Page 23 - NCERT Science Class 10 English Medium

Q U E S T I O N

1. You have been provided with three test tubes. One of them contains
distilled water and the other two contain an acidic solution and a basic ?
solution, respectively. If you are given only red litmus paper, how will
you identify the contents of each test tube?

.
UNDERSTANDING THE CHEMICAL PROPERTIES OFPROPERTIES OF
1 UNDERSTANDING THE CHEMICANDING THE CHEMICAL PROPERTIES OF
UNDERST
UNDERST
2 2 2 2
2.1 .1.1 .1 UNDERSTANDING THE CHEMICANDING THE CHEMICAL PROPERTIES OFAL PROPERTIES OF
AL
ACIDS AND BASESAND BASES
ACIDS
ACIDS AND BASES
BASES
ACIDS AND
ACIDS AND BASES
2.1.1 Acids and Bases in the Laboratory
Activity 2.1
Activity 2.12.1
2.1
Activity
Activity
Activity 2.1
n Collect the following solutions from the science laboratory–
hydrochloric acid (HCl), sulphuric acid (H SO ), nitric acid (HNO ),
2 4 3
acetic acid (CH COOH), sodium hydroxide (NaOH), calcium
3
hydroxide [Ca(OH) ], potassium hydroxide (KOH), magnesium
2
hydroxide [Mg(OH) ], and ammonium hydroxide (NH OH).
2 4
n 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.
n What change in colour did you observe with red litmus, blue litmus,
phenolphthalein and methyl orange solutions for each of the
solutions taken?
n Tabulate your observations in Table 2.1.
Table 2.1
Sample Red Blue Phenolph- Methyl
solution litmus litmus -thalein orange
solution solution solution 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.

2.2
Activity 2.2
Activity
Activity
Activity 2.22.2
Activity 2.2
n 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.
n Take two of these cloth strips and check their odour.
n 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.

18 Science

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