Name: oxidation states in redox reactions
Uploaded: 2020-03-26T07:22:24.000Z
Duration: 4 min 56 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry

CHEM.9

CHEM.9.B

Redox Reactions

חמצון-חיזור, שהוא קיצור של חיזור-חמצון, הוא סוג של תגובה כימית המסווגת על ידי העברה נטו של אלקטרונים. בתגובה זו, מולקולה אחת מאבדת אלקטרונים, הנקראים חמצון, והמולקולה השנייה מקבלת אלקטרונים, הנקראים חיזור.
כדי לעזור לכם להבדיל בין השניים, זכרו את הביטוי 'OIL-RIG', ראשי תיבות של 'חמצון הוא הפסד, הפחתה היא רווח'. המולקולה המחומצנת נקראת חומר מחזר מכיוון שהיא מפחיתה את המגיב השני. באופן דומה, המולקולה המופחתת נקראת הגורם המחמצן מכיוון שהיא מחמצנת את המולקולה השנייה.
עכשיו שיש לנו את המינוח מסודר, בואו נסתכל על דוגמה של תגובת חמצון-חיזור, היווצרות של תחמוצת מגנזיום מינרלית. במהלך התגובה, כל אטום מגנזיום מאבד שני אלקטרונים. לכן, מגנזיום מחומצן. כל אטום חמצן צובר שני אלקטרונים; לכן, חמצן מופחת.
עם זאת, לא כל התגובות הן תגובות חמצון-חיזור. לדוגמה, התגובה של תחמוצת סידן עם פחמן דו חמצני ליצירת סידן פחמתי אינה תגובת חמצון-חיזור. אם כן, כיצד נוכל לזהות תגובת חיזור?
כדי לעשות זאת, אנו עוקבים אחר מספר החמצון של כל יסוד כשהוא עובר ממגיב למוצר. מספר החמצון הוא המטען ההיפותטי שהיה לאטום אם הקשרים שלו ליסודות שונים היו יוניים, כלומר האלקטרונים מוקצים לאטום האלקטרושלילי יותר. סכום מספרי החמצון במולקולה שווה למטען הכולל שלה.
בואו נסתכל אחורה על תחמוצת מגנזיום. זוהי תרכובת נייטרלית, ולכן סכום מספרי החמצון עבור מגנזיום וחמצן שווה לאפס. מגנזיום יכול לתת שני אלקטרונים, ולכן מספר החמצון שלו הוא פלוס שניים. חמצן יכול לקבל שני אלקטרונים, ולכן מספר החמצון שלו הוא מינוס שניים.
מה דעתך על התגובה? לתרכובות יסוד נייטרליות טהורות יש מספר חמצון של אפס. לכן, גם מגנזיום וגם חמצן מתחילים עם מספרי חמצון של אפס. גם מספרי החמצון של מגנזיום וגם של חמצן השתנו במהלך התגובה, כך שזוהי תגובת חמצון-חיזור.
עכשיו, בואו נסתכל על תגובת הסידן הפחמתי שראינו קודם. שני המגיבים ניטרליים, ולכן סכום מספרי החמצון עבור שתי התרכובות הוא אפס. כפי שראינו עם תחמוצת מגנזיום, לסידן יש מספר חמצון של פלוס שתיים וחמצן מינוס שתיים. לאחר מכן, לפחמן במולקולת הפחמן הדו-חמצני יש מספר חמצון של פלוס ארבע וכל חמצן מינוס שניים.
מה לגבי המוצר? סידן הוא פלוס שניים ופחמן פלוס ארבע, בדיוק כמו במגיבים. כל חמצן הוא מינוס שתיים, בסך הכל מינוס שש, עם מספר חמצון נטו אפס. מכיוון שאף אחד ממספרי החמצון לא השתנה, לא מדובר בתגובת חיזור.
עכשיו בואו נציג את ארבעת הסוגים של תגובות חיזור. הראשונה היא תגובת תזוזה יחידה, שבה אטום אחד מחליף אטום אחר. אתם תראו את זה בתגובת תרמיט, שבה מתכת אחת מופחתת, והמתכת השנייה מחומצנת.
הסוג הבא הוא תגובת בעירה, המתרחשת בין דלק למחמצן ליצירת מוצרים מחומצנים וחום. רואים את זה במעבדה במהלך בעירה של מתאן עם חמצן בעת שימוש במבער בונזן.
השלישית היא תגובת סינתזה, שבה שני מגיבים משתלבים ליצירת תוצר אחד, כמו בסינתזה של אמוניה, שבה חנקן משולב עם מימן ליצירת אמוניה.
לבסוף, הסוג הרביעי הוא תגובת פירוק, שבה מגיב סופג מספיק אנרגיה כדי לשבור את קשריו וליצור תרכובות קטנות יותר. זה מה שקורה עם זיקוקים, שבו אשלגן כלורט מתפרק אשלגן כלורי וחמצן לאחר חימום.
במעבדה זו תבצעו ותזהו סוגים שונים של תגובות חמצון-חיזור שהופכות נחושת מוצקה לתחמוצת נחושת, ואז שוב לנחושת מוצקה.

תגובות חיזור

<h4>חמצון וחיזור</h4>
תגובות כימיות מסוימות יכולות להיות מסווגות כתגובות חיזור-חמצון, או תגובות חמצון-חיזור. חמצון הוא תהליך של חומר, כמו אטום או מולקולה יונית, המאבד אלקטרון אחד או יותר, וחיזור הוא התהליך שבו החומר צובר אלקטרונים אחד או יותר.
<h4>מצבי חמצון</h4>
לכל אטום במולקולה יש מצב חמצון או מספר חמצון משלו. מצב החמצון מתאר עד כמה מולקולה מחומצנת ביחס לצורתה היסודית החופשית. מצב החמצון מבוטא כמטען שהיה לאטום אם כל אחד מהקשרים שלו ליסודות אחרים היה יוני בלבד. משמעות הדבר היא שהאלקטרונים בקשר מוקצים לאטום האלקטרושלילי יותר. מצב החמצון של אטום בצורתו היסודית החופשית מוגדר כ-0.
ישנם מספר כללים שעוקבים אחריהם כדי לקבוע את מצב החמצון. ליסודות בקבוצה I ובקבוצה II יש בדרך כלל מצבי חמצון של +1 ו- +2, בהתאמה. למימן ולחמצן יש בדרך כלל מצבי חמצון של +1 ו-2, בהתאמה, ולהלוגנים יש בדרך כלל מצב חמצון של -1. בנוסף, מצבי החמצון של האטומים במולקולה תמיד מסתכמים במטען על המולקולה. לפיכך, לעתים קרובות ניתן להסיק את מצב החמצון של אטום שאינו מפורט לעיל. לדוגמה, חשבו על פחמן דו-חמצני (CO2), שהוא מולקולה ניטרלית. אם כל אחת משתי מולקולות החמצן תורמת -2, מצב החמצון של פחמן חייב להיות +4 כדי לבטל את ה-4- מהחמצן.
לגישה כללית יותר, ציירו את מבנה לואיס של המולקולה, זהו את הקשרים בין אטומים שונים, והקצו כל קשר לאטום האלקטרושלילי יותר. לאחר מכן, ספרו את מספר האלקטרונים על כל אטום, כאשר כל קשר תורם שני אלקטרונים. הפחת את מספר האלקטרונים הנמצאים כעת על האטום מהמספר הסטנדרטי של אלקטרונים ערכיים עבור אותו אטום כדי לקבל את מספר החמצון.
חשבו שוב על פחמן דו-חמצני. לכל חמצן יש שני זוגות אלקטרונים בודדים והוא מחובר לפחמן המרכזי על ידי קשר כפול. חמצן הוא יותר אלקטרושלילי מאשר פחמן, ולכן כל קשר C=O, המהווה ארבעה אלקטרונים, מוקצה לחמצן שלו. לפיכך, לכל חמצן מוקצים בסך הכל שמונה אלקטרונים (ארבעה מהזוגות הבודדים וארבעה מהקשר הכפול), ולפחמן לא מוקצה אף אחד. מספר ברירת המחדל של אלקטרונים ערכיים לחמצן הוא שישה, ולכן מספר החמצון עבור כל חמצן הוא 6 – 8 = -2. מספר ברירת המחדל של אלקטרונים ערכיים לפחמן הוא ארבעה, ולכן מספר החמצון של פחמן הוא 4 – 0 = +4.
<h4>תגובות חיזור</h4>
לא כל התגובות הכימיות מסווגות כתגובת חיזור. תגובת חמצון-חיזור היא כל תגובה שבה יש שינוי במצב החמצון של האטום. לכן, כדי לבדוק אם תגובה היא תגובת חמצון-חיזור, לקבוע את מצבי החמצון של כל אטום במגיבים ובתוצרים ולחפש שינויים.
תגובות חמצון-חיזור רבות כרוכות בהעברה של אלקטרונים ישירות ממולקולה או אטום אחד למשנהו. בתגובות אלה, אם מולקולה, או אטום, מרוויחים אלקטרון, מולקולה אחרת או אטום, חייבים לאבד אלקטרון. דרך פשוטה אחת לזכור את ההגדרות של חמצון וחיזור היא באמצעות הביטוי OIL-RIG, שמשמעותו: Oxidation Is Losing – Reduction Is Gaining.
המולקולה שצוברת אלקטרון מצטמצמת, אבל היא נקראת מחמצן או גורם מחמצן כי היא מחמצנת את המולקולה השנייה. באופן דומה, המולקולה שמאבדת אלקטרון עוברת חמצון, אבל היא נקראת רדוקציה או חומר מחזר מכיוון שהיא מפחיתה את המולקולה השנייה.
ישנם ארבעה סוגי תגובה עיקריים הכוללים בדרך כלל תהליכי חמצון-חיזור.
<ol>
	<li style="font-size:17px">תגובת תזוזה יחידה: אטום מחליף אטום אחר שהוא חלק מתרכובת, ומחליף אותו.</li>
	<li style="font-size:17px">תגובת בעירה: תרכובת מופחתת על ידי מחמצן חזק, בדרך כלל גז חמצן. תגובות בעירה המתרחשות בין פחמימנים ותרכובות אורגניות מייצרות בדרך כלל פחמן דו חמצני ומים.</li>
	<li style="font-size:17px">תגובת סינתזה: שני מגיבים יוצרים מוצר אחד.</li>
	<li style="font-size:17px">תגובת פירוק: מגיב יחיד נשבר לשני מוצרים או יותר.</li>
</ol>
<h4>הפניות</h4>
1. האריס, ד 'סי (2015). אנליזה כימית כמותית. ניו יורק, ניו יורק: W. H. Freeman and Company.

חמצון וחיזור
תגובות כימיות מסוימות יכולות להיות מסווגות כתגובות חיזור-חמצון, או תגובות חמצון-חיזור. חמצון הוא תהליך של ...

Education

JoVE Lab Manual

כימיה

oxidation states in redox reactions

Oxidation states help identify redox reactions. In a redox reaction, oxidation is the loss of one or more electrons, and reduction is the gain of one or more electrons. These reactions are often tracked by changes in oxidation state, also called oxidation number.

Each atom in a molecule has an oxidation state. This number shows how oxidized an atom is compared with its free elemental form. It is written as the charge an atom would have if every bond were purely ionic. In that model, bonding electrons are assigned to the more electronegative atom. An atom in its elemental form has an oxidation state of 0.

Several rules help determine oxidation states. Group I elements usually have +1, and Group II elements usually have +2. Hydrogen is typically +1, oxygen is typically -2, and halogens usually are -1. The oxidation states in a molecule or ion must add up to the total charge, so unknown values can often be found from the rest.

Carbon dioxide is a clear example. CO2 is neutral, so its total oxidation states must add to zero. Each oxygen is usually -2, so carbon must be +4 to balance the two oxygens. Another way to find oxidation numbers is to draw the Lewis structure, assign each bond to the more electronegative atom, and count electrons on each atom.

In CO2, oxygen is more electronegative than carbon, so each C=O bond is assigned to oxygen. Each oxygen gets eight electrons total, including lone pairs and bonding electrons. Oxygen has six valence electrons by default, so its oxidation number is 6 - 8 = -2. Carbon has four valence electrons by default and is assigned none, so its oxidation number is 4 - 0 = +4.

A reaction is a redox reaction when an atom’s oxidation state changes from reactants to products. To check for redox, compare oxidation states on both sides of the reaction. Many redox reactions also involve direct electron transfer between atoms or molecules. If one species gains an electron, another must lose one.

The phrase OIL-RIG helps remember the process: oxidation is losing, and reduction is gaining. The species that gains electrons is reduced, but it is also called the oxidizing agent or oxidant because it oxidizes the other species. The species that loses electrons is oxidized, but it is also called the reducing agent or reductant because it reduces the other species.

Four major reaction types often involve redox processes. In single displacement reactions, one atom replaces another atom in a compound. In combustion reactions, a compound is reduced by a strong oxidant, usually oxygen gas, and hydrocarbons or other organic compounds often produce carbon dioxide and water. In synthesis reactions, two reactants form one product. In decomposition reactions, one reactant breaks into two or more products.

Oxidation States in Redox Reactions

lab techniques

Measuring with Accuracy in the Lab

Measuring with accuracy in the lab starts with careful records, the right tools, and correct reading of data. Scientists use lab notebooks to record how an experiment was done. These notes include the amounts of materials used and each step of the procedure. Without that record, an experiment cannot be repeated in the same way. Balances and glassware are used to measure solids and liquids for experiments. The precision of a measurement depends on the equipment used. Digital balances show the...

scientific measurement and lab skills

Graphs, Curve Fit, and Standard Deviation

Two-dimensional graphs help students compare an independent variable with a dependent variable in science data. In a chemistry example, temperature is the independent variable and volume is the dependent variable. After data are collected, the relationship between the two measurements must be quantified so it can be evaluated and compared with other relationships. A graph can also show when no relationship exists between the two variables. To make a two-dimensional graph, each data point needs...

stoichiometry, product yield, and limiting reactants

stoichiometry-product-yield-and-limiting-reactants

Balancing Equations and Reactant Limits

Chemical equations show how reactants change into products during a reaction. Stoichiometry is the study of the relative amounts of reactants and products. It is based on the Law of Conservation of Mass, which says matter is neither created nor destroyed. Because atoms are only rearranged, the number and identity of atoms must match on both sides of a reaction. That is why a chemical equation must be balanced. A balanced equation has the same number of atoms for each element in the reactants...

redox reactions

Oxidation states help identify redox reactions. In a redox reaction, oxidation is the loss of one or more electrons, and reduction is the gain of one or more electrons. These reactions are often tracked by changes in oxidation state, also called oxidation number. Each atom in a molecule has an oxidation state. This number shows how oxidized an atom is compared with its free elemental form. It is written as the charge an atom would have if every bond were purely ionic. In that model, bonding...

ideal gas law

Gas Laws Behind the Ideal Gas Equation

The ideal gas equation brings together the main gas laws used in chemistry. Gases have molecules that are far apart, so their behavior is described with four measurable variables: pressure, volume, number of moles, and temperature. The ideal gas law links these variables with the gas constant, R, which equals 8.314 J·K−1 mol−1. Boyle’s law describes the link between pressure and volume. When temperature and the number of moles stay constant, pressure and volume change in opposite directions.

acid and base concentrations

Acids, Bases, and pH in Titration

Acids, bases, and pH explain how acidic or basic a solution is. An Arrhenius acid releases hydrogen ions when it dissolves in water, while an Arrhenius base releases hydroxide ions. These reactions also create conjugate partners: an acid forms a conjugate base after losing hydrogen, and a base forms a conjugate acid after losing hydroxyl. Every acid has a conjugate base, and every base has a conjugate acid. pH measures the amount of hydrogen ions in a solution. The pH scale runs from 0 to 14...

buffers

Buffer pH and the Common Ion Effect

Buffer solutions help keep pH steady when acids or bases are added. In water, an Arrhenius acid (HA) dissociates into hydrogen ions, H+, and a conjugate base, A-. More hydrogen ions make a solution more acidic and lower its pH. An Arrhenius base (BOH) dissociates into a conjugate acid, B+, and hydroxide ions, OH-. Strong acids and strong bases usually change pH a lot because they react completely in water and raise the amount of H+ or OH-. Buffers reduce those pH changes. A buffer usually...

enthalpy of reaction

Reaction Heat, Hess’s Law, and Calorimetry

Reaction heat is explained through enthalpy, Hess’s law, and calorimetry. These ideas show how heat moves during chemical reactions and how scientists measure it. Thermodynamics is the study of heat energy and other forms of energy, such as work. Its laws are used across science, from biology to physics. The first law says energy is conserved in an isolated system. Energy can change form, such as thermal energy becoming work, but it cannot be created or destroyed. The second law of...

solubility

Solubility in Water and Other Solvents

Solubility describes how much of a solute can dissolve in a specific solvent. It is usually reported as solute mass per solvent volume or as solute mass per solvent mass. For example, sodium chloride has a solubility of 36 g per 100 mL of water at room temperature. If solubility is given by solvent mass, that mass must be converted to volume for later calculations. Temperature changes solubility. Sodium carbonate dissolves at about 7 g per 100 mL of water at 0 °C, 22 g per 100 mL at room...

metal flame emission

Flame Test Metal Color Clues

Flame testing uses a metal sample and a flame to identify a substance by its color. Each element gives off a characteristic light emission in the flame, so the color can help distinguish one element from another. This same idea appears in fireworks, where different metal components create different colors. The color comes from energy absorbed by the metallic component. When a species absorbs energy, that energy can go into translation, vibration, rotation, or electron excitement. Electron...

balmer series

Hydrogen Emission Lines

Hydrogen emission lines show how electrons move between fixed energy levels in the Bohr model. Niels Bohr proposed this model for the hydrogen atom in 1913. In this model, an electron can only occupy certain orbits, and it cannot exist between them. These energy states are labeled with the quantum number n. The ground state is n = 1. Higher values, such as n = 2, 3, 4, and so on, are excited states. An electron changes state only by absorbing or emitting energy equal to the difference between...

beer's law

Absorbance Spectra and Beer-Lambert Analysis

Absorbance spectra and the Beer-Lambert Law show how light can be used to study molecules in solution. When light hits a substance, it may be absorbed, transmitted, or reflected. A substance often interacts with a range of wavelengths, and each wavelength can affect the molecules or atoms in a different way. When a molecule absorbs light, that energy can be used for translation, vibration, rotation, or electron excitement. Electron excitement is especially important in spectroscopy because it...

concentration dependence

Reaction Order and Rate Constants

Chemical kinetics describes the speed of a chemical reaction. The rate depends on the reaction mechanism, the complexity of the reaction, and the number of reactants involved. Reactant concentration also affects how fast a reaction happens. The rate law is the experimental relationship that connects these factors to reaction rate. In the rate law, each reactant contributes through a reaction order. The general form is r = k[A]^m[B]^n for aA + bB + ... → cC. Here, r is the reaction rate, k is...

temperature dependence

Reaction Rate, Arrhenius, and Catalysts

Chemical kinetics explains how fast a reaction happens and why that speed changes. The reaction rate is the speed of a chemical reaction. It is defined as the change in concentration of a reactant or product over time. Reaction speed depends on several factors, including the concentration of the reactants and the temperature of the reaction. Each reactant affects the rate in a specific way. That relationship is described by the rate law. The rate law is an equation that connects the...

galvanic cells

Battery Power from Redox Reactions

Electrochemistry studies how chemical change and electrical energy are linked. In this branch of chemistry, electrons move from one species to another. That movement can either produce current or be driven by an applied current. The main reaction in electrochemistry is the oxidation-reduction, or redox, reaction. A redox reaction has two half-reactions. Oxidation is the loss of electrons, and reduction is the gain of electrons. These changes also shift the oxidation state of each substance. The...

electrolytic cells

Electroplating with Electrolytic Cells

Electrochemistry links electrical energy with chemical change, and electrolytic cells show how electricity can drive a nonspontaneous reaction. In these reactions, electrons move from one species to another. The key chemistry is a redox reaction, or oxidation-reduction reaction, which happens in two half-reactions. Oxidation is the loss of electrons, and reduction is the gain of electrons. The substance that loses electrons is the reducing agent, and the substance that gains electrons is the...

proper lab notebook keeping

Recording a Reproducible Lab Experiment

Accurate lab notebook records are essential in science and organic chemistry labs. Without clear notes, descriptions, quantities, and observations, an experiment cannot be repeated or checked. Good record keeping supports reproducibility, which means other people can follow the same work and get similar results. A laboratory notebook is useful in school labs, research settings, and industry. It can also become a legal record when an idea, process, substance, or technique is patented and...

basic organic chemistry techniques

Organic Lab Glassware and Safe Handling

Organic chemistry labs use specific glassware, careful weighing steps, and controlled heating to keep reactions safe and accurate. Beakers and Erlenmeyer flasks are often used for mixing or holding solvents, but they are not meant for measuring volume unless only an approximate amount is needed. Volumetric glassware is used when a precise volume matters. This group includes graduated cylinders, volumetric pipettes, and volumetric flasks. A graduated cylinder is commonly used in the organic lab...

melting points

How Impurities Change Melting Points

Melting point helps identify an organic compound by showing the temperature where a solid turns into a liquid at 1 atmosphere of pressure. It is a physical property, like solubility, density, color, and electronegativity. Because the exact start of melting is hard to measure, the result is reported as a range. The lower end is when the first drops of liquid appear. The upper end is when the last solid has melted. Scientists compare this range with literature values to help identify a compound. <br...

boiling points

Boiling Point and Vapor Pressure

Boiling point and vapor pressure are key physical properties of a liquid. For a pure compound, the boiling point can help identify the substance. In experiments, the boiling point is usually recorded as a range because exact values are hard to measure and may differ by a few degrees from the literature value. Vapor pressure explains why a liquid boils. In a sealed container, some molecules at the liquid surface gain enough energy to escape into the gas phase. At the same time, some gas...

recrystallization

Purifying Crystals by Solubility

Purifying crystals by solubility is a key organic chemistry technique. Recrystallization uses differences in solubility to separate a desired solid product from starting materials, solvent, and impurities. It is one of the three standard purification methods, along with distillation and extraction. Solubility is the maximum amount of a substance that can dissolve in a fixed volume of solvent at a given temperature. Different solutes dissolve in different solvents, and their behavior can vary...

extraction

Separating Mixtures with Solvent Extraction

Solvent extraction is a common way to separate and isolate a target compound in organic chemistry. In this process, a solute moves from one phase to another so it can be separated from unreacted starting materials or impurities. Extraction is also useful when a product is dissolved in a reaction solvent that is hard to remove by evaporation, such as a solvent with a high boiling point. There are three main types of extraction. In solid-liquid extraction, the solute moves from a solid phase...

simple distillation

Separating Liquids by Boiling Point

Separating liquids by boiling point is the goal of distillation. A miscible mixture contains liquids that mix evenly, and it can be heated so that the more volatile liquid evaporates first. Volatility is a liquid’s tendency to vaporize, and boiling begins when bubbles form in the liquid phase. In a closed container, liquid and vapor can reach equilibrium, which means the rate of vaporization equals the rate of condensation. The pressure from the vapor above the liquid is called vapor pressure.

steam distillation

Steam Distillation and Low-Boiling Separation

Steam distillation is a separation method for temperature-sensitive organic compounds. It works best when the organic compound is immiscible in water, meaning the two liquids do not mix. The method helps remove the organic molecule from a non-volatile contaminant without using the higher temperatures needed for many other separations. In steam distillation, the immiscible mixture is heated until both water and the volatile organic compound distill together. The vapor rises to a condenser,...

thin-layer chromatography

TLC Separation by Polarity

Thin-layer chromatography (TLC) separates compounds in a mixture by polarity. It uses the same basic parts as other chromatography methods: a stationary phase, a mobile phase, and the solute. In TLC, the stationary phase is a thin coating on a plate instead of material packed into a column. The stationary phase in most TLC systems is polar silica gel, a form of silicon dioxide. Its surface has OH groups that can form hydrogen bonds. The sample is first spotted on a pencil start line with a...

column chromatography

Separating Mixtures by Polarity

Column chromatography separates compounds in an organic chemistry lab by using differences in physical properties. It is especially useful for microscale separations when less than 10 grams of material is available for analysis. The method can separate a mixture based on solubility, polarity, hydrophobicity, size, and charge. Any chromatography system has three main parts: the stationary phase, the mobile phase, and the sample mixture. In column chromatography, the stationary phase is usually...

hydrolysis of an ester

Soap Formation from Triglycerides

Triglycerides are lipids made of a glycerol backbone linked to three fatty acids. They are common in vegetable oils and animal fats. Plant lipids are the basis of vegetable oils, while animal lipids are used as lard or general sources of fats. A fatty acid has a long carbon chain, usually between 12 and 20 carbons, with a weak organic acid at one end. Some fatty acids contain double bonds. These are unsaturated fats. The double bond usually gives the chain a bent, cis shape. As a result,...

synthesis of luminol

Luminol Chemiluminescence in Forensics

Luminol chemiluminescence shows how a chemical reaction can produce light and help with blood detection. Chemical reactions may be endothermic or exothermic, depending on whether they absorb or release heat as reactants become products. The enthalpy of a reaction is the energy difference between reactants and products, or ΔH. A positive ΔH means the reaction is endothermic. A negative ΔH means it is exothermic. Many reactions do not happen in a single step. They can pass through intermediates...

esterification

Ester Formation and Everyday Fragrances

Esters are organic compounds with a carbonyl group attached to an oxygen that connects to another alkyl or aryl group. Their general formula is RCOOR'. They are often made by reacting a carboxylic acid with an alcohol in an esterification reaction. In this process, the hydroxyl group of the acid is replaced by an alkyl or aryl group. Many simple esters have familiar fruit and flower smells because their structures are small and less complex. Formic acid and methanol can combine to form methyl...

identification of unknown aldehydes and ketones

identification-of-unknown-aldehydes-and-ketones

Carbonyl Tests for Aldehydes and Ketones

Aldehydes and ketones are carbonyl compounds, which means they contain a C=O functional group. A ketone has two alkyl or aryl groups attached to the carbonyl carbon. Acetone is the simplest ketone, with two methyl groups. An aldehyde is similar, but it has at least one hydrogen attached to the carbonyl carbon. Formaldehyde is the simplest aldehyde, and acetaldehyde has one hydrogen and one methyl group. The carbonyl carbon in both aldehydes and ketones is electrophilic because the oxygen atom...

uv-vis spectroscopy of dyes

How Dyes Absorb Visible Light

Dyes absorb visible light because their molecular structure lets them interact with specific wavelengths. When light hits a substance, some light is absorbed and the rest is reflected or transmitted. The color we see depends on the wavelength that is reflected. A blue substance reflects blue light, around 430 to 480 nm, and absorbs the complementary orange region, around 590 to 630 nm. Compounds that do not absorb in the visible range appear colorless to the human eye. Light also has energy and...

identifying alcohols

Alcohol Tests for Primary, Secondary, and Tertiary

Alcohol tests can help sort alcohols by structure and reactivity. Alcohols are organic molecules with a hydroxyl group attached to an alkyl or aryl group, written as ROH. If the carbon with the hydroxyl group has one R group, the alcohol is primary. If it has two R groups, it is secondary. If it has three R groups, it is tertiary. Alcohols can also be aromatic when they contain a benzene ring. Phenol is the simplest aromatic alcohol. To identify an alcohol, chemists can use its chemical...

chemistry

Comprehensive, curriculum-focused videos for both instructors and students in introductory chemistry lab courses.

https://cloudfront.jove.com/files/banners/scicat/labbio.jpg

Learn how oxidation states reveal redox reactions, how to assign oxidation numbers, and why oxidation, reduction, and agents matter in chemistry.

Oxidation States in Redox Reactions | JoVE K12

Florida Department of Education

Physical Science

SC.912.P.8

SC.912.P.8.10

Georgia Standards of Excellence

9-12

SC3.

Indicators of Chemical Reactions

התכוננו ללמד את תגובות חיזור עם מדריך מדריכים זה באורך 6 דקות. כולל שלבי הכנה מרכזיים עבור מעבדת כימיה ב-JoVE Lab Manual.

תגובות חיזור | הכנת מדריך, חומרים והכנת מעבדה | JoVE Lab Manual

עקבו אחר הנהלים של תגובות חיזור שלב אחר שלב בסרטון פרוטוקול סטודנטים זה באורך 15 דקות. חלק מאוסף כימיה ב-JoVE Lab Manual.

תגובות חיזור | פרוטוקול סטודנטים, הליך ותוצאות | JoVE Lab Manual

Balancing Redox Equations

Electrochemistry is the science involved in the interconversion of electrical and chemical reactions. Such reactions are called reduction-oxidation, or ...

ionic-compounds-formulas-and-nomenclature

Ionic Compounds: Formulas and Nomenclature

An element composed of atoms that readily lose electrons (a metal) can react with an element composed of atoms that readily gain electrons (a nonmetal) to ...

molecular-compounds-formulas-and-nomenclature

Molecular Compounds: Formulas and Nomenclature

Molecular compounds or covalent compounds result when atoms share electrons to form covalent bonds. Since there is no electron transfer, molecular ...

formula-mass-and-mole-concepts-of-compounds

Formula Mass and Mole Concepts of Compounds

Formula Mass of Covalent Compounds

Chemical formulas represent the elemental makeup of substances. For covalent compounds, the formula represents the ...

experimental-determination-of-chemical-formula

Experimental Determination of Chemical Formula

The elemental makeup of a compound defines its chemical identity, and chemical formulas are the most concise way of representing this elemental makeup. ...

Chemical Equations

Chemical equations represent the identities and relative quantities of substances involved in a chemical reaction. The substances undergoing reaction are ...

CHEM.9.A

Chemical Reactions in Aqueous Solutions

Chemical substances interact in many different ways. Certain chemical reactions exhibit common patterns of reactivity. Due to the vast number of chemical ...

Precipitation Reactions

In a precipitation reaction, aqueous solutions of soluble salts react to give an insoluble ionic compound &#x2013; the precipitate. The reaction occurs ...

Oxidation-Reduction Reactions

Oxidation&ndash;Reduction Reactions

Earth&rsquo;s atmosphere contains about 20% molecular oxygen, O2, a chemically reactive gas that plays an essential ...

Oxidation Numbers

In redox reactions, the transfer of electrons occurs between reacting species. Electron transfer is described by a hypothetical number called the ...

Oxidation and Reduction
Some chemical reactions can be classified as reduction-oxidation reactions, or redox reactions. Oxidation is the process of ...

Acids, Bases and Neutralization Reactions

An acid-base reaction is one in which a hydrogen ion, H+, is transferred from one chemical species to another. Such reactions are of central importance to ...

Reaction Stoichiometry

A balanced chemical equation provides a great deal of information in a very succinct format. Chemical formulas provide the identities of the reactants and ...

Limiting Reactant

The relative amounts of reactants and products represented in a balanced chemical equation are often referred to as stoichiometric amounts. However, in ...

Reaction Yield

The theoretical yield of a reaction is the amount of product estimated to form based on the stoichiometry of the balanced chemical equation. The ...

Stoichiometry, Product Yield, and Limiting Reactants

Chemical equations represent how a chemical reaction proceeds from reactants to products through physical or chemical change using chemical formulas.
...

CHEM.9.C

Science concepts. The student understands how matter is accounted for in chemical reactions. The student is expected to:

Oxidation States in Redox Reactions

Description

Transcript

More videos by Standards