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(a) What is an indicator? Name three common indicators.
(b) Name the acid-base indicator extracted from lichen.
(c) What colour does the turmeric paper turn when put in an alkaline solution?
(a) An indicator is a "dye" that shows a distinct change in colour (or smell in case of olfactory indicator) when put in acid or base.
Litmus, Methyl orange and phenolphthalein are examples for indicators.
(b) Litmus is the acid-base indicator extracted from lichen.
(c) When turmeric paper is dipped in alkaline solution it will turn red.
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- The indicator which produces a pink colour in an alkaline solution:(a) Methyl orange(b) Turmeric paper(c) Phenolphthalein(d) Litmus paper
- (a) What is produced if an acid is added to a base?(b) Why does dry HCl gas not change the colour of dry litmus paper?(c) What colour does phenolphthalein indicator turn when added to an alkali (such as sodium hydroxide)?
- What is the common name of :(a) methanoic acid, and (b) ethanoic acid?
- Answer the following questions:-1. Turmeric is(a) an acid (b) a base (c) salt (d) an indicator2. What are indicators? Name two olfactory indicators.3. Name two other natural indicators. How do they behave with acids and bases?
- Solution A turns universal indicator blue to purple whereas solution B turns universal indicator orange to red.(a) What will be the action of solution A on litmus? (b) What will be action of solution B on litmus? (c) Name any two substances which can give solutions like A. (d) Name any two substances which can give solutions like B. (e) What sort of reaction takes place when solution A reacts with solution B?
- What colours do the following indicators turn when added to an acid (such as hydrochloric acid)(a) litmus (b) methyl orange
- 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) and (c)(iv) only (d)
- If the point $P( x,\ y)$ is equidistant from the points $A( a\ +\ b,\ b\ –\ a)$ and $B( a\ –\ b,\ a\ +\ b)$. Prove that $bx=ay$.
- Simplify the following using the formula: $(a - b) (a + b) = a^2 - b^2$:
(i) $(82)^2 – (18)^2$
(ii) $(467)^2 – (33)^2$
(iii) $(79)^2 – (69)^2$
(iv) $197 \times 203$
(v) $113 \times 87$
(vi) $95 \times 105$
(vii) $1.8 \times 2.2$
(viii) $9.8 \times 10.2$ - If \( P A \) and \( P B \) are tangents from an outside point \( P \). such that \( P A=10 \mathrm{~cm} \) and \( \angle A P B=60^{\circ} \). Find the length of chord \( A B \).
- In \( \triangle A B C, \angle A \) is obtuse, \( P B \perp A C, \) and \( Q C \perp A B \). Prove that \( B C^{2}=\left(A C \times C P +A B \times B Q\right) \).
- From an external point \( P \), tangents \( P A=P B \) are drawn to a circle with centre \( O \). If \( \angle P A B=50^{\circ} \), then find \( \angle A O B \).
- What is the common name of (a) NaHCO3 and (b) Na2CO3.10H2O?
- Prove that the points $P( a,\ b+c),\ Q( b,\ c+a)$ and $R( c,\ a+b)$ are Collinear.
- (a) Name the gas evolved when ethanol reacts with sodium.(b) What type of compound is formed when a carboxylic acid reacts with an alcohol in the presence of conc. H2SO4? (c) What will you observe when dilute ethanoic acid and dilute hydrochloric acid are put on universal indicator paper, one by one? What does it show?

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