Acids, Bases, and Salts PDF - Science Textbook

Okay, here is the conversion of document or image into a structured markdown format. ### Synthetic Indicator Indicators that are made in laboratory are called synthetic indicators. For example; phenolphthalein, methyl orange, etc. ### Litmus: A Natural Indicator The most commonly used natural indi...

Okay, here is the conversion of document or image into a structured markdown format. ### Synthetic Indicator Indicators that are made in laboratory are called synthetic indicators. For example; phenolphthalein, methyl orange, etc. ### Litmus: A Natural Indicator The most commonly used natural indicator is litmus. Litmus is extracted from lichens. Lichen is a composite organism. It consists of fungi and algae living in symbiotic relationship. ### Red litmus paper Litmus is available in the form of solution or paper strips of two colours blue and red. Liquid litmus and litmus paper are used to detect the acidic or basic nature of a substance. ### Blue litmus paper Litmus gives a purple colour in distilled water. In acidic solution blue litmus paper turns into red, while red litmus remains red. Red litmus paper turns into blue when dipped in basic solution, while blue litmus paper remains blue. ### Activity-1 To test the effect of acidic and basic solutions on litmus paper. Multidisciplinary Approach Materials required: Blue and red litmus paper, Dropper, Dilute lemon juice, Detergent, Shampoo, Vinegar, Salt and sugar solution, Milk of magnesia etc. Procedure: 1. Put a drop of dilute lemon juice on a strip of the red litmus paper. Observe the colour of the litmus paper and repeat the same on blue litmus paper. Is there any change in the colour of the litmus paper ? Repeat the same Activity for different solutions and record your observations in the following table. Observation : |S. No. |Sample solution |Effect on litmus paper |Inference | | :--- | :--- | :--- | :--- | | | |Blue |Red | | |1.|Lemon Juice |Turns red |Remains red |Acidic solution | |2.|Detergent |Blue |Blue |Basic | |3.|Shampoo |Blue |Blue |Basic | |4.|Vinegar |Red |Red |Acid | |5.|Salt |Blue |Red |Netwal | |6.|Sugar |Blue |Red |Natural| |7.|Milk of Magnesia |Blue |Blue |Basic | **Conclusion:** The solution of lemon juice, are acidic in nature while the Detergent are basic in nature. ### Naturally Naturally occuring acids produced by plants and animals (except hydrochloric acid) are called organic acids. The acids which are prepared with minerals are called mineral acids. Nitric acid, sulphuric acid and hydrochloric acid are some mineral acids. ### Uses of Acids Acids have many important uses. * Hydrochloric acid is used to clean wash basins and other sanitary wares. * It is also used as a reagent in laboratories. * Sulphuric acid is used in automobile batteries and in industries. * Goldsmiths use nitric acid to clean jewellery. ### Bases Bases are bitter in taste. Substances like baking soda are bitter in taste due to presence of bases in them. If you rub the solution of baking soda between the fingers, it fells soapy. Soap solution, washing soda are other examples of bases. The chemical nature of substances that contain base is said to be basic. Some common bases are calcium hydroxide (in lime water), sodium hydroxide or potassium hydroxide (in soap solution), ammonium hydroxide (in window cleaner) and magnesium hydroxide (in milk of magnesia). Many bases do not dissolve in water, but some bases like sodium hydroxide. potassium hydroxide or calcium hydroxide dissolve in water. The bases which dissolve in water are called alkalies. Thus all alkalies are bases but all bases are not alkalies. ### Uses of Bases Bases are used in * soap, textile, plastic and many other industries. * petroleum refining. * cleaning processes. * antacids. ### INDICATORS It is not always possible to know the acidic or basic nature of substances by tasting them. Tasting a substance in laboratory is not also advisable because it may be harmful. Thus, to test the chemical nature (acidic or basic nature) of the substances a special kind of substance called indicator is used. An indicator changes its colour to show the nature of a substance. Indicators can be divided into two types. Natural Indicator: Indicators that are obtained from naturally occurring substances are called natural indicators. For example; litmus, turmeric, China rose, etc. ### ACTIVITY-2 To demonstrate the neutralisation reaction. Multidisciplinary Approach Materials required : Test tubes, Dropper, Phenolphthalein indicator, Dilute hydrochloric acid Colution and Dilute sodium hydroxide solution. Procedure: * Take about 5 mL of dilute solution of sodium hydroxide (NaOH) in a test tube. * Add 2 drops of phenolphthalein indicator to it. * The solution in the test tube turns pink. * Now add dilute solution of hydrochloric acid (HCl) dropwise using a dropper and shake the test tube to mix the solution. * Stop adding hydrochloric acid when the pink colour of the solution just disappears. * Now add a drop of sodium hydroxide solution and shake the test tube to mix the solution. What do you see? * Keep repeating the addition of sodium hydroxide and hydrochloric acid solutions one after the other and watch the appearance and disappearance of pink colour. * Touch the test tube after the reaction is over. Does it appear warm ? Observation : * The solution turns pink. The pink colour disappears. When a drop of HCl solution is added to the solution in the test tube. * The test tube appears warm on touching. **Conclusion:** The addition of hydrochloric acid (HCl) solution destroys the alkaline nature of sodium hydroxide (NaOH). On the other hand, the addition of sodium hydroxide (NaOH) solution destroys the acidic nature of hydrochloric acid (HCl). That is, both sodium hydroxide (NaOH) and hydrochloric acid (HCl) appear to cancel the effect of each other. Such a reaction between an acid and a base is called neutralisation reaction. Salt formed because of neutralisation reaction may be acidic or basic in nature. Acidic or basic nature of salt depends on the strength of acid and base. In a neutralisation reaction heat is evolved. It is due to this heat that the test tube appears warm in Activity-2. Reactions in which heat is evolved are called exothermic reactions. On the other hand, reactions in which heat is absorbed are called endothermic reactions. Thus, neutralisation reaction is an exothermic reaction. In Activity-2, when solution of sodium hydroxide is mixed with the solution of hydrochloric acid, both neutralise each other and common salt (Sodium chloride) is formed. Since, it is an exothermic reaction, so reaction mixture becomes slightly hot. The reaction involved in this can be written as follows: $Sodium + Hydrochloric acid \longrightarrow Sodium + Water + Heat$ $(NaOH) + (HCI) \longrightarrow (NaCl) + (H_2O)$ ### Synthetic Indicators Synthetic indicators are made in laboratories. Phenolphthalein and methyl orange are most commonly used synthetic indicators. Phenolphthalein is colourless. It remains colourless in acidic solution but imparts pink colour in basic solution. Methyl orange has originally orange colour. It turns into red in acidic medium and yellow in basic medium. ### ACID RAIN Carbon dioxide, sulphur dioxide and nitrogen dioxide which are released from vehicles and chimneys mix with droplets of rain and turn the rainwater acidic. When this acidic rainwater falls over earth, it is known as acid rain. Acid rain damages the buildings and is harmful for plants and animals. Taj Mahal, which is made of marble is in threat because of acid rain. Many parts of Taj Mahal and other many historical buildings and monuments have got damaged due to acid rain. ### Characteristics of Acids and Bases |Property |Acids |Bases | |:--- |:--- |:--- | |1. Taste |Sour in taste. |Bitter in taste. | |2. Touch |Abrasive/Rough |Slippery (soapy) | |3. Effect on litmus paper|Turn blue litmus paper red.|Turn red litmus paper blue.| |4. Effect on China rose solution |Turn the solution of China rose to dark pink colour (magenta).|Turn solution of China rose to green.| |5. Effect on turneric paper |Not affect turneric paper. |Turn turneric paper to red. | |6. Effect on phenolphthalein |Remain colourless |Turn pink | |7. Effect on methyl orange |Turn red |Turn yellow | |8. Solubility |Most of the acids are soluble in water. |Bases may or may not be soluble in water.| ### NEUTRALISATION When solution of an acid is mixed with the solution of a base, both of them neutralise each other and a third substance; called salt; is formed. This process is called neutralisation or neutralisation reaction. The solution formed because of mixing of solution of acid and base is neither acidic nor basic in nature. Such solution is said to be neutral in nature. In other words, $Acid + Base \longrightarrow Salt + Water$ Another neutralisation reaction is the reaction between limewater and dilute sulphuric acid. $Lime + Sulphuric acid \longrightarrow Calcium + Water + Heat$ $[Ca(OH)_2] + (H_2SO_4) \longrightarrow (CaSO_4) + (H_2O)$ The reaction mixture becomes warm due to evolution of heat in this reaction. ### NEUTRALISATION IN EVERYDAY LIFE The process of neutralisation plays very important role in our daily life. Some of its applications are described below. #### Indigestion Our stomach releases hydrochloric acid to kill bacteria; if any present in food. Hydrochloric acid also helps in the digestion of food. Sometimes our stomach produces more hydrochloric acid than required. Production of more hydrochloric acid in the stomach causes indigestion. This condition called acidity, can be painful and causes pain burning sensation in the stomach. To get rid of this, any antacid such as milk of magnesia (a base) is taken. Milk of magnesia, being a base (contains magnesium hydroxide) neutralises the effect of hydrochloric acid and gives relief from acidity. #### Ant sting An ant or a bee injects formic acid (also called methanoic acid) into our skin, while biting. Injection of acid by ant or bee results in pain at that place. Rubbing baking soda over the skin gives relief from pain due to ant or bee sting. Baking soda, which is a base, neutralises the effect of acid injected by the bee or ant. Another base, such as zinc carbonate (Calamine solution) is also used in case of ant or bee sting. #### Soil Treatment Sometimes soil becomes too acidic or basic due to excess use of fertilisers or wrong method of harvesting. Acidic or basic nature of soil affects the yield as plants do not grow properly on such soil. Acidic soil is treated with slaked lime or quick lime. Slaked lime (Calcium hydroxide) and quick lime (Calcium oxide) are basic in nature. Use of slaked lime or quick lime neutralises the acidic nature of soil. Basic soil is treated with organic matter such as manure. Organic matter releases acid and neutralises the basic nature of soil. #### Factory Wastes Wastes of most of the factories are highly acidic. If such acidic wastes are flushed into rivers, or other water bodies, acid present in them will damage the aquatic organisms and pollute the water. Thus, factory wastes are treated with basic substances to neutralise the effect of acid present in them before being discharged into the water bodies. ### Turmeric: Another Natural Indicator Turmeric is also used as another natural indicator. Turmeric is of yellow colour. It turns into red when dipped into basic solution. Turmeric does not change its colour in acidic solution. Have you ever noticed that a turmeric stain turns red when washed with a detergent? I is because detergents are basic in nature. Repeat Activity-1 with a turmeric paper and record your observations in a same table as in Activity-1. You can use both the indicators to test the acidic and basic nature of different solutions and tabulise your results as below. |S. No. |Test Solution |Effect on Litmus Paper |Effect on Turmeric Paper | |:---|:---|:---|:---| |1.|Lemon juice|Blue litmus turns red|Remains yellow| |2.|Vinegar|Blue litmus turns red|Remains yellow| |3.|Soap solution|Red litmus turns blue|Turns reddish brown| |4.|Milk of magnesia|Red litmus turns blue|Turns reddish brown| ### China Rose as Indicator China rose is another natural indicator extracted from China rose petals. In an acidic medium, it exhibits dark pink (magenta colour), while in a basic medium, it exhibits green colour. You can easily make China rose solution. Collect some China rose petals and keep them in a beaker. Add some warm water into the beaker. After some time the water becomes coloured. Now use this solution as an indicator to test the acidic and basic nature of different substances. Some common solutions exihibit the following results with China rose indicator. |S. No.|Test Solution|Effect on China rose| |:---|:---|:---| |1.|Lemon juice|Dark red| |2.|Vinegar|Dark red| |3.|Detergent|Green| |4.|Baking soda|Green| |5.|Orange juice|Dark red| **A turmeric paper can be made by depositing a thick turmeric paste on a blotting or filter paper. Cut the paper into strips after it dries completely. Use these strips to test different solutions.**