Question 1

Which separation techniques will you apply for the separation of the following?(a) Sodium chloride from its solution in water.(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.(c) Small pieces of metal in the engine oil of a car.(d) Different pigments from an extract of flower petals.(e) Butter from curd.(f) Oil from water.(g) Tea leaves from tea.(h) Iron pins from sand.(i) Wheat grains from husk.(j) Fine mud particles suspended in water.

Accepted Answer

a) Sodium chloride from its solution in water  Evaporation.(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride    Sublimation.(c) Small pieces of metal in the engine oil of a car  Filtration(d) Different pigments from an extract of flower  Chromatography.(e) Butter from curd  Centrifugation.(f) Oil from water  Using separating funnel(g) Tea leaves from tea  Filtration(h) Iron pins from sand  Magnetic Separation(i) Wheat grains from husk  Winnowing(j) Fine mud particles suspended in water  Centrifugation.

Question 2

Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.

Accepted Answer

Steps involved in tea making:(i) Tea can be prepared by the following steps: Take 100ml of water as a solvent and boil it a few minutes.(ii) Now add one teaspoon sugar, one teaspoon tea leaves and 50ml of milk. Here sugar, tea leaves and milk are solutes.(iii) Now boil it again for a few minutes so that sugar will dissolves in solution as sugar is soluble in water(iv) Now filter the solution. Collect the filtrate in a cup. The insoluble tea leaves will be left behind as residue.

Question 3

Pragya tested the solubility of three different substances at different temperatures and collected the data as given below(results are given in the following table, as grams of substance dissolved in 100grams of water to form a saturated solution).(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50grams of water at 313K?(b) Pragya makes a saturated solution of potassium chloride in water at 353K and leaves the solution to cool at room temperature. What would she observe as the solution cools? Explain.(c) Find the solubility of each salt at 293K. Which salt has the highest solubility at this temperature?(d) What is the effect of change of temperature on the solubility of a salt?

Accepted Answer

(a) At 313 K 62 g of potassium nitrate dissolved in 100 g of water. So to produce a saturated solution of potassium nitrate in 50 g of water we need 10062​×50=31 g of potassium nitrate.(b)Some soluble potassium chloride will separate out in the form of crystal at room temperature because the solubility of potassium chloride will decrease.(c)(i)  Solubility of Potassium nitrate at 293 K is 32 g.(ii)  Solubility of sodium chloride at 293 K is 36 g.(iii) Solubility of Potassium chloride at 293 K is 35 g.(iv) Solubility of Ammonium chloride at 293 K is 37 g.                                                      The solubility of Ammonium chloride is highest at this temperature.(d)The solubility of salt increases with the increase in temperature.

Question 4

Explain the following giving examples.(a) Saturated solution(b) Pure substance(c) Colloid(d) Suspension

Accepted Answer

(a) The term saturated solution is used in chemistry to define a solution in which no more solvent can be dissolved. It is understood that saturation of the solution has been achieved when any additional substance that is added results in a solid precipitate or is let off as a gas. Eg: Saltwater(b) Pure substance: A material that is composed of only one type of particle.Eg: Gold, oxygen and water.(c) Colloid: A homogeneous non-crystalline substance consisting of large molecules or ultramicroscopic particles of one substance dispersed through a second substance.Eg: Gels, sols and emulsions.  d) Suspension: A suspension is a heterogeneous mixture in which solute-like particles settle out of a solvent-like phase sometime after their introduction. We apply the word suspension when particles are big enough to eventually settle.Eg: wheat flour and water.

Question 5

Classify each of the following as a homogeneous or heterogeneous mixture: Soda water, wood, air, soil, vinegar, filtered tea.

Accepted Answer

A homogeneous mixture has the same uniform composition and appearance.A heterogeneous mixture consists of visibly different phases or substances.From the list of given substances,Homogeneous mixtures are soda water, air, vinegar, and filtered tea.Heterogeneous mixtures are wood and soil.

Question 6

How would you confirm that a colourless liquid given to you is pure water?

Accepted Answer

Take a sample of colourless liquid and put on stove if it starts boiling exactly at 100∘C then it is pure water. Any other colourless liquid such as vinegar always have different boiling point. Also observe carefully that after some time whole liquid will convert into vapour without leaving any residue.We can check it by checking reactivity with some metals that reacts violently with water.

Question 7

Which of the following materials fall in the category of a pure substance?(a) Ice(b) Milk(c) Iron(d) Hydrochloric acid(e) Calcium oxide(f) Mercury(g) Brick(h) Wood(i) Air.

Accepted Answer

Pure substances are defined as substances that are made of only one type of atom or molecule. The pure substances are:(a) Ice (c) Iron (d) Hydrochloric acid (e) Calcium oxide (f) Mercury

Question 8

Identify the solutions among the following mixtures.(a) Soil(b) Sea water(c) Air(d) Coal(e) Soda water.

Accepted Answer

A solution is a homogeneous mixture of two or more substances.Out of the above mixtures, seawater, air, and soda water are solutions.

Question 9

Which of the following will show "Tyndall effect"?

Accepted Answer

The Tyndall effect is shown by a colloidal solution.Salt solution and copper sulphate solutions are true solutions. Here milk and starch solutions are colloids therefore milk and the starch solutions will show the Tyndall effect.Hence, Options "B" & "D" are the correct answers.

Question 10

Classify the following into elements, compounds and mixtures.(a) Sodium(b) Soil(c) Sugar solution(d) Silver(e) Calcium carbonate(f) Tin(g) Silicon(h) Coal(i) Air(j) Soap(k) Methane(l) Carbon dioxide(m) Blood

Accepted Answer

Classification of the given substances into elements compounds and mixtures:Elements:     Sodium, Silver, Tin and Silicon.Compounds: Calcium carbonate, Methane and carbon dioxide.Mixtures:      Soil, Sugar solution, Coal, Air, Soap and Blood.

Question 11

Which of the following are chemical changes?(a) Growth of a plant(b) Rusting of Iron(c) Mixing of iron fillings and sand(d) Cooking of food(e) Digestion of food(f) Freezing of water(g) Burning of a candle.

Accepted Answer

A chemical change is a change that brings a change in the chemical properties of matter and a new substance is formed.Examples of chemical changes from the given list of changes are:Growth of a plant, Rusting of iron, Cooking of food, Digestion of food, and Burning of a candle.

Question 12

A solution contains 40 g of common salt in 320 g of water. Calculate the concentration in terms of mass by mass percentage of the solution.

Accepted Answer

Mass of solute (salt) =40 g
Mass of solvent ( water )=320 g
We know,
Mass of solution = Mass of solute +Mass of solvent
=40 g+320 g
=360 g
Mass percentage of solution
= Mass of solution  Mass of solute ​×100
=36040​×100=11.1%

Question 13

A solution contains 40 g of common salt in 320 g of water. Calculate the concentration in terms of mass by mass percentage of the solution.

Accepted Answer

Mass of solute (salt) =40 g
Mass of solvent ( water )=320 g
We know,
Mass of solution = Mass of solute +Mass of solvent
=40 g+320 g
=360 g
Mass percentage of solution
= Mass of solution  Mass of solute ​×100
=36040​×100=11.1%

Chapter 2 : Is Matter Around Us Pure?