Chemistry Past Paper PDF - Acids and Bases

## 2.1 Understanding the Chemical Properties of Acids and Bases ### 2.1.1 Acids and Bases in the Laboratory #### Activity 2.1 - Collect the following solutions from the science laboratory: - Hydrochloric acid (HCl) - Sulphuric acid (H2SO4) - Nitric acid (HNO3) - Acetic acid (CH3CO...

## 2.1 Understanding the Chemical Properties of Acids and Bases ### 2.1.1 Acids and Bases in the Laboratory #### Activity 2.1 - Collect the following solutions from the science laboratory: - Hydrochloric acid (HCl) - Sulphuric acid (H2SO4) - Nitric acid (HNO3) - Acetic acid (CH3COOH) - Sodium hydroxide (NaOH) - Calcium hydroxide [Ca(OH)2] - Potassium hydroxide (KOH) - Magnesium hydroxide [Mg(OH)2] - Ammonium hydroxide (NH4OH) - Put a drop of each of the above solutions on a watch-glass one by one and test with a drop of the indicators shown in Table 2.1. - What change in colour did you observe with red litmus, blue litmus, phenolphthalein and methyl orange solutions for each of the solutions taken? - Tabulate your observations in Table 2.1. | Sample solution | Red litmus solution | Blue litmus solution | Phenolphthalein solution | Methyl orange solution | |:---|:---|:---|:---|:---| | ... | ... | ... | ... | ... | | ... | ... | ... | ... | ... | These indicators tell us whether a substance is acidic or basic (by change in colour). There are some substances whose odour changes in acidic or basic media. These are called olfactory indicators. Let us try out some of these indicators. #### Activity 2.2 - Take some finely chopped onions in a plastic bag along with some strips of clean cloth. Tie up the bag tightly and leave overnight in the fridge. The cloth strips can now be used to test for acids and bases. - Take two of these cloth strips and check their odour. - Keep them on a clean surface and put a few drops of dilute HCl solution on one strip and a few drops of dilute NaOH solution on the other. ## What are different kinds of nutrients? ## What are the common means to break down food? Which process is used by unicellular organisms to acquire food? ## Why do chemical reactions need to produce energy? ### Carbon molecules are food - Complex & kinds - Oxidation reduction - Break food - Unicellular ### Simple diffusion - CO2 + H2O + Sunlight > (CH2O) n + O2 - Chloroplast - Nutritional - External source of food - Provide Energy - Respiration - Transportations - Excretion - Food to different parts - Discharge form food - Unwanted by-product ### Simple diffusion - The processes which together perform this maintenance job are class, even if we are just asleep, this maintenance job has to go on, life processes. - Since these maintenance processes are needed to prevent damage outside the body of the individual organism. So there must be a process to transfer a source of energy from outside the body of the organism which we call food, to the inside, a process we commonly call nutrition - If the body size of the organisms is to grow, additional raw material will also be needed from outside. Since life on earth depends on carbon based molecules, most of these food sources are also carbon-based. - Depending on the complexity of these carbon sources, different organisms can then use different kinds of nutritional processes. - The outside sources of energy could be quite varied, since the environment is not under the control of the individual organism. These sources of energy, therefore, need to be broken down or built up in the body, and must be finally converted to a uniform source of energy that can be used for the various molecular movements needed for maintaining living structures, as well as to the kind of molecules the body needs to grow, For this, a series of chemical reactions in the body are necessary. ### Oxidising - reducing reactions - Oxidising - reducing reactions are some of the most common chemical means to break-down molecules. For this, many organisms use oxygen sourced from outside the body. The process of acquiring oxygen from outside the body, and to use it in the process of break-down of food sources for cellular needs, is what we call respiration. - In the case of a single-celled organism, no specific organs for taking in food, exchange of gases or removal of wastes may be needed because the entire surface of the organism is in contact with the environment. - But what happens when the body size of the organism increases and the body design becomes more complex? In multi-cellular organisms, all the cells may not be in direct contact with the surrounding environment. Thus, simple diffusion will not meet the requirements of all the cells, especially in the functions they perform. - We have seen previously how, in multi-cellular organisms, various body parts have specialised in the functions they perform. We are familiar with the idea of these specialised tissues, and with their organisation in the body of the organism. It is therefore not surprising that the uptake of food and oxygen will also be the function of specialised tissues. However, this poses a problem, since the food and oxygen are now taken up at one place while all parts of the body need them. This situation creates a need for a transportation system for carrying food and oxygen from one place to another in the body while all parts of the body need them. - This situation creates a need for a transportation system for carrying food and oxygen from one place to another in the body while all parts of the body need them. - This situation creates a need for a transportation system for carrying food and oxygen from one place to another in the body while all parts of the body need them. - This situation creates a need for a transportation system for carrying food and oxygen from one place to another in the body while all parts of the body need them. We will discuss all these aspects in the unit on "Nutrition in Plants and Animals".