Explore topic-wise InterviewSolutions in Current Affairs.

(a) Liquid state, is represented by Fig 1. 

(b) In Fig. 3 the inter particle attraction will be maximum, because it is in solid state. 

(c) Fig. 2 cannot be contained in an open vessel, as it is in gaseous state. 

(d) Fig. 1 can take the shape of its container, as it is in liquid state.

A colloidal solution, occasionally identified as a colloidal suspension, is a mixture in which a substances regularly suspended in a fluid. A colloid is a minutely small material that is regularly spread out all through another substance.

The components of a colloidal solution are the dispersed phase and the dispersion medium. The solute-like component or the dispersed particles in a colloid form the dispersed phase, and the component in which the dispersed phase is suspended is known as the dispersing medium. Colloids are classified according to the state (solid, liquid or gas) of the dispersing medium and the dispersed phase.

Colloidal solutions have three sub-classifications: Foams, emulsions and sol. 

Foam in this setting is created by ensnaring a gas in a liquid. The substance being dispersed would be the gas, triggering the fluid to become frothy and foamy. A sample of this would be shaving cream. 

An emulsion is a combination of liquids; it’s basically when one liquid is consistently dispersed all through another liquid. 

A sample of this would be mayonnaise or milk. The third form is called a sol, which is when a solid is evenly dispersed throughout a fluid. Samples of sols include paint, blood and silver aquasols.

Sedimentation, decantation, filtration, evaporation, and condensation.

Fruit Salad:

Discard the skin of banana, papaya, orange, apple, pine apple, guava and make small slices. Add pomegranate and grapes. Then mix with cream milk and honey. Now the fruit salad is ready. As this Fruit Salad is a physical combination of two or more substances, it is a mixture.

Vegetable Salad: 

It is prepared with the primary ingredients of tomato, cucumber, onion, carrot, mint, lemon juice and dried chili peppers. As this Vegetable Salad is a physical combination of two or more substances, it is a mixture.

Food is the basic requirement for life. It should be pure, nutritious and free from any type of adulteration.

Adulteration : 

Sometimes, things that we buy in the market are mixed with harmful and unwanted substances. Food can also get adulterated due to carelessness or lack of proper handling. It will not possible to check for adulteration on visual examination. Following tests will help even a layman or non-technical person to detect adulterants in the some of the products.

Detection: 

Milk: Adulterants used can be water, starch, urea, sucrose, detergents, neutralizer, formalin etc. These adulterants are used to increase thickness, viscosity and shelf life of milk.

Test: Put a drop of milk on polished vertical surface. The drop of pure milk either stops or flows slowly leaving a white trail behind it. Whereas milk adulterated with water will flow immediately without leaving a mark. We can also use Lactometer for measuring specific density of milk.

Sugar: Adulterant: Chalk 

Test: Dissolve sugar in a glass of water,chalk will settle down at the bottom

Ice Cream: Adulterant: washing Powder 

Test: Put some lemon juice on ice-cream, bubbles come out in the presence of washing powder

Test: Take one teaspoonful of melted ghee or butter with equal quantity of cone. Hydrochloric acid in a test tube and add to it a pinch of cane sugar. Shake well for one minute and let it stand for five minutes. Appearance of crimson colour in lower layer shows the presence of vanaspathi.

We must be careful about the common adulterants in our food. We might be eating a dangerous dye, sawdust, industrial starch or other contaminated foods which are a major source of diseases. And thus, we invite diseases rather than good health. Food adulteration is basically lowering the quality of food. So, we must be aware of such adulteration.

Cream and milk differ in their density. Cream is denser than milk. When milk is churned (shaking or spinning of container containing milk by applying a rotating force) the denser particles (cream) tend to remain at the bottom, whereas the lighter particles (milk) stay at the top, along with the direction of spin. This process is called centrifugation.

Homogeneous mixture: soda water, air, vinegar, filtered tea, tree.

Heterogeneous mixture: soil.

The correct answer is (c) Copper metal is ductile and has low electrical resistance

1. Take Tea powder and Milk 

2. Heat the milk, then add tea powder. 

3. Add sugar to taste and, Stirr well. 

4. The sugar will be dissolved in the mixture. 

5. Filter the mixture. Tea (filtrate) flows down through filter paper. 

6. Tea leaves settle as residue on the filter paper.

Milk, copper sulphate, solution and starch solution shows ‘Tyndall effect’.

Take a kettle or a teapot. Add water to it. Boil the water and add tea powder/tea leaves to it based on your choice. The more tea you add, the stronger the liquid becomes. Note that tea is the solute and water is the solvent. Also, the tea powder insoluble in water, but the essence is absorbed by the liquid. Once the tea+mixture starts to boil, dissolve sugar (another solute) in it. You may add sugar as long it is soluble in it for maximum sweetness. To this solution, add milk if you need milk tea. Once it is boiled, remove it from the heat source and filter the solution for tea powder. You can see that the residue you get is tea powder, and the filtrate (the liquid after filtration) is black/milk tea.

The phenomenon where the path of the light beam is visible as a result of scattering of light by colloidal particles is called Tyndall effect. The size of the particle should be such that it should scatter light. Particles which are very small (in the case of true solutions) or very large (in the case of suspensions) do not scatter light. So, the Tyndall effect is not observed in true solutions or suspensions.

This is the general case. In certain special cases, if the particle size of suspension is small enough to scatter light, then suspensions also show Tyndall effect.

(i) Observe the color change of litmus paper and tabulate. 

(ii) Name the acid and alkali that react to form each salt given above? 

(iii) Can you explain the color change of the litmus paper on the basis of the nature of the acid and alkali that react to form the salt?

(hint: Potassium chloride is a salt formed by the reaction between a strong acid and a strong alkali)

(i) Salts formed by the reaction between a strong acid and a strong base will be neutral in nature,

eg: KCI 

(ii) Salts formed by the reaction between a strong base and weak acid will be slightly basic 

eg: Na₂CO₃ 

(iii) Salts formed by the reaction between a weak base and strong acid will be slightly acidic

eg:(NH₄)₂SO₄

A basic salt is formed when a strong base combines with a weak acid

Steps for preparing tea:

1. Take water in a vessel. Here water is solvent.

2. Add solutes like sugar and tea powder. Sugar dissolves tea powder is insoluble.

3. While boiling add milk to it.

4. By filtration, we get tea (filtrate) only leaving behind tea powder as residue.

Substance which is present in smaller quantity in a mixture is called solute.

i. The name and chemical formula of the calcium compound used for disinfecting drinking water is:- 

Chemical name - Calcium oxychloride

Formula - CaOCl₂ 

ii. This compound is manufactured by the action of chlorine on dry slaked lime as per the following reaction: 

Ca(OH)₂ + Cl₂→ CaOCl₂ + H₂O

Uses of Sodium carbonate

• For the manufacture of glass.

• For washing purposes in laundries.

• For the manufacture of other sodium compounds like sodium silicates, sodium hydroxide,  borax, hypo etc.

• As a household cleansing agent.

• In paper and soap/detergent industries.

• For the softening of water.

• A mixture of NaCO₃ and KCO₃ is used as a fusion mixture.

• In textile industry and petroleum refining.

Solvent dissolves solute particles by overcoming the intermolecular forces between the solute (or one can call it the solute-solute interaction). So, to dissolve a solute, the solute-solute interaction must be broken by the solvent particles.

When the temperature increases, the kinetic energy of the solvent particles increases, causing to break the solute-solute interactions more effectively. This allows the addition of more solute particles, as there is space to accommodate more solute particles. So the solubility increases with increase in temperature. Lowering the temperature does the opposite. It decreases the solubility of the solute.

Sodium Hydrogen Carbonate, (NaHCO₃)

Sodium hydrogen carbonate is also known as sodium bicarbonate or baking soda because it decomposes on heating to generate bubbles of carbon dioxide (leaving pores in cakes or pastries and making them light and fluffy).

1. Pass the CO₂ gas through lime water [Ca(OH)₂]. 

2. The lime water appears as milky white. 

3. The reaction is Ca(OH)₂ + CO₂ → CaCO₃ ↓ + H₂O. 

4. The milky white is caused by CaCO₃.

The answer is (c) (ii) only 

Required material : 

Stand, test tubes, delivery tube, thistle funnel, two hole rubber corks, Ca(OH)₂ , NaHCO₃, HCl.

Experimental procedure :

1. Take NaHCO₃ in a test tube and fix two hole cork to the test tube. 

2. Fix thistle funnel in one hole of cork and insert delivery tube in the second hole of the cork. Insert the second end of the delivery tube in the other test tube which is containing Ca(OH)₂ /lime water. 

3. Pour dil. HCl into the test tube using thistle funnel. 

4. Due to chemical reaction, gas is evolved and pass into the Ca(OH)₂ through delivery tube. It turns in to milky. We can conclude that it is CO₂ gas.

Correct option is (a) 0.875 M

The answer is (a) (i) and (ii)

• Reaction between Sodium hydrogen carbonate and acetic acid lead to evolution of carbon-dioxide gas. 
• CO₂ turns the lime water milky and extinguish a burning splinter.

The answer is (b) Wash the hand immediately with plenty of water and apply a paste of sodium hydrogencarbonate

• Washing affected hand with plenty of water will reduce the concentration of the acid. 
• Remaining traces of the acid can be neutralized by applying a paste of Hydrogen carbonate which is basic in nature. 
• Though NaOH is also a base but it is corrosive in nature hence it is not used to neutralize the acid.

Correct option is B) Q

Rays coming parallel to the principal axis of a concave mirror is focused at focal point. Based on this property solar cooker is made.

Properties of a convex mirror :

1. If the reflecting surface is convex, then it is called a convex mirror. 

2. Always form erect and virtual images. 

3. These are used in rear view mirrors of the vehicles.

The shift is maximum for violet light.

Hint: The shift is maximum for violet light because the refractive index of glass is the most for the violet light and apparent = (real depth)/(refractive index)

It mainly depends upon the optical density of the two media through which a ray of light travels.

According to the principle of reversibility the path of light ray is reversible. 

1. Wavelength varies 

2. Frequency remains unchanged.

(a) travel from denser to rarer medium.

In dim light, the iris expands the pupil to allow more light to enter the eye. So, when we come out of a darkroom into the bright sunlight, a large amount of light enters into our eyes and due to glare feeling, we are not able to see the things clearly. Gradually, the iris contracts the pupil to allow less light to enter the eye to see the objects clearly. It take some time for the pupil. For that time interval, person is unable to see the things.

(i) When a ray of light travels from rarer to denser medium it bends towards the normal. 

(ii) When a ray of light travels from denser to rarer medium it bends away from the normal. 

(iii) The ray goes straight into second medium without any bending. 

When a ray is incident from a denser medium to a rarer medium at angle equal to critical angle (i=i_c), the angle of refraction becomes 90°.

The rays converge at a point (or) appear to diverge from a point lying on the focal plane.

The distance between the lens and the object is very much greater than when compared to object size is known as object at infinity. Parallel rays fall on the lens. The object at infinity means distant object. The rays falling on the lens from an object at infinity are parallel to principal axis.

If we place an object beyond centre of curvature of a concave mirror, diminished image will be formed between focus and centre of curvature,

Critical angle for diamond is 24° means that the angle of incidence of light in diamond is such that the angle of refraction for it in air is 90°. The critical angle is related to the refractive index of the material as 1/sin ic = µ, where µ = refractive index

The critical angle for diamond is 24°. This implies that at an incident angle of 24° within the diamond the angle of refraction in the air will be 90°. And if incident angle will be more than this angle then the ray will suffer total internal reflection without any refraction.

• There is usually some reflection that occurs at an interface between the two materials but most often of light passing through. 
• Imagine you are inside in the dark. A person outside in bright sunlight is sending out (reflection) lots of light, most of which would come through the window to you, so you see them clearly. 
• Since it is so bright outside, there is also a good amount of light which reflects back towards them. 
• This can distract them from little bit of light from you that is going towards them, so they have much harder time seeing you.

B) on the same wall as the window

Critical angle for water is 49°. The rays of light entering in water from below, suffer refraction. If these rays strike the water-air surface at an angle which is greater than 48°, they get totally internally reflected. These rays on emerging out of water, appear to came from the upper surface of water, which in turn appears silvery.