Question

Q 7 Write scientific reasons :
a) Hydrogen is combustible, oxygen helps combustion, but water helps to extinguish
fire.

b) Constituent substances of a colloid cannot be separated by ordinary filtration.

c) Lemon sherbat has sweet, sour, and salty taste and it can be poured in a glass.

d) A solid matter has the properties of definite shape and volume.

Answer 1

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Q] Write scientific reasons :

a) Hydrogen is combustible, oxygen helps combustion, but water helps to extinguish  fire.

⬩ Answer:

• Water is a compound of hydrogen and oxygen.
• In a compound, the  constituents do not retain their individual properties.
• Hence, though hydrogen is  combustible and oxygen supports combustion, water is neither combustible nor  supports combustion, but it helps to extinguish the fire.

b) Constituent substances of a colloid cannot be separated by ordinary filtration.

⬩ Answer:

• A colloidal solution is heterogeneous.
• The diameters of the colloid particles are around 10-5 m.
• The pore size of an ordinary filter paper is larger than 10-5 m.
• Hence, the constituents of a colloid cannot be separated by ordinary filtration.

c) Lemon sharbat has a sweet, sour, and salty taste and it can be poured in a glass.

⬩ Answer:

• Lemon sharbat is a mixture.
• It is made up of lemon juice, sugar, salt and water.
• Formation of lemon sherbat does not involve any chemical reaction.
• In a mixture, the properties of constituent substances are retained.
• Hence, lemon sherbat is sweet, sour and salty to taste and it can be poured in a  glass.

d) A solid matter has the properties of definite shape and volume.

⬩ Answer:

• An intermolecular force of attraction acts between particles (atoms or  molecules) of matter.
• The extent of particle movements is determined by the strength of this force.
• The particles of solid are very close to each other and vibrate at their fixed  positions.
• Due to this solids have definite shape and volume.

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Apologies for the mistakes <3

Answer 2

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$\:\sf\blue{a)}$ Though water is made up of two atoms of hydrogen and one atom of oxygen by forming an ionic compound, it does not possess the characteristics of them because a compound does not have the properties of its constituent elements. Therefore, water has its own properties, which helps to extinguish the fire.

$\:\sf\purple{b)}$ Constituent substances of a colloid cannot be separated by ordinary filtration because the size of the particles in colloids (or colloidal solution) is bigger than those in a true solution but smaller than those in suspension. It is in between 1nm to 100nm in diameter.

$\:\sf\orange{c)}$ Reason on lemon sharbat has sweet sour and salty taste and it can be poured in a glass: ... The other solute that is present in the solventIs sugar and sugar again dissolves completely in water leaving the sweet taste it has in it.

$\:\sf\red{d)}$The solid matter has the property of definite shape and volume because the molecules present in a solid are tightly packed so the molecules do not flow and there is no change in volume.