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Tuesday, March 17, 2020

Buffer Definition - Chemistry and Biology

Buffer Definition - Chemistry and Biology A buffer is a  solution containing either a weak acid and its salt or a weak base and its salt, which is resistant to changes in pH. In other words, a buffer is an aqueous solution of either a weak acid and its conjugate base or a weak base and its conjugate acid. A buffer may also be called a pH buffer, hydrogen ion buffer, or buffer solution. Buffers are used to maintain a stable pH in a solution, as they can neutralize small quantities of additional acid of base. For a given buffer solution, there is a working pH range and a set amount of acid or base that can be neutralized before the pH will change.  The amount of acid or base that can be added to a buffer before changing its pH is called its buffer capacity.   The Henderson-Hasselbalch equation may be used to gauge the approximate pH of a buffer.  In order to use the equation, the initial concentration or stoichiometric concentration is entered instead of the equilibrium concentration. The general form of a buffer chemical reaction is: HA â‡Å' H   A− Examples of Buffers blood - contains a bicarbonate buffer systemTRIS bufferphosphate buffer As stated, buffers are useful over specific pH ranges. For example, here is the pH range of common buffering agents: Buffer pKa pH range citric acid 3.13., 4.76, 6.40 2.1 to 7.4 acetic acid 4.8 3.8 to 5.8 KH2PO4 7.2 6.2 to 8.2 borate 9.24 8.25 to 10.25 CHES 9.3 8.3 to 10.3 When a buffer solution is prepared, the pH of the solution is adjusted to get it within the correct effective range. Typically a strong acid, such as hydrochloric acid (HCl) is added to lower the pH of acidic buffers. A strong base, such as sodium hydroxide solution (NaOH), is added to raise the pH of alkaline buffers. How Buffers Work In order to understand how a buffer works, consider the example of a buffer solution made by dissolving sodium acetate into acetic acid. Acetic acid is (as you can tell from the name) an acid: CH3COOH, while the sodium acetate dissociates in solution to yield the conjugate base, acetate ions of CH3COO-. The equation for the reaction is: CH3COOH(aq) OH-(aq) ⇆ CH3COO-(aq) H2O(aq) If a strong acid is added to this solution, the acetate ion neutralizes it: CH3COO-(aq) H(aq) ⇆ CH3COOH(aq) This shifts the equilibrium of the initial buffer reaction, keeping the pH stable. A strong base, on the other hand, would react with the acetic acid. Universal Buffers Most buffers work over a relative narrow pH range. An exception is citric acid because it has three pKa values. When a compound has multiple pKa values, a larger pH range becomes available for a buffer. Its also possible to combine buffers, providing their pKa values are close (differing by 2 or less), and adjusting the pH with strong base or acid to reach the required range. For example, McIvaines buffer is prepared by combining mixtures of Na2PO4 and citric acid. Depending on the ratio between the compounds, the buffer may be effective from pH 3.0 to 8.0. A mixture of citric acid, boric acid, monopotassium phosphate, and diethyl barbituic acid can cover the pH range from 2.6 to 12! Buffer Key Takeaways A buffer is an aqueous solution used to keep the pH of a solution nearly constant.A buffer consists of a weak acid and its conjugate base or a weak base and its conjugate acid.Buffer capacity is the amount of acid or base that can be added before the pH of a buffer changes.An example of a buffer solution is bicarbonate in blood, which maintains the bodys internal pH. Sources Butler, J. N. (1964).  Ionic Equilibrium: A Mathematical Approach. Addison-Wesley. p.  151.Carmody, Walter R. (1961). Easily prepared wide range buffer series. J. Chem. Educ. 38 (11): 559–560. doi:10.1021/ed038p559Hulanicki, A. (1987). Reactions of acids and bases in analytical chemistry. Translated by Masson, Mary R. Horwood. ISBN 0-85312-330-6.Mendham, J.; Denny, R. C.; Barnes, J. D.; Thomas, M. (2000). Appendix 5. Vogels Textbook of Quantitative Chemical Analysis (5th ed.). Harlow: Pearson Education. ISBN 0-582-22628-7.Scorpio, R. (2000). Fundamentals of Acids, Bases, Buffers Their Application to Biochemical Systems. ISBN 0-7872-7374-0.

Sunday, March 1, 2020

New York State Unit Study - Geography, State Symbols Facts

New York State Unit Study - Geography, State Symbols Facts These state unit studies are designed to help children learn the geography of the United States and learn factual information about every state. These studies are great for children in the public and private education system as well as homeschooled children. Print the United States Map and color each state as you study it. Keep map at the front of your notebook for use with each state. Print the State Information Sheet and fill in the information as you find it. Print the New York State Outline Map and fill in the state capital, large cities and state attractions that you find. Answer the following questions on lined paper in complete sentences. State Capital What is the capital?Virtual Tour of the State CapitolState Flag What is Justice holding and what do they represent?Flag Quiz/PrintoutState Flower When was the state flower officially adopted?State Fruit When was the state fruit adopted?State Bird When do these birds return north?State Animal What is the state animal?State Fish Where are these fish found?State Insect How does this insect help gardeners?State Fossil What crab is this fossil related to?State Shell How do these scallops swim?State Tree When was the state tree adopted?State Gem What color is this gem?State Song Who wrote the state song?State Seal When was the current seal created?State Motto What is the state motto and what does it mean?State Muffin Make this state muffin and enjoy with the state beverage!State Beverage What is the state beverage? New York Printable Pages - Learn more about New York with these printable worksheets and coloring pages. Fun in the Kitchen - The official muffin of New York State, the Apple Muffin, was created by elementary school children in North Syracuse, New York. Try their official recipe. Presidents born in New York: Theodore RooseveltFranklin Delano Roosevelt History - Learn about the history of New York. Big Apple Factoids - A New York Matching Game - be sure to read the facts after you find the match! New York Underground - New Yorkers go about unaware of what is happening just beneath their feet: Power pulses, information flies, and steam flows. Go on this virtual field trip underground! Niagara: The Story of the Falls - Take a journey down the perilous Niagara River, play the daredevil trivia adventure, explore the timeline of falls firsts, and discover surprising stories in snapshots of the falls. Empire State Building - Find fun facts, go on a photo tour, and play some games. The Chrysler Building - Pictures of this New York City skyscraper. Word Search - Find the hidden New York related words. Coloring Book - Print and color these pictures of the New York state symbols. Fun Facts - What is the states longest river? Read these fun New York facts and find out. Capitol Minutes - Short audio presentation of historical and educational interest. Buck Mountain - Take a virtual hike up Buck Mountain. Crossword Puzzle - Can you solve the crossword puzzle? Word Find - Find the hidden New York State Regions. Word Scramble - Can you unscramble these New York State symbols? Odd New York Law: It used to be illegal to ring the doorbell and disturb the occupant of a house.