Model Test – Solved ഉത്തരങ്ങൾ

Brass is an alloy (ലോഹസങ്കരം) of zinc (solute) dissolved in copper (solvent) – both solids, so it is a solid solution (ഖരലായനി). Soda water and tincture of iodine are liquid solutions; air is a gaseous solution.

At that temperature no more solute can dissolve: extra solute stays at the bottom. That is a saturated solution.

In muddy water the particles can be seen, they settle when it stands and they are left on filter paper – a suspension, a heterogeneous mixture. Sugar solution is a homogeneous true solution.

True solution 0.01–1 nm; colloid (കൊളോയിഡുകൾ) 1–1000 nm; suspension more than 1000 nm (1 nm = 10⁻⁹ m).

Colloidal particles are big enough to scatter light, so the path of the beam is seen – the Tyndall effect, like a cinema projector beam in a dusty hall.

The solubility of a gas increases with pressure – soda water is made by dissolving CO₂ under high pressure. Warming the water, lowering the pressure or opening the bottle makes the gas escape.

Solubility (ലേയത്വം) is the mass of solute in grams needed to saturate 100 g of solvent at a given temperature. (The saturated solution is 24.24 %, because its mass is 32 + 100 = 132 g: 32 ÷ 132 × 100 = 24.24. So (d) is wrong.)

Table 6.5: tartrazine – yellow; erythrosine – red; indigo carmine – blue.

(a) Mass of solution = mass of solute + mass of solvent = 12 + 68 = 80 g.

(b) Mass percentage (മാസ് പെർസെന്റേജ്) = (mass of solute ÷ mass of solution) × 100 = (12 ÷ 80) × 100 = 15 %.

(a) A solution with more solute dissolved than is needed to saturate it at that temperature is a supersaturated solution (അതിപൂരിത ലായനി).

(b) A supersaturated solution is not stable. The small crystals act as seed crystals: the extra dissolved sugar comes out of the solution and deposits on them, so they grow into big crystals. Crystals forming from a supersaturated solution in this way is crystallization (പരലീകരണം).

(a) Pressure: CO₂ is dissolved in water under high pressure and the bottle is sealed. The solubility of a gas increases with pressure.

(b) On opening, the pressure falls, so the water can hold less CO₂; the extra gas escapes as bubbles. The solubility of a gas decreases as the temperature rises, so a warm drink holds even less CO₂ and goes flat faster.

(a) The component in the smaller amount is the solute: tin (12 %); the larger, copper (88 %), is the solvent. The solvent is a solid, so bronze is a solid solution (ഖരലായനി).

(b) Solute acetic acid, solvent water – an aqueous solution (ജലീയ ലായനി); it is a liquid, like its solvent.

(a) Mist: tiny water droplets (liquid – dispersed phase, ഡിസ്പേർസ്ഡ് ഫേസ്) spread in air (gas – dispersion medium, ഡിസ്പേർഷൻ മീഡിയം) – a liquid aerosol.

(b) Soap lather: air bubbles (gas) spread in soap solution (liquid) – a foam.

(a) 5 % means 5 g of salt in every 100 g of solution. Salt = 5 × 400 ÷ 100 = 20 g; water = 400 − 20 = 380 g.

(b) NaOCl = 3.62 × 500 ÷ 100 = 18.1 g.

(c) 30 g must be 12 % of the solution: mass of solution = 30 × 100 ÷ 12 = 250 g; water = 250 − 30 = 220 g, that is 220 mL (1 mL of water has a mass of about 1 g).

(a) Sodium chloride: 36 g → 38 g only – its curve is almost flat. Potassium nitrate: 13 g → 138 g – the steepest curve.

(b) At 30 °C, 37 g saturates 100 g of water, so 200 g of water needs 37 × 2 = 74 g.

(c) At 70 °C the 100 g of water holds 138 g; at 30 °C it can hold only 46 g. The rest separates as crystals: 138 − 46 = 92 g. This is crystallization (പരലീകരണം).

(a) Compare each with the solubility, 37 g: P 25 g < 37 → unsaturated (അപൂരിത ലായനി); Q 37 g = 37 → saturated (പൂരിത ലായനി); R 42 g > 37 → supersaturated (അതിപൂരിത ലായനി).

(b) P: the crystal dissolves. Q: the crystal stays as it is (no more can dissolve). R: the crystal acts as a seed – more crystals form on it and the extra 42 − 37 = 5 g separates, leaving a saturated solution.

(c) 37 − 25 = 12 g.

(a) The solubility of gases decreases as the temperature rises. The warm water of the pond holds less dissolved oxygen, so the fish come up for air.

(b) Like dissolves like (സമാനമായത് സമാനമായതിനെ ലയിപ്പിക്കും): grease is non-polar (നോൺപോളാർ) and dissolves in non-polar kerosene, not in polar (പോളാർ) water.

(c) Mist is a colloid (a liquid aerosol). Its droplets scatter the light, so the path of the beam is seen – the Tyndall effect (ടിൻഡൽ പ്രഭാവം). Clear air has no such particles.

(a) Dissolve: sugar, salt (also the lime juice and the CO₂ of the soda). Do not dissolve: basil seeds, lime pieces (also the chilli). So the sarbath is a mixture of a solution and things that stay undissolved.

(b) Mass of syrup = 600 + 400 = 1000 g; mass percentage = (600 ÷ 1000) × 100 = 60 %.

(c) 100 g of syrup has 60 × 100 ÷ 100 = 60 g of sugar. New mass of solution = 100 + 500 = 600 g. Mass percentage = (60 ÷ 600) × 100 = 10 % – a more dilute solution (നേർത്ത ലായനി).

(d) A stabiliser (സ്റ്റെബിലൈസറുകൾ) keeps the particles of flavour and colour from settling, so the drink stays uniform. A preservative (പ്രിസർവേറ്റീവുകൾ) – here sodium benzoate, which acts against yeast and moulds – keeps the drink from spoiling for a long time.

(e) The fresh sarbath: it is made from natural things (lime, salt, sugar, basil seeds) with no added chemicals, and fresh lime juice has nutritional value. Artificial drinks (കൃത്രിമ പാനീയങ്ങൾ) are mostly sugar, colour and flavour with little nutrition, and the textbook warns of harmful effects of some additives. (Even the sarbath has a lot of sugar – drink it in moderation.)

(a) In B and C. In B the colloidal particles of milk scatter the light – the Tyndall effect (ടിൻഡൽ പ്രഭാവം). (In C the large chalk particles also scatter light.)

(b) C – the chalk particles settle under gravity, and they are left as a residue on the filter paper. The particles of A and B pass through the filter paper.

(c) A – true solution (യഥാർഥ ലായനി), 0.01–1 nm; B – colloid (കൊളോയിഡുകൾ), 1–1000 nm; C – suspension (സസ്പെൻഷൻ), more than 1000 nm.

(d) The particles in A are far too small (less than 1 nm) to scatter light; the colloidal particles in B (1–1000 nm) are big enough to scatter it, though still too small to settle or be filtered.

(e) The clear solution slowly turns milky (cloudy) and the path of the beam becomes visible: very fine particles of sulphur form, of colloidal size – the Tyndall effect. Later the particles grow bigger and yellowish sulphur settles – it has become a suspension.