Basic chemistry

properties and classification of acids  We can categorize a substance as an acid or a base according to the properties. Let us learn the characteristics properties of acids. Properties of acids The following are the characteristic properties of acids: 1.Taste :  The sour taste of many unripe fruits , lemon , vinegar and sour milk is caused by the acids present in them. Hence , we can say that acids have a sour taste.                                                                            Acids present in some substances . 2. Action on indicators .  Indicators show different colours in presence of acid and bases . The three commonly used indicator in presence of acids.                                  colour of some indicator in presence of acids .  3. Conduction of electricity and dissociation of acids  When acids are dissolve in water they produce ions which help in conducting the electricity. This process is known as dissociation . More specifically , acids

 INDICATORS   The substances which are neither acidic nor basic and are chemically inert in nature. Touching or tasting of acid or base is very harmful and hence typical indicators are used to recognise them. The substances which change their colours in presence of acid or base are called ‘Indicators’.  you might have seen that the spot of turmeric on cloth becomes red when soap is applied on it. what do you think has happened? Tumeric has acted as an indicator of base present in soap. There are many substances that shows one colour in an acidic medium and another colour in a basic medium. such substances are called acid base indicator.  litums is a natural dye founded in certain lichens. It was the earliest indicator to be used. it shows red colour in acidic medium and blue colour in basic solutions . phenolphthalein and methyl orange are some other indicators. The colour of these indicator in acidic, neutral and basic solutions are given below in the table. Indicato

ACIDS AND BASES     For thousands of years, people have known that vinegar, lemon juice, amla, tamarind and many other food items taste sour. However, only a few hundred years ago it was proposed that these things taste sour because they  contain 'acids'. The term acid comes from Latin term 'accre' which means sour . It was first used in the seventeenth century by robert boyle to label substance as acids and bases according to the following characteristics.   While Robert Boyle was sussessful in characterising acids and bases he could not explain their behaviour on the basis of their chemical structure.This was accomplished by Swedish scientist  Svante Arrhenius in the late nineteenth century. He proposed thaton dissolving in water , manycompounds dissociate and form ions and their properties are mainly the properties of the ions they form. Governed by this, he identified the ions furnished by acids and bases responsible for thier characteristics behaviour a

              UNITS OF MEASUREMENT       Many  properties of matter are quantitative in nature.  When you measure something, you are  comparing it with some standard. The standard  quantity is reproducible and unchanging.       Many properties of matter such as mass,  length, area, pressure, volume, time, etc.  are quantitative in nature. Any quantitative  measurement is expressed by a number  followed by units in which it is measured.  For example, length of class room can be  represented as 10 m. Here 10 is the number and  'm' denotes metre-the unit in which the length  is measured. The standards are chosen orbitrarily  with some universally acceped criteria. ''The  arbitrarily decided and universally accepted  standards are called units.''      There are several systems in which units  are expressed such as 1.C.G.S. System  :Length (centimetre), Mass (gram), Time (second) 2.M.K.S. System : Length (metre), Mass (kilogram), Time  (sec