Richard H. Langley

Article / Updated 05-03-2023

Acid-base reactions and their associated calculations play a primary role in many chemical, biological, and environmental systems. Whether you’re determining hydrogen ion concentration, [H+]; hydroxide ion concentration, [OH˗]; pH; or pOH, an equation and a calculator are important tools to have in your toolbox. Following are some handy formulas for solving acid/base problems. Calculating hydrogen or hydroxide ion concentration The following equation allows you to calculate the hydrogen ion concentration, [H+], at 25°C if you know the hydroxide ion concentration, [OH–]; you can also find [OH–] if you know [H+]. Just divide 1 × 10–14 by the concentration given, and you get the concentration that you need. Tip: To use scientific notation on your calculator, use the EE or EXP key (followed by the exponent) rather than the × 10^ keys. Calculating hydrogen or hydroxide ion concentration from the pH or pOH Be familiar with how to solve for [H+] or [OH–] when given the pH or pOH (or vice versa). Use the following formulas: Many scientific and graphing calculators differ in how they handle inputting values and taking logarithms, so know the proper keystroke order for your calculator. Be sure to review your calculator manual or look online. Calculating pH when given the pOH Calculating pH when you know the pOH (or vice versa) is probably the easiest of the acid-base calculations. Here’s the formula: pH + pOH = 14 Simply subtract the given value from 14 (keeping significant digits in mind) to get the value that you need. Doing titration calculations with a 1:1 acid-to-base ratio When you’re given titration calculations where the acid and base are reacting in a 1:1 ratio according to the balanced equation, the following equation offers a quick and easy way to solve for either the concentration of one of the substances or the volume necessary to complete the titration: MAVA = MBVB If the acid and base aren’t reacting in a 1:1 ratio, use stoichiometry (or dimensional analysis) to solve for your unknown quantity. By the way, stoichiometry works for the 1:1 ratio questions, too; it just takes one or two more steps. Remember: Keep track of your units! Cancel what you need to get rid of and make sure that you still have the units you need in your final answer.

Article / Updated 05-03-2023

The hyperbolic functions are certain combinations of the exponential functions ex and e–x. These functions occur often enough in differential equations and engineering that they’re typically introduced in a Calculus course. Some of the real-life applications of these functions relate to the study of electric transmission and suspension cables.

Cheat Sheet / Updated 01-09-2023

Organic Chemistry II is one of the toughest courses you can take. Surviving isn’t easy — you probably know that from your Organic Chemistry I class. Preparation is key: If you study the basics of organic chemistry the right way, prepare for your tests, and know your aromatic systems, you’re off to a great start!

Cheat Sheet / Updated 02-23-2022

Studying amino acids (the building blocks of proteins, which humans need to grow and develop) is essential in biochemistry. The four subgroups of amino acids are nonpolar, polar and uncharged, acidic, and basic. This Cheat Sheet provides a handy, quick reference to these four subgroups.

Cheat Sheet / Updated 02-17-2022

Solving chemistry problems is a great way to master the various laws and calculations you encounter in a typical chemistry class. This Cheat Sheet provides some basic formulas, techniques, and tips you can refer to regularly to make solving chemistry problems a breeze (well, maybe not a breeze, but definitely easier).

Article / Updated 03-26-2016

In an Organic Chemistry II class you often add groups to aromatic systems. If you’re wondering where the substitution will take place, check out this table for some guidelines. When using this table, remember two things: O-p-directors always beat m-directors. Strong activators always beat weak activators. Classification of Various Aromatic Substituents Ortho-Para-Directors Very Strong Activators -NH2, -NHR, -NR2, -OH, -O– Moderate Activators -OR, -NH-CO-R, -O-CO-R Weak Activators -R, -C6H5 Mild Deactivators -F, -Cl, -Br, -I Meta-Directors Very Strong Deactivators -N+R3, -NO2, -CN, -CCl3, -CF3 Moderate to Mild Deactivators -CN, -SO3H, -CO-R, -COOH, -COOR, -CONH2, -N+H3

Article / Updated 03-26-2016

Organic Chemistry II doesn’t have to be as difficult as you think. Follow these study tips to improve your understanding of organic chemistry, from carbon atom bonds to unnamed reactions, and everything in between: Don’t simply memorize concepts, learn the concepts by working exercises. Keep up with the material by studying Organic Chemistry II a minimum of six days a week. Buy and use a model kit. For each reaction you study, know where and why the electrons are moving. Learn those named (and unnamed) reactions. Use other resources in addition to your textbook (like the excellent Organic Chemistry II For Dummies, written by John T. Moore and Richard H. Langley and published by Wiley). Read ahead in your textbook before class. Take really good class notes and recopy them as soon as possible. If you need help, ask questions.

Article / Updated 03-26-2016

Taking an Organic Chemistry II test has a completely deserved reputation for being tough. Make life easier by following these tips before you take your next organic chemistry exam: Remember that the carbon atom forms four bonds. Don’t cram the night (or even a week) before a test. Attend class religiously. Correct the mistakes you made on previous exams and don’t make the same mistakes again. Assign formal charges and use them to help decide most probable structure, sites for nucleophilic/electrophilic attack, and so on. When writing an organic reaction, be sure you don’t lose any carbon atoms. Relax and get enough sleep the night before an exam. Include E/Z, R/S, and cis/trans prefixes when naming organic structures. Think of spectroscopic data, especially NMR, as puzzle pieces and try to fit them together. Work problem sets and practice exams twice. If you find you’ve drawn a compound in which a carbon doesn’t have four bonds, go back to the beginning of this list.

Article / Updated 03-26-2016

Amino acids are important to the study of biochemistry because they're the building blocks of proteins found in all cells. The basic group of amino acids is represented here:

Article / Updated 03-26-2016

Amino acids play an important role in the study of biochemistry. The following nonpolar amino acids are hydrophobic, or water-hating. They don't gratefully interact with (dissolve in) water. Here are the nonpolar amino acids: