Consider the following statements:
(a) Both acids and bases change colour of all indicators.
(b) If an indicator gives a colour change with an acid, it does not give a
change with a base.
(c) If an indicator changes colour with a base, it does not change colour
with an acid.
(d) Change of colour in an acid and a base depends on the type of the
indicator.
Which of these statements are correct?
(i) All four (ii) a and d (iii) b, c and d (iv) only d
Blue litmus paper is dipped in a solution. It remains blue. What is the
nature of the solution? Explain.
The dimensions of a godown are 40 m, 25 m and 10 m. If it is filled
with cuboidal boxes each of dimensions 2 m × 1.25 m × 1 m, then
the number of boxes will be
(a) 1800 (b) 2000 (c) 4000 (d) 8000
A regular hexagon is inscribed in a circle of radius r. The perimeter
of the regular hexagon is
(a) 3r (b) 6r (c) 9r (d) 12r
Three liquids are given to you. One is hydrochloric acid, another is
sodium hydroxide and third is a sugar solution. How will you identify
them? You have only turmeric indicator.
Explain why:
(a) An antacid tablet is taken when you suffer from acidity.
(b) Calamine solution is applied on the skin when an ant bites.
(c) Factory waste is neutralised before disposing it into the water
bodies.
Dorji has a few bottles of soft drink in his restaurant. But, unfortu-
nately, these are not labelled. He has to serve the drinks on the demand
of customers. One customer wants acidic drink, another wants basic
and third one wants neutral drink. How will Dorji decide which drink is
to be served to whom?
Mark ‘T’ if the statement is true and ‘F’ if it is false:
(i) Nitric acid turn red litmus blue. (T/F)
(ii) Sodium hydroxide turns blue litmus red. (T/F)
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and
form salt and water. (T/F)
(iv) Indicator is a substance which shows different colours in acidic
and basic solutions. (T/F)
(v) Tooth decay is caused by the presence of a base. (T/F)
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