Sabtu, 27 Agustus 2022

 Is the Water Hard or Soft?

Introduction
Homeowners frequently hear from telemarketers peddling everything from magazines to vacuum
cleaners. Telemarketers for water purification systems seem especially common lately. They offer
free testing of household water in hopes that they can show that an expensive water softener
should be purchased. A consumer advocate wishing to help homeowners test their own water has
asked for your group’s help in developing a technique for testing water hardness at home.
To determine if a home really needs an expensive new water softener, you should address several
questions. How do you know whether your water is hard or soft? How hard is it? Which
chemicals work to soften the water? As a group, your team will investigate the above concerns.
The technique you develop might be endorsed by a consumer advocate company.
Goals
As you complete this investigation you will:
1. Develop a method for determining the hardness of a water sample.
2. Use this method to measure the temporary and permanent hardness of the water.
3. Use this method to measure the relative effectiveness of various chemicals as water softeners.
4. Report your results as directed by your instructor
Materials
0.00100 M CaCl2 solution, which has a hardness of 100 ppm
Soap solution
Water sample
Distilled water sample
Borax, Na2B4O7(s)
Sodium chloride, NaCl(s)
Sodium carbonate (washing soda), Na2CO3(s)
Sodium phosphate, Na3PO4(s)
Sodium sulfate, Na2SO4(s)
Plastic droppers
Balances
Graduated cylinders, burets, pipets, or other volume measuring devices
Other supplies by request

Getting Started
Water that contains the impurities Ca2+, Mg2+, and sometimes Fe3+, along with the anions Cl–,
SO42–, and HCO3–, is called hard water because the metal ions cause an undesirable precipitate of
soap scum when soap is added. For example, some soaps contain compounds of the anion,
C17H35CO2–. This anion can react with calcium ions present in hard water to make an insoluble
compound:
Lathering will not occur until the metal ions associated with water hardness are consumed. The
formation of a permanent lather can be used as a measure of the hardness of the water. When
developing your method for determining hardness, however, be sure to consider whether suds
would form with the first addition of soap in the absence of any hardness. You might begin by
comparing the hardness of tap water and deionized or distilled water. A solution of 0.00100 M
calcium chloride is provided. This solution has a hardness of 100 part per million. This solution
can be used as a hard water standard to quantify your results.
Hardness is considered to be permanent if it remains after water is boiled. Hardness that is
removed by boiling is called temporary hardness. The temporary hardness is caused by
bicarbonate compounds, which are converted to insoluble carbonate compounds by heating:
Since the calcium is removed as a carbonate precipitate, it is no longer present as free calcium
ions in solution. Permanent hardness is caused by chloride or sulfate salts, which are not changed
by heating. When testing the use of various solid chemicals as water softeners, be sure to compare equal amounts of the solids and make sure that the solids are completely dissolved.

Report
Submit a report as directed by your instructor. It may be returned to you for corrections if it is not
acceptable. Your discussion should address the different types of hardness and the relative
efficiency of the various salts as water softeners. You should also compare various watersoftening
systems, such as the new magnetic systems and older methods such as ion exchange,
distillation, and reverse osmosis. Useful information about water softening can be found on the
internet. Compare the costs of the different systems. Could you use inexpensive chemicals to
soften the water?

source: (Brooks Cole Laboratory Series for General Chemistry) Richard Bauer, James Birk, Doug Sawyer - Laboratory Inquiry in Chemistry, 2009

ANGKET VARIABEL INVESTASI

 

Sabtu, 18 Juni 2022

 ANGKET DASS 42 (DEPRESSION ANXIETY STRESS SCALE)

S. H. Lovibond & P. F. Lovibond, 1995

DI ADAPTASI KE BAHASA INDONESIA OLEH EVELINA DEBORA DAMANIK


             http://eprints.undip.ac.id/51201/1/PROPOSAL_NUR_LELA_FITRIANI.pdf

Senin, 11 Mei 2020

PROPILEN GLIKOL


Etilen Glikol/propilen glikol

Meskipun digunakan dalam kosmetik, sintesis kimia, dan aplikasi lain, kebanyakan etilena glikol digunakan sebagai bahan utama formulasi antibeku dan antibodi untuk radiator mobil.


Etilen glikol (titik leleh, -13°C; titik didih, 198°C) disintesis oleh oksidasi etilena menjadi etilen oksida, diikuti oleh hidrolisis senyawa yang terakhir:

Paparan toksik terhadap etilen glikol jarang terjadi karena tekanan uapnya yang rendah, tetapi terhirup tetesannya bisa sangat berbahaya. Sejumlah besar kematian manusia yang disebabkan oleh keracunan etilena glikol telah didokumentasikan. Dari terbatasnya informasi yang tersedia, LD50 Untuk manusia diperkirakan sekitar 110 g. Etilen glikol yang dicerna awalnya merangsang pusat sistem saraf, dan kemudian menekannya. Korban dapat menderita asidemia dari kehadiran perantara asam glikolat metabolit. Kerusakan ginjal terjadi kemudian, dan bisa berakibat fatal. Ginjal rusak karena pengendapan kalsium oksalat padat, yang dihasilkan dari keseluruhan proses berikut:
Perantara penting dalam proses ini adalah glikolaldehida, glikolat, dan glioksilat:
Gagal ginjal dari pembentukan metabolisme kalsium oksalat telah umum terjadi pada kucing spesies, yang memiliki selera rakus untuk etilen glikol dalam antibeku. Deposit kalsium padat oksalat juga telah diamati di hati dan jaringan otak korban keracunan etilen glikol.

Manahan, Stanley E., Toxicological chemistry and biochemistry, 2002:309


Gliserol MUNGKIN AMAN bila diminum dalam waktu singkat. Gliserol dapat menyebabkan efek samping termasuk sakit kepala, pusing, kembung, mual, muntah, haus, dan diare.









Minggu, 10 Mei 2020

Thermodynamic quantities of cell reactions


Thermodynamic quantities of cell reactions

The Gibbs free energy change at a given temperature for the overall cell reaction for an electrochemical cell can be obtained from the reversible e.m.f. (E) of the cell determined by Poggendorf’s compensation method.
ΔG= –nF E
where n is the number of faradays of electricity delivered by the cell. E is positive by convention and being an intensive quantity, does not depend on how the stoichiometric equation for the spontaneous overall cell reaction is written. But ΔG being an extensive quantity does depend on how the overall cell reaction is written. The same is true about the corresponding enthalpy and the entropy changes (ΔH and ΔS). These thermodynamic quantities are usually expressed in kJ mol–1 (ΔS in J K–1 mol–1) when these become intensive quantities.
From thermo dynamics we have,
Δ = – [ ∂ΔG/∂T]p
or ΔS = nF[∂E/∂T]p
since –ΔG = nF E
The temperature coefficient of the cell e.m.f., (∂E/∂T)p can be obtained by determining the e.m.f at various temperatures.
Again from thermodynamics we have,
          ΔG = ΔH – TΔS
Or     –n F E = ΔH – TΔS
or     ΔH = – n F E + TΔS
or     ΔH = – nF E + TnF [ ∂E/∂T]p
Thus the enthalpy change associated with the overall cell reaction for a reversible cell can be determined from the reversible e.m.f. (E) and the temperature coefficient of the reversible e.m.f. of the cell, .The equilibrium constant is related to standard Gibbs free energy, ΔGO (or – n F EO ). Hence we obtain
Since ΔGO = – RT ln K
Or     – n F EO = – RT ln K
         ln K = —[ nF EO/RT]
The above equation enables one to calculate the equilibrium constant of an overall cell reaction at a given temperature from the experimentally determined value of the standard e.m.f. of the cell at the same temperature.
We have seen earlier that the Weston Cadmium Cell has an e.m.f. (E) of 1.01463 V at 298 K and a temperature coefficient of -5.00 × 10–5 V K–1. These two data help us to calculate the thermodynamic quantities of the overall cell reaction.
ΔG = – n F E
      = – 2 × 96500 C mol–1 × 1.01463 V
      = –195824 Jmol-1
ΔS = nF[ ∂ E/∂T]p
     = 2 (96500 C mol–1) × (– 5.00 × 10–5) V K–1
     = – 9.65 Jmol-1 K–1
ΔH = ΔG + T ΔS
      = – 195824 Jmol-1 + 298 K (– 9.65 Jmol-1 K–1)
      = -198700 Jmol-1


Electrochemistry II: Voltaic or Galvanic cells
Suhaschandra Ghosh and Animesh Kumar Rakshit, 2010, 16






FOOD PRESERVATIVE TEST


FOOD PRESERVATIVE TEST

Food additives (food additives) are used so that food looks more attractive and durable; these ingredients can be preservatives, colorings, flavorings and aromas, anti-oxidants, and others. So the ingredient is not nutritionally valuable, but is added to food in the manufacture or transportation to influence or maintain the special characteristics of the food.
Some food additives have a bad influence on human health; therefore the Ministry of Health has regulated / stipulated the types of food additives that may and may not be used in food processing. Additional ingredients that are prohibited from being used in food are formalin (formaldehyde) and boric acid (the salt is sodium tetraborate / borax).

BORAX
Borax is a sodium salt Na2B4O7.10H2O which is widely used in various non-food industries, especially paper, glass, solder, cleaning materials, wood preservatives, antiseptics, cockroach controls and ceramics. The famous pyrex glass is made with a mixture of borax.
Borax is used as a solder, cleaning agent, wood preservative, antiseptic and cockroach control. Borax is a poisonous and dangerous material for humans, because it can cause toxic effects, but the mechanism of toxicity is different from formaldehyde.
What is dangerous, borax can be absorbed by the body and stored cumulatively in the liver, brain, intestines or testicles so that the dose in the body becomes high. If consumed yearly can cause cancer. Borax is also often misused in food. Usually added to crackers, meatballs, rice cake and others. Laymen know borax by the name of Bleng (Indonesian) or Cetitet.
Symptoms can include nausea, vomiting, diarrhea, decreased body temperature, weakness, headaches, erythermatous rash, and can even cause shock. Death in adults can occur in doses of 15-25 grams, whereas in children in 5-6 grams doses. The danger of Borax on health is absorbed through the intestines, damaged skin and mucous membranes.
Following are some of the characteristics of foods containing borax. Although it is not too typical but can help distinguish it from food without borax.
a.      Wet noodles containing borax: The texture is very chewy, usually more shiny, not sticky and does not break quickly.
b.      Meatballs contain borax: The texture is very chewy, the color is not brown like the use of meat but is more likely to whitish
c.      The characteristics of crackers contain borax: The texture is very crispy, can give a bitter taste
WHAT IS FORMALDEHYDE
Another name for formalin is Formaldehyde or Metanal with the general formula HCHO. Formalin is a colorless and pungent solution, at room temperature in the form of a gas that can dissolve in alcohol, acetone or water.
In the chemical industry, it is very important as a disinfectant, fungicide, bactericide, basic material for making resins, preservatives of human beings / animals. Formaldehyde is a toxic in humans that can cause: Abdominal pain, skin irritation, Lack of protein (proteinuria), Excess acid (acidosis), Headaches to death, and Carcinogens / causes of cancer.
BORAX TEST
Tests on borax containing samples were carried out by adding 10 drops of conc. H2SO4 and 2 ml of methanol. Let stand for a while and then burned. This test produces the same yellowish green color as the flame test of pure borax compounds. This proves that the sample does indeed contain borax.
For test samples that do not contain borask the procedure is carried out the same as in test samples containing borax. But the results obtained do not cause a yellowish green flame.
The other ways to test for the presence of preservatives, especially borax, are:
To 0.5 ml the sample solution is added:
a.      Silver nitrate, white sediment will occur from metaborac silver. In heating, black Ag2O deposits will occur
b.      Saturated barium chloride, white barium metaborate will occur
FORMALIN TEST
A. Fehling Test
Take 10 grams of sample (tofu / wet noodles / meatballs) then puree using a mortar. Add 10 ml of water, stir until smooth. Then strain. Take ± 2ml of the filtered result, put it into a test tube. Add 3 ml of Fehling's solution. Heat 5-10 minutes. Observe and record the changes that occur. Solution contains formaldehyde if the initially blue solution turns green and yellow or red precipitate is formed.

B. Potassium permanganate test
               Test tube containing 10 ml of milk spiked with 1 drop of 1N KMnO4 solution. The white milk solution will turn pink. The length of time the pink color is lost from a drop of a potassium permanganate solution into a test tube containing a sample of fresh milk is an indicator of possible formalin content in the milk.
               If 1 hour there is no change in color (stable pink) it means that the milk does not contain formaldehyde (or rather say it does not use formaldehyde as a preservative), and is followed by another series of tests before being declared acceptable as raw material. If the pink color of the potassium permanganate solution immediately fades / disappears to become colorless, it means there is a possibility in milk samples containing formalin which is reacting to eliminate the color (reducing) potassium permanganate.
               False positive (false results) can occur if the food contains other reducing agents that react with potassium permanganate such as oxalic acid, etc. But most of the preserved foods are plant / animal foods (wet fish, meatballs, tofu) that have high protein content are very unlikely to contain oxalic acid naturally.


Assessment Of Learning


Assessment Of Learning

1.      Definition of Learning Assessment
From the point of view of language, judgment is defined as the process of determining the value of an object. To be able to determine a value or price of an object requires the size or criteria. For example, to be able to say good, moderate, less, there needs to be a clear measure of how good, medium, and less. The measure is called the criterion. From this understanding, it can be said that the characteristics of assessment are the existence of the object or program being assessed and the existence of criteria as a basis for comparing what is achieved with the criteria that must be achieved. Comparison can be absolute, it can also be relative.
Comparison is absolute meaning that the results of the comparison describe the position of the object being evaluated in terms of applicable criteria. While the relative comparison means the result of the comparison is more describing the position of an object that is valued against other objects based on the same criteria. Thus, the core assessment is the process of determining the value of a particular object based on certain criteria. The process of giving value takes place in the form of interpretation which ends with judgment. Interpretation and judgement is a theme of assessment that implies a comparison between criteria and reality in the context of a particular situation. On that basis, in the assessment activities there are always objects / programs that are assessed, there are criteria, and there are interpretations / judgments.
Assessment of learning outcomes is the process of assigning grades to learning outcomes achieved by students with certain criteria. This implies that the object judged is the result of student learning. Student learning outcomes are essentially change in behavior. Behavior as a result of learning in a broad sense covers the fields of cognitive, affective, and psychomotor. Therefore, in the assessment of learning outcomes the formulation of abilities and behaviors desired by students (competence) becomes an important element as a basis and reference for assessment. Assessment of the learning process is an effort to give value to teaching and learning activities carried out by students and teachers in achieving teaching objectives.

2.      Learning Assessment Function
The purpose of learning is essentially a change in behavior in students. Therefore, the assessment should be examined to what extent changes in student behavior have occurred through the learning process. For example by making changes in teaching strategies, providing guidance and learning assistance to students. In other words, the results of the assessment are not only useful for knowing whether changes in student behavior have been achieved, but also as feedback for efforts to improve the learning process.
In this assessment seen the extent to which the effectiveness of the learning process in seeking changes in student behavior. Therefore, the assessment of learning outcomes and processes are interrelated with each other because the learning outcomes achieved by students are a result of the learning process that they go through (their learning experiences). In line with the above understanding, the evaluation functions as follows:
a.      Tool to find out whether learning objectives are achieved. With this function then the assessment must refer to the formulations of learning objectives as a translation of the subject competencies.
b.      Feedback for improving the teaching and learning process. Improvements might be made in terms of learning objectives, student learning activities or experiences, learning strategies used by the teacher, learning media, etc.
c.      The basis for compiling reports on student learning progress to his parents. In the report, students' ability and study skills were expressed in various fields of study or subjects in the form of achievement values.

3.      Purpose of Learning Assessment
In line with the assessment function above, the purpose of the assessment of learning outcomes is to:
a.      Describe students' learning skills so that their strengths and weaknesses can be identified in various fields of study or subjects they take. By describing the skills, it can also be seen the position of the ability of students compared to other students
b.      Knowing the success of the education and learning process in school, in aspects of intellectual, social, emotional, moral, and skills, namely how far the effectiveness in changing the behavior of students towards the expected educational goals. The success of education and learning is important, considering its role as an effort to humanize or civilize humans, in this case students to become qualified human beings
c.      Determine the follow-up of the results of the assessment, namely to make improvements and improvements in terms of education and learning programs and their implementation strategies. Failure of students in learning outcomes they achieve should not be seen as lacking solely in students themselves, but can also be caused by learning programs that are given to them or by strategic mistakes in executing these programs. For example, inaccuracies in choosing and use teaching methods and learning aids
d.      Provide accountability (accountability) from the school to the parties concerned. The parties in question include the government, the community, and parents of students. In accounting for the results it has achieved, the school reports various strengths and weaknesses in the implementation of the education system and the obstacles it faces. Reports are submitted to interested parties, for example the local education office through officers who handle it. While accountability to the community and parents is conveyed through student learning progress reports (report cards) at the end of each program/semester

4.      Principles of Learning Assessment
In addition to the purpose and function of assessment, teachers must also understand the principles of assessment. The principles of assessment referred to include the following:
a.      Assessment of learning outcomes should be an integral part of the learning process. This means that every teacher carrying out the learning process he must carry out assessment activities. The intended evaluation is formative assessment. There is no learning process without assessment. Thus the progress of student learning can be known and the teacher can always improve the quality of the learning process carried out.
b.      Assessment of learning outcomes should be clearly designed what abilities should be assessed, the material or content of the teaching material being tested, the assessment tools to be used, and the interpretation of the results of the assessment. As a benchmark or signs in designing assessment of learning outcomes is a curriculum that applies primarily the objectives and competencies of subjects, the scope of the content or teaching material and guidelines for its implementation.
c.      The assessment must be carried out comprehensively, meaning that the abilities measured include cognitive, affective and psychomotor aspects. In cognitive aspects include: knowledge, understanding, application, analysis, synthesis, and evaluation proportionally.
d.      Assessment tools must be valid and reliable. Valid means measuring what should be measured (accuracy). Reliability means that the results obtained from the assessment are consistent or consistent.
e.      Assessment of learning outcomes should be followed by no further. Assessment data is very useful for teachers as material to perfect learning programs, improve learning weaknesses, and tutoring activities for students who need them.
f.       Assessment of learning outcomes must be objective and fair so that they can describe the actual abilities of students.

Indonesian Education Ministry, 2008