HEY YA'LL :) We're done discussing about the Stoichiometry So, here's a little of everything .... You can choose between the two or you can answer both:
You know the atoms of different elements have different masses. Thousands of experiments led to the organization of a scale of relative atomic masses. The scale is based on the mass of carbon-12. The mass of an atom relative to the mass of carbon-12 is the Atomic Mass of the Atom. The SI unit for atomic mass is amu.
On the scale, the atomic mass of hydrogen is 1.0079 amu, oxygen is 15.994 amu and sulfur is 32.06 amu. This means that the mass of oxygen atoms are about 16 times the mass of hydrogen atoms, while sulfur atoms are nearly 32 times as heavy as hydrogen atoms.
10.2 Formula Mass or Molecular Mass
Molecular Mass - is used for compounds that are composed of molecules and covalent compounds like CO2 and sucrose or table sugar C12H22O11. However, the term formula mass is usually used for both ionic and covalent compounds.
Formula Mass - is used for ionic compounds like NaCl or for compounds that ionize in aqueous solutions like H2SO4
- It is the sum of the atomic masses of each atom in a chemical formula. To calculate the formula mass of H2SO4 refer to the periodic table for the atomic mass values of each of the elements that constitute
the compund and the compute it as follows
You can watch this for further explanation :)
10. 3 The Mole
In chemistry, particles are counted by the Mole (mol), a unit that contains 6.02 x 1023 species.
This very large number is called Avogadro's number, after Amedeo Avogadro (1776-1856), an Italian physicist who contributed to the development of the concept of the atomic nucleus.
Avogadro's Number
602 000 000 000 000 000 000 000 = 6.02 x 1023
This is used to indicate very small species that make up matter like atoms, ions, or molecules. It is also the number of atoms in 12 grams of 126C. One mole of any element always has Avogadro's Number of atoms.
You should watch the video clearly because it shows how to calculate for the mole.
This video is very useful. So i recommend you to watch and understand it :)
10. 4 Molar Mass
It is not possible to weigh a single atom or molecule. Even the most accurate balance available cannot weigh very small masses. In the laboratory, you will use a balance that measures in grams. When you weigh one mole of a substance, you would weigh its mass in grams which is numerically equal to its mass in atomic mass unit. The mass in grams of one mole of a substance is called its Molar Mass.
Example
What is the molar mass of one mole of ascorbic acid?
Solution
For more convient tutorial, watch this video :)
10. 5 Percentage Composition
In the laboratory, you perform experiments that will require you to prepare solutions or to verify the purity of some substances. If you are asked to prepare 10% salt solution, you dissolve 10g of salt in 90g of water to make a 100g salt solution. Thus you need to know how to calculate the percent compositions of compounds.
The percent by mass of an element in a compound is obtained by using the equation
Example
5.00 g of Calcium reacts completely with 10.0 g of Sulfur. What is the percent composition of the calcium sulfide produced?
Solution
A total of 100%
The mass of CaS is obtained by adding the masses of the components.
Watch this video for easier explanation :)
10. 6 Empirical and Molecular Formulas
Empirical or simplest formula gives the smallest whole-number ratio of the elements in a formula. Using the mole, and empirical formula is the lowest whole-number ratio of moles of atoms of the elements in the compound. An empirical formula may or may not be the same as a molecular formula. For example, the simplest empirical formula and molecular formula for water are both H2O. However, for hydrogen peroxide they are HO and H2O2 respectively.
When the molecular formula is different from the empirical formula, it is some whole number multiple of the empirical formula. Consider formaldehyde and glucose. They have the same empirical formula, CH2O. The molecular mass of the formaldehyde and glucose are 30 g/mol and 180 g/mol,
respectively. Thus, the empirical formula is also the molecular formula of formaldehyde,
while the molecular formula of glucose is 6 (CH2O). The mutiple 6 is obtained by dividing the
molecular mass of glucose (180 g/mol) by the given empirical mass (30 g/mol)
Therefore, the molecular formula of glucose is C6H12O6
Example
What is the empirical formula of a compound that contains 27.27% carbon
and 72.72% oxygen?
Solution
a. Convert the percent composition in terms of mass and express the mass of each element
into moles.
b. Determine the smallest whole number ratio for carbon and oxygen by dividing by the
least number obtained.
c. The ratios obtained in the calculation are the subscripts of the elements in the formula
to represent their mole ratio.
The empirical formula of the compound is CO2
Here is another example. Kindly watch the video :)
10. 7 Stoichiometry
The focus is on the stoichiometry of individual compounds (ratios of atoms in chemical formulas) In this section, the same ideas are extended to chemical reactions. Moles, grams, and number of atoms and molecules are used to specify the amount of substances used in chemical reactions.
In a balanced chemical equation, if the amount of one reactant or product is given, stoichiometry indicates the amount of every other reactant and product. This is so because a balanced equation summarizes the quantitative relationships among the amounts of reactants and products.
Reaction Stoichiometry - is the study of the quantitative relationships among reactants and products in a chemical reaction.
Here is one example. Try watching it :)
10. 8 Limiting Reagent
In the previous problems, the reactants supplied are in the exact ratio described by the balanced equation. They are said to be in stoichiometric amounts. But in actual applications, this is hardly the case. Most often, reactants available are in other proportions. In a situation where a reactant exceeds that of the required amount, the reactant is called the excess reagent and the reactant that is completely used up is called the limiting reagent.
View this video for further explanation on how to solve :)
Before we start our further lessons about Chemistry.
Lets us first discuss ... What is Chemistry?
CHEMISTRY
It is the study of matter - all things that occupy space and have mass. Some of these you can see, some you cannot; some are found in nature, some are man-made or synthetic; some are edible, others are poisonous. In chemistry we study the composition, properties and structure of matter. We also study the changes that matter undergoes and the energy involved in these changes.
Also, some of the properties of matter can be perceived by our senses but others may require special instruments to observe and measure. The study of the structure of matter is concerned with the building blocks of matter, the atoms and molecules.
OBJECTIVES:
Explain why a knowledge of chemistry is central to many human activities
Cite the relevance of chemistry in a variety of careers or occupations
Discuss recent technological applications of chemistry
Name some Filipino heroes in Chemistry
Identify the SI units of measurement and convert from one unit to another
Calculate the corresponding temperature in °F or K given the temperature in °C and vice versa
Differentiate precision from accuracy
Determine the number of significant figures in given measurements
Express measurements in scientific notations
Use conversion factors in solving problem.
Examples of Filipino Heroes in Chemistry
JULIAN A. BANZON
Dr. Julian A. Banzon is the grand man of chemistry in the Philippines. His research on fuels using coconut as a renewable source of chemicals and fuels was a breakthrough because our usual source of energy is crude oil. He used coconut as a source of liquid fuel and showed that coconut diesel can be a substitute for diesel oil. He studied the use of gasonol, gastaria, pure kerosene, and mixture of pure kerosene and crude oil as fuels.
ALFREDO C. SANTOS
Dr. Alfredo C. Santos is the father of natural products research. He extracted alkaloids from Philippine plants. Alkaloids are bitter components found in the roots, leaves, fruits, seeds and barks of plants. They are usually poisonous but some of them have been found to be therapeutic.
Measurements
THE INTERNATIONAL SYSTEM OF UNITS
Scientific Notation
Many numbers used in chemistry are either very large or very small that the number of zeros becomes difficult to handle. For accuracy and convenience, these numbers are written in scientific notation. A number in scientific notation has two parts. The first part is a number between 1 and 10 (N). The second part is a power of 10y as shown below
N x 10y
The exponent y can be a positive or a negative integer.
To write numbers in scientific notation, move the decimal point such that you have a number between 1 and 10. Determine the correct exponent by counting the number of times the decimal point is moved. When the decimal point is moved to the right, the exponent is written as a negative number. When the decimal point is moved to the left, the exponent is written as a positive number.
Example: 1.) 0.00567 ----- 5.67 x 10 -3 2.) 456000 ----- 4.56 x 10 5\
Okay. So this is just the Introduction of what Chemistry is all about.
Stay tuned to our lessons here. You'll learn a lot. Trust me :)
