MYRDA JUMIANA

Sabtu, 14 April 2012

ph larutan

a. Titration of NaOH by HClDiketahui: The concentration of NaOH = mLVHCl NNaOHVNaOH = 10 = 2 M NHCl mLMHCl = 0.1 = 0.1 NDitanya: MNaOH = ..... Answer: NHCl. VHCl = MNaOH. VNaOH

0.1. 2 = MNaOH. 100.2 = 10. MNaOH = 0.02 M b. Titration of HCl by NaOHDiketahui: The concentration of NaOH = NNaOHVNaOH = 2.85 mLMHCl mLVHCl = 10 = 0.1 M = 0.1 NHCl NDitanya:

MNaOH = ..... Answer: NHCl. VHCl = MNaOH. VNaOH0, 1. 10 = X. XX 2.851 = 2.85 = 0.35 MB. Pembahasan1. Making Solvent-making process NaOHPada NaOH solution, with distilled water into the fire to the point labutakar tera, and then shake until a homogeneous, makaterjadi reaction is characterized by a hot solution, the reaction occurs eksotermal, danketika diluted solution became clear. Chemical reactions occur: NaOH (s) + H2O HCl aqueous

2. Titration of NaOH with HCl as HCl titration of NaOH titranPada a visible color change when HCl ditetesimetil red. The use of methyl red indicator in the titration of weak bases and amoniumhidroksida because it has a pH from 4.2 to 6.2. Color changes to yellow, then turned into a pink solution of HCl and NaOH drops of methyl red. Dilution obtained for molarity of 0.02 M. Yangterjadi chemical reactions, yaituHCl H2O3 + NaCl + NaOH. HCL titration with NaOH as titranIndikator fenoftalein has a pH between 8 to 9.6 because fenoftalein including asamlemah in an ionized state. The color change that occurs is menjadikuning, then the color changes again after the solution of NaOH and HClditetesi fenoftalein buret and the color to pink. Yangdihasilkan molarity is 0.03 M. Reaction occurs, ie HCl + NaOH NaCl + H2OVI. KESIMPULANKesimpulan that can be drawn from this experiment are: 1. The process used to determine accurately the concentration of a larutandikenal as standardization.

2. Indicators used in titration

pH adalah derajat keasaman yang digunakan untuk menyatakan tingkat keasaman atau kebasaan yang dimiliki oleh suatu larutan. Ia didefinisikan sebagai kologaritma aktivitas ion hidrogen (H⁺) yang terlarut. Koefisien aktivitas ion hidrogen tidak dapat diukur secara eksperimental, sehingga nilainya didasarkan pada perhitungan teoritis. Skala pH bukanlah skala absolut. Ia bersifat relatif terhadap sekumpulan larutan standar yang pH-nya ditentukan berdasarkan persetujuan internasional.^[1]

Konsep pH pertama kali diperkenalkan oleh kimiawan Denmark Søren Peder Lauritz Sørensen pada tahun 1909. Tidaklah diketahui dengan pasti makna singkatan "p" pada "pH". Beberapa rujukan mengisyaratkan bahwa p berasal dari singkatan untuk powerp^[2] (pangkat), yang lainnya merujuk kata bahasa Jerman Potenz (yang juga berarti pangkat)^[3], dan ada pula yang merujuk pada kata potential. Jens Norby mempublikasikan sebuah karya ilmiah pada tahun 2000 yang berargumen bahwa p adalah sebuah tetapan yang berarti "logaritma negatif"^[4].

Air murni bersifat netral, dengan pH-nya pada suhu 25 °C ditetapkan sebagai 7,0. Larutan dengan pH kurang daripada tujuh disebut bersifat asam, dan larutan dengan pH lebih daripada tujuh dikatakan bersifat basa atau alkali. Pengukuran pH sangatlah penting dalam bidang yang terkait dengan kehidupan atau industri pengolahan kimia seperti kimia, biologi, kedokteran, pertanian, ilmu pangan, rekayasa (keteknikan), dan oseanografi. Tentu saja bidang-bidang sains dan teknologi lainnya juga memakai meskipun dalam frekuensi yang lebih rendah.

pH didefinisikan sebagai minus logaritma dari aktivitas ion hidrogen dalam larutan berpelarut air.^[5] pH merupakan kuantitas tak berdimensi.

dengan a_H adalah aktivitas ion hidrogen. Alasan penggunaan definisi ini adalah bahwa a_H dapat diukur secara eksperimental menggunakan elektrode ion selektif yang merespon terhadap aktivitas ion hidrogen ion. pH umumnya diukur menggunakan elektrode gelas yang mengukur perbedaan potensial E antara elektrode yang sensitif dengan aktivitas ion hidrogen dengan elektrode referensi. Perbedaan potensial pada elektrode gelas ini idealnya mengikuti persamaan Nernst:

dengan E adalah potensial terukur, E⁰ potensial elektrode standar, R tetapan gas, T temperatur dalam kelvin, F tetapan Faraday, dan n adalah jumlah elektron yang ditransfer. Potensial elektrode E berbanding lurus dengan logartima aktivitas ion hidrogen.

Definisi ini pada dasarnya tidak praktis karena aktivitas ion hidrogen merupakan hasil kali dari konsentrasi dengan koefisien aktivitas. Koefisien aktivitas ion hidrogen tunggal tidak dapat dihitung secara eksperimen. Untuk mengatasinya, elektrode dikalibrasi dengan larutan yang aktivitasnya diketahui.

Definisi operasional pH secara resmi didefinisikan oleh Standar Internasional ISO 31-8 sebagai berikut: ^[6] Untuk suatu larutan X, pertama-tama ukur gaya elektromotif E_X sel galvani

elektrode referensi | konsentrasi larutan KCl || larutan X | H₂ | Pt

dan kemudian ukur gaya elektromotif E_S sel galvani yang berbeda hanya pada penggantian larutan X yang pHnya tidak diketahui dengan larutan S yang pH-nya (standar) diketahui pH(S). pH larutan X oleh karenanya

Perbedaan antara pH larutan X dengan pH larutan standar bergantung hanya pada perbedaan dua potensial yang terukur. Sehingga, pH didapatkan dari pengukuran potensial dengan elektrode yang dikalibrasikan terhadap satu atau lebih pH standar. Suatu pH meter diatur sedemikiannya pembacaan meteran untuk suatu larutan standar adalah sama dengan nilai pH(S). Nilai pH(S) untuk berbagai larutan standar S diberikan oleh rekomendasi IUPAC.^[7] Larutan standar yang digunakan sering kali merupakan larutan penyangga standar. Dalam prakteknya, adalah lebih baik untuk menggunakan dua atau lebih larutan penyangga standar untuk mengijinkan adanya penyimpangan kecil dari hukum Nerst ideal pada elektrode sebenarnya. Oleh karena variabel temperatur muncul pada persamaan di atas, pH suatu larutan bergantung juga pada temperaturnya.

Pengukuran nilai pH yang sangat rendah, misalnya pada air tambang yang sangat asam,^[8] memerlukan prosedure khusus. Kalibrasi elektrode pada kasus ini dapat digunakan menggunakan larutan standar asam sulfat pekat yang nilai pH-nya dihitung menggunakan parameter Pitzer untuk menghitung koefisien aktivitas.^[9]

pH merupakan salah satu contoh fungsi keasaman. Konsentrasi ion hidrogen dapat diukur dalam larutan non-akuatik, namun perhitungannya akan menggunakan fungsi keasaman yang berbeda. pH superasam biasanya dihitung menggunakan fungsi keasaman Hammett, H₀.

Umumnya indikator asam-basa sederhana yang digunakan adalah kertas lakmus yang berubah menjadi merah bila keasamannya tinggi dan biru bila keasamannya rendah

Selain menggunakan kertas lakmus, indikator asam basa dapat diukur dengan pH meter yang bekerja berdasarkan prinsip elektrolit / konduktivitas suatu larutan.

[sunting] p[H]

Menurut definisi asli Sørensen ^[2], p[H] didefinisikan sebagai minus logaritma konsentrasi ion hidrogen. Definisi ini telah lama ditinggalkan dan diganti dengan definisi pH. Adalah mungkin untuk mengukur konsentrasi ion hidrogen secara langsung apabila elektrode yang digunakan dikalibrasi sesuai dengan konsentrasi ion hidrogen. Salah satu caranya adalah dengan mentitrasi larutan asam kuat yang konsentrasinya diketahui dengan larutan alkali kuat yang konsentrasinya juga diketahui pada keberadaan konsentrasi elektrolit latar yang relatif tinggi. Oleh karena konsentrasi asam dan alkali diketahui, adalah mudah untuk menghitung ion hidrogen sehingga potensial yang terukur dapat dikorelasikan dengan kosentrasi ion. Kalibrasi ini biasanya dilakukan menggunakan plot Gran.^[10] Kalibrasi ini akan menghasilkan nilai potensial elektrode standar, E⁰, dan faktor gradien, f, sehingga persamaan Nerstnya berbentuk

Persamaan ini dapat digunakan untuk menurunkan konsentrasi ion hidrogen dari pengukuran eksperimental E. Faktor gradien biasanya lebih kecil sedikit dari satu. Untuk faktor gradien kurang dari 0,95, ini mengindikasikan bahwa elektrode tidak berfungsi dengan baik. Keberadaan elektrolit latar menjamin bahwa koefisien aktivitas ion hidrogen secara efektif konstan selama titrasi. Oleh karena ia konstan, maka nilainya dapat ditentukan sebagai satu dengan menentukan keadaan standarnya sebagai larutan yang mengandung elektrolit latar. Dengan menggunakan prosedur ini, aktivitas ion akan sama dengan nilai konsentrasi.

Perbedaan antara p[H] dengan pH biasanya cukup kecil. Dinyatakan bahwa^[11] pH = p[H] + 0,04. Pada prakteknya terminologi p[H] dan pH sering dicampuradukkan dan menyebabkan kerancuan.

[sunting] pOH

pOH kadang-kadang digunakan sebagai satuan ukuran konsentrasi ion hidroksida OH⁻. pOH tidaklah diukur secara independen, namun diturunkan dari pH. Konsentrasi ion hidroksida dalam air berhubungan dengan konsentrasi ion hidrogen berdasarkan persamaan

[OH⁻] = K_W /[H⁺]

dengan K_W adalah tetapan swaionisasi air. Dengan menerapkan kologaritma:

pOH = pK_W − pH.

Sehingga, pada suhu kamar pOH ≈ 14 − pH. Namun hubungan ini tidaklah selalu berlaku pada keadaan khusus lainnya.

experiments to determine the color of the akandihasilkan. By using the appropriate indicator will then be able to read sifatlarutan tersebut.3. Calculation results obtained for the concentration of acid-base titration of 0.02 M, to the acid-base titration by 0.35 MDAFTAR PUSTAKABaroroh, Umi L. U. , 2004. I. Basic chemistry dictates Gastric University Mangkurat.Banjarbaru.Brady, J. E. Of 1999. University Chemistry Principles and Structure. Binarupa Literacy: Jakarta.Gunawan, Adi and Roeswati. , 2004. Chemical agile. Kartika. Surabaya.Khopkar, S. M. 1990. Basic Concepts of Analytical Chemistry. University of Indonesia:

indikator

surface tension and contac angle

Surface Tension and Contact Angle
Knowledge of surface tension and contact angle has a very large role of particles in life. For example, the liquid will spread on the surface or it will be small droplets depends on the properties of the material or fluid.
Surface tension is the force caused by an object acting on the surface of the liquid along the surface that touches it. If F = force (newtons) and L = length (m), the voltage-surface, S can be written as S = F / L. The surface tension caused by the interaction of liquid molecules on the surface of the liquid. In the fluid inside a molecule surrounded by other molecules around it, but there is no liquid on the surface of another molecule at the top of the liquid molecules. This led to the emergence of molecular restoring force is attractive when it is lifted away from the surface of the molecule, the molecule that is in the bottom surface of the liquid. Conversely, if the molecules on the surface of the liquid is pressed
Capillarity is caused by the interaction of the molecules in the liquid. In the liquid molecules can be subjected to adhesion and cohesion. Style of cohesion is the attraction between molecules in a liquid while the adhesion force is the attraction between molecules with other molecules that are not similar, ie materials in which the liquid container is located. If the adhesion is greater than the cohesion as in water with a glass surface, the water will interact strongly with the surface of the glass so the water over the glass and the liquid surface will be curved (concave). This situation can cause the liquid to rise to the top of the surface tension limit of him up until the upward force to balance gravity fluid is reached. So the water can rise up in a small tube called a capillary tube. This is what happens when the water rises from the ground up through the wall.

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van der waals

Senin, 09 April 2012

termodinamics

HEAT AND INTERNAL ENERGY
At the outset, it is important that we make a major distinction between internal energy
and heat. Internal energy is all the energy of a system that is associated
with its microscopic components—atoms and molecules—when viewed
from a reference frame at rest with respect to the object. The last part of this
sentence ensures that any bulk kinetic energy of the system due to its motion
through space is not included in internal energy. Internal energy includes kinetic
energy of translation, rotation, and vibration of molecules, potential energy within
molecules, and potential energy between molecules. It is useful to relate internal
energy to the temperature of an object, but this relationship is limited—we shall
find in Section 20.3 that internal energy changes can also occur in the absence of
temperature changes.
As we shall see in Chapter 21, the internal energy of a monatomic ideal gas is
associated with the translational motion of its atoms. This is the only type of energy
available for the microscopic components of this system. In this special case,
the internal energy is simply the total kinetic energy of the atoms of the gas; the
higher the temperature of the gas, the greater the average kinetic energy of the
atoms and the greater the internal energy of the gas. More generally, in solids, liquids,
and molecular gases, internal energy includes other forms of molecular energy.
For example, a diatomic molecule can have rotational kinetic energy, as well
as vibrational kinetic and potential energy.
Heat is defined as the transfer of energy across the boundary of a system
due to a temperature difference between the system and its surroundings.
When you heat a substance, you are transferring energy into it by placing it in
contact with surroundings that have a higher temperature. This is the case, for example,
when you place a pan of cold water on a stove burner—the burner is at a
higher temperature than the water, and so the water gains energy. We shall also
use the term heat to represent the amount of energy transferred by this method.
Scientists used to think of heat as a fluid called caloric, which they believed was
transferred between objects; thus, they defined heat in terms of the temperature
changes produced in an object during heating. Today we recognize the distinct
difference between internal energy and heat. Nevertheless, we refer to quantities
20.1
U
Heat
James Prescott Joule British
physicist (1818–1889) Joule received
some formal education in
mathematics, philosophy, and chemistry
but was in large part selfeducated.
His research led to the
establishment of the principle of
conservation of energy. His study of
the quantitative relationship among
electrical, mechanical, and chemical
effects of heat culminated in his discovery
in 1843 of the amount of work
required to produce a unit of energy,
called the mechanical equivalent of
heat. (By kind permission of the President
and Council of the Royal Society)
10.3
604 CHAPTER 20 Heat and the First Law of Thermodynamics
using names that do not quite correctly define the quantities but which have become
entrenched in physics tradition based on these early ideas. Examples of such
quantities are latent heat and heat capacity.
As an analogy to the distinction between heat and internal energy, consider
the distinction between work and mechanical energy discussed in Chapter 7.
The work done on a system is a measure of the amount of energy transferred to
the system from its surroundings, whereas the mechanical energy of the system
(kinetic or potential, or both) is a consequence of the motion and relative positions
of the members of the system. Thus, when a person does work on a system,
energy is transferred from the person to the system. It makes no sense to talk
about the work of a system—one can refer only to the work done on or by a system
when some process has occurred in which energy has been transferred to or
from the system. Likewise, it makes no sense to talk about the heat of a system—
one can refer to heat only when energy has been transferred as a result of a temperature
difference. Both heat and work are ways of changing the energy of a
system.
It is also important to recognize that the internal energy of a system can be
changed even when no energy is transferred by heat. For example, when a gas is
compressed by a piston, the gas is warmed and its internal energy increases, but no
transfer of energy by heat from the surroundings to the gas has occurred. If the
gas then expands rapidly, it cools and its internal energy decreases, but no transfer
of energy by heat from it to the surroundings has taken place. The temperature
changes in the gas are due not to a difference in temperature between the gas and
its surroundings but rather to the compression and the expansion. In each case,
energy is transferred to or from the gas by work, and the energy change within the
system is an increase or decrease of internal energy. The changes in internal energy
in these examples are evidenced by corresponding changes in the temperature
of the gas.
Units of Heat
As we have mentioned, early studies of heat focused on the resultant increase in
temperature of a substance, which was often water. The early notions of heat based
on caloric suggested that the flow of this fluid from one body to another caused
changes in temperature. From the name of this mythical fluid, we have an energy
unit related to thermal processes, the calorie (cal), which is defined as the
amount of energy transfer necessary to raise the temperature of 1 g of water
from 14.5°C to 15.5°C.1 (Note that the “Calorie,” written with a capital “C”
and used in describing the energy content of foods, is actually a kilocalorie.) The
unit of energy in the British system is the British thermal unit (Btu), which is defined
as the amount of energy transfer required to raise the temperature of
1 lb of water from 63°F to 64°F.
Scientists are increasingly using the SI unit of energy, the joule, when describing
thermal processes. In this textbook, heat and internal energy are usually measured
in joules. (Note that both heat and work are measured in energy units. Do
not confuse these two means of energy transfer with energy itself, which is also measured
in joules.)
The calorie
1 Originally, the calorie was defined as the “heat” necessary to raise the temperature of 1 g of water by
1°C. However, careful measurements showed that the amount of energy required to produce a 1°C
change depends somewhat on the initial temperature; hence, a more precise definition evolved.
20.1 Heat and Internal Energy 605
The Mechanical Equivalent of Heat
In Chapters 7 and 8, we found that whenever friction is present in a mechanical
system, some mechanical energy is lost—in other words, mechanical energy is not
conserved in the presence of nonconservative forces. Various experiments show
that this lost mechanical energy does not simply disappear but is transformed into
internal energy. We can perform such an experiment at home by simply hammering
a nail into a scrap piece of wood. What happens to all the kinetic energy of the
hammer once we have finished? Some of it is now in the nail as internal energy, as
demonstrated by the fact that the nail is measurably warmer. Although this connection
between mechanical and internal energy was first suggested by Benjamin
Thompson, it was Joule who established the equivalence of these two forms of
energy.
A schematic diagram of Joule’s most famous experiment is shown in Figure
20.1. The system of interest is the water in a thermally insulated container. Work is
done on the water by a rotating paddle wheel, which is driven by heavy blocks
falling at a constant speed. The stirred water is warmed due to the friction between
it and the paddles. If the energy lost in the bearings and through the walls is neglected,
then the loss in potential energy associated with the blocks equals the work
done by the paddle wheel on the water. If the two blocks fall through a distance h,
the loss in potential energy is 2mgh, where m is the mass of one block; it is this energy
that causes the temperature of the water to increase. By varying the conditions
of the experiment, Joule found that the loss in mechanical energy 2mgh is proportional
to the increase in water temperature T. The proportionality constant was
found to be approximately 4.18 J/g °C. Hence, 4.18 J of mechanical energy raises
the temperature of 1 g of water by 1°C. More precise measurements taken later
demonstrated the proportionality to be 4.186 J/g °C when the temperature of the

electrochmistry

Oxidation-Reduction (Redox) Reactions Involve a
Transfer of Electrons from One Species to Another
One form of energy that has tremendous practical signifi cance is electric energy.
A day without electricity from either the power company or batteries is unimaginable
in our technological society. The branch of chemistry that studies the interconversion
of electric energy and chemical energy is called electrochemistry.
Electrochemical processes are oxidation-reduction reactions (or redox reactions)
in which the energy released by a spontaneous reaction is converted to electricity
or in which electric energy is used to cause a nonspontaneous reaction to occur.
In redox reactions, electrons are transferred from one substance to another. The
reaction between magnesium metal and hydrochloric acid is an example of a redox
reaction:
Mg(s) 1 2HCl(aq) ¡MgCl2 1 H2(g)
In this reaction, the Mg metal loses two electrons, and the two H1 ions in the
HCl solution gain one electron each. Species that lose electrons in a redox reaction
are said to be oxidized, and those that gain electrons are said to be reduced. In the
reaction of magnesium metal with hydrochloric acid, for example, Mg metal is oxidized
and H1 ions are reduced. The Cl2 ions are spectator ions because they do not
participate directly in the redox reaction.
Oxidation-reduction reactions are very much a part of the world around us. They
range from the burning of fossil fuels to the action of household bleach. Additionally,
most metallic and nonmetallic elements are obtained from their ores by the process
of oxidation or reduction. Many important redox reactions take place in water (rusting,
for example), but not all redox reactions occur in aqueous solution. Some, such as
the formation of calcium oxide (CaO) from calcium and oxygen, occur when a solid
interacts with a gas:
2Ca(s) 1 O2(g) ¡2CaO(s)
CaO is an ionic compound made up of Ca21 and O22 ions. In this reaction, two Ca atoms
give up or transfer four electrons to two O atoms (in O2). For convenience, we can think
of this process as two separate steps, one involving the loss of four electrons by the two
Ca atoms and the other being the gain of four electrons by an O2 molecule:
2Ca¡2Ca21 1 4e2
O2 1 4e2¡2O22
Each of these steps is called a half-reaction, and each half-reaction explicitly shows
the electrons involved in the oxidation portion or the reduction portion of a redox
reaction. The sum of the oxidation half-reaction and the reduction half-reaction gives
the overall redox reaction.
An oxidation reaction is the half-reaction that involves a loss of electrons. Chemists
originally used oxidation to denote the combination of elements with oxygen.
Now, however, “oxidation” has a broader meaning that includes reactions not involving
oxygen. A reduction reaction is a half-reaction that involves a gain of electrons.
In the formation of calcium oxide, calcium is oxidized. It acts as a reducing agent
because it donates electrons to oxygen and causes oxygen to be reduced. Oxygen is
reduced and acts as an oxidizing agent because it accepts electrons from calcium,
causing calcium to be oxidized. An oxidation reaction cannot occur without a concomitant
reduction reaction, and vice versa. The number of electrons lost by a reducing
agent must equal the number of electrons gained by an oxidizing agent

prhedching wheather

The chemical reactions that are most important to us occur in water—
in aqueous solutions. Virtually all of the chemical reactions that keep
each of us alive and well take place in the aqueous medium present in our
bodies. For example, the oxygen you breathe dissolves in your blood,
where it associates with the hemoglobin in the red blood cells. While attached
to the hemoglobin it is transported to your cells, where it reacts
with fuel (from the food you eat) to provide energy for living. However,
the reaction between oxygen and fuel is not direct—the cells are not tiny
furnaces. Instead, electrons are transferred from the fuel to a series of
molecules that pass them along (this is called the respiratory chain) until
they eventually reach oxygen. Many other reactions are also crucial to our
health and well-being. You will see numerous examples of these as you
continue your study of chemistry.
In this chapter we will study some common types of reactions that
take place in water, and we will become familiar with some of the driving
forces that make these reactions occur. We will also learn how to predict
the products for these reactions and how to write various equations to describe
them.
Predicting Whether a Reaction Will Occur
To learn about some of the factors that cause reactions to occur.
In this text we have already seen many chemical reactions. Now let’s consider
an important question: Why does a chemical reaction occur? What
causes reactants to “want” to form products? As chemists have studied reactions,
they have recognized several “tendencies” in reactants that drive them
to form products. That is, there are several “driving forces” that pull reactants
toward products—changes that tend to make reactions go in the direction
of the arrow. The most common of these driving forces are
1. Formation of a solid
2. Formation of water
3. Transfer of electrons
4. Formation of a gas
When two or more chemicals are brought together, if any of these
things can occur, a chemical change (a reaction) is likely to take place. Accordingly,
when we are confronted with a set of reactants and want to predict
whether a reaction will occur and what products might form, we will
consider these driving forces. They will help us organize our thoughts as we
encounter new reactions.
Reactions in Which a Solid Forms
To learn to identify the solid that forms in a precipitation reaction.
One driving force for a chemical reaction is the formation of a solid, a
process called precipitation. The solid that forms is called a precipitate,
and the reaction is known as a precipitation reaction. For example,
7.2 Reactions in Which a Solid Forms 167
OBJECTIVE:
7.1
OBJECTIVE:
7.2
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A burning match involves several
chemical reactions.