What is the pH scale?
pH scale. The fundamentals of acids and bases and how the pH scale is used to measure them. Because of uncertainty about the physical significance of the hydrogen ion concentration, the definition of the pH is an operational one; i.e., it is based on a method of measurement.
What does pH mean in the biosphere?
biosphere: ph. The relative acidity or alkalinity of a solution is reported by the pH scale, which is a measure of the concentration of hydrogen ions in solution. Neutral solutions have a pH of 7. A pH of less than 7 denotes acidity (an increased hydrogen…. bacteria: pH.
How to measure pH?
The pH is usually measured with a pH meter, which translates into pH readings the difference in electromotive force (electrical potential or voltage) between suitable electrodesplace d in the solution to be tested. Fundamentally, a pH meter consists of a voltmeterattached to a pH-responsive electrode and a reference (unvarying) electrode. The pH-responsive electrode is usually glass, and the reference is usually a mercury-mercurous chloride (calomel) electrode, although a silver-silver chloride electrode is sometimes used. When the two electrodes are immersed in a solution, they act as a battery. The glass electrode develops an electric potential(charge) that is directly related to the hydrogen-ion activity in the solution, and the voltmeter measures the potential difference between the glass and reference electrodes. The meter may have either a digital or an analog(scale and deflected needle) readout. Digital readouts have the advantage of exactness, while analog readouts give better indications of rates of change. Battery-powered portable pH meters are widely used for fieldtests of the pH of soils. Tests of pH may also be performed, less accurately, with litmuspaper or by mixing indicator dyes in liquid suspensions and matching the resulting colours against a colour chart calibratedin pH.
What is the purpose of a pH meter?
The pH is usually measured with a pH meter, which translates into pH readings the difference in electromotive force (electrical potential or voltage) between suitable electrodes placed in the solution to be tested. Fundamentally, a pH meter consists of a voltmeter attached to a pH-responsive electrode and a reference (unvarying) electrode.
What is the most important property of soil moisture?
In agriculture, the pH is probably the most important single property of the moisture associated with a soil, since that indication reveals what crops will grow readily in the soil and what adjustments must be made to adapt it for growing any other crops. Acidic soils are often considered infertile, and so they are for most conventional agricultural crops, although conifersand many members of the family Ericaceae, such as blueberries, will not thrive in alkaline soil. Acidic soil can be “sweetened,” or neutralized, by treating it with lime. As soil acidity increases so does the solubilityof aluminumand manganesein the soil, and many plants (including agricultural crops) will tolerate only slight quantities of those metals. Acid content of soil is heightened by the decomposition of organic material by microbial action, by fertilizer salts that hydrolyze or nitrify, by oxidation of sulfur compoundswhen saltmarshes are drained for use as farmland, and by other causes.
What is the charge of a glass electrode?
When the two electrodes are immersed in a solution, they act as a battery. The glass electrode develops an electric potential (charge) that is directly related to the hydrogen-ion activity in the solution, and the voltmeter measures the potential difference between the glass and reference electrodes.
Why is pH based on a method?
Because of uncertainty about the physical significance of the hydrogen ion concentration, the definition of the pH is an operational one; i.e., it is based on a method of measurement. The U.S. National Institute of Standards and Technologyhas defined pH values in terms of the electromotive forceexisting between certain standard electrodes in specified solutions.
What is the pH scale?
Lesson Summary. The pH scale measures how acidic or basic something is on a scale of 0 to 14. Things with a lower pH, like grapefruit juice and vinegar, are acidic, while things with a higher pH, like bleach and drain cleaner, are basic (alkaline). In the middle, water has a neutral pH of 7. To unlock this lesson you must be a Study.com Member.
Why do lemons pucker up?
Have you ever tasted a lemon and puckered up? Lemons have that puckery taste because they're acidic, just like vinegar and some other foods. In this lesson, you'll learn about the pH scale, which scientists use to describe whether something is acidic or basic. Basic is the opposite of acidic.
Why is baking soda used in cooking?
Baking soda is used to change the texture of food - for example, pancakes are so fluffy and light because they have baking soda in them. Moving on up the pH scale, we start moving away from food and into dangerous cleaning chemicals. Things with a very high pH are often very powerful disinfectants, like bleach.
What is the purpose of the pH scale?
Scientists use the pH scale to measure how basic (alkaline) or acidic things are. Learn about the pH scale and take a look at some familiar foods and cleaning products with different pHs, like water, milk, and baking soda.
What would the pH be if you took a cup of water out of the ocean?
If you took a cup of water out of the ocean instead of pouring it from a faucet, the pH would be about 8. A drink of ocean water probably won't hurt you, but it would taste pretty disgusting, so maybe don't try that at home. Moving on up the pH scale, baking soda is next at a pH around 9.5.
What does it mean to enroll in a course?
Enrolling in a course lets you earn progress by passing quizzes and exams.
What is the pH of plain water?
We'll start with the middle of the pH scale: with a pH of 7 , plain water is exactly in the center. So if you want to feel and taste something with a neutral pH, go pour yourself a glass of water and take a big drink.
Why is 4.6 pH important?
The pH of 4.6 is critical because of one particular bacterium, Clostridium botulinum. Clostridium botulinum produces a dormant form called a spore. These spores are found in the soil and in many other places. Spores are extremely hard to kill and may survive for many years waiting for a favorable environment to grow.
What temperature can you can food to kill spores?
Only a pressure canner can raise food to the temperatures (240°F to 250°F) necessary to destroy spores. Clostridium botulinum produces an extremely potent neurotoxin that is one of the deadliest poisons known. Eating food containing the toxin causes botulism; even trace amounts of the toxin are enough to kill.
What is the function of pH?
What is pH? The pH value of a food is a direct function of the free hydrogen ions present in that food. Acids present in foods release free hydrogen ions; the hydrogen ions give acid foods their distinctive sour flavor. Thus, pH may be defined as a measure of free acidity.
What is the pH of canning food?
Why is pH important in canning foods? Foods are typically classified as “acid foods” (low pH; pH of 4.6 or lower) or “low-acid foods” (high pH; pH of more than 4.6).
Can Clostridium botulinum grow in food?
Eating food containing the toxin causes botulism; even trace amounts of the toxin are enough to kill. Fortunately, the spores of Clostridium botulinum will not grow if the pH of a food is 4.6 or less.
Can you boil pickles in a water bath?
Acid foods such as fruits and pickles may be safely canned in a boiling water bath canner; the combination of acidity and boiling water (212°F) destroys spoilage organisms such as molds and yeast. A proper boiling water canning process is important to prevent growth of the acid tolerant molds and yeasts that may result in increased pH.
Is pH a measure of free acidity?
Thus, pH may be defined as a measure of free acidity. More precisely, pH is defined as the negative log of the hydrogen ion concentration. The range of pH extends from zero to 14. A pH value of 7 is neutral, because pure water has a pH value of exactly 7.
pH and Water
No, you don't often hear your local news broadcaster say "Folks, today's pH value of Dryville Creek is 6.3!" But pH is quite an important measurement of water. Maybe for a science project in school you took the pH of water samples in a chemistry class ... and here at the U.S. Geological Survey we take a pH measurement whenever water is studied.
pH: Definition and measurement units
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Importance of pH
The pH of water determines the solubility (amount that can be dissolved in the water) and biological availability (amount that can be utilized by aquatic life) of chemical constituents such as nutrients (phosphorus, nitrogen, and carbon) and heavy metals (lead, copper, cadmium, etc.).
Diagram of pH
As this diagram shows, pH ranges from 0 to 14, with 7 being neutral. pHs less than 7 are acidic while pHs greater than 7 are alkaline (basic). Normal rainfall has a pH of about 5.6—slightly acidic due to carbon dioxide gas from the atmosphere. You can see that acid rain can be very acidic, and it can affect the environment in a negative way.
Measuring pH
The U.S. Geological Survey analyzes hundreds of thousands of water samples every year. Many measurements are made right at the field site, and many more are made on water samples back at the lab. pH is an important water measurement, which is often measured both at the sampling site and in the lab. There are large and small models of pH meters.
pH and water quality
Excessively high and low pHs can be detrimental for the use of water. High pH causes a bitter taste, water pipes and water-using appliances become encrusted with deposits, and it depresses the effectiveness of the disinfection of chlorine, thereby causing the need for additional chlorine when pH is high.
Variation of pH across the United States
The pH of precipitation, and water bodies, vary widely across the United States. Natural and human processes determine the pH of water. The National Atmospheric Deposition Program has developed maps showing pH patterns, such as the one below showing the spatial pattern of the pH of precipitation at field sites for 2002.
What is the equation for pH?
Equation for pH. pH is the logarithm of the hydrogen ion concentration of an aqueous (water-based) solution: pH = -log [H+] log is the base 10 logarithm and [H+] is hydrogen ion concentration in the units moles per liter. It's important to keep in mind a solution must be aqueous to have a pH.
What is the meaning of pH?
pH Definition and Origin. pH is the negative log of hydrogen ion concentration in a water-based solution. The term "pH" was first described by Danish biochemist Søren Peter Lauritz Sørensen in 1909. pH is an abbreviation for "power of hydrogen" where "p" is short for the German word for power, potenz and H is the element symbol for hydrogen.
Why is the H capitalized?
The "H" is capitalized because it is the hydrogen element symbol. pH is a measure of how acidic or basic an aqueous solution is. It is calculated as the negative logarithm of hydrogen ion concentration.
Is a pH of 7 more acidic than a pH of 5?
Each whole pH value below 7 (the pH of pure water) is ten times more acidic than the higher value and each whole pH value above 7 is ten times less acidic than the one below it. For example, a pH of 3 is ten times more acidic than a pH of 4 and 100 times (10 times 10) more acidic than a pH value of 5. So, a strong acid may have a pH of 1-2, ...
Can a solution have a pH?
It's important to keep in mind a solution must be aqueous to have a pH. You cannot, for example, calculation pH of vegetable oil or pure ethanol.
