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CHEMISTRY [2 Mark Question Answer]

Water · ICSE STD 8 (ICSE - English Medium). 14 questions.

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[2 Mark Question Answer]

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14 questions · timed · auto-graded

Question 12 Marks
Magnesium bicarbonate in temporary hard water to magnesium carbonate by boiling.
Answer
$\ce{Mg\left[HCO_3\right]_2} \xrightarrow{\text { Boiling }} \underset{\text { Magnesium carbonate }}{ \ce{MgCO_3} \downarrow}+ \ce{CO_2}+ \ce{H_2O}$
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Question 32 Marks
Sulphur dioxide to sulphurous acid using a neutral liquid.
Answer
$\underset{\text { Sulphur dioxide }}{ \ce{SO_2}}+\underset{\text { Neutral liquid }}{ \ce{H_2 O }} \longrightarrow \underset{\text { Sulphurous acid }}{ \ce{H_2SO_3}}$
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Question 52 Marks
Calcium sulphate in permanent hard water to calcium carbonate using sodium carbonate.
Answer
Image
Sodium carbonate In hard water Cal. carbonate Sodium sulphate
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Question 62 Marks
Differentiate between $–$
$(a)$ Hard $\&$ soft water
$(b)$ Temporary $\&$ permanent hard water $–$ with suitable examples.
Answer
$(a)$ Hard water: It does not lather readily with soap and soap is wasted.
Soft water : Soft water form lather easily with soap
$(b)$ Temporary hard water contains bicarbonate of calcium or magnesium. Hardness can be removed by boiling water. Permanent hard water contains sulphates or chlorides of calcium and magnesium. Hardness cannot be removed by boiling water.
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Question 72 Marks
The process of separation or deposition of crystals from a hot saturated solution on gentle cooling of the solution is called ‘crystallisation’. With reference to the statement explain what is meant by ‘water of crystallisation’. State which physical properties of a crystal are correlated with the water of crystallisation.
Answer
Water of crystallisation is the number of water molecules that combine chemically in definite proportion with the $–$ concerned salt in the crystalline state.
OR
Some salts, while crystallising out from their solutions unite with a definite quantity of water, which is known as water of crystallisation. Physical properties are that crystals are solid, definite regular shapes.
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Question 82 Marks
Explain the meaning of the term ‘saturated solution’. State two methods to convert a saturated solution to an unsaturated solution.
Answer
Saturated solution : “A solution in which no more solute can be dissolved at that temperature, is called saturated solution.”
Two methods to convert a saturated solution into an unsaturated solution are :
$(i)$ By increasing temperature
$(ii)$ By increasing the amount of solvent.
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Question 92 Marks
Give four examples of each of the above types of solutions i.e. true solution, colloidal solution $\&$ suspension. Give a reason why a true solution does not exhibit ‘Tyndall effect’.
Answer
Examples of :
$(a)$ True solution : Salt solution, vinegar, copper sulphate solution, sugar in water solution, air, brass.
$(b)$ Colloidal solution : Milk, ink, blood, soap solution, starch sol.
$(c)$ Suspension : Milk of magnesia, flour in water, chalk $-$ water solution, muddy water. A true solution cannot exhibit ‘Tyndall effect’ because ‘the size of particles is very small and cannot reflect light falling on them.”
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Question 102 Marks
How are solutions generally classified. What is the basis of this classification.
Answer
Solutions are classified into:
$(a)$ True solutions.
$(b)$ Colloidal solution.
$(c)$ Suspensions.
The basis of classification is the size of dissolved or dispersed particles in the medium.
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Question 112 Marks
Give the importance of $–$
$(a)$ Dissolved minerals $\&$ salts
$(b)$ Dissolved air $–$ in water.
Answer
Importance in water of :
$(a)$ Dissolved minerals $\&$ salts : Provide taste to water and are useful for metabolic functions of the human body.
$(b)$ Air : Air containing various gases gives taste to water.
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Question 122 Marks
Name the solute, solvent $\&$ solution in the statement $–$ ‘sodium chloride dissolves in water to give sodium chloride solution’. Define each of the terms in italics.
Answer
Solute $($sodium chloride$)$ : The substance which dissolves or disappears in solvent, i.e. liquid to form a solution.
Mostly solvent is which is in less quantity.
Solvent $($water$)$ : The substance which allows the solute to dissolve in it. It is the substance which is in more quantity. Solution $($sodium chloride solution$)$ : The homogenous mixture of solute and solvent is called solution.
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Question 132 Marks
Give a reason why water is called a ‘universal solvent’ but, an alkali is not.
Answer
Water is a polar covalent compound. When it comes in contact with any substance it breaks the electrostatic forces holding the molecules of that substance. Thus, the molecules break loose from the substance and hence dissolve in water. Thus, water is called a universal solvent and an alkali is not.
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Question 142 Marks
Name a ‘pure form’ and an ‘impure form’ of water in the natural state.
Answer
Rain water $–$ pure natural water.
Sea water, lake water $–$ impure form of natural water.
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[2 Mark Question Answer] - CHEMISTRY STD 8 Questions - Vidyadip