ANSWER THE FOLLOWING:
1. What are acids ? Give some examples .(2mark )
An acid is a chemical substance that has a sour taste.
Many food items such as lemons, curd, vinegar and orange taste sour because of the presence of acid in them.
Natural Acids are the acids that occur in nature, for example, acids found in fruits are natural acids.
2.What are Bases? Give some examples.(2marks)
A base is a chemical substance that has a bitter taste and a soapy texture.
Bases are found in different substances such as bleach, ammonia, washing powder and soap.
Bases are also called Alkaline.
3.Define the following:(1mark)
A.Neutral Substance: Any substance which is neither acidic nor basic in nature.eg: salt sugar.
B.Indicator : An indicator is a substance that can determine if another substance is acidic or basic in nature.
4. What is the role of indicators? Give some examples.(2mark)
The indicators indicate the presence of an acid or base in a substance by changing their colour.
For Example Turmeric, China rose petals and Litmus are some natural indicators.
5. How litmus paper acts as an indicator?(3marks)
a.Litmus :Litmus is a natural indicator which is obtained from Lichens.
Litmus is available in a solution form and paper strips (red litmus and blue litmus paper).
Acid - (BLUE TO RED)changes blue litmus paper into red and shows no change with red litmus paper.
Base - (RED TO BLUE) Changes red litmus paper to blue and shows no change with blue litmus paper.
6.How to use Turmeric as an indicator?(2marks)
To use turmeric as an indicator it is generally mixed with water to form a paste which is then put on blotting paper and dried this is used to find the acid or base nature of a substance.
Turmeric :
1. ACID - NO CHANGE IN COLOUR
2. BASE - CHANGES TO RED COLOUR
7. What colour change do you observe in acid and base soloution on adding chinarose and phenolphthalein as indicators?(2marks)
A.China rose as indicator:
ACID - MAGENTHA(DARK PINK).
BASE - GREEN.
B.Phenolphthalein is pink in colour it is an synthetic indicator:
ACID - COLOURLESS
BASE - remains in PINK (no change).
8.what is a Neutralization reaction ?write it's general equation.(2 marks)
When correct amount of an acid is mixed with a base salt and water is produced with a release of heat ,this reaction is called Neutralization reaction.
ACID+BASE GIVES SALT+WATER .
(heat is released)
9.Write the Neutralization reaction in our day to day life.(5 marks)
1.Indigestion : due to over secretion of hydrochloric acid(HCl) in our stomach indigestion occurs.
An antacid like milk of magnesia (gelusil liquid) is taken to neutralize the effect.
( Milk of magnesia is base in nature).
2.Antbite : when ant bite us formic acid is secreted by it which cause irritation and pain
To neutralize it baking soda or calamine solution is applied (both are base in nature).
3.soil treatment:
Plants need a soil which is neutral in nature but using chemical fertilizers on soil can turn it into acidic.
To treat acidic soil we use quicklime (calcium oxide) or slaked lime (calcium hydroxide).
Basic soil can be treated by adding organic substances to it as they release acids while decomposing into the soil.
4.Factory wastes :
The factory waste is acidic in nature and cannot be directly dumped anywhere. Hence bases are added to it before it falls off into a river or stream so that the aquatic life does not get affected.
