Name: acids, bases, and ph in titration
Uploaded: 2020-03-26T07:22:25.000Z
Duration: 6 min 35 s
Channel: JoVE

K12 Standards

Minnesota Academic Standards in Science

9-12

Chemistry

1.2.1 9L.4.2.2.1

Acid and Base Concentrations

Arrhenius acid는 물에 용해될 때 수소 이온을 생성하는 물질이고 염기는 수산화물 이온을 생성하는 물질입니다. 수소 이온은 즉시 물과 반응하여 히드로늄 이온을 형성하지만 단순화를 위해 계속 수소 이온으로 생각할 것입니다. 용액에 있는 수소 이온 또는 수산화물 이온의 양에 따라 산성 또는 염기성으로 간주됩니다.
우리는 수소 이온 농도의 음의 로그로 계산되는 pH를 사용하여 산도 또는 염기성의 양을 측정합니다. 따라서 7 미만의 pH 값은 산성이고 7 이상의 pH 값은 염기성입니다. pH 7은 중성입니다.
산과 염기는 또한 pH와 다른 강도에 따라 비교됩니다. 산의 강도는 수소 이온이 켤레 염기라고 하는 음이온에서 얼마나 쉽게 해리되는지와 관련이 있습니다. 수산화물 이온(hydroxide ion)과 그 공액산(conjugate acid)과 관련하여 염기에 대해서도 동일한 아이디어가 이어집니다. 산 해리 상수 또는 Ka를 사용하여 해당 강도에 값을 할당할 수 있습니다.
Ka는 비해리산(non-dissociated acid)과 해리된 수소 이온 및 접합체 염기의 농도를 사용하여 정의된다. 이 관계는 종종 Ka의 음수 로그인 pKa로 표시되는 것을 볼 수 있습니다. pKa가 작을수록 산이 더 강해집니다.
염산과 같은 일부 산은 단양성자인데, 이는 수소 이온을 하나만 해리할 수 있음을 의미합니다. 인산과 같은 폴리프로트산은 여러 수소 이온을 해리할 수 있습니다. 각 해리에는 고유한 pKa가 있습니다.
그렇다면 pKa를 어떻게 결정할 수 있을까요? 한 가지 방법은 산-염기 적정을 수행하는 것입니다. 적정은 농도를 알 수 없는 용액에 농도가 알려진 용액을 천천히 첨가하면서 이들 사이의 반응을 관찰하여 수행됩니다. 이 경우, 산은 중화 반응에서 염기와 반응하여 소금과 물을 형성합니다.
따라서 산에서 수소 이온의 농도를 측정하려면 산이 중화될 때까지 알려진 수산화물 이온 농도를 가진 강한 염기로 간단히 적정할 수 있습니다. 적정을 정확하게 수행하려면 염기를 표준화해야 하며, 이는 정확한 수산화물 이온 농도를 알고 있어야 함을 의미합니다. 이것이 항상 간단한 것은 아닙니다.
예를 들어, 실험에 사용할 NaOH는 흡습성이 매우 높아 대기에서 물을 흡수합니다. 이것은 NaOH에 고체와 용액 모두에서 발생합니다. 따라서 NaOH 용액의 실제 농도는 예상보다 낮을 수 있습니다.
NaOH의 정확한 농도를 측정하려면 먼저 산-염기 적정을 수행해야 합니다. 이렇게하려면 염기를 사용하여 알려진 농도의 산을 적정해야합니다. 칼륨 수소 프탈레이트(KHP)는 비흡습성산이므로 질량에서 농도를 정확하게 계산할 수 있습니다.
적정이 완료되었을 때(산이 중화되었음을 의미함) 페놀프탈레인(phenolphthalein)과 같은 pH 지시약을 사용하여 확인할 수 있습니다. Phenolphthalein은 약 pH 0에서 pH 8 사이에서 중성이며 무색입니다.
pH가 증가함에 따라 두 개의 수소 이온이 해리됩니다. 이 음이온 형태는 분홍색입니다. 따라서 적정을 시작할 때 KHP 용액은 산성이고 페놀프탈레인은 무색입니다. NaOH를 첨가하고 수소 이온이 중화되면 pH가 증가합니다.
이 반응에서, 용액은 동일한 양의 산과 염기가 함께 혼합되었을 때 중성입니다. 그 후 NaOH를 조금 더 첨가하면 pH가 염기되고 용액이 분홍색으로 변합니다. 이를 엔드포인트라고 합니다. KHP의 몰과 이를 중화하는 데 사용되는 NaOH의 부피를 알고 있다면 염기의 정확한 농도를 계산할 수 있습니다.
표준화된 염기가 확보되면 pH를 모니터링하면서 표준화된 염기로 알려진 농도의 산을 적정하여 산의 pKa를 측정할 수 있습니다. 첨가된 염기의 부피 대비 pH의 플롯을 적정 곡선이라고 합니다. 곡선은 일반적으로 S 또는 시그모이드 모양을 따르며, 곡선의 가장 가파른 부분의 변곡점은 등가 점을 나타냅니다.
여기서 수산화물 이온과 해리된 수소 이온의 몰은 동일합니다. pKa와 마찬가지로 해리된 수소 이온 각각에 대해 하나의 당량점을 볼 수 있습니다. 따라서 monoprotic acid는 당량점이 하나뿐이고 triprotic acid는 3 개입니다.
적정을 수행할 때 pH 지시약이 무색에서 분홍색으로 간신히 변할 때 당량점을 통과했음을 알 수 있습니다. 이를 적정 종말점이라고 합니다. 염기를 표준화할 때와 마찬가지로, 이것은 용액에 약간의 수산화물 이온이 과량하여 약간 염기성인 경우입니다.
그래프의 또 다른 변곡점은 당량점의 중간에서 발생합니다. 여기서, 해리된 산과 해리되지 않은 산의 농도는 동일합니다. 따라서 이 지점의 pH는 pKa와 같습니다. 따라서 적정을 수행하고 당량점 부피를 측정하면 pKa를 이 부피의 절반에서 pH로 계산할 수 있습니다.
이 실험실에서는 먼저 염기를 표준화한 다음 표준화된 염기를 사용하여 적정을 수행하여 폴리프로트산의 2pKa를 측정합니다.

산 및 염기 농도

<h4>산과 염기</h4>
Arrhenius 산은 물에 용해될 때 수소 이온을 생성합니다.
HA + H2O → H+(aq) + A-(aq)
여기서 HA는 비해리산, H+는 수소 양이온, A-는 접합 염기라고 하는 용매 음이온입니다. Arrhenius 염기는 물에 용해될 때 수산화물 이온을 생성합니다.
BOH + H2O → B+(aq) + OH-(aq)
여기서 BOH는 해리되지 않은 염기, OH-는 수산화물 이온, B+는 공액산이라고 하는 용매 양이온입니다. 켤레 염기는 산이 수소 이온을 잃고 수소를 얻을 수 있는 잠재력을 가질 때 형성됩니다. 켤레 산(conjugate acid)도 마찬가지인데, 이는 염기가 수산기를 잃고 이를 회복할 가능성이 있을 때 형성됩니다. 모든 산에는 켤레 염기가 있고 모든 염기에는 켤레 산이 있습니다.
<h4>산도</h4>
pH는 용액의 산도 정도이며 용액 내 수소 이온의 양을 측정한 것입니다. pH 척도는 대수이며 0에서 14까지입니다. pH가 7 미만인 수용액은 산성으로 설명되고 pH가 7 이상인 수용액은 알칼리성 또는 염기성으로 설명됩니다. pH 7의 용액은 중성으로 간주됩니다.
용액의 pH는 용액 내 수소 이온 농도의 음의 로그 염기 10과 같습니다.
<img src="/CDNSource/lm/labs/44/44_Concepts_3.jpg">
물은 수소 이온과 강하게 상호 작용하는데, 이는 수소 이온의 강한 양전하가 주변 물 분자의 음극을 끌어당기기 때문입니다. 사실, 그들은 매우 강하게 상호 작용하여 공유 결합과 히드로늄이라고 하는 H3O+ 양이온을 형성합니다. 위의 방정식은 이를 반영하기 위해 다시 작성되었습니다.
<img src="/CDNSource/lm/labs/44/44_Concepts_4.jpg">
단순화를 위해 pH를 논의할 때 히드로늄 이온 대신 수소 이온의 농도를 언급하겠습니다. 용액의 pH 값이 낮을수록 더 많은 수소 이온이 존재하고 더 나아가 용액의 산성도가 높아집니다. 예를 들어, 황산 1mM의 pH는 2.75인 반면 염산 1mM의 pH는 3.01입니다. 황산 용액 내 수소 이온의 농도는 1 × 10-2.75로 계산되는 반면, 염산 용액 내 수소 이온의 농도는 1 × 10-3.01이다. 따라서 황산에는 더 많은 수소 이온이 존재하며 더 산성입니다. 두 용액의 pH가 pH 값의 절반 정도만 변할 수 있지만 pH 척도의 로그 특성으로 인해 수소의 양이 크게 변한다는 점을 기억하십시오.
<h4>산과 염기의 강도</h4>
산의 강도는 공액 염기의 전기 음성도와 산성 수소의 극성에 영향을 받습니다. 따라서 강도는 수소 양이온(H+)이 음이온에서 얼마나 쉽게 분리되는지를 나타냅니다. 강산과 염기는 수용액에서 완전히 해리되는 반면, 약산과 염기는 접합 이온으로 부분적으로만 해리됩니다.
해리 상수 Ka는 산의 강도를 나타냅니다. Ka는 비해리산 HA의 농도, 수소 양이온 및 공액 염기의 농도 A-를 사용하여 계산됩니다. Ka 값이 높을수록 더 강한 산을 나타내고 Ka 값이 작을수록 더 약한 산을 나타냅니다.
<img src="/CDNSource/lm/labs/44/44_Concepts_5.jpg">
Ka 는 수치적으로 매우 작으며 Ka 의 음의 로그 밑 10 인 pKa 형태로 보고되는 경우가 많습니다. pKa 값이 낮으면 산이 더 강하고 pKa 값이 높으면 산이 약합니다.
<img src="/CDNSource/lm/labs/44/44_Concepts_6.jpg">
일부 산은 하나의 수소 이온만 해리하므로 1pKa 값을 갖습니다. 이러한 산을 단양성자라고 합니다. 그러나 일부 산은 하나 이상의 수소 이온을 해리할 수 있으며 이를 다양성자라고 합니다. 이러한 산은 각 수소 이온 해리에 대한 pK 값을 갖습니다.
pKa는 Henderson-Hasselbalch 방정식에 표시된 것처럼 산-염기 반응의 평형 pH를 계산하는 데에도 사용할 수 있습니다.
<img src="/CDNSource/lm/labs/44/44_Concepts_7.jpg">
Henderson-Hasselbalch 방정식은 공액 염기와 약산의 농도가 알려진 경우 pH를 계산하거나 pH와 농도가 알려진 경우 pKa를 계산하는 데 사용됩니다.
<h4>적정</h4>
산-염기 반응은 적정을 사용하여 정량적으로 연구됩니다. 적정 실험에서는 표준 용액이라고 하는 알려진 농도의 용액을 사용하여 다른 용액의 농도를 측정합니다. 산-염기 적정을 위해 표준화된 염기 용액을 농도를 알 수 없는 산에 천천히 첨가합니다(또는 산이 염기에 첨가됨). 산-염기 반응은 소금과 물을 형성하는 중화 반응입니다. 산에 있는 수소 이온의 몰이 염기에서 첨가된 하이드록실 이온의 몰과 같을 때 용액은 중성 pH에 도달합니다.
산-염기 적정을 수행하기 위해 뷰렛을 사용하여 미지의 산의 교반 플라스크에 표준화된 염기를 천천히 첨가하여 부피를 측정하고 염기를 적가할 수 있습니다. 용액의 pH는 산에 첨가된 pH 지시약을 사용하여 적정 전반에 걸쳐 면밀히 모니터링됩니다. 일반적으로 페놀프탈레인은 용액이 염기성이 될 때까지 무색으로 유지되어 연한 분홍색으로 변하기 때문에 사용됩니다.
적정이 당량점(수소 이온의 몰이 추가된 수산기 이온의 몰과 같을 때)에 가까워짐에 따라 pH 지시약은 과도한 수산기 이온으로 인해 일시적으로 색상을 변경합니다. 플라스크가 소용돌이치면 pH 지시약의 산성 색상이 돌아옵니다. 적정이 완료되었으며 소량의 하이드록실 이온이 지표자를 영구적으로 기본 색상으로 변경할 때 종말점에 도달했습니다.
적정 곡선은 용액의 pH 대 첨가된 표준화된 염기의 부피를 비교한 그래프입니다. 당량점은 곡선의 변곡점에 위치하며 적정 곡선의 2차 도함수로 계산됩니다.
산이 다양성자인 경우 각 수소 이온 해리에 대해 하나씩 여러 개의 당량 점을 갖습니다. 단프로트산의 경우 당량점의 중간 지점 또는 폴리프로트산의 경우 당량점 사이의 pH는 산의 pKa와 같습니다.
<h4>참조</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2012). 화학 및 화학 반응성. 캘리포니아 벨몬트 : Brooks / Cole, Cengage Learning.</li>
	<li style="font-size:17px">Silberberg, M.S. (2009). 화학: 물질과 변화의 분자적 성질. 매사추세츠주 보스턴: McGraw-Hill.</li>
	<li style="font-size:17px">Harris, D.C. (2015). 정량적 화학 분석. 뉴욕, 뉴욕 : WH 프리먼 앤 컴퍼니.</li>
</ol>

산과 염기
Arrhenius 산은 물에 용해될 때 수소 이온을 생성합니다.
HA + H2O → H+(aq) + A-(aq)
여기서 HA는 해리되지 않은 ...

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화학

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 and is logarithmic, so small changes in pH can mean large changes in hydrogen ion concentration. Solutions below pH 7 are acidic, solutions above pH 7 are basic or alkaline, and solutions at pH 7 are neutral. Water strongly attracts hydrogen ions and forms hydronium, H3O+, but pH is often discussed using hydrogen ion concentration for simplicity.

Lower pH means more hydrogen ions and greater acidity. For example, 1 mM sulfuric acid has a pH of 2.75, while 1 mM hydrochloric acid has a pH of 3.01. Because the pH scale is logarithmic, even a difference of about half a pH unit can reflect a large difference in hydrogen ion amount. In this example, sulfuric acid is more acidic because it contains more hydrogen ions.

Acid and base strength describes how readily hydrogen ions separate from the anion. Strong acids and bases dissociate completely in water, while weak acids and bases dissociate only partly into their conjugate ions. Acid strength is measured with the dissociation constant, Ka, which uses the concentrations of the non-dissociated acid HA, hydrogen cations, and conjugate base A-. Larger Ka values indicate stronger acids, and smaller values indicate weaker acids. Ka is often written as pKa, the negative base-10 log of Ka, so lower pKa means a stronger acid and higher pKa means a weaker acid.

Some acids release only one hydrogen ion, so they have one pKa and are called monoprotic. Others release more than one hydrogen ion and are polyprotic, with a pKa value for each step. The Henderson-Hasselbalch equation uses pKa to find the equilibrium pH of an acid-base reaction when the weak acid and conjugate base concentrations are known, or to find pKa when pH and concentrations are known.

Acid-base reactions can also be studied by titration. In a titration, a standard solution with a known concentration is used to find the concentration of another solution. For acid-base titrations, a standardized base is added slowly to an unknown acid, or the acid is added to the base. The reaction is a neutralization reaction that produces salt and water. When the moles of hydrogen ions match the moles of hydroxyl ions added, the solution reaches neutral pH.

During the experiment, the standardized base is added drop by drop from a burette to a stirring flask of acid. The pH is monitored with an indicator such as phenolphthalein, which stays colorless until the solution turns basic and becomes light pink. Near the equivalence point, the indicator may change color because of a temporary excess of hydroxyl ions, but swirling can return its acidic color. The endpoint is reached when a tiny extra amount of hydroxyl ions makes the basic color stay permanent.

A titration curve plots pH against the volume of standardized base added. The equivalence point appears at the inflection point of the curve and is found from the second derivative. Polyprotic acids have multiple equivalence points, one for each hydrogen ion dissociation. For monoprotic acids, the pH halfway to the equivalence point, or between equivalence points for polyprotic acids, is equal to the pKa.

Acids, Bases, and pH in Titration

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 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...

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 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

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Learn how acids, bases, pH, Ka, and pKa connect to titration, neutralization, and titration curves in high school chemistry.

Acids, Bases, and pH in Titration | JoVE K12

new-york-state-science-learning-standards

New York State Science Learning Standards

High School

Physical Science

HS. Chemical Reactions

HS-PS1-11.

Georgia Standards of Excellence

SC3.

Indicators of Chemical Reactions

SC6.

Neutralization Reactions

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Types of Chemical Bonds

Chemical bonding theories were pioneered by American chemist Gilbert&#xA0;N. Lewis. He developed a model called the Lewis model to explain the type and ...

Matter and Its Interactions: Plan and conduct an investigation of acid-base reactions to test ideas about the concentrations of the hydronium ion in an aqueous solution (pH). (P:3, CC: 3, CI: PS1)

9C.1.2.1.2

Covalent Bonding and Lewis Structures

Compared to ionic bonds, which results from the transfer of electrons between metallic and nonmetallic atoms, covalent bonds result from the mutual ...

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

Acids and Bases
An Arrhenius acid produces hydrogen ions when it is dissolved in water:
HA + H2O &#8594; H+(aq) + A-(aq)
Here, HA is the non-dissociated ...

Strong Acid and Base Solutions

A strong acid is a compound that dissociates completely in an aqueous solution and produces a concentration of hydronium ions equal to the initial ...

Polyprotic Acids

Acids are classified by the number of protons per molecule that they can give up in a reaction. Acids such as HCl, HNO3, and HCN that contain one ...

Water: A Bronsted-Lowry Acid and Base

The reaction between a Br&#248;nsted-Lowry acid and water is called acid ionization. For example, when hydrogen fluoride dissolves in water and ionizes, ...

Weak Base Solutions

Some compounds produce hydroxide ions when dissolved by chemically reacting with water molecules. In all cases, these compounds react only partially and ...

Weak Acid Solutions

Few compounds act as strong acids. A far greater number of compounds behave as weak acids and only partially react with water, leaving a large majority of ...

The potential of hydrogen (pH) is a measure of the acidity or basicity of a water-based solution determined by the concentration of hydronium ions (H3O+). ...

water-quality-analysis-via-indicator-organisms

Water Quality Analysis via Indicator Organisms

Source: Laboratories of Dr. Ian Pepper and Dr. Charles Gerba -The University of Arizona
Demonstrating Author: Luisa Ikner
Water quality analysis monitors ...

Matter and Its Interactions: Obtain and communicate information about how Minnesota American Indian Tribes and communities and other cultures construct solutions to mitigate threats to biodiversity.* (P: 8, CC: 7, CI: LS2, ETS1)

1 Exploring phenomena or engineering problems
 1.2 Planning and carrying out investigations
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Acids, Bases, and pH in Titration

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