When citing the strength of an acid, chemists often use the dissociation constant, Ka, but this number can vary by several orders of magnitude from one acid to another. If you already know the pKa value for an acid and you need the Ka value, you find it by taking the antilog. In practice, this means raising both sides of the equality to exponents of In the Bronsted-Lowry formulation of acids in solution, the acid donates a proton and the solution accepts one.
The solution becomes one containing a conjugate base — which is the product of the acid having lost a proton — and a conjugate acid. Theoretically, this reaction can happen in both directions. When the solvent is water, this is written as:. It's possible to determine this strength of the original acid by dividing the concentrations of the conjugate acid and base by the concentrations of the original acid and base.
How do you calculate a Ka value from pKa?
When the solvent is water, it's left out of the equation. This operation gives you the dissociation constant Ka:. When Ka is large, it means the conjugate ions aren't strong enough to move the reaction in the opposite direction, which indicates a strong acid. The dissociation constant for a strong acid can be as high as 10 7while for a weak acid it can be as low as 10 To create a more manageable number, chemists created the pKa value:.
A strong acid with a dissociation constant of 10 7 has a pKa of -7, while a weak acid with a dissociation constant of 10 has a pKa of Besides being easier to work with, pKa values have an inverse relationship to acid strength. In other words, a low pKa indicates a strong acid and vice versa. In some tables, you may find the pKa value listed, but you may need the Ka value to plug into your equations.
You solve this by raising both sides of the original relationship to powers of 10 to get:. When pKa is a whole number, such as -7, this operation is easy to perform, but when it contains a fraction, such as 7. Remember that pKa is expressed as a common logarithm base 10 and not as a natural logarithm base eso you want to find a table or select a function on your calculator that raises the number to a power of 10 rather than a power of e.
Chris Deziel holds a Bachelor's degree in physics and a Master's degree in Humanities, He has taught science, math and English at the university level, both in his native Canada and in Japan. He began writing online inoffering information in scientific, cultural and practical topics. His writing covers science, math and home improvement and design, as well as religion and the oriental healing arts.
About the Author. Copyright Leaf Group Ltd.You have no doubt heard of the pH scale, which is used to measure how acidic a solution e. You probably think of acids as being tart for example, citric acid is a common ingredient in sour candies and at times dangerous most people learn to associate the word "acid" with "potential skin damage" before reaching adulthood, even if only from Hollywood movies or dire news reports.
But what is an acid, chemically speaking? And are there individual properties of different acids that make determining the pH of a solution easier, as long as you know the molar concentration of the acid dissolved in that solution?
That "signature" trait is called the acid dissociation constant K a. Sometimes informally written as ka, you can calculate pH in a mathematically straightforward manner.
An acid is a molecule that can donate a proton and rarely, more than one proton in sequence in aqueous solution, i. The molecule left behind is an anion. Strong acids such as hydrochloric acid HCl more "eagerly" donate protons than the far more numerous weak acids, meaning that they can offload protons even in a low-pH environment, i.
Weak acids are only eager to donate their protons when the ambient pH is high, that is, the proton concentration is relatively low. Above, you read that a low pH implies an environment with lots of protons freed of their parent acids. As it happens, the pH scale is a logarithmic or "log" scale that for practical purposes ranges from 1 to 14, from most to least acidic. The equation for pH is:.
Every tenfold increase in proton concentration drives the pH down by one integer unit and conversely. K a thus offers a measure of an acid's "enthusiasm" to offload protons and thus is strength; the more strongly dissociated the acid at equilibrium, the higher the numerator in relation to the denominator in this equation and the higher the K a.
You can calculate the pH of a solution given the pKa of the acid and the concentrations above, that of the donated protons excluded. Computing pK a from K a means performing the same operation as with pH: Take the negative logarithm of K aand there is your answer. The derivation is involved, but the Henderson-Hasselbach equation relates these quantities in the following manner:. Example: The K a of acetic acid, the main component of vinegar, is 1.
This means that at pH lower than acetic acid's pKa, less than half will be dissociated, or ionized; at higher pH values, more than half will be ionized. Kevin Beck holds a bachelor's degree in physics with minors in math and chemistry from the University of Vermont. Formerly with ScienceBlogs. More about Kevin and links to his professional work can be found at www.
Example: What is the pH of a solution of 0. About the Author. Copyright Leaf Group Ltd.There are related scales in chemistry used to measure how acidic or basic a solution is and the strength of acids and bases. Although the pH scale is most familiar, pKaKapKband Kb are common calculations that offer insight into acid-base reactions.Ka and pKa Derivation
Here's an explanation of the terms and how they differ from each other. Whenever you see a "p" in front of a value, like pH, pKaand pKb, it means you're dealing with a -log of the value following the "p". For example, pKa is the -log of Ka.
Because of the way the log function works, a smaller pKa means a larger Ka. If you know pH, you can calculate pOH. If you know an equilibrium constant, you can calculate the others. The pH scale ranges from 0 to A low pH value indicates acidity, a pH of 7 is neutral, and a high pH value indicates alkalinity. The pH value can tell you whether you're dealing with an acid or a base, but it offers limited value indicating the true strength of the acid of a base.
The formulas to calculate pH and pOH are:. Ka, pKa, Kb, and pKb are most helpful when predicting whether a species will donate or accept protons at a specific pH value. They describe the degree of ionization of an acid or base and are true indicators of acid or base strength because adding water to a solution will not change the equilibrium constant.
Ka and pKa relate to acids, while Kb and pKb deal with bases. Like pH and pOHthese values also account for hydrogen ion or proton concentration for Ka and pKa or hydroxide ion concentration for Kb and pKb.
Ka and Kb are related to each other through the ion constant for water, Kw:. Ka is the acid dissociation constant. Similarly, Kb is the base dissociation constant, while pKb is the -log of the constant.
Acids and bases dissociate according to general equations:. In the formulas, A stands for acid and B for base. A large Ka value indicates a strong acid because it means the acid is largely dissociated into its ions. A large Ka value also means the formation of products in the reaction is favored.
A small Ka value means little of the acid dissociates, so you have a weak acid. The Ka value for most weak acids ranges from 10 -2 to 10 These can include maltodextrin, natural flavors, food starch, and a host of others that you'll find in all kinds of foods. Especially while you're adjusting your shopping habits, it's a great thing to have printed out and in your purse or wallet:As you find products that you can eat, write them down.
pH, pKa, Ka, pKb, and Kb Explained
That way, you'll save time at the grocery store instead of having to read the nutrition label every time. I didn't have anything like this when I ended up having emergency surgery, and my poor husband had some frustrating experiences trying to find things for me. Another issue you need to be aware of is cross-contamination. The simple act of putting a gluten-free bagel in your toaster can transfer small amounts of gluten to this previously safe food.
If you live with people who don't share your diet, you really need to be careful. When it comes to cutting boards, avoiding wood is a good idea, since it's absorbent. I use plastic, and I have one that's just for gluten-containing foods and one that's kept free of them.
Same goes for your colander. To save on dishes, you can also prepare your food first and then re-use things for everyone else's. In my kitchen, you'll also find two butter dishes in use so I can keep mine from free from all those little glutinous crumbs that are transferred from the knife. My butter is kept on a higher shelf as well, so my kids don't accidentally grab it.
The toaster is an annoying one because it can be expensive. I considered two options: adding a second toaster to my kitchen, or buying a four-slice model with good separation between "their" side and mine. Because I don't have the space for two, I opted for a four-slice one. I get the two slots on the left, while everyone else uses the right.
How to Convert pKa to Ka
Because gluten is responsible for the textures we're used to in baked goods, you may find that the things you bake with gluten-free flours just don't measure up. I've even found mixes that end up dry and crumbly. Something that really helps is using xanthan gum or guar gum.
They help bind the food together and have a better texture. I don't bake a tremendous amount, but for everything I have baked with gluten-free flour, a multi-purpose blend with a little xanthan gum has worked really well.We got to stay at the MGM, go quad biking across the desert, front-row tickets to the Cirque du Soleil and a helicopter trip over the strip.
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You can do just that and keep track using the Competitions Time forum board. Scroll down to the bottom of the forum board to the 'display options' box.
Now tell it to sort threads in order of 'thread start time' from the beginning, and 'descending'. This will sort the competitions into chronological order to reduce the chances of missing the deadline on each. Use the page numbers to go back to the page showing the oldest (still open) competitions. This is usually page 200ish. At the end of a session, write down the last competition you entered.
This way you have a record of where you got up to for next time. Some promoters exclude people who enter multiple times. To keep track of completed contests, press the tick button at the bottom of the post.
Next time you visit the board, it will show a green tick next to that comp. Alternatively, press X to skip one. You must register and log on to the forum to do this. Don't forget to thank the MoneySaver who posted the comp by clicking the button below their post.
So take steps to avoid being deluged with marketing bumf. Never use your normal email address. It'll be immediately flooded with spam. Instead, set up a dedicated email account. As a powerful free option, Gmail is among the best. There's usually a way to choose not to get 'further communications' to avoid most of the marketing.
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A Sim is the small (roughly 2cm by 1cm) microchip card you insert into a phone when it's first set up.Pectin also promotes moisture retention in bread and can be used as a vegan substitute in gluten-free bread recipes. Look for citrus or apple pectin at health food stores or at grocery stores where jam and jelly making ingredients are kept.
Expandex adds wheat-like texture to gluten-free bread. It can be added directly to your mixes or you can use a mix like Jules' Gluten-Free All Purpose Flour Mix which contains Expandex. My recipe for Gluten-Free Honey Buckwheat English Muffins is made with Jules Gluten-Free Flour Mix and this is my family's favorite gluten-free "bread" recipes. Learn More About Expandex and How to Use it in Gluten-Free RecipesGo buy one of these priceless, yet inexpensive gadgets.
A digital, or "instant read" thermometer will save you lots of frustration because it lets you easily measure the internal temperature of your bread. When the internal temperature is approximately 206 degrees F it's done.
No more gooey loaves - no more dried out loaves. Top Instant Read Kitchen ThermometersLook for lidded Pullman loaf pans at King Arthur Flour or check out this smaller Pullman loaf pan at Kitchenworks. An easy way to create a good environment for gluten-free bread to rise is to turn your oven to 200 degrees F. When it reaches this temperature, turn the oven off and place a shallow baking pan partially filled with hot water in the oven.
Lightly cover the loaf pan with a damp towel and place in the oven for 20 to 30 minutes or until the dough rises to the top of the loaf pan. This method really does speed up the time it takes for gluten-free bread to rise.
Just be sure to carefully watch the process so that your bread does rise over the top of the pan before baking. Work With Room Temperature IngredientsYeast loves a warm environment and bread will rise more quickly and completely when ingredients are at room temperature rather than cold. The Waste-free LunchboxIt has been estimated that on average a school-age child using a disposable lunch generates 67 pounds of waste per school year.
That equates to 18,760 pounds of lunch waste for just one average-size elementary school. If you're like us, you're always on the lookout for small changes that make a real difference in the world, and packing a waste-free lunch is once such change that's easy to make.
If you walk around at lunchtime and take a good look at the lunches our children bring to school, here's what the typical lunch will look like: In this scenario very little trash is generated because foods are bought in bulk or in larger packages.
The packaging is left at home for reuse or recycling. Food waste also decreases because with a reusable lunch container, children can re-pack uneaten food instead of dumping it, packaging and all, into the school trash can. Education is the first step in the transition to a waste-free lunch. Talk to your children about why the school has decided to institute a waste-free lunch program.
Provide them with age-appropriate information about the negative impact of a disposable lunch. Below is a list of suggestions that will help build communication and foster understanding.
Read this list with your children. Ask them to circle the foods they'd like to see in their lunchboxes. The above information was excerpted from The Laptop Lunch User's Guide: Fresh Ideas for Making Wholesome, Earth-friendly Lunches Your Children Will Love.
Copyright 2002, Morning Run Press. Sign up for our free monthly e-newsletter. Email: Tips for Parents It has been estimated that on average a school-age child using a disposable lunch generates 67 pounds of waste per school year. Understanding the Problem The Typical Lunch: If you walk around at lunchtime and take a good look at the lunches our children bring to school, here's what the typical lunch will look like: sandwiches in disposable plastic bags fruits and vegetables in plastic bags prepackaged chips, cookies, fruit bars, granola bars, cheeses, and fruit leathers single-use yogurts, applesauces, and puddings crackers, pretzels, chips, and other snack foods sealed in plastic bags disposable juice boxes, juice pouches, juice cans, water bottles, and milk cartons plastic forks and spoons paper napkins reusable lunchboxes and disposable paper and plastic bags A Waste-free Lunch: sandwiches and other main dishes, fresh fruits and, fresh vegetables, and treats in a reusable lunch container or containers cloth napkins stainless-steel forks and spoons reusable drink containers reusable lunchboxes In this scenario very little trash is generated because foods are bought in bulk or in larger packages.
Educating Your Family Education is the first step in the transition to a waste-free lunch. Teach children about recycling at home. Encourage them to help separate the recyclables from the non-recyclables. When you choose not to buy an excessively packaged item, point it out to your children and ask if they can think of some earth-friendly packaging alternatives.James Harden is playing MVP-caliber basketball right now by averaging 33.
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Houston Rockets vs Utah Jazz MatchupThe Utah Jazz sport a record of 13-12 and 15-10 ATS heading into this matchup, while the Houston Rockets sit at 18-4 and 13-9 ATS on the NBA season.
Stay Informed: follow us on Twitter for odds specials, betting line moves and Utah vs Houston injuries news. The betting Power Rankings at OddsShark have the No.
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