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CBSE Questions for Class 7 Chemistry Acids Bases And Salts Quiz 5 - MCQExams.com
CBSE
Class 7 Chemistry
Acids Bases And Salts
Quiz 5
The nature of solution which turns blue litmus paper red is ......... .
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acidic
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basic
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neutral
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none of these
Explanation
it must be acidic as an acidic solution turns blue litmus red.
An organic dye, cousins used to detect the endpoint of precipitation titration by the process of
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absorption
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adsorption
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chemical reaction
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none of the above
Explanation
An organic dye, cosine used to detect the endpoint of precipitation titration by adsorption, is called an adsorption indicator. This is also called Argentometry titration.
Argentometry
is a type of titration involving the silver(I) ion. Typically, it is used to determine the amount of chloride present in a sample. The sample solution is titrated against a solution of silver nitrate of known concentration. Chloride ions react with silver(I) ions to give the insoluble silver chloride:
$$Ag^+ +Cl^- \longrightarrow AgCl (K=5.88\times 10^9$$)
The yellow fluorescein is a common example used for the reaction i.e., -
$$NaCl (aq) + AgNO_3 (aq)\rightarrow AgCl (s) +NaNO_3 (aq)$$
The acidic or basic nature of a substance is tested by using:
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Indicator
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Litmus paper
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Salt solution
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Both A and B
Explanation
Litmus paper is used to detect the acidic or basic nature of a substance. Color of litmus paper in acid: Blue litmus paper turns red when dipped in acidic solution.
Acid-base indicators (also known as pH indicators) are substances that change color with pH.
A teacher gave two test tubes, one containing water and the other containing sodium hydroxide solution, to the students and asked them to identify the test tube containing sodium hydroxide solution. Which one of the following can be used for correctly identifying the test tube containing sodium hydroxide solution?
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Blue litmus paper
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Red litmus paper
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Sodium carbonate solution
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Dilute hydrochloric acid
Explanation
Red litmus paper will turn blue when it is dipped in a basic solution. So, the student can use red litmus paper to identify the test tube containing sodium hydroxide solution, which is basic.
The chemical name of "Oil of Vitriol" is:
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nitric acid
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hydrochloric acid
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potassium hydroxide
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sulphuric acid
Explanation
Sulphuric acid was first discovered by the liquefaction of green vitriol ($$ { Fe }{ SO }_{ 4 }.7{ H }_{ 2 }O $$). Hence, it is called the oil of vitriol.
Which solution is a conjugate acid/base pair with differing spectral absorbencies?
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Chemical pH indicator
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Acid/base buffer
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Anhydrous solution
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Hypotonic solution
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Supersaturated solution
Explanation
Chemical pH indicator is a conjugate acid/base pair with differing spectral absorbencies.
It is used to indicate the endpoint of the titration.
For example, phenolphthalein is colourless in acid solution and pink in colour in alkaline solution.
Also, litmus is red in acid solution and blue in alkaline solution.
Hence, the correct option is A.
The colours of red litmus paper in acidic, neutral, and basic solutions are:
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red, orange and blue respectively
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blue, violet and red respectively
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red, colourless and blue respectively
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red, red and blue respectively
Explanation
Solution
Colour of red litmus paper
Acidic
Red
Neutral
Red
Basic
Blue
So, the correct option is D.
Litmus is an extract of which of the following?
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China rose
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Beetroot
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Lichen
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Blur berries
Explanation
Litmus is extracted from different species of 'lichens'. Litmus solution or paper is commonly used to test whether the solution is acidic or basic in nature.
Study the given table carefully
Compounds
Colour change on adding
China rose indicator
(i) Hydroxide of group 2 element
Magenta
(ii) Oxide of element (group 16 and period 3)
Magenta
(iii) Oxide of element (electronic configuration 2,4)
Magenta
(iv) Hydroxide of element (at. no. 19)
Green
(v) Lime water
Magenta
Which of the following are correctly matched?
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(i), (ii) and (iv)
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(ii), (iii) and (iv)
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(ii), (iii) and (v)
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(i), (ii) and (iv)
Ant bite is treated by application of __________.
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washing soda
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baking soda
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neutral solution
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acidic solution
Explanation
$$\bf{Hint-}$$
Study about the reactions of acids and bases.
$$\bf{Concept-}$$
When acid is mixed with the base it neutralizes the reaction and gives salt as a product.
$$\bf{Explanation-}$$
The ant bites are acidic in nature. So, its effects can be neutralized by bicarbonate of soda such a baking soda or an alkali (i.e basic in nature).
$$\bf{Correct\ option-}$$
Option B is correct.
An indicator $$InH$$ has $${K_{In}}$$ value of $${10^{ - 7}}$$, it may exist in its molecular and ionic state in approximately $$1:1$$ ratio in which substance:
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lemon juice
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black coffee
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milk
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lime water
Choose the correct answer from the alternatives given.
Hydrochloric acid is secreted by the cells lining the __________________.
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oral cavity
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stomach
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small intestine
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large intestine
Explanation
Hydrochloric acid is secreted by the cell lining of the stomach. Hydrochloric acid helps in the digestion of food. Hence option B is correct.
______ indicator has natural origin.
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Litmus
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Methyl orange
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Universal indicator
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Phenolphthalein
Explanation
Litmus is the indicator extracted from the Lichen plant whereas methyl orange, universal indicator and phenolphthalein are made in laboratory. So option A is correct.
Indigestion is painful. So to relieve indigestion, we take an antacid such as milk of magnesia, which
contains:
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magnesium hydroxide
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hydrochloric acid
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tartaric acid
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calcium hydroxide
Explanation
Milk of magnesia (also known as magnesium hydroxide; $$ { Mg }{ (OH) }_{ 2 } $$) is basic in nature and one of the most important ingredients of an antacid.
The hydroxide ions from
$$ { Mg }{ (OH) }_{ 2 } $$) undergo neutralisation with
$$ { H }Cl $$ in the stomach produced during indigestion or gastric problems, to produce water. Equation is as follows :
$$ \quad 2HCl\quad +\quad Mg{ (OH) }_{ 2 }\quad \rightarrow \quad Mg{ (Cl) }_{ 2 }\quad +\quad 2{ H }_{ 2 }O $$
Hence option $$A$$ is correct.
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