Acids
We encounter Acids on daily basis. Most of the fruits, carbonated beverages, tea etc. are acids.
An acid is a chemical species that donates protons and/or accepts electrons. Many acids have bonded Hydrogen atom which they can release to form an Anion in solution. The word acid comes from the Latin words acidus or acere, which means "sour", since one of the characteristics of acid is its 'sour' taste. Common examples of acid includes Sulfuric Acid (), Vinegar (which contains acetic acid), Citric Acid (found in citrus fruits like Lemons).
An acid is a chemical species that donates protons and/or accepts electrons. Many acids have bonded Hydrogen atom which they can release to form an Anion in solution. The word acid comes from the Latin words acidus or acere, which means "sour", since one of the characteristics of acid is its 'sour' taste. Common examples of acid includes Sulfuric Acid (), Vinegar (which contains acetic acid), Citric Acid (found in citrus fruits like Lemons).
Indicator
Chemical indicator, any substance that gives a visible sign, usually by a colour change, of the presence or absence of a threshold concentration of a chemical species, such as an acid or an alkali in a solution. An example is the substance called methyl yellow, which imparts a yellow colour to an alkaline solution.
Olfactory Indicators
A substance whose smell varies depending on whether it is mixed with an acidic or basic solution is known as 'Olfactory indicator'. Such substances can be used in the laboratory to test whether a solution is a base or an acid, and this process is called olfactory Titration. Onion, Vanilla extract are common examples of Olafactory Indicators.
1.Onion:- Paste or juice of onion loses its smell when added with base.It does not change its smell with acid.
2.Vanilla:- The smell of vanilla vanishes with base, but its smell does not vanish with an acid.
1.Onion:- Paste or juice of onion loses its smell when added with base.It does not change its smell with acid.
2.Vanilla:- The smell of vanilla vanishes with base, but its smell does not vanish with an acid.
Natural Indicators
Indicators obtained from natural sources are called 'Natural Indicators'. The color of a natural acidbase indicator depends on pH. One of the most well known effects of natural indicators in plants occurs in the hydrangea or snowball plant. Hydrangea flowers are blue when grown in acidic soils and pink or red in basic soils.
Other common examples of Natural indicators include Turmeric, Beetroot juice etc.
Other common examples of Natural indicators include Turmeric, Beetroot juice etc.
Common Acid-Base Indicators
Substances which change colour with pH are known as 'Acid - Base indicators (also known as pH indicators)'. They are usually weak acids or bases, which when dissolved in water dissociate slightly and form ions. Consider an indicator which is a weak acid, with the formula .
At equilibrium, the following equilibrium equation is established with its conjugate base:
The acid and its conjugate base have different colours. Suppose acid has color A and base has color B.
At low pH values the concentration of is high and so the equilibrium position lies to the left. The equilibrium solution has the colour A. At high pH values, the concentration of is low - the equilibrium position thus lies to the right and the equilibrium solution has colour B. This way, we can use indicator during the acid base titration.
At equilibrium, the following equilibrium equation is established with its conjugate base:
The acid and its conjugate base have different colours. Suppose acid has color A and base has color B.
At low pH values the concentration of is high and so the equilibrium position lies to the left. The equilibrium solution has the colour A. At high pH values, the concentration of is low - the equilibrium position thus lies to the right and the equilibrium solution has colour B. This way, we can use indicator during the acid base titration.
Common Acid-Base Indicators
Phenolphthalein is a common example of an indicator which establishes this type of equilibrium in aqueous solution (Please see the image). Phenolphthalein is a colourless, weak acid which dissociates in water forming pink anions. Under acidic conditions, the equilibrium is to the left,and the concentration of the anions is too low for the pink colour to be observed. However, under alkaline conditions, the equilibrium is to the right, and the concentration of the anion becomes sufficient for the pink colour to be observed.
Other common examples of acid base indicators are Methyl Orange, Litmus etc.
Other common examples of acid base indicators are Methyl Orange, Litmus etc.
Effect of pH on plants and animals
High levels of either acidity or alkalinity can be harmful to plants and animals.
Effect on Plants:
Most of the plants do best when soil'd pH is in the neutral range i.e. 6 to 7.
Acidic soil can prevent certain nutrients from being absorbed by plants that are best absorbed in alkaline soil. In very alkaline soil, certain important micro-nutrients such as zinc and copper become chemically unavailable to plants.
Effect on Animals:
Effect of pH is most observed for the animals that stay in water. Acidic water robs fish and other aquatic species of sodium in the blood and oxygen in the tissues. Additionally, it affects the functioning of fish gills. Acidic water also poisons fish eggs, as they will not hatch if water pH is too low.
In addition to the direct effects on fish, acid water also destroys ecosystems by killing organisms lower on the food chain.
Effect on Plants:
Most of the plants do best when soil'd pH is in the neutral range i.e. 6 to 7.
Acidic soil can prevent certain nutrients from being absorbed by plants that are best absorbed in alkaline soil. In very alkaline soil, certain important micro-nutrients such as zinc and copper become chemically unavailable to plants.
Effect on Animals:
Effect of pH is most observed for the animals that stay in water. Acidic water robs fish and other aquatic species of sodium in the blood and oxygen in the tissues. Additionally, it affects the functioning of fish gills. Acidic water also poisons fish eggs, as they will not hatch if water pH is too low.
In addition to the direct effects on fish, acid water also destroys ecosystems by killing organisms lower on the food chain.
Importance of pH
Our body works within the range of 7.0 to 7.8. Living organisms can survive only in a narrow range of change. When of rain-water is less than 5.6, it is called acid rain. When acid rain flows into the rivers, it lowers the of the river water. The survival of aquatic life in such rivers becomes difficult.
pH of soil in backyard
Soil pH is dictated by type of parent material from which soil is formed, rainfall, organic matter content among others. Soil in the backyard would mean it consists of kitchen garden growing grass, vegetables, trees etc., and it would have been supplied with some kind of organic amendments, fertilizers etc., over a period of time. In such a scenario pH of acidic soils would improve and move towards neutral and pH of alkali soils would also move towards neutral.
pH in digestive system
The in the human digestive tract varies greatly. The of saliva is usually between 6.5 - 7.5. The fundic or upper portion of the stomach has a between 4.0 - 6.5, lower portion of the stomach secrete hydrochloric acid and pepsin until it reaches a between 1.5 - 4.0.
Effect of pH on tooth decay
The saliva in a healthy mouth has a pH of 7.1. Certain foods increase the acidity of the mouth and reduce the pH level. Saliva helps neutralize the acid, but the pH of saliva can become more acidic after eating acidic foods. It can take between a few minutes to a few hours for the pH of the mouth to neutralize. In that time, the lower pH of the mouth creates an optimal environment for bad bacteria, which eventually causes tooth decay.
Self defence by animals and plants through chemical warfare
The evolution of chemical defenses in plants is linked to the emergence of chemical substances that are not involved in the essential photosynthetic and metabolic activities.
Wasp stings basic liquid while ants bees injects acid.
Wasp stings basic liquid while ants bees injects acid.
pH in growing crops
pH is a scale that chemists use to measure acidity. Values below 7 are considered acidic, values above 7 are alkaline ( the opposite of acidic) and 7 is neutral. Most plants can tolerate a wide pH range in solution culture, but they cannot tolerate a wide range of acidity in the soil.
pH of Salts
Salts, when placed in water, will often react with the water to produce or . This is known as a Hydrolysis reaction. Based on how strong the ion acts as an acid or base, it will produce varying pH levels. When water and salts react, there are many possibilities due to the varying structures of salts. A salt can be made of either a weak acid and strong base, strong acid and weak base, a strong acid and strong base, or a weak acid and weak base.
1. Salts that are from strong bases and strong acids do not hydrolyze. The pH will remain neutral at 7. Halides and alkaline metals dissociate and do not affect the as the cation does not alter the and the anion does not attract the from water. This is why NaCl is a neutral salt. In General: Salts containing halides (except ) and an alkaline metal (except ) will dissociate into spectator ions.
2. Salts that are from strong bases and weak acids do hydrolyze, which gives it a pH greater than 7. The anion in the salt is derived from a weak acid, most likely organic, and will accept the proton from the water in the reaction. This will have the water act as an acid that will, in this case, leaving a hydroxide ion (). The cation will be from a strong base, meaning from either the alkaline or alkaline earth metals and, like before, it will dissociate into an ion and not affect the .
3. Salts of weak bases and strong acids do hydrolyze, which gives it a pH less than 7. This is due to the fact that the anion will become a spectator ion and fail to attract the , while the cation from the weak base will donate a proton to the water forming a hydronium ion.
4. Salts from a weak base and weak acid also hydrolyze as the others, but a bit more complex and will require the and to be taken into account. Whichever is the stronger acid or weak will be the dominate factor in determining whether it is acidic or basic.
1. Salts that are from strong bases and strong acids do not hydrolyze. The pH will remain neutral at 7. Halides and alkaline metals dissociate and do not affect the as the cation does not alter the and the anion does not attract the from water. This is why NaCl is a neutral salt. In General: Salts containing halides (except ) and an alkaline metal (except ) will dissociate into spectator ions.
2. Salts that are from strong bases and weak acids do hydrolyze, which gives it a pH greater than 7. The anion in the salt is derived from a weak acid, most likely organic, and will accept the proton from the water in the reaction. This will have the water act as an acid that will, in this case, leaving a hydroxide ion (). The cation will be from a strong base, meaning from either the alkaline or alkaline earth metals and, like before, it will dissociate into an ion and not affect the .
3. Salts of weak bases and strong acids do hydrolyze, which gives it a pH less than 7. This is due to the fact that the anion will become a spectator ion and fail to attract the , while the cation from the weak base will donate a proton to the water forming a hydronium ion.
4. Salts from a weak base and weak acid also hydrolyze as the others, but a bit more complex and will require the and to be taken into account. Whichever is the stronger acid or weak will be the dominate factor in determining whether it is acidic or basic.
Range of pH scale
The range of pH scale is from 0 to 14. The pH value from 0 to 7 indicates the acidic nature of solution whereas from 7 to 14 indicates the basic nature of solution. The intermediate value that is 7 indicates neutral nature of solution such as pure water.
Ammonia or Sodium Hydroxide show the pH value in the range 7-14, which reflects their basic nature.
On the contrary, acidic substances like vinegar, stomach acid, battery acid, coke etc show pH range from 0-7 that shows their acidic nature.
Ammonia or Sodium Hydroxide show the pH value in the range 7-14, which reflects their basic nature.
On the contrary, acidic substances like vinegar, stomach acid, battery acid, coke etc show pH range from 0-7 that shows their acidic nature.
pH scale
Acidity and alkalinity are measured with a logarithmic scale called pH. The pH scale measures how acidic or basic a substance is. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic. A pH greater than 7 is basic.
The pH scale is logarithmic and hence, each whole pH value below 7 is ten times more acidic than the next higher value. For example, pH 4 is ten times more acidic than pH 5 and 100 times (10 times 10) more acidic than pH 6. The same holds true for pH values above 7, each of which is ten times more basic than the next lower whole value. For example, pH 10 is ten times more alkaline than pH 9 and 100 times (10 times 10) more alkaline than pH 8.
The pH scale is logarithmic and hence, each whole pH value below 7 is ten times more acidic than the next higher value. For example, pH 4 is ten times more acidic than pH 5 and 100 times (10 times 10) more acidic than pH 6. The same holds true for pH values above 7, each of which is ten times more basic than the next lower whole value. For example, pH 10 is ten times more alkaline than pH 9 and 100 times (10 times 10) more alkaline than pH 8.
Limitations of pH scale
- pH values of the solutions do not give us immediate idea of the relative strengths of the solutions
- pH value zero is obtained in solution of strong acid.
- A solution of an acid having very low concentration can not have pH 8, as shown by pH formula but the actual pH value will be less than 7.
Bleaching powder
Formula:
Properties:1. It is a pale yellow powder. It has a strong smell of chlorine. It is soluble in water but a clear solution is never formed due to the presence of impurities.
2. On long standing, it undergoes auto-oxidation into calcium chlorate and calcium chloride.
3. On account of the formation of nascent oxygen, it shows oxidising and bleaching properties.
Properties:1. It is a pale yellow powder. It has a strong smell of chlorine. It is soluble in water but a clear solution is never formed due to the presence of impurities.
2. On long standing, it undergoes auto-oxidation into calcium chlorate and calcium chloride.
3. On account of the formation of nascent oxygen, it shows oxidising and bleaching properties.
Bleaching of paper
Bleaching of wood pulp is the chemical processing carried out on various types of wood pulp to decrease the color of the pulp, so that it becomes whiter. The main use of wood pulp is to make paper where whiteness is an important characteristic.
Pulp is bleached for a number of reasons. To produce high quality paper a pulp is required which does not discolour during storage or go yellow when exposed to sunlight, and which retains its strength. Bleaching achieves all three requirements and has the additional advantage of improving absorption capacity, removing any small pieces of bark or wood left behind as well as giving a high level of purity.
Pulp is bleached for a number of reasons. To produce high quality paper a pulp is required which does not discolour during storage or go yellow when exposed to sunlight, and which retains its strength. Bleaching achieves all three requirements and has the additional advantage of improving absorption capacity, removing any small pieces of bark or wood left behind as well as giving a high level of purity.
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