What are Acids and Bases

Acids and bases are determined by their properties. The word acid comes from the Latin word acidus, which means sour. For example, lemon juice tastes sour because it contains citric acid. Sauerkraut, another sour-tasting food, is cabbage fermented in lactic acid. In fact, sauer (pronounced almost exactly like the English word sour) in German means acid. Sour cream also has lactic acid in it. 

Substances can have other properties that define them as acids. For example, acids can dissolve some metals, such as lead and zinc. They change litmus (a dye made from lichens) from blue to pink, and they react with bases to form a salt and water. 

Bases have specific properties that mark them as bases, too. Bases taste bitter, but most bases are not food, so they should not be tasted. In fact, no chemical substance should ever be tasted unless you are positive it is safe. Bases also feel slippery to 

Acids and bases are almost always found as aqueous solutions— that is, dissolved in water. Solutions of both acids and bases are called electrolytes. Electrolytes conduct electricity, which is the movement of electrons or other charged particles. When an acid or a base is dissolved in water, they break down into their ions, which 

Robert Boyle (1627-1691), an Irish chemist, was the first person to classify certain chemicals as either acids or bases. Boyle based his classifications on their properties. He was unable to explain, however, why acids and bases have the properties that they do. It would be another 200 years before a scientist came along to answer that question. That scientist was the Swedish chemist Svante Arrhenius (1859-1927). 

In aqueous chemistry, an acid is a substance that increases the concentration of H30 (hydronium ion). Conversely, a base decreases the concentration of H30 in aqueous solution. As we shall see shortly, a decrease in H30 concentration necessarily requires an increase in OH (hydroxide) concentration. Therefore a base is also a substance that increases the concentration of OH in aqueous solution. 

A more general definition of acids and bases given by Br0nsted and Lowry is that an acid is a proton donor and a base is a proton acceptor. This definition includes the one already stated. For example, HCl is an acid because it donates a proton to H2O to form H30  

The Br0nsted-Lowry definition can be extended to nonaqueous solvents and to the gas phase  

Any ionic solid, such as ammonium chloride, is called a salt. In a formal sense, a salt can be thought of as the product of an acid-base reaction. When an acid and a base react, they are said to neutralize each other. Most salts are strong electrolytes. 

Br0nsted-Lowry acid proton donor Br0nsted-Lowry base proton acceptor 

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Table 10.2 on the next page summarizes the observable properties of acids and bases. These observable properties include their physical characteristics and their chemical behaviour. The Express Lab on page xxx provides you with an opportunity to compare some of these properties. What are acids and bases, however How does chemical composition determine whether a substance is acidic or basic You will consider one possible answer to this question starting on page 373. 

So what are acids and bases Vinegar is actually a dilute solution of acetic acid in water, about a 5 percent solution, but it rather nicely displays the characteristic properties of acids they are sour, they turn purple-cabbage indicator red or pink, and they react with bases to form water. A solution of sodium bicarbonate nicely displays several of the characteristics of basic solutions it tastes bitter, it turns purple-cabbage indicator blue, and it reacts with acids to form water. The last property, listed for both acid and base, the ability to react with each other, is really the defining property because acid-base reactions, like redox reactions, occur in tandem one substance acts as an acid and one substance acts as a base. Acid neutralizes base and base neutralizes acid. 

What are acids and bases Acids are compounds that release hydrogen ions (protons) when dissolved in aqueous solution. In other words, they are proton donors. Bases are compounds that are proton acceptors. 

When ants sense danger to the ant colony, they emit a substance called formic acid that alerts the entire colony. Acids in rainwater hollow out enormous limestone caverns and destroy valuable buildings and statues. Acids flavor many of the beverages and foods you like, and it s an acid in your stomach that helps digest what you eat. Bases also play a role in your life. The soap you use and the antacid tablet you may take for an upset stomach are bases. Perhaps you have already concluded that the household products you used in the DISCOVERY LAB are acids and bases. 

In this chapter, I cover a few topics from the chemistry of consumer products. 1 show you the chemistry behind soaps, detergents, and cleaners. 1 talk a little bit about medicines and drugs, and 1 show you some things about personal care products, permanents, tanning products, and perfumes. 1 hope that you ll gain an appreciation for chemistry and what it has done to make your life better and easier. (Note that lots of common chemicals in the home are acids and bases. Chapter 12 s main thing is acids and bases, which makes it nice complementary reading to this chapter.)... 

At what concentration are acids and bases generally considered to be corrosive ... 

In Chapter 6 we survey what has been accomplished and indicate directions for future research. Furthermore, we critically review the influence of water on Lewis acid - Lewis base interactions. This influence has severe implications for catalysis, in particular when hard Lewis acids and bases are involved. We conclude that claims of Lewis-acid catalysis should be accompanied by evidence for a direct interaction between catalyst and substrate. 

Acids and bases are a big part of organic chemistry but the emphasis is much different from what you may be familiar with from your general chemistry course Most of the atten tion m general chemistry is given to numerical calculations pH percent loniza tion buffer problems and so on Some of this returns m organic chemistry but mostly we are concerned with the roles that acids and bases play as reactants products and catalysts m chemical reactions We 11 start by reviewing some general ideas about acids and bases... 

The problem with the Arrhenius definitions is that they are specific to one particular solvent, water. When chemists studied nonaqueous solvents, such as liquid ammonia, they found that a number of substances showed the same pattern of acid-base behavior, but plainly the Arrhenius definitions could not be used. A major advance in our understanding of what it means to be an acid or a base came in 1923, when two chemists working independently, Thomas Lowry in England and Johannes Bronsted in Denmark, came up with the same idea. Their insight was to realize that the key process responsible for the properties of acids and bases was the transfer of a proton (a hydrogen ion) from one substance to another. The Bronsted-Lowry definition of acids and bases is as follows ... 

In this chapter, we see what acids and bases are and why they vary in strength. We shall use thermodynamics, particularly equilibrium constants, to discuss the strengths of acids and bases quantitatively and thereby develop our insight into their behavior. We then use our knowledge of equilibria involving acids and bases to examine systems in which more than one equilibrium is taking place simultaneously. 

Metals typically form basic oxides and nonmetals typically form acidic oxides, but what about the elements that lie on the diagonal frontier between the metals and nonmetals Along this frontier from beryllium to polonium, metallic character blends into nonmetallic character, and the oxides of these elements have both acidic and basic character (Fig. 10.7). Substances that react with both acids and bases are classified as amphoteric, from the Greek word for both. For example, aluminum oxide, A1203, is amphoteric. It reacts with acids ... 

Many of the reactions that take place in water have analogous reactions in liquid ammonia, (a) Write the chemical equation for the autoprotolysis of NH,. (b) What are the formulas of the acid and base species that result from the autoprotolysis of... 

These reactions are equilibria. What the rule actually says is that the position of equilibrium will be such that the weaker acid predominates. However, this needs to be taken into account only when the acid and base are close to each other in the table (within 2 p f units). 

Since Arrhenius, definitions have extended the scope of what we mean by acids and bases. These theories include the proton transfer definition of Bronsted-Lowry (Bronsted, 1923 Lowry, 1923a,b), the solvent system concept (Day Selbin, 1969), the Lux-Flood theory for oxide melts, the electron pair donor and acceptor definition of Lewis (1923, 1938) and the broad theory of Usanovich (1939). These theories are described in more detail below. 

What makes indicators change color in the presence of acids and bases A color change is often the sign that a chemical reaction has occurred, and this is no exception Acid-base indicators are actually acids or bases themselves. They change colors because the acid and its conjugate base (or the base and its conjugate acid) are different colors. For example, suppose an acidic indicator, abbreviated HIn (this is not really a chemical formula, it is just a way to show an indicator that has hydrogen ions to donate), is dissolved in water. It... 

In general, acids react with bases to form water and a salt. The salt will depend upon what acid and base are used ... 

The above equation has an equilibrium constant that is less than 1. What are the relative strengths of the acids and bases ... 

Imagine that you are asked to design a chemistry kit for young children to use. In one of the experiments, the properties of acids and bases are studied. What chemicals are appropriate for this experiment What safety precautions would you include ... 

It is possible to be consistent with our E and C equation and view intermolecular interactions in terms of concepts we could call hardness, softness and strength. However, in doing this, we will have to modify the qualitative ideas presented by Pearson (2) about what hardness and softness mean, vide infra. The approach involves converting the E and C equation to polar coordinates. Our acids and bases are represented as vectors in E and C space in Fig. 7. The dot product of these two vectors is given as... 

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