A salt is formed when hydrogen ions are replaced by a metal or an ammonium ion in an acid. A base is a material that reacts with an acid to produce just water and salt. When an acid reacts with a base, it produces a salt.
An ionisable compound, when dissolved in water or in its molten state, dissociates into ions almost entirely. Examples: NaCl, HCl, KOH, etc.
A non-ionisable compound does not dissociate into ions when dissolved in water or in its molten state. Examples: glucose, acetone, etc.
Acid And Base Grade 12 Notes Pdf Download
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An acid is any hydrogen-containing substance that is capable of donating a proton (hydrogen ion) to another substance. A base is a molecule or ion able to accept a hydrogen ion from an acid. Acidic substances are usually identified by their sour taste.
An indicator is a chemical substance which shows a change in its physical properties, mainly colour or odour, when brought in contact with an acid or a base.
Below mentioned are commonly used indicators and the different colours they exhibit:
Acids produce carbon dioxide, as well as metal salts and water, when they react with metal carbonates or metal bicarbonates. Sodium chloride, carbon dioxide, and water are formed when sodium carbonate interacts with hydrochloric acid. Allowing carbon dioxide gas to travel through lime water turns it milky.
A very common acid is hydrochloric acid. The reaction between strong acid, says hydrochloric acid and strong base say sodium hydroxide, forms salt and water. The complete chemical equation is shown below.
Dilution is the process of reducing the concentration of a solution by adding more solvent (usually water) to it.
It is a highly exothermic process.
To dilute acid, the acid must be added to water and not the other way round.
Acidic substances are used by animals and plants as a self-defence mechanism. For example, bee and plants like nettle secrete a highly acidic substance for self-defence. These secreted acidic substances have a specific pH.
A salt of a strong acid and a strong base will be neutral in nature. pH = 7 (approx.).
A salt of a weak acid and a strong base will be basic in nature. pH > 7.
A salt of a strong acid and a weak base will be acidic in nature. pH < 7.
The pH of a salt of a weak acid and a weak base is determined by conducting a pH test.
Sodium chloride is a common salt. NaCl is its molecular formula. The fundamental element in our meals is sodium chloride. It is used in our food as a flavour enhancer as well as a preservative. From common salt, we may make the following four compounds.
Bleaching powder is soluble in water and is used as a bleaching agent in textile industries. It is also used as an oxidizing agent and a disinfectant in many industries. It should also be noted that bleaching powder is synthesized by the reacting chlorine gas on dry slaked lime i.e. Ca(OH)2.
Sodium bicarbonate, also known as baking soda or bicarbonate of soda, is a chemical compound with the formula NaHCO3 and the IUPAC designation sodium hydrogen carbonate. A sodium cation (Na+) and a bicarbonate anion (HCO3) combine to form this salt. Sodium bicarbonate is a white, crystalline substance that is commonly found as a fine powder. It tastes slightly salty and alkaline, like washing soda (sodium carbonate).
The process by which a solid form, in which the atoms or molecules are strongly arranged into a structure known as a crystal, is known as crystallisation. Precipitation from a solution, freezing, and, more rarely, direct deposition from a gas are some of the ways crystals form.
Plaster of Paris is a widely used chemical compound that is extensively used in sculpting materials and gauze bandages. Plaster of Paris is a white powdery chemical compound that is hydrated calcium sulphate that is usually obtained by calcining gypsum. While we have seen many applications of this material in our everyday lives, if we try to understand its chemistry, we will find that it is a white powdery chemical compound that is hydrated calcium sulphate that is usually obtained by calcining gypsum. To put it another way, Plaster of Paris is often manufactured of heated gypsum at a high temperature.
pH is a measure of hydrogen ion concentration in a solution. The higher the hydrogen ion concentration, the lower the pH. Acids which give rise to more hydrogen ions are more acidic than acids which give fewer hydrogen ions. Thus, the lower the pH, the higher the acidic nature of the solution. Thus, Y has more hydrogen ion concentration than X.
Acids react with metals to produce the respective metal salt along with hydrogen gas. Therefore, when hydrochloric acid (HCl) reacts with metals, it evolves hydrogen gas along with the formation of corresponding metal salt.
In this chapter learners will explore acid-base reactions and redox reactions. Redox reactions were briefly introduced in gr10. The concepts of acids, bases, reduction, oxidation and oxidation numbers are all introduced here. The following list provides a summary of the topics covered in this chapter.
This chapter begins by revising all the concepts done on acids and bases up to this point. Learners are reminded what an acid and a base are (in particular the Bronsted-Lowry definition) and how the definition and concept have changed over time. Although the most recent definition of an acid and a base is the Lowry definition this is not covered at school level and the Bronsted-Lowry definition serves as a good working model for the acids and bases that learners encounter at school.
The concept of a polyprotic acid is introduced although it is not in CAPS. This is done to help learners understand how to handle acids such as sulfuric acid in reactions. You should try to use polyprotic acids sparingly in your examples.
The concept of conjugate acids and bases requires learners to think about reactions going in reverse. By writing the equation in reverse, learners can see how the acid becomes a base. This base is said to be the conjugate base of the acid since it is conjugated (linked) to the acid.
This topic is placed after redox reactions in CAPS but must be taught before redox reactions and so is placed before redox reactions in this book. This topic provides the tools needed to understand redox reactions.
In grade 10 learners learnt how to balance chemical equations by inspection. In this topic they will learn how to balance redox reactions which often cannot be balanced by inspection. The simpler examples can be balanced by inspection and this can be used as a comparison for the two techniques. Learners need to be able to break a reaction up into two parts and follow different chemical species through an equation. This skill starts with conjugate acids and bases and carries over into this topic.
Coloured text has been used as a tool to highlight different parts of reactions. Ensure that learners understand that the coloured text does not mean there is anything special about that part of the reaction, this is simply a teaching tool to help them identify the important parts of the reaction.
All around you there are chemical reactions taking place. Green plants are photosynthesising, car engines are relying on the reaction between petrol and air and your body is performing many complex reactions. In this chapter we will look at two common types of reactions that can occur in the world around you and in the chemistry laboratory. These two types of reactions are acid-base reactions and redox reactions.
Most acids share certain characteristics, and most bases also share similar characteristics. It is important to be able to have a definition for acids and bases so that they can be correctly identified in reactions.
One of the first things that was noted about acids is that they have a sour taste. Bases were noted to have a soapy feel and a bitter taste. However you cannot go around tasting and feeling unknown substances since they may be harmful. Also when chemists started to write down chemical reactions more practical definitions were needed.
A number of definitions for acids and bases have developed over the years. One of the earliest was the Arrhenius definition. Arrhenius (1887) noticed that water dissociates (splits up) into hydronium \((\text{H}_{3}\text{O}^{+})\) and hydroxide \((\text{OH}^{-})\) ions according to the following equation:
Arrhenius described an acid as a compound that increases the concentration of \(\text{H}_{3}\text{O}^{+}\) ions in solution and a base as a compound that increases the concentration of \(\text{OH}^{-}\) ions in solution.
However, this definition could only be used for acids and bases in water. Since there are many reactions which do not occur in water it was important to come up with a much broader definition for acids and bases.
In 1923, Lowry and Bronsted took the work of Arrhenius further to develop a broader definition for acids and bases. The Bronsted-Lowry model defines acids and bases in terms of their ability to donate or accept protons.
We highlight the chlorine and the nitrogen so that we can follow what happens to these two elements as they react. We do not highlight the hydrogen atoms as we are interested in how these change. This colour coding is simply to help you identify the parts of the reaction and does not represent any specific property of these elements.
Notice in these examples how we looked at the common elements to break the reaction into two parts. So in the first example we followed what happened to chlorine to see if it was part of the acid or the base. And we also followed nitrogen to see if it was part of the acid or the base. You should also notice how in the reaction for the acid there is one less hydrogen on the right hand side and in the reaction for the base there is an extra hydrogen on the right hand side.
Depending on what water is reacting with it can either react as a base or as an acid. Water is said to be amphoteric. Water is not unique in this respect, several other substances are also amphoteric. 152ee80cbc