To pass the general chemistry exam, you must have understood the fundamentals, have a good knowledge of basic mathematics, know how to use a calculator for complex equations and have the desire to learn something really different. Chemistry studies matter and its properties. Everything around you is part of chemistry, even the simplest objects you take for granted, like the water you drink and the properties of the air you breathe. Maintain an open minded attitude as you study, down to the atomic level, everything that happens around you. The first approach to chemistry could be problematic, but exciting at the same time.
Steps
Part 1 of 5: Developing a Good Study Method
Step 1. Introduce yourself to the teacher or professor
To pass the chemistry exam with the highest possible grade, you need to take some time to get to know the teacher and let him know how difficult his subject is for you.
Many professors can give you handouts to help you and receive students who need support in their office
Step 2. Organize or join a study group
Don't be ashamed if chemistry is tough for you. This is a particularly difficult subject for almost everyone.
When working in a group, some members find some topics easier than others and can share their study method. Divide et impera
Step 3. Study the chapters
The chemistry textbook is not always the most interesting book to read, but you need to take the time to read the sections that have been assigned to you and underline those parts that don't seem to make sense. Try to make a list of questions or concepts that you can't understand.
Afterwards, try to address these topics again with a fresh mind. If they are still unclear, talk to your study group, teacher, or assistant
Step 4. Answer the verification questions
Even if you feel that you are overwhelmed by all the material you have studied, know that you may have learned more than you think. Try to answer the questionnaire found at the end of each chapter.
Most textbooks provide other information that tells you what the correct answer should be and helps you understand what you missed during your study
Step 5. Concerns the diagrams, images and tables
Books often use graphic means of communication to be clearer and better convey information to the reader.
Look at the pictures and pay attention to their description that you find in the chapter. They might help you clear up some confusing passages
Step 6. Ask for permission to be able to record the lessons
Taking notes and observing everything the teacher writes or projects on the blackboard is not easy at all, especially for a subject as complex as chemistry.
Step 7. Obtain the texts of the previous exams or the old handouts
Most of the faculties allow you to have, in a completely legitimate way, the texts of past exams to help students pass the most important tests.
Don't just memorize the answers. Chemistry is a subject you need to understand if you want to be able to answer the same question in different words
Step 8. Don't neglect online study sources
Also study through the internet by reading the sources and links provided by your faculty chemistry department.
Part 2 of 5: Understanding Atomic Structures
Step 1. Start with the basic structures
To pass the chemistry exam, you must fully understand the building blocks that make up everything that has mass.
Understanding the basic element of matter, the atom, is the first step in chemistry. All the topics that will be covered in class will be an extension of this basic information. Take your time to understand matter at the atomic level
Step 2. Assimilate the concept of atom
This is considered the smallest building block of any object that has mass, including what we cannot see, such as gases. However, even the small atom is made up of even smaller parts that form its structure.
- An atom is made up of three parts. These are the neutrons, protons and electrons. The center of the atom is called the nucleus and contains protons and neutrons. Electrons are particles that gravitate around the outside of the atom, just like planets revolve around the sun.
- The size of an atom is incredibly small but, to give you a comparison, think of the largest stage you can imagine. If you look at this stadium as an atom, the nucleus would be the size of a pea in the center of the field.
Step 3. Learn the atomic structure of an element
The term element defines a naturally occurring substance that cannot be broken down into other basic elements and is in its simplest form. Elements are made of atoms.
The atoms present in an element are all the same. This means that each element, in its atomic structure, has a known and unique number of neutrons and protons
Step 4. Study the core
Neutrons, which are found in the nucleus, have a neutral electrical charge. Protons, on the other hand, have a positive charge. The atomic number of an element corresponds exactly to the number of protons contained in its nucleus.
You don't have to do any mathematical calculations to know the number of protons of an element. This value is printed in each box of each element of the periodic table
Step 5. Calculate the number of neutrons in the nucleus
You can use the information provided by the periodic table for this purpose. The atomic number of each element is equal to the number of protons in the nucleus.
- The atomic mass is indicated in each box of the periodic table and is located at the bottom, just below the element name.
- Remember that only protons and neutrons are found in the nucleus. The periodic table lets you know what the number of protons and the atomic mass number are.
- At this point, the calculation is pretty straightforward. Just subtract the number of protons from the atomic mass and get the number of neutrons that are in the nucleus of the element's atom.
Step 6. Find the number of electrons
Remember that opposites attract. Electrons are negatively charged particles that float around the nucleus, just like planets gravitate around the sun. The number of negatively charged electrons attracted to the nucleus depends on the number of positively charged protons present in the nucleus.
Since an atom has a total neutral charge, all positive and negative charges must be in equilibrium. For this reason the number of electrons is equal to that of protons
Step 7. Look at the periodic table
If you are having trouble understanding the properties of the elements, take some time to review all the material available on the periodic table and, more importantly, study the table very carefully.
- Understanding this table is essential to pass the first part of the chemistry exam.
- The periodic table is made up of elements only. Each of them is represented with a one or two letter symbol. The symbol uniquely identifies the element. For example, Na indicates sodium. The full name of the element is usually written under the symbol.
- The number printed above the symbol is the atomic number. This corresponds to the number of protons found in the nucleus.
- The number written under the symbol corresponds to the atomic mass and indicates the total number of neutrons and protons found in the nucleus.
Step 8. Interpret the periodic table
This is a tool full of information, from the color chosen for each column to the criterion by which the elements are arranged from left to right and from top to bottom.
Part 3 of 5: Predicting Chemical Reactions
Step 1. Balance a chemical equation
During a chemistry class, you are expected to be able to predict how elements react to each other. In other words, you need to know how to balance a reaction.
- In a chemical equation the reactants are on the left side, followed by a right pointing arrow indicating the products of the reaction. The two sides of the equation must be in balance with each other.
- For example: reagent 1 + reagent 2 → product 1 + product 2.
- Here is an example using the symbols for tin, which is Sn, in its oxidized form (SnO2), which is combined with hydrogen in gaseous form (H2). We will therefore have: SnO2 + H2 → Sn + H2O.
- However, this equation is not balanced, because the quantity of reactants is not equal to that of the products. The left side of the reaction has one more atom of oxygen than the right side.
- Using simple mathematical calculations we can balance the equation by placing two units of hydrogen on the left and two water molecules on the right. The balanced reaction, in the end, will be: SnO2 + 2 H2 → Sn + 2 H2O.
Step 2. Think of the equations differently
If you have trouble balancing the reactions, imagine that these are part of a recipe, but you have to change the doses to increase or decrease the final product.
- The equation gives you the ingredients, on the left side, but does not give you information on the doses. However, the equation lets you know what you get as a product, always omitting quantities. You have to understand this information.
- Always taking advantage of the previous example, SnO2 + H2 → Sn + H2O, evaluate why the reaction, written in this way, does not work. The amounts of Sn on both sides of the equation are equal, as are the "doses" of H2. However, on the left we have two parts of oxygen and on the right only one.
- Change the right side of the equation to indicate that there are two parts of H2O (2 H2O). The number 2 written before H2O doubles all quantities. At this point the "doses" of oxygen are balanced, but not those of hydrogen, since there are more parts of hydrogen on the right than on the left. For this reason you have to go back to the left side of the equation, change the quantities of the H2 ingredient and double them by placing a coefficient 2 in front of H2.
- You have finally balanced all the doses of the ingredients on both sides of the equation. The ingredients of your recipe are equal (balanced) with the products.
Step 3. Add more details to the equation in equilibrium
During your chemistry class, you will have learned to add symbols that represent the physical state of the elements. These symbols are "s" for solids, "g" for gases and "l" for liquids.
Step 4. Recognize the changes that occur during a chemical reaction
The reactions start from the basic elements or from elements already combined with each other, called reactants. The combination of two or more reagents generates one or more products.
To pass the chemistry exam, you need to be able to solve equations involving reactants, products, and take into account other factors that influence their behavior
Step 5. Study the various types of reactions
Chemical reactions occur for a number of factors that go beyond the simple combination of "ingredients".
- The typical reactions that are studied in a chemistry course and that you need to know are those of synthesis, substitution, acid-base, redox, combustion, hydrolysis, decomposition, metathesis and isomerization.
- During chemistry class, your teacher may exhibit other types of reactions as well, depending on the schedule. Obviously the high school chemistry program is not as detailed as that of the university.
Step 6. Take advantage of all the educational resources that have been provided to you
You must be able to recognize the differences between the various reactions that have been explained in class. Use whatever study tools you have at your disposal to understand these concepts and don't be afraid to ask questions.
The differences between the reactions can sometimes create a bit of confusion in the mind and understanding the various chemical mechanisms may be the most complicated part of the whole course
Step 7. Analyze chemical reactions logically
Don't make the process more complicated than it already is by getting caught up in the terminology. The types of reactions you have to study involve an action that transforms matter into something else.
- For example, you already know that by combining two molecules of hydrogen with one of oxygen you get water. Also, you know that putting water in a pot and heating it on the stove triggers a change. You have created a chemical reaction. If you put water in the freezer, the same thing happens. You have introduced a factor that alters the initial reagent, in our case water.
- Review each type of reaction, one at a time, until you have assimilated it; then move on to the next. Focus on the source of energy that triggers the reaction and the main change that takes place.
- If you have trouble getting through these concepts, make a list of what you don't understand and review it with your teacher, study group, or someone who has a deep understanding of chemistry.
Part 4 of 5: Performing the Calculations
Step 1. Learn the sequence of mathematical calculations
In chemistry, sometimes very detailed calculations are required but, in other cases, elementary operations are sufficient. However, it is essential to know the exact sequence of operations to complete and solve the equations.
- Memorize a simple acronym. Students use different phrases to memorize some concepts and the order of operations is no exception. The acronym PEMDAS (which derives from the English phrase "Please Excuse My Dear Aunt Sally") helps you remember in which order to perform the mathematical operations: first do everything in the P.arentesi, then the ANDsponenti, the M.oltiplications, the D.ivisions, the TOdictions and finally the S.ottrations.
- Perform the calculations of this expression 3 + 2 x 6 = _, following the order of operations as indicated by the acronym PEMDAS. The solution is 15.
Step 2. Learn to round very large values
Although rounding is not a common practice in chemistry, sometimes solving complex mathematical calculations is too long a number to write. Pay particular attention to the instructions given by the problem regarding rounding.
Know when to round down and when to round up. If the digit after the point where you want to truncate the number is 4 or less, then you need to round down; if it is 5 or more, you must round up. For example, consider the number 6, 666666666666. The problem tells you to round the solution to the second decimal place, so the answer is 6.67
Step 3. Understand the concept of absolute value
In chemistry, many numbers refer to the absolute value and have no true mathematical value. The absolute value indicates the distance of a number from zero.
In other words, you must not consider a number as negative or positive, but as a difference from zero. For example, the absolute value of -20 is 20
Step 4. Familiarize yourself with the accepted units of measurement
Here are some examples.
- The amount of matter is expressed in moles (mol).
- The temperature is expressed in degrees Fahrenheit (° F), Kelvin (° K) or Celsius (° C).
- The mass is indicated in grams (g), kilograms (kg) or milligrams (mg).
- Volume and liquids are indicated with liters (l) or milliliters (ml).
Step 5. Learn how to convert values from one measurement scale to another
Among the skills you need to master to pass the chemistry exam is knowing how to convert measurements into units of measurement accepted by the international system. This means knowing how to transform temperatures from one scale to another, go from pounds to kilograms and from ounces to liters.
- Sometimes, the teacher may ask you to express the solution of a problem in a different unit of measure than the initial one. For example, you may need to solve an equation that predicts degrees Celsius but write the final result in Kelvin.
- The Kelvin scale is the international standard for expressing temperatures and is the most used in chemical reactions. Learn to convert degrees Celsius to Kelvin or Fahrenheit.
Step 6. Take some time to do the exercises
During the lessons you will be "bombarded" with a lot of information, so you will have to take the time to learn how to convert the numbers into the various scales and units of measurement.
Step 7. Learn to calculate concentrations
Review your math knowledge about percentages, proportions, and ratios.
Step 8. Practice with the nutrition labels found on food packaging
To pass the chemistry course, you have to perform the calculations of proportions, percentages, ratios and their inverse operations with a certain ease. If you have trouble with these concepts, then you need to practice with other common units of measurement, such as those found on nutrition labels.
- Observe these labels on all foods. You will find calories per serving, percentages of recommended daily allowances, total fat, calories from fat, total carbohydrates and a detailed breakdown of the various types of carbohydrates. Practice calculating the different ratios and percentages using the values of the various categories as denominators.
- For example, calculate the amount of monounsaturated fat out of the total fat content. Convert the value to a percentage. Calculate how many calories the entire product provides using the number of calories per serving and the amount of servings contained in the package. Calculate the amount of sodium present in half of the packaged product.
- If you practice conversions of this type, regardless of the unit of measurement used, you will feel much more comfortable when you have to exchange units of measurement in chemical quantities, such as moles per liter, grams per milliliter and so on..
Step 9. Learn to use Avogadro's number
This represents the number of molecules, atoms or particles that are found in a mole. Avogadro's number is equal to 6.022x1023.
For example, how many atoms are there in 0.450 moles of Fe? The answer is 0, 450 x 6, 022x1023.
Step 10. Think about carrots
If you can't figure out how to apply Avogadro's number in chemistry problems, think about this value in terms of cores rather than atoms, molecules or particles. How many carrots are there in a dozen? You know full well that a dozen represents a group of 12, so there are 12 carrots in a dozen.
- Now try to answer this question: how many carrots are there in a mole? Instead of multiplying by 12, use Avogadro's number. So there are 6, 022x1023 carrots in one mole.
- The Avogadro number is used to convert the amount of matter into the corresponding amount of atoms, molecules or particles per mole.
- If you know the number of moles of an element, then you can know how many molecules, atoms or particles are present in that amount of matter thanks to the Avogadro number.
- Learn to convert particles to moles; it is an important knowledge to pass the chemistry exam. Molar conversions are included in the calculation of ratios and proportions. This means knowing the quantity of an element expressed in moles in relation to something else.
Step 11. Strive to understand the concept of molarity
Consider the number of moles of a substance dissolved in a liquid environment. This is a very important example to understand, because we are dealing with molarity, i.e. the quantity of one substance in relation to the quantity of another expressed in moles per liter.
- In chemistry, molarity is used to express the amount of a substance contained in a liquid environment, i.e. the amount of solute present in a liquid solution. Molarity is calculated by dividing the number of moles of the solute by the liters of solution. Its unit of measurement is the mole per liter (mol / l).
- Calculate the density. This quantity is also widely used in chemistry and expresses the mass per unit volume of a substance. The most common unit of measurement, in this case, is the gram per liter (g / l) or gram per cubic centimeter (g / cm3), which, in fact, are the same thing.
Step 12. Convert the equations to the corresponding empirical formula
This means that the final solution of the equation will be considered wrong until you have reduced it to its lowest terms.
This kind of description does not apply to molecular formulas because they represent the exact proportions between the chemical elements that make up the molecule
Step 13. Study what a molecular formula comprises
You cannot change this type of formula down to the smallest terms, that is, in empirical formula, because it expresses exactly how the molecule is composed.
- A molecular formula is written using the abbreviations of the elements and numbers that indicate how many atoms for each element contribute to the formation of the molecule.
- For example, the molecular formula of water is H2O. This means that each water molecule contains two hydrogen atoms and one oxygen atoms. The molecular formula of acetaminophen is C8H9NO2. Each chemical compound is represented with the molecular formula.
Step 14. The mathematics applied to chemistry is called stoichiometry
During the chemistry course you will encounter this term many times which indicates the quantitative study of chemical reactions using mathematical terms. When using stoichiometry (the mathematics applied to chemistry) compounds are considered in terms of moles, percentages of moles, moles per liter or moles per kilogram.
One of the most common mathematical operations is to convert grams to moles. The atomic mass unit of an element, expressed in grams, is equal to one mole of this substance. For example, calcium has a mass of 40 units. So 40 g of calcium is equal to one mole of calcium
Step 15. Ask the teacher questions to give you more examples
If calculations and math conversions cause you any difficulty, talk to your professor or teacher. Ask him to give you more exercises to do on your own until all concepts regarding this topic are clear to you.
Part 5 of 5: Using the Language of Chemistry
Step 1. Study the Lewis structures
These structures, also called Lewis formulas, are graphical representations with dots showing the unpaired and paired electrons found on the outermost shell of an atom.
These structures are very useful for drawing simple diagrams and identifying bonds, such as covalent ones, that are shared between elements at the atomic or molecular level
Step 2. Learn the octet rule
Lewis structures are based on this rule which states that atoms are stable when they have eight electrons on the outermost electron layer (valence shell).
Step 3. Draw a Lewis structure
To do this you have to write the symbol of the element surrounded by a series of points, arranged according to a certain logic. Think of this diagram as a still image from a movie. Instead of "seeing" the electrons gravitating around the nucleus, they are "frozen" at a given moment.
- The structure shows a stable arrangement of the electrons that are bonded to the next element, it also provides information about the strength of the bonds, indicating whether they are covalent or double.
- Try to plot the Lewis structure of carbon (C) taking into account the octet rule. After writing the symbol, draw two points in the four cardinal positions, that is, two points to the north, two to the east, two to the south and two to the west. Now draw an H to represent the hydrogen atom, write one next to each pair of dots. This complete Lewis diagram represents a carbon atom surrounded by four hydrogen atoms. Electrons are joined by a covalent bond, which means that carbon shares an electron with each hydrogen atom and the same is true for hydrogen.
- The molecular formula of this example is CH4, that of methane gas.
Step 4. Learn the arrangement of electrons based on how elements bond together
Lewis structures are a simplistic graphical representation of what chemical bonds are.
Discuss with your professor or your study group if some concepts of Lewis bonds and formulas are not clear to you
Step 5. Learn the terminology of compounds
Chemistry has its own rules regarding nomenclature. The types of reactions that occur in compounds, the loss or addition of electrons on the outer shell, the stability or instability of the compound are all factors that determine the name of the compound itself.
Step 6. Don't underestimate the section dealing with terminology
In most cases, the first chemistry lessons are mainly focused on nomenclature and, in some courses, getting the names of the compounds wrong results in a rejection.
If possible, study the terminology before starting the course. There are many workbooks and textbooks that you can buy or browse online
Step 7. Learn what superscript and subscript numbers mean
This is a critical step for the success of your exam.
- The numbers placed as apex follow the pattern that you can also find in the periodic table and indicate the total charge of the element or chemical compound. Review the table and you will see that the elements arranged along the same vertical column (group) share the same apexes.
- Subscript numbers are used to identify how many atoms of a given element contribute to the formation of the compound. As already described above, the subscript 2 in the molecule H. 2Or indicates that there are two hydrogen atoms.
Step 8. Learn how atoms react to each other
Part of the nomenclature used in chemistry provides specific rules for naming compounds, which are also based on how the reagents interact with each other.
- One of these reactions is redox. It is a reaction in which electrons are acquired or lost.
- A trick to remember the mechanism that occurs in a redox reaction is to use the acronym OPeRa: "Ox Perde Red Buy" to remember that during oxidation electrons are lost and during reduction electrons are acquired.
Step 9. Remember that subscript numbers can indicate the formula for a compound with stable charge
Scientists use them to define the final molecular formula of a stable, neutral-charged compound.
- To arrive at a stable electronic configuration, the positive ion (cation) must be balanced by a negative ion (anion) of equal intensity. The charges are identified with the apexes.
- For example, the magnesium ion has a positive charge of +2 and the nitrogen ion has a negative charge of -3. The numbers +2 and -3 will be indicated as quotes. To properly combine the two elements and arrive at a neutral molecule, 3 magnesium atoms must be used for every 2 nitrogen atoms.
- The nomenclature that identifies the use of these subscripts is: Mg3No.2.
Step 10. Recognize anions and cations by their position on the periodic table
The elements belonging to the first group are considered alkali metals and have a +1 positive charge; sodium (Na +) and lithium (Li +) are examples.
- Alkaline earth metals are found in the second group and form 2+ charged cations, such as magnesium (Mg2 +) and barium (Ba2 +).
- The elements of the seventh column are called halogens and form negatively charged anions -1 such as chlorine (Cl-) and iodine (I-).
Step 11. Learn to recognize the most common cations and anions
In order to successfully pass the chemistry course, you need to familiarize yourself as much as possible with the nomenclature related to the groups of elements for which the superscript values do not change.
In other words, magnesium is always represented as Mg and always has a +2 positive charge
Step 12. Try not to get overwhelmed by the topic
It is not easy to understand and remember all the detailed information about the different chemical reactions, the sharing of electrons, the change in charge of an element or compound and how the reactions develop.
Break down the toughest topics in descriptive terms. For example, learn to express what you do not understand in redox reactions or what you are not clear about how elements with negative and positive charges combine. If you can express your difficulties for some concepts, you will understand that you have learned more than you think
Step 13. Make regular appointments with your teacher or assistant
Make a list of the topics you can't solve and ask for help. This way you have a chance to assimilate the difficult concepts before the lessons touch on more complex areas of chemistry that might just confuse you even more.
Step 14. Think of chemistry as the process of learning a foreign language
Formulas written to indicate the charges, the number of atoms in a molecule, and the bonds that form between molecules are all part of the language of chemistry. It is a way to represent graphically and in writing what happens in a chemical reaction that we cannot see.
- It would all be much easier if we could see with our eyes what is happening; however, chemistry foresees the need to understand the terminology used to describe phenomena, as well as to understand the mechanisms of reactions.
- If you find that this is a really difficult subject for you, know that you are not alone, but do not be disheartened by this awareness. Talk to your teacher, study in a group, talk to your teacher's assistant, or ask for help from someone who knows chemistry very well. You can learn all the subject, but you have to ask for it to be explained to you in such a way that you can understand it.
Advice
- Get enough rest and give yourself some free time. Distracting yourself from the chemistry will help you be cooler by the time you return to the studio.
- Get a good night's sleep before an exam. Memory and problem-solving skills are best when you are well rested.
- Review the topics you have assimilated. The various concepts of chemistry are interrelated and you need to know the basics well before moving on to the next topics. However, you must continually "refresh" your memory if you don't want to be surprised by a question during the exam.
- Go to class well prepared. Study the topics and perform the assigned tasks and exercises. You will fall further and further behind if you do not understand what is explained in class and the teacher will proceed with increasingly complex topics.
- Prioritize your time. Spend more hours studying chemistry if it's really tough for you, but don't get overwhelmed. There are other subjects you need to pay attention to.
