If you have a yeast-free recipe, any fluffiness in the final biscuit is usually due to carbon dioxide formed from baking powder. One popular brand of boxed mix uses a combination of sodium bicarbonate and sodium aluminum sulfate to produce the CO 2. The reaction is seen below:. If all goes well, the biscuits rise, the pancakes are fluffy, and everybody is happy.
A salt is an ionic compound that is formed when an acid and a base neutralize each other. While it may seem that salt solutions would always be neutral, they can frequently be either acidic or basic. Consider the salt formed when the weak acid hydrofluoric acid is neutralized by the strong base sodium hydroxide. The molecular and net ionic equations are shown below.
Since sodium fluoride is soluble, the sodium ion is a spectator ion in the neutralization reaction. The fluoride ion is capable of reacting, to a small extent, with water, accepting a proton. The hydroxide ion that is produced as a result of the above reaction makes the solution slightly basic. Salt hydrolysis is a reaction in which one of the ions from a salt reacts with water, forming either an acidic or basic solution.
When solid sodium fluoride is dissolved into water, it completely dissociates into sodium ions and fluoride ions. This is sometimes true, but the salts that are formed in these reactions may have acidic or basic properties of their own, as we shall now see. A solution is neutral when it contains equal concentrations of hydronium and hydroxide ions. When we mix solutions of an acid and a base, an acid-base neutralization reaction occurs. However, even if we mix stoichiometrically equivalent quantities, we may find that the resulting solution is not neutral.
It could contain either an excess of hydronium ions or an excess of hydroxide ions because the nature of the salt formed determines whether the solution is acidic, neutral, or basic. The following four situations illustrate how solutions with various pH values can arise following a neutralization reaction using stoichiometrically equivalent quantities:. Our stomachs contain a solution of roughly 0. The burning sensation associated with heartburn is a result of the acid of the stomach leaking through the muscular valve at the top of the stomach into the lower reaches of the esophagus.
The lining of the esophagus is not protected from the corrosive effects of stomach acid the way the lining of the stomach is, and the results can be very painful. When we have heartburn, it feels better if we reduce the excess acid in the esophagus by taking an antacid. As you may have guessed, antacids are bases. One of the most common antacids is calcium carbonate, CaCO 3. The reaction,. Milk of Magnesia is a suspension of the sparingly soluble base magnesium hydroxide, Mg OH 2.
It works according to the reaction:. The hydroxide ions generated in this equilibrium then go on to react with the hydronium ions from the stomach acid, so that :. This reaction does not produce carbon dioxide, but magnesium-containing antacids can have a laxative effect. Several antacids have aluminum hydroxide, Al OH 3 , as an active ingredient. The aluminum hydroxide tends to cause constipation, and some antacids use aluminum hydroxide in concert with magnesium hydroxide to balance the side effects of the two substances.
Cooking is essentially synthetic chemistry that happens to be safe to eat. There are a number of examples of acid-base chemistry in the culinary world. One example is the use of baking soda, or sodium bicarbonate in baking. NaHCO 3 is a base. Many people like to put lemon juice or vinegar, both of which are acids, on cooked fish Figure 1.
It turns out that fish have volatile amines bases in their systems, which are neutralized by the acids to yield involatile ammonium salts. Pickling is a method used to preserve vegetables using a naturally produced acidic environment.
The vegetable, such as a cucumber, is placed in a sealed jar submerged in a brine solution. The brine solution favors the growth of beneficial bacteria and suppresses the growth of harmful bacteria. The beneficial bacteria feed on starches in the cucumber and produce lactic acid as a waste product in a process called fermentation.
The lactic acid eventually increases the acidity of the brine to a level that kills any harmful bacteria, which require a basic environment. Without the harmful bacteria consuming the cucumbers they are able to last much longer than if they were unprotected.
A byproduct of the pickling process changes the flavor of the vegetables with the acid making them taste sour. When we neutralize a weak base with a strong acid, the product is a salt containing the conjugate acid of the weak base. This conjugate acid is a weak acid. For example, ammonium chloride, NH 4 Cl, is a salt formed by the reaction of the weak base ammonia with the strong acid HCl:. Consequently, the bonded water molecules' O—H bonds are more polar than in nonbonded water molecules, making the bonded molecules more prone to donation of a hydrogen ion:.
The conjugate base produced by this process contains five other bonded water molecules capable of acting as acids, and so the sequential or step-wise transfer of protons is possible as depicted in few equations below:. This is an example of a polyprotic acid, the topic of discussion in a later section of this chapter.
Aside from the alkali metals group 1 and some alkaline earth metals group 2 , most other metal ions will undergo acid ionization to some extent when dissolved in water. The acid strength of these complex ions typically increases with increasing charge and decreasing size of the metal ions. The first-step acid ionization equations for a few other acidic metal ions are shown below:.
An ICE table with the provided information is. Substituting the expressions for the equilibrium concentrations into the equation for the ionization constant yields:. The ICE table defined x as equal to the hydronium ion concentration, and so the pH is calculated to be. As an Amazon Associate we earn from qualifying purchases. Want to cite, share, or modify this book? This book is Creative Commons Attribution License 4.
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