Chapter 1: States of Matter and Phase ChangesLong Questions with Answers
13 long (comprehensive) questions of 9th Class Chemistry Chapter 1, States of Matter and Phase Changes, answered in full with headings, diagrams and tables, including important board-paper questions beyond the book. Punjab Board new syllabus.
Long answers, explained in full with headings. Learn the structure: definition, explanation, diagram or table, example.
Set A: Textbook comprehensive questions 8 questions
The long questions at the end of the chapter in your book.
Long Q 1.1
Mention the name of the branch of chemistry in which you will study each of the following topics: (a) rate of a reaction (b) digestion of food in the human body (c) properties of plasma (d) ecosystem (e) reactions taking place during fireworks (f) measurement of the absorption of wavelength with the help of an ultraviolet spectrometer.
Answer
Topic
Branch
Reason (book)
(a) Rate of a reaction
Physical chemistry
used to predict and change the rates of reactions
(b) Digestion of food
Biochemistry
vital processes occurring in living organisms
(c) Properties of plasma
Physical chemistry
how substances behave at atomic and molecular levels
(d) Ecosystem
Environmental chemistry
chemical species in the air, soil and water
(e) Fireworks
Inorganic chemistry
reactions of metal salts, nitrates and sulphur
(f) UV spectrometer
Analytical chemistry
analysis with modern instruments
Long Q 1.2
What are allotropic forms? Explain the allotropic forms of carbon and sulphur. How does coal differ from diamond?
Answer
Allotropy
Elements may exist in more than one structural form which can exhibit quite different physical and chemical properties. These forms are called allotropic forms and the phenomenon is called allotropy. Element oxygen exists in two allotropic forms, namely oxygen (O₂) and ozone (O₃).
Allotropes of carbon
Carbon exists in three main allotropic forms: diamond, graphite and buckminster fullerene.
Diamond, graphite and fullerene.
Diamond has a giant macromolecular structure: every carbon atom is bonded to four others. It is the hardest substance, used in cutting and drilling tools, and does not conduct electricity.
Graphite has a layered structure of hexagonal rings of carbon. The layers slide over each other, so it is soft and slippery (lubricant, pencils); mobile electrons between the layers make it a conductor (electrodes).
Buckminster fullerene (C₆₀) consists of spheres made of atoms arranged in pentagons and hexagons. Fullerenes are stable at high temperatures and pressures and soluble in organic solvents. The molecule is not charged, has no boundaries and no unpaired electrons: a cage-like structure. C₆₀ has a low melting point, is soft and cannot conduct electricity.
Allotropes of sulphur
Element sulphur exists in two crystalline allotropic forms, rhombic and monoclinic; the former is more stable than the latter (monoclinic needles are stable only above about 96 °C).
Coal and diamond
Coal
Diamond
Amorphous form of carbon (no regular arrangement)
Crystalline form, regular 3-D network
Black, dull, soft, impure
Transparent, brilliant, hardest
Used as a fuel in power stations
Used in jewellery and cutting tools
Long Q 1.3
What are supercritical fluids? How are they different from ordinary liquids?
Answer
Definition
Matter also exists in intermediate states where liquid meets gas. Supercritical fluids are highly compressed states which show both properties of gases and liquids. A substance becomes supercritical when it is held above its critical temperature and critical pressure.
Example
Carbon dioxide above about 31 °C and 73 atm becomes supercritical CO₂.
Differences from ordinary liquids
Ordinary liquid
Supercritical fluid
Has a surface (meniscus) separating it from its vapour
No boundary: one uniform phase
Has a fixed volume
Expands to fill its container like a gas
Flows slowly, spreads slowly into solids
Very low viscosity: penetrates solids like a gas
Dissolving power fixed by temperature
Dissolving power changed by changing pressure
Importance
Chemical reactions which may not be carried out in conventional solvents may possibly be carried out in supercritical carbon dioxide. It is also used to remove caffeine from coffee and leaves no harmful solvent behind.
Long Q 1.4
Define solubility of a solute. How does the solubility of solutes change with the increase in temperature?
Answer
Definition
The solubility of a solute is the amount of solute which can dissolve in 100 g of a solvent at a particular temperature. Different solutes have different solubilities: at 20 °C, 36 g of NaCl but 203.9 g of table sugar dissolve in 100 g of water.
Solubility curves
Solubility against temperature.
Effect of temperature
Change in temperature has different effects on the solubility of different compounds. Usually the solubility increases with the increase in temperature but it cannot be taken as a general rule.
Decreases: lithium carbonate (Li₂CO₃), calcium chromate (CaCrO₄) and calcium hydroxide.
Gases: the solubility of gases in water also decreases with the increase in temperature.
Activity
Take 100 g of water in a beaker and prepare a saturated solution of sugar at room temperature. Heat the beaker on a spirit lamp, add a little more sugar and stir: it dissolves. By heating, the quantity of sugar dissolved in water has increased, i.e. the solubility of sugar has increased.
Long Q 1.5
What types of movements are present in gaseous and liquid molecules?
Answer
Kinds of molecular motion
Translational: moving from one place to another.
Rotational: spinning about an axis.
Vibrational: moving to and fro about a position.
In gases
In gases, molecules are very widely apart with no order whatsoever and very weak intermolecular forces. They have all three motions: they move freely and randomly in straight lines between collisions (translational), spin (rotational) and vibrate. This is why gases spread and fill their containers.
In liquids
Liquids have molecules which are closely attached but moving randomly; significant intermolecular forces exist between them. They also have all three motions, but their translational motion is restricted: they slide over one another, which makes liquids flow.
In solids (for comparison)
The particles in solids remain fixed at their positions where they can only oscillate about their mean positions.
Particle motion in the three states.
Long Q 1.6
Differentiate between the areas which are studied under inorganic and organic chemistry.
Answer
Inorganic chemistry
Organic chemistry
Study of the synthesis, composition, properties and structure of elements and compounds that contain little or no carbon
Deals with the carbon compounds (hydrocarbons and their derivatives)
Substances composed of metals, non-metals or their mixtures, salts, acids and bases
Structure, formation, properties, composition and reactions of carbon-containing compounds
Includes simple carbon salts like carbonates, bicarbonates, oxides and carbides
Excludes those simple salts of carbon
Used as fertilisers, medicines, catalysts, pigments, coatings
Found in all forms of life and essential for life
Long Q 1.7
(Investigative) Preparation of solutions leads to an important process which enables us to purify a compound through crystallisation. Describe a process in which potassium nitrate is purified by crystallising it in water.
Answer
Principle
The increase in the solubility of solids in liquids with increase in temperature may be used to purify them. Pure solids commonly appear as beautifully shaped crystals. KNO₃ is far more soluble in hot water than in cold (about 169 g per 100 g at 80 °C but only about 32 g at 20 °C). Impurities, present in small amounts, stay dissolved when the solution cools.
Method
Dissolve the impure KNO₃ in the minimum amount of hot water to make a hot saturated solution.
Filter it while hot to remove insoluble impurities such as sand.
Let the filtrate cool slowly; pure KNO₃ crystals form as its solubility falls.
Filter off the crystals; the soluble impurities stay in the remaining solution.
Wash the crystals with a little cold water and dry them between filter papers.
The steep KNO₃ curve is why cooling gives so many crystals.
Result
Worked exampleFrom 100 g of water
At 80 °C about 169 g dissolves; at 20 °C only about 32 g stays dissolved.
Answerabout 137 g of pure KNO₃ crystallises out
Long Q 1.8
(Investigative) Graphene is called a miracle material and the material of the future. Which of its many properties makes it very useful in electronics?
Answer
Graphene is an example of a two-dimensional crystal, a single layer of carbon atoms arranged in a hexagonal pattern. It is a tough, flexible and light material with a high resistance.
Very high electrical conductivity: electrons move through it faster than through copper or silicon, so devices can be faster.
Only one atom thick and transparent: suitable for touch screens and see-through electrodes.
Flexible yet very strong: it can be used in bendable phones and wearable electronics.
Excellent conductor of heat: it carries heat away from chips, so they do not overheat.
Very large surface area: useful in sensors and fast-charging batteries.
Conclusion
Its outstanding electrical conductivity, combined with being thin, strong and flexible, is what makes graphene so promising in electronics.
Set B: More important long questions 5 questions
Long questions often set in board papers from this chapter, answered in the same full style.
Imp. LQ 1
What are elements, compounds and mixtures? Give the differences between them with examples.
Answer
Matter in this world exists in the form of elements, compounds and mixtures.
Element
Element is the simplest form of matter. It is a pure substance containing the same kind of atoms. It cannot be broken down into simpler substances by ordinary chemical reactions. Elements exist in all three forms, but most elements found in this world exist in solid form. Elements may be a metal, a non-metal, a metalloid or a noble gas, and can exist as atoms, molecules, ions and isotopes. Examples: sodium, potassium, carbon, nitrogen, oxygen, chlorine, copper, gold, mercury.
Compound
Compound is also a pure substance. It is made up of two or more different elements chemically combined in a fixed ratio. When elements come together they react and form chemical bonds that are not easy to break. Compounds may be molecular, ionic, intermetallic and coordination complexes, and inorganic or organic. Examples: water, ammonia, methane, carbon dioxide, sodium carbonate, potassium chloride, starch, proteins.
Mixture
A mixture is formed when more than one type of elements or compounds are mixed together in any ratio. Air, soil, milk and tap water are everyday examples. A mixture may be homogeneous (a solution of salt in water, uniform throughout) or heterogeneous (a sample of rock, whose composition differs from part to part).
Particles in an element, a compound and a mixture.
Differences
Element
Compound
Mixture
An element is the simplest form of matter. It is a pure substance containing the same kind of atoms.
A compound is a pure substance formed by the chemical combination of two or more atoms of different elements.
A mixture is an impure substance: more than one type of elements or compounds mixed in any ratio.
It is not possible to break down an element into simpler particles by ordinary chemical reactions.
In a compound the atoms combine in a fixed ratio by weight; in water H : O = 1 : 8.
Each component of a mixture retains its identity and specific properties.
When it exists as atoms it is represented by a symbol, e.g. Na and Ca.
It can be broken into its elements by a chemical reaction, e.g. ammonia → nitrogen + hydrogen.
It may be homogeneous (salt solution) or heterogeneous (rock).
Gaseous elements exist as independent molecules (N₂, O₂, Cl₂); noble gases are monatomic (He, Ar).
Its properties are always different from those of its elements (water vs hydrogen and oxygen).
Components are not chemically bound and can be separated by physical methods.
—
Compounds exist as molecules (HCl, NH₃, H₂O) or as networks (NaCl, SiO₂).
The properties of a mixture are the sum of those of its components.
Imp. LQ 2
Compare the properties of solids, liquids and gases. What is plasma?
Answer
States of matter
A state of matter is one of the many distinct forms in which matter can exist. The three primary states, solid, liquid and gas, are different from each other due to the different strength of intermolecular forces, the arrangement of particles and the distance between the particles.
Solid, liquid and gas.
Gases
In gases, molecules are very widely apart with no order and very weak intermolecular forces. This makes gases easily compressible, and their densities are very low.
Liquids
Liquids have molecules which are closely attached but moving randomly, with significant intermolecular forces. Liquids are therefore not easily compressible and their densities are higher than those of gases.
Solids
Solids have a definite shape and a fixed volume. Particles are closely packed with very strong attractions and remain fixed at their positions, oscillating about their mean positions. Solids are relatively incompressible and rigid, have very high densities and are the only state that does not need a container.
Solid
Liquid
Gas
Arrangement
closely packed, fixed
close, random
far apart, no order
Forces
very strong
significant
very weak
Density
very high
higher than gases
very low
Compressibility
almost none
not easily
easily
Fluidity
none
flows
flows freely
Shape / volume
fixed / fixed
not fixed / fixed
not fixed / not fixed
Plasma
Plasma is composed of particles with very high kinetic energy. It exists in fluorescent tubes, lightning and welding arcs. Plasma can be considered as a partially ionised gas containing electrons, ions, photons, etc. It is regarded as the fourth state of matter; most of the matter in the rest of the universe exists in this state.
Imp. LQ 3
Differentiate between a true solution, a colloidal solution and a suspension with examples.
Answer
Behaviour on standing and on filtering.
True solution
A solution is such a mixture in which solute particles are completely homogenised in the solvent, e.g. sodium chloride or copper sulphate in water. The particles cannot be seen by the naked eye, and on filtering they pass through the pores of filter paper leaving no residue.
Suspension
A suspension is a mixture in which solute particles do not dissolve in the solvent. We can see these particles. If kept for some time they settle down, and on filtering they cannot pass through the filter paper and are collected as a residue. Example: chalk in water.
Colloidal solution
In a colloidal solution the solute particles do not homogenise with the solvent. They are a little bigger than those of a true solution but not big enough to be seen with the naked eye. If kept for some time they do not settle down, and on filtration they pass through the filter paper. Examples: starch solution, white of an egg.
True solution
Colloid
Suspension
Particles visible?
no
no
yes
Settle on standing?
no
no
yes
Pass through filter paper?
yes
yes
no (residue)
Example
salt water
starch, egg white
chalk in water
Imp. LQ 4
Explain saturated, unsaturated and supersaturated solutions with the help of a solubility curve.
Answer
Unsaturated solution
Take about 100 g of water in a beaker, add 5 g of table sugar and stir: it dissolves; another 5 g also dissolves. A solution which can dissolve more amount of a solute at a particular temperature is called an unsaturated solution.
Saturated solution
Continue adding sugar. A stage comes when no more sugar will dissolve at this temperature and any more settles at the bottom. A solution in which the maximum amount of the solute has been dissolved in a particular amount of a solvent at a particular temperature is called a saturated solution.
Supersaturated solution
Definition
Supersaturated solution
Holds more solute than a saturated solution at that temperature. It is unstable: a small crystal added makes the extra solute crystallise out. It is made by cooling a hot saturated solution slowly without disturbing it.
On a solubility curve
Points below, on and above the KNO₃ curve.
A point below the curve: unsaturated.
A point on the curve: saturated.
A point above the curve: supersaturated.
Worked exampleKNO₃ at 40 °C (solubility about 64 g per 100 g water)
30 g dissolved: unsaturated.
64 g dissolved: saturated.
Cooled from 60 °C holding 100 g without crystallising: supersaturated.
Answerthe curve tells which kind a solution is
Imp. LQ 5
Describe the main branches of chemistry.
Answer
To understand the widely spread complex subject of chemistry and to concentrate on its specific aspects, chemistry is divided into many distinct branches.
Physical chemistry investigates how substances behave at atomic and molecular levels; it is used to predict and change the rates of reactions and optimise industrial conditions.
Inorganic chemistry is the study of the synthesis, composition, properties and structure of elements and compounds that contain little or no carbon; used as fertilisers, medicines, catalysts, pigments and coatings.
Organic chemistry deals with carbon compounds (hydrocarbons and their derivatives) other than simple salts like carbonates, bicarbonates, oxides and carbides; organic compounds are essential for life.
Environmental chemistry is the study of the chemical and biochemical phenomena in this planet: sources, reactions, effects and fates of chemicals in air, soil and water; causes and solutions of pollution.
Analytical chemistry deals with the analysis of substances: separation, identification and determination of concentration, with modern instruments.
Biochemistry is the branch in which we understand life through chemical processes: proteins, carbohydrates, lipids and nucleic acids.
Nuclear chemistry deals with reactions in the nucleus of an atom: radioactivity; applications in agriculture, medicine, industry and research.
Polymer chemistry focuses on the properties, structure and synthesis of polymers, large molecules made by linking building blocks (proteins, cellulose, nucleic acids).
Geochemistry is the study of the chemical composition of the Earth and its minerals; mineral exploration, environmental monitoring, forestry, medical research.
Medicinal chemistry: the chemist designs and synthesises medicines; discovery, delivery, absorption and metabolism of drugs.
Astrochemistry is the study of molecules and ions in space and interstellar space and their interaction with radiation.
