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CBSE Questions for Class 7 Chemistry Acids Bases And Salts Quiz 2 - MCQExams.com
CBSE
Class 7 Chemistry
Acids Bases And Salts
Quiz 2
State true or False.
Nitric acid turns red litmus blue.
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True
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False
Explanation
Nitric acid is acidic in nature. Thus, it would turn blue litmus to red. Hence, given statement is false.
Observe the given flowchart carefully and mark the appropriate option correctly representing I, II, and III.
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Sweet $$\quad$$ Calamine $$\quad$$ Formic acid
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Bitter $$\quad$$ Formic acid $$\quad$$ Baking soda
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Bitter $$\quad$$ Baking soda $$\quad$$ Calamine
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Sweet $$\quad$$ Formic acid $$\quad$$ Baking soda
Explanation
Acids are sour in taste and when ants bite they inject formic acid ($$\text{HCOOH}$$) into the victim
. Hence $$II$$ is Formic acid.
This formic acid can be neutralized by a base. Baking soda is sodium bicarbonate which is alkaline in nature and can neutralize the formic acid. Hence $$III$$ is Baking soda.
It is bitter in taste ($$I$$).
Hence, option $$B$$ is correct.
Sodium hydroxide turns blue litmus red.
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True
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False
Explanation
Sodium hydroxide is a base. So, its solution turns red litmus paper blue.
So, the given statement is false.
Wasp stings can be treated with:
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baking soda
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vinegar
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washing soda
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milk of magnesia
Explanation
Wasp sting has basic venom. So an acid could be used to treat it.
Vinegar $$(CH_3COOH)$$
is used to treat the wasp sting.
Hence, option B is correct.
A solution of sodium chloride salt in water does not change the colour of any litmus paper.
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True
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False
Milk of magnesia is an/a:
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acid
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antacid
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alkali
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rock salt
Explanation
$$\bf{Hint:}$$ Antacid are alkaline compounds which used to relieve acidity.
$$\bf{Explanation:}$$
Magnesium hydroxide $$Mg(OH)_{2}$$ is known as milk of magnesia which is a weak alkaline base and also used to treat acidity problems as it reacts with acid and neutralized it.
Milk of magnesia, $$Mg(OH)_2$$, dissolves in water to form a basic solution. It is, therefore, called an alkali.
The reaction of milk of magnesia with acid is shown as below;
$$\underbrace{Mg(OH)_2}_{Base}+\underbrace{H_2SO_4}_{Acid}\longrightarrow \underbrace{MgSO_4}_{Neutral\ salt}+2H_2O$$
Other common antacid includes aluminum hydroxide, calcium carbonate, etc.
$$\bf{Final \ answer:}$$ O
ption $$B$$ and $$C$$
To protect tooth decay we are advised to brush our teeth regularly. The nature of the toothpaste commonly used is:
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Acidic
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Basic
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Neutral
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Corrosive
Explanation
$$\textbf{Concept Applied:}$$
The neutralization reaction is the one in which an acid reacts with an equimolar amount of base to give salt and water.
$$NaOH+HCl\rightarrow NaCl+H_2O$$
$$\textbf{Correct Option:}$$ B
$$\textbf{Explanation for correct option:}$$
Mouth has salivary amylase enzyme and the process of digestion starts from mouth making the acidic environment which causes the tooth decay so it is neutralized by using toothpaste basic in nature.
$$\textbf{Explanation for incorrect options:}$$ according to given concept toothpaste should be in basic nature so rest all other are wrong.
Milk of magnesia $$Mg(OH)_2$$ is a/an:
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acid
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antacid
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alkali
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rock salt
Explanation
Milk of Magnesia is a white suspension of hydrated magnesium carbonate in water, used as an antacid or laxative.
$$Mg(OH)_2$$ may be termed as an alkali but due to its low solubility in water it is considered as an atypical alkali.
Therefore antacid is the most appropriate answer.
Sulphurous acid turns _________ litmus paper __________.
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blue, red
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red, blue
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red, red
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blue, blue
Explanation
Sulphurous acid turns blue litmus red as it is the property of acids to turn blue litmus red.
The solution of calcium oxide turns red litmus blue.
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True
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False
Explanation
$$\text{True}$$
$$CaO$$ is a basic oxide which on reaction with water forms slaked lime $$Ca(OH)_2$$ which is a base. So, it turns red litmus blue.
$$CaO+H_2O\longrightarrow Ca(OH)_2$$
Carbon dioxide
gas turns moist blue litmus red.
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True
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False
Explanation
Litmus paper test
Acid - Turns litmus paper from blue to red
Base - Turns litmus paper from red to blue
$$CO_{2}$$ gas is acidic, hence the acidic property turns blue litmus red.
Which of the following base is used as antacid to neutralize stomach acidity?
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$${ Mg(OH) }_{ 2 }$$
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$$KOH$$
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$${ Ca(OH) }_{ 2 }$$
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$$NaOH$$
Explanation
Magnesium hydroxide is also known as milk of magnesia and it is a common component of antacids and laxatives. It interferes with the absorption of folic acid and iron. It carries away much of the body's supply of potassium and neutralizes the stomach acid.
An aqueous solution turns red litmus blue. Excess addition of which of the following solutions would reverse the change?
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Water
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Ammonium hydroxide solution
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Hydrochloric acid
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None of these
Explanation
Red litmus is turned to blue by the addition of base or alkali. To reverse this reaction, i.e. turning blue litmus to red, we need to add an acid like hydrochloric acid.
Water being neutral, and ammonium hydroxide solution being basic, will not reverse the change.
Oxygen gas is neutral to moist litmus.
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True
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False
Explanation
LITMUS PAPER TEST
ACID - Blue to Red
NEUTRAL - No change
BASE - Red to Blue
Due to the neutral nature of oxygen gas, the litmus paper showing no change.
One of the following that does not inject an acidic liquid into the skin through its sting. This is
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Honey bee
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Ant
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Wasp
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Nettle leaf hair
Explanation
A honey bee, ant and a nettle leaf hair inject methanoic acid into the skin through their stings. But a wasp injects an alkaline solution into the skin through its sting.
Which of the following is a use of $$Al(OH)_3$$?
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It is used in fire extinguisher as a foaming agent
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It is used in the preparation of fertilizers
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It is used in removing stains of grease from cloths
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It is used as an antacid
Explanation
$$Al(OH)_3$$ is used in fire extinguisher as a foaming agent.
Which of the following is a use of sodium hydroxide?
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It is used in the manufacture of soaps and paper.
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It is used in the manufacture of synthetic fibers like rayon.
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It is an important constituent of drain cleaners.
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All of the above.
Explanation
Sodium hydroxide is used in the manufacture of soaps, paper; in the manufacture of synthetic fibers like rayon and is important constituent in drain cleaners.
Hence option D is correct
Solution of which of the following bases is used for whitewashing
walls:
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$$NaOH$$
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$$KOH$$
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$$NH_4OH$$
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$$Ca(OH)_2$$
Explanation
Calcium hydroxide reacts slowly with the carbon dioxide in the air to form a thin
layer of calcium carbonate on the walls. Calcium carbonate is formed after two to
three days of whitewashing and gives a shiny finish to the walls.
$$Ca(OH)_2(aq) + CO_2(g)\longrightarrow CaCO_3(s) + H_2O(l)$$
Which of the following base is preferred in the manufacture of soaps?
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$$Ca(OH)_2$$
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$$NaOH$$
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$$Sr(OH)_2$$
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$$Cs(OH)$$
Explanation
Calcium hydroxide, strontium hydroxide, and cesium hydroxide are not preferred for soap making. But, s
odium hydroxide causes saponification and, is the essential ingredient in soap making. So option B is the correct one.
Toothpaste is _________ in nature.
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acidic
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basic
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neutral
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None of these
Explanation
The $$pH$$ in our mouth is $$5.5$$ which is slightly acidic. If the $$pH$$ in our mouth decreases it results in tooth decay due to the formation of certain acids. Toothpaste is basic in nature which neutralizes the acid and protects from tooth decay.
Which base is employed as the electrolyte in alkaline batteries?
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$$NaOH$$
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$$Al(OH)_3$$
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$$FeOH$$
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$$KOH$$
Explanation
Aqueous potassium hydroxide is employed as the electrolyte in alkaline batteries based on nickel-cadmium, nickel-hydrogen, and manganese dioxide-zinc. Potassium hydroxide is preferred over sodium hydroxide because its solutions are more conductive.
A
substance that dissolves in water to furnish $$\displaystyle H^{+}$$ ions is called an acid.
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True
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False
Explanation
$$\textbf{True}$$
A substance that dissolves in water to furnish or to give $$H^+$$ ions is called an acid.
For example, $$HCl + H_2O \longrightarrow H^+ + Cl^-$$
Which of the following base is used in the manufacturing of bleaching powder?
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Sodium hydroxide
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Calcium hydroxide
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Magnesium oxide
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Ammonium hydroxide
Explanation
Bleaching powder is manufactured from calcium hydroxide.
Bleaching powder is $$CaOCl_2\cdot 2H_2O$$
$$2Ca(OH)_2+2Cl_{2}→Ca(OCl)_2+CaCl_{2}+2H_{2}O$$
Which of the following base is used for cleaning and commonly known as lye?
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$$Ca(OH)_2$$
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$$NaOH$$
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$$KOH$$
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All of the above
Explanation
A common base used for cleaning is sodium hydroxide, known commonly as lye or caustic soda. It is not to be taken internally, because it is highly damaging to humans tissue particularly the eyes. Lye appears in drain cleaners, such as Drano, and oven cleaners, such as Easy-Off, which make use of its ability to convert fats to water-soluble soap.
$$HCl$$ is produced in the tissues lining the stomach.
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True
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False
Explanation
Hydrochloric Acid $$(HCl)\rightarrow$$ Produced in stomach
Acetic Acid $$(CH_3COOH)\rightarrow$$ Vinegar
Sulphuric Acid $$(H_2SO_4)\rightarrow$$ Car Batteries
Acetic acid and Sulphuric acid are not natural.
Critric Acid $$\rightarrow $$ Lemon, Orange
Malic Acid $$\rightarrow $$ Apple
Butyric Acid $$\rightarrow $$ Decomposition of Butter
Lactic Acid $$\rightarrow $$ Milk Digestion
Sodium Hydroxide $$\rightarrow $$ Washing soda
Bases like Sodium Hydroxide are generally not found in food as they taste bitter.
Which of the following is a natural indicator?
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China rose
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Blueberry
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Morning glory
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All of above
Explanation
Natural indicators are obtained from natural sources. All the above examples are natural indicators. A solution of china rose turns green in a basic solution, and bright pink or magenta in an acidic solution. Morning glories contain an anthocyanin called "heavenly blue anthocyanin" which changes from purplish red at $$pH\: 6.6$$ to blue at $$pH\: 7.7$$. Blueberries change from blue (around $$pH \:2.8-3.2$$) to red in a strongly acidic solution.
What appearance will the blue litmus paper have after being dipped into an acidic solution?
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Red
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Blue
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White
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Pink
Explanation
Litmus paper is a commonly used acid-base indicator.
The red litmus paper turns blue in a basic medium but it remains unaffected in an acidic medium.
The blue litmus paper turns red in the acidic medium but it remains unaffected in the basic medium.
Hence, the correct answer is an option (A).
Which indicator is correctly paired up with its proper color if it were added to a base?
i. Litmus - blue
ii. Phenolphthalein - pink
iii. Methyl orange - yellow
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(i) only
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(ii) only
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(iii) only
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(i) and (iii) only
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(i), (ii) and (iii)
Explanation
Litmus - It is a type of natural indicator which is made up of lichens. In an acidic solution, its colour turns red. In the basic solution, its colour changes to blue.
Phenolphthalein - It is an acid-base indicator that turns colourless in acidic solution, and turns pink to red in alkaline solution. Here it is a weak base.
Methyl orange - It is a pH indicator. It turns red in acidic solution and yellowish in basic solution.
Hence, the correct option is E.
A student puts a drop of the reaction mixture of a saponification reaction first on a blue litmus paper and then on a red litmus paper. He may observe that:
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there is no change in the blue litmus paper and the red litmus paper turns white
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there is no change in the red litmus paper and the blue litmus paper turns red
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there is no change in the blue litmus paper and the red litmus paper turns blue
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no change in colour is observed in both the litmus papers
Explanation
Saponification is the alkaline hydrolysis of the fatty acid esters.
Hence the solution is basic, bases with blue litmus give no color change.
On dipping red litmus paper in a mixture of saponification reaction, it turns blue.
Option C is correct.
State whether true or false:
Neutral oxides turn blue litmus to red.
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True
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False
Explanation
The statement is false. Neutral Oxides are
oxides which
do not react with acids and bases. Neutral oxides do not react with water and form acid or base thus not changing the colour of litmus paper. $$NO, N_2O$$ and $$CO$$ are some examples of neutral oxides.
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