# How to transfer the amount in weight of : Information for students

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Very often at school at lessons of physics or chemistry are considered problem of finding the mass of a substance.Problems of this kind are very practical, because in real life with the weight and volume calculations we encounter every day.How many liters in the bottle?What's harder: petrol or water?How much will it weigh a full canister of acetone?Answers to all these questions can be obtained by knowing how to translate the volume into mass and vice versa.

In physics and chemistry of the substance is characterized not only by their number, but also its density.Density - is a constant (for each substance is its own), which is calculated by dividing the mass of a substance to its volume.weight and volume measurements are carried out under normal conditions (20 degrees Celsius, 760 mm. Hg) and recorded in a special table of densities.

Sometimes scientists to calculate the density necessary to resort to such a bag

of tricks, how to calculate the molar mass of a substance, because in practice it is difficult to weigh the substance or too little.The unit of measurement of density - grams divided by centimeter per cubic meter to cubic or kilogram.In practice, also conveniently measured in kilograms per liter (also known as a cubic decimeter).This value, expressed by the Greek letter rho (ρ).Turning to the question of how to find the mass of the density, look at a specific example.Find the mass of copper ingots in the volume of 740 cubic cm.Looking at the table, determine the density of copper is 8.2 (g / cc).Next, multiply the volume by the density: 740 cc..* 8.2 g / cc.cu.= 0.8, the obtained results always need to be reversed in the SI system.This is roughly equal to 6.6 kilograms.

A similar problem is how to find a lot of knowing the volume.It is also necessary to multiply the volume by the density of matter.Consider a more complex task.Brass bar volume of 0.8 cubic decimeters was placed in an empty two-liter capacity, the rest is filled with water.Find the mass of the contents of a two-liter tank, the mass of the container can be neglected.To begin with we find the volume of water: 2 liters - 0.8 liters (ie a liter cubic dm =....) = 1.2 liters.

Let us turn to the problem of how to find a lot of water and brass.The density of water is 1 kg / liter, so the mass is equal to 1 * 1.2 = 1.2 kg.The average density of brass is equal to 8.5 kg / liter, hence the mass of 0.8 liters will be equal to 0.8 * 8.5 = 6.8 kg.Next, we add up the calculated mass: 1.2 kg + 6.8 kg = 8 kg.The problem is solved.Table densities can always be found in every school library or on the Internet.