the loaded test tube, the density data will be falsified. Therefore, weigh the test tube after taking note of the volume to be weighed, and without losing even a minimum amount of water.
- Calculating the density of water. Now we are going to calculate the density of the water that you have measured and is in the measuring cylinder. First of all, subtract from the weight of the same filled with the water that you wrote down, the weight of the empty test tube. That is, the test tube with the water inside it weighed 40 grams, and the empty test tube weighed 15 grams. Consequently, the mass of the water in the measuring cylinder or tube is 25 grams. What was the measurement of volume? 40 milliliters. Now you just have to solve the simple equation of dividing the mass by the volume, that is, 40/40 = 1 gram/milliliter. That is the density of water. Actually, that is always its density, so it doesn’t matter if you measure larger or smaller amounts of water, and it is the equivalence between measurements, from pure water, so a milliliter is a gram of weight, and a liter or thousand milliliters is a kilogram.
- The formula. Density in physics is represented by the Greek letter rho, p. Density is equal to the mass of a body divided by its volume. The equation is: p=m/v. Density is a physically easy concept to verify as an empirical reality, as seen in the famous trick question: “What weighs more, a kilo of straw or a kilo of iron?” and on the other, what makes their densities so different, so low that of straw compared to that of iron.
- Changes in density. The density is not immutable, but can vary depending on the pressure applied or the temperature of that body, in this case, the water. If the pressure increases, the density also. And if the temperature increases, the density decreases, and vice versa. An example, at 0 degrees Celsius temperature, the density of water is 0.9998 g/ml, and however, if the water is close to the boiling point, at 80 degrees Celsius, the density drops to 0.9718 g /ml.
Tips for Calculating Density
- Handle with the necessary care and attention the instruments you need to check the density of the water, in particular, with the test tube or measuring tube, which in many cases is made of glass and can break and injure you.
- When weighing the water and measuring its volume, pay attention that not a drop of water is spilled, so that the parameters are exact and there are no falsified results.