STOICHIOMETRY

A. UNDERSTANDING STOICHIOMETRY

          Stoichiometry comes from two Greek syllables Stoicheion meaning "element" and Metron which means "measurement". Stoichiometry is a subject in chemistry involving the linkage of reactants and products in a chemical reaction to determine the quantity of each reacting agent.

B. DEFINITION CONCEPT MOL

            

One mole of each element: carbon (black powder of charcoal), Sulfur (yellow powder), iron (nails), copper wire, and mercury (metal in liquid form)

   To simplify the number of these extraordinarily small particles, the concept of moles is used. Mol represents the unit of quantity of matter. Unit amount of this substance as well as the simplification of the amount of a good. For example, 1 dozen is used to simplify 12 pieces of glassware and 1 ream to declare 500 sheets of paper. This simplification needs to be done because the chemical processes that take place in everyday life involve a very small collection of very small particles. The units of the particles are too difficult to observe.

1 mol = L particles

L = Avogadro Number = 6.02 x 1023

 Thus, the concept of moles is the unit of quantity of matter that expresses the number of particles of matter.

FORM CONCEPT MOL

Thus, 1 mol of the substance contains 6.02 x 1023 particles. The relationship between the number of moles and the number of particles can be formulated as follows:

Number of moles of X (n) = number of particles X / L

 Or

Number of particles X = n x L

 The Avogadro (L) number was discovered by Johann Loschmidt in 1865. The name Avogadro was chosen as a tribute to Avogadro because he was the first to propose the need for a unit of particle count. The name Loschmidt is immortalized as a symbol of that number, L. The value of the Avogadro number is L = 6.02 x 1023. Can you imagine the magnitude of that number? Had it collected 6.02 x 1023 rice grains, the rice could be dumped on the surface of the Australian continent with a height of one kilometer! Or, if an atom is the size of a marble and spread on the surface of the earth, the entire surface of the earth will be covered with marbles with a layer thickness of 80 km! This enormous number is chosen to express the number of atoms because of their practicality and precision. Imagine, it would be complicated if the number of atoms expressed in units of grains, dozen, gross, kodi, or other units.

1. MASS MOLAR

                    The molar mass is the mass of a substance equal to the atomic mass or the mass of the formula of the substance expressed in grams. This molar mass is equal to the mass possessed by a mole of substance equal to the relative atomic mass (Ar) or relative molecular mass (M).

2. Volume of gas molar

        The molar volume of the gas (Vm) is the volume occupied by 1 mole of gas at a temperature (T) and a certain pressure (P). Because the laws of gas do not depend on the  identity of the gas. In other words, any gas, at a certain temperature and pressure will be the same volume. This implies that, one mole per gas contains the same number of molecules as the avogadro constant (L = 6.02 x 1023 molecules). According to Avogadro's law, the gases must fill the same volume at a certain temperature and pressure. The volume of one mole of this gas is known as the molar volume of the gas. At standard pressure (0 oC and 1 atm), the volume of one mole of gas was found to be 22.4 Liters. (Remember yes only at 0 oC and 1 atm, if not in these conditions then the volume of the molars will not be 22.4 L).
If there is one mole of ideal gas at 0 ° C and 1 atm pressure, then from the ideal gas law, the gas volume in that state is

 This 22.4 liter volume is called the ideal gas molar volume.

3. Molarity

             In chemistry, molarity (M) is a measure of the concentration of the solution. The molarity of a solution expresses the number of moles of a substance per liter of solution. For example 1.0 liter of solution contains 0.5 mol of X compound, then this solution is called 0.5 molar solution (0.5 M). Generally the concentration of aqueous aqueous solution is expressed in molar units. The advantage of using molar units is the ease of calculation in stoichiometry, since concentrations are expressed in number of moles (proportional to the number of actual particles).

 

4. substance levels

            Substance levels are generally expressed in percent mass (% mass). To get a percent mass can use the formula:

5. Determining the Empirical Formula and the Compound Molecular Formula

            In chemistry lessons are known 2 types of chemical formulas, namely Empirical Formulas and Molecular Formulas. The empirical formula is the formula which expresses the smallest comparison of atoms from the constituent elements of the compound. While the molecular formula is a formula that shows the number of atomic elements that make up a compound. This molecular formula is a multiple of the empirical formula.

(Empirical Formula) _ {n} = Molecular Formulas

The value of n above corresponds to the relative molecular mass (Mr) of the two chemical formulas. If Mr. of the empirical formula is multiplied by n, then yields Mr. molecular formula. This principle is used as the basis for finding the molecular formula of the compound.

 How to Determine Empirical Formulas and Molecular Formulas :

1. Find the mass comparisons of the constituent elements.

2. Find the mole ratio by dividing the elemental mass by its relative atomic mass (Ar).

3. From the comparison of the simplest mole obtained Empirical Formula.

4. Determine the Molecular Formula by looking for the multiplier n factor. The formula used       is (Mr. RE) n = Mr.

C. CHEMICAL CALCULATIONS

        Stoichiometry is closely related to chemical calculations. To solve the problem of chemical calculation, the stoichiometric principles are used, they are chemical equation and mole concept. In this lesson we will learn first about the principles of stoichiometry, then after that we will study stoichiometry application on chemical calculation and sample problem and how to solve it.

1. Example of the Law of Conservation of Mass in Chemical Reactions:     Copper wire is burned in a bunsen burner to form copper oxide (CuO).

2Cu (s) + O2 (g) → 2CuO (s)

 If the weight of Cu is initially 32 g and CuO is formed 40 g, how much weight of O2 reacts? Resolution:

 According to the Law of Conservation of Mass, in chemical reactions there is no mass change. Therefore, the weight of O2 reacting is 40 g - 32 g = 8 g 32 g

Cu (s) + 8 g O2 (g) → 40 g CuO (s)

USE OF CHEMICALS IN DAILY LIFE

      Chemistry is a science related to everyday life or natural phenomena, because starting from the affairs of food and clothing, fuel, medicine to building construction materials, electronic industry materials and products involving chemistry chemistry. What distinguishes chemistry from other sciences is that chemistry specializes in the structure, structure, properties and changes of matter, and the energy that accompanies material change.Chemistry has an important position and is required by other fields of science. Some of the real benefits that it is the benefits of chemistry in human life are not even so realized. Here are some of the benefits of chemistry in human life that can not be replaced by other science.

1 .In Agriculture
               For example when plants need water and fertile soil. But in the field of modern agriculture, has been using fertilizers and pesticides. Benefits of fertilizer for plants is Stimulate the growth of roots, stems and leaves fiber Improve quality and number of good results. Because the fertilizer is an inorganic chemical compound found in nature or made by humans that have direct or indirect nutrient value for the plant. The use of pesticides can destroy pests, and increase the production of plants quickly. But can be harmful to human health because exposure to pesticides that enter the human body either through the skin, nose, or mouth can cause various health problems or illness. After the body is exposed by pesticides, then attacks the body organs including the lungs and respiratory system, liver, kidneys and urinary tract, nervous system, blood and bone marrow, heart and blood vessels, skin and reproductive system, immune system, bone, Muscles, and glands. So that health problems or diseases that caused such as cancer, infertility, autism, Parkinson's, diabetes, infants born with disabilities, anemia, stunting (short stature), goiter (enlargement gland), and others.

2. Bananas Faster Fast
               Maybe when we take a banana from our own garden the bananas are still green. While we are eager to eat bananas, there is a quick way to ripen bananas in a safe, natural way by using apples and tomatoes, by simply covering the bananas in a paper bag, along with ripe apples or tomatoes. Apples or tomatoes emit ethylene, which is a material that functions for the natural chemical fruiting of the fruit. But instead, if we want to keep the bananas that have been ripe and do not want to quickly rot or too ripe, then we should not place the banana fruit in a fruit bowl with other ripe fruit.

3. Adding Salt To Make Coffee Sense Better
Have we ever ordered or made coffee and it tastes so sour? One ingenious solution to the sour coffee taste is to sprinkle it with a pinch of salt. Salt dissolves in coffee to release sodium ions. Coffee will not change better, but it will taste better because sodium blocks the taste receptors that detect the bitter. If we brew your own coffee, we can add salt during the coffee-making process. Another way to reduce bitterness is to avoid making a coffee solution with super-hot water. Too much heat during brewing increases the extraction of a bitter-tasting molecule.

 4. Offering Poisonous Animal Poisons

               Often in our daily lives bitten or stung by venomous venom, of course it feels very sore and hot, although for animals such as snakes that mengingit into the blood is often recommended to suck it but, for other cases we can use chemistry to mengatsi problems of sting and Bite of venomous animals, if we are stung by the wasps on the face we fear not only but the swelling that is caused, so do the other venomous animals. In general can be from an animal is an acid compound, then the armpit bitten or stung as much as possible we use alkaline compounds to neutralize aasam compounds from the can, the basic compounds that are often young we can around the house are kitchen ash, soap or lime.

5. Enter the sugar in a glass first before the water when making tea in a glass
               May have used a glass that when exposed to hot water will break and crack, then one prevent it is to enter the sugar first before the hot water, this can prevent cracking because sugar can absorb the heat which simultaneously increase the boiling point of the solution, so with The presence of sugar can then withstand the temperature of the boiling water becomes lower, of course using thicker glass material is one of the other precise solutions.

6. Field of medicine  

            Chemistry has a vital advantage, it can be felt by the existence of various medical science concerning aspects of chemistry. The use of medicines in medical science made on the basis of research into a reaction of a process due to chemicals carried out by the branch of pharmaceutical science.

7. Benefits of Chemistry in the Field of Machinery
               Studying the properties and composition of metal are good for machine making, studying the nature, composition of fuel, and engine oil. Those are the benefits of Chemistry in the field of machinery.

8. Chemistry in Biology
Biology is the study of the special thing about living things. Chemical processes that take place in living things include digestion of food, breathing, metabolism, photosynthesis, and others. To learn this, knowledge of the structure and properties of existing compounds, such as carbohydrates, proteins, vitamins, enzymes, is necessary. Although in general this is more closely related to the Science of Biology, but the benefits of Chemistry also in fact a little more influential in this biological field.

9. Chemistry in Civil Engineering
               The materials used in this field are cement, wood, paint, nails, iron, paralon (PVC pipe), glue, and so on. All these materials are produced through research based on Chemistry. The benefits of Chemistry in the field of civil engineering is that the building materials can be known advantages and disadvantages. So as to minimize accidents in the future.

10. Chemistry in the Arts
               The chemical industry produces paint to embellish a material or a building. Chemicals present in wall paints include calcium carbonate, titanium dioxidapolivinyl, acrylic, water.

ARTICLE 1

THE DEVELOPMENT OF THEORY OF ATOM

        

          Atoms are a basic unit of matter, composed of atomic nuclei and the negatively charged electron clouds that surround it. The atomic nucleus consists of a positively charged proton, and neutrons with neutral charge (except in the nucleus of Hydrogen-1 atom, which has no neutrons).

               The term atom comes from Greek (ἄτομος / átomos, α-τεμνω), which means it can not be cut or something that can not be divided again. The concept of atom as an indivisible component was first proposed by Indian and Greek philosophers. In the seventeenth and eighteenth centuries, chemists laid the foundations of this idea by showing that certain substances could not be further divided using chemical methods. During the late nineteenth and early twentieth centuries, physicists managed to discover the structure and subatomic components within the atom, proving that 'atoms' are not indivisible. The principles of quantum mechanics used by physicists then succeeded in modeling atoms.

1. The Atomic Theory of Jonh Dalton

            John Dalton put forward the hypothesis of atoms under the law of conservation of mass (Lavoisier) and the law of fixed comparison (Proust). Dalton's proposed theory: Atom is the smallest part of matter that can not be divided again. Atoms are described as very small solid spheres, an element having identical and different atoms for different elements. The atoms combine to form compounds with simple and integer ratios. For example water consists of hydrogen atoms and oxygen atoms Chemical reactions are the separation or amalgamation of the atoms, so that atoms can not be created or destroyed.

The atomic model of dalton The advantage of Dalton's theory is to start an interest in research on the atomic model.

The disadvantage is not to explain the relationship of oceans of compounds and electric current conductivity, if atoms are the smallest part of a element and can not be subdivided.

2. Atomic Model Joseph John Thompson

               Joseph John Thompson is the inventor of electrons. Thompson tried to explain the existence of electrons using his atomic theory and model. According to Thompson, the electrons are evenly distributed in atoms considered to be a positively charged ball.

    The atom model proposed by Thompson is often referred to as a model of raisin bread with bread as positively charged atoms and raisins as the electrons are spread evenly across the bread section. Atom as a whole is neutral.

3. Atomic Model Ernest Rutherford

               The study of alpha-light shooting on a thin gold plate allowed Rutherford to propose atomic theory and models to improve the theory and model of Thompson atoms. According to Rutherford, the atom has a positively charged nucleus and is the center of the mass of atoms and electrons around it.

               Rutherford found that the nuclei of positively charged atoms and electrons were outside the nucleus of the atom. However, Rutherford's theory and model of atoms also still have weaknesses: this theory can not explain the phenomenon of why electrons can not fall into the nucleus. Whereas according to classical physics, particles including electrons orbiting the path will release energy in the form of radiation so that electrons will orbit spirally and eventually fall to iti atom.

4. Atoms Model Niels Bohr

            Niels Bohr further refined the model of the atom expressed by Rutherford. Bohr's explanation is based on his research on the spectrum of hydrogen atomic lines.

Some of the things described by Bohr area. Electrons orbit at certain energy levels called skin
b. Each electron has a certain energy that matches the energy level of the skin
c. In a stationary state, the electrons do not release and absorb energy
d. Electrons can move from high energy levels to low energy levels and vice versa absorbing and releasing energy.

5. Atomic Model of Wave Mechanics

            The development of the latest atomic model proposed by atomic model based on quantum mechanics. This explanation is based on three theories namely The theory of the duality of electron particle waves proposed by de Broglie in 1924 Uncertainty principle expressed by Heisenberg in 1927 The wave equation theory by Erwin Schrodinger in 1926.

    According to this model of the atom, the electrons do not orbit on a particular path so that the path proposed by Bohr is not a truth. This atomic model explains that the electrons are in orbitals with a certain energy level. Orbital is the area with the greatest possibility to find electrons around the atomic nucleus.