Set A: Textbook exercise short questions 8 questions
The short questions at the end of the chapter in your book.
Short Q 1.1
Why is there a need to divide chemistry into many branches? Give three reasons.
Answer
To understand the widely spread complex subject of chemistry and to concentrate on its specific aspects, chemistry is divided into many distinct branches. These branches have distinct areas of study for the scientists to focus on and to achieve breakthroughs and advancements.
- Chemistry is too vast and complex for one person to master all of it.
- Each branch lets scientists focus on one area and go deep into it, which leads to breakthroughs and advancements.
- Each branch has its own methods and applications (medicine, industry, environment), which makes study, research and careers easier to organise.
Short Q 1.2
Reactions may take place due to electrons outside the nucleus or inside the nucleus. Which branches of chemistry cover these two types of reactions?
Answer
Reactions of the electrons outside the nucleus are ordinary chemical reactions; they are studied in physical, inorganic and organic chemistry (and the other branches that deal with chemical changes).
Nuclear chemistry deals with the reactions taking place in the nucleus of an atom. It deals with radioactivity, nuclear processes and transformation in the nuclei of atoms.
Short Q 1.3
What types of problems are solved in analytical chemistry?
Answer
Analytical chemistry deals with the analysis of different substances. It involves separation, identification and determination of the concentration of the components present in material things, nowadays with modern and sophisticated instruments.
- What substances does a sample contain? (identification)
- How much of each is present? (concentration)
- How can a mixture be separated into its components?
- Examples: testing the purity of medicines and food, checking pollutants in water, forensic tests.
Short Q 1.4
Both graphite and graphene have hexagonal layered structures. What is the difference?
Answer
Graphite has a layered structure of hexagonal rings of carbon: many layers stacked on top of each other and held by weak forces.
Graphene is an example of a two-dimensional crystal, a single layer of carbon atoms arranged in a hexagonal pattern. So graphene is just one layer of graphite.
Short Q 1.5
Why are supercritical fluids important?
Answer
Supercritical fluids are highly compressed states which show both properties of gases and liquids. Chemical reactions which may not be carried out in conventional solvents may possibly be carried out in supercritical carbon dioxide.
Supercritical CO₂ is non-toxic and leaves no residue; it is used, for example, to remove caffeine from coffee.
Short Q 1.6
In which state does matter exist in the Sun?
Answer
In the plasma state. Plasma is regarded as the fourth state of matter; most of the matter present in the rest of the universe, including the Sun and stars, exists in this state. The Sun's very high temperature ionises its gases into electrons and positive ions.
Short Q 1.7
What is the importance of graphene?
Answer
Graphene is 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 to breaking.
It also conducts electricity and heat very well, so it is used or being developed for fast electronics, touch screens, sensors, batteries and strong lightweight materials.
Short Q 1.8
Which form of matter do most of the material things in this world belong to?
Answer
Solids. Elements exist in all three forms, solid, liquid and gas, but most of the elements found in this world exist in solid form; liquid and gaseous elements are very few. (In the rest of the universe most matter is plasma.)
Set B: More short questions 55 questions
The book's in-text exercises first, then short questions on every topic of the chapter (SLO-based), as asked in board papers.
Practice exercise questions (in text)
SQ 1.1
A lunar mission has recently brought samples from the Moon. Point out the branch of chemistry each experiment is related to: (1) determining its composition, (2) studying the physical properties of the materials it contains, (3) carrying out chemical reactions with usual inorganic reagents.
Answer
| Experiment | Branch of chemistry |
|---|
| 1. Determining its composition | Analytical chemistry |
| 2. Studying the physical properties of its materials | Physical chemistry |
| 3. Chemical reactions with usual inorganic reagents | Inorganic chemistry |
SQ 1.2
Which elements are found in the pure state on Earth?
Answer
Elements that are unreactive occur uncombined (native): gold, platinum and silver (sometimes copper) as metals; carbon as diamond and graphite; sulphur near volcanoes; and the gases nitrogen, oxygen and the noble gases in air.
SQ 1.3
Which elements are present in very small amounts on Earth?
Answer
Rare elements such as astatine and francium (radioactive; only a few grams exist in the whole crust at any time); precious elements such as gold, platinum and iridium; and the noble gases xenon and krypton in air. Technetium and promethium hardly occur naturally at all.
SQ 1.4
How can the variation of solubility at different temperatures be useful for us?
Answer
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. Generally the solubility of gases decreases with increase in temperature, so soda water bottles are stored in the refrigerator to keep carbon dioxide dissolved for a longer time.
- Crystallisation: KNO₃ dissolved in hot water gives pure crystals on cooling.
- More sugar dissolves in hot tea than in cold.
- Cold drinks keep their fizz longer.
Chemistry and its branches
SQ 1.5
Define chemistry.
Answer
Chemistry is the branch of science which deals with the properties, composition and the structure of substances. It also deals with the physical and chemical changes in matter and the laws or principles which govern these changes.
SQ 1.6
What is meant by the composition and the structure of matter?
Answer
Determination of composition represents finding out the percentages of elements and compounds in a sample of matter. Structure of matter means the arrangement of atoms in matter. Both physical and chemical changes may be brought about by absorption or evolution of energy.
SQ 1.7
Define physical chemistry.
Answer
This branch investigates how substances behave at atomic and molecular levels. It explains how fundamental physical laws cause atoms and molecules to show specific characteristics. Physical chemistry is also used to predict and change the rates of reactions and thus optimise the conditions to carry out reactions on an industrial scale.
SQ 1.8
Define inorganic chemistry. Give uses of inorganic compounds.
Answer
It is the study of the synthesis, composition, properties and structure of elements and compounds that contain little or no carbon. An inorganic substance can be composed of metals, non-metals or a mixture of these, salts, acids and bases. Inorganic compounds are used as fertilisers, medicines, catalysts, pigments, coatings and much more.
SQ 1.9
Define organic chemistry.
Answer
It is the branch of chemistry that deals with the carbon compounds (hydrocarbons and their derivatives) other than its simple salts like carbonates, bicarbonates, oxides and carbides. In this branch we study the structure, formation, properties, composition and reactions of carbon-containing compounds. Organic compounds are found in all forms of life and are essential for life.
SQ 1.10
What is environmental chemistry?
Answer
It is the scientific study of the chemical and biochemical phenomena that occur in this planet. We study the sources, reactions, effects and fates of chemical species in the air, soil and water environments. It helps in understanding the causes, effects and solutions of different types of pollution.
SQ 1.11
What is analytical chemistry?
Answer
This branch of chemistry deals with the analysis of different substances. It involves separation, identification and determination of the concentration of the components present in material things, using modern and sophisticated instruments.
SQ 1.12
What is biochemistry?
Answer
It is the branch of chemistry in which we understand life through chemical processes. It is the study of chemical substances and vital processes occurring in living organisms, and gives insight into the structure and function of proteins, carbohydrates, lipids and nucleic acids.
SQ 1.13
What is nuclear chemistry? Where is it applied?
Answer
Nuclear chemistry deals with the reactions taking place in the nucleus of an atom. It deals with radioactivity, nuclear processes and transformation in the nuclei of atoms. It has many applications in agriculture, medicine, industry and research.
SQ 1.14
What is polymer chemistry? Give examples of natural polymers.
Answer
Polymers are large molecules made by linking together a series of building blocks. Polymer chemistry focuses on the properties, structure and synthesis of polymers and macromolecules. Many materials in living organisms, including proteins, cellulose and nucleic acids, are naturally occurring polymers.
SQ 1.15
What is geochemistry?
Answer
The study of the chemical composition of the Earth and its sources and minerals is called geochemistry. Apart from its use in mineral exploration, geochemical mapping today has applications in environmental monitoring, forestry and medical research.
SQ 1.16
What is medicinal chemistry?
Answer
In this branch of chemistry, the chemist tries to design and synthesise medicines or drugs which are beneficial for mankind. It includes the discovery, delivery, absorption and metabolism of drugs in the human body.
SQ 1.17
What is astrochemistry?
Answer
It is the study of molecules and ions occurring in space and interstellar space. In this discipline we study the abundance and reactions of atoms, molecules and ions in the universe and the interaction of these species with radiation.
SQ 1.18
What is a geothermal heat pump?
Answer
A geothermal heat pump uses a pump to transfer underground water into buildings during the winter to heat them and in the summer to cool them.
States of matter
SQ 1.19
Define matter. Is energy matter?
Answer
This world is made up of matter and energy. Energy is non-material in nature. Anything other than energy which carries weight and occupies volume is called matter.
SQ 1.20
What is a state of matter? Name the states of matter.
Answer
A state of matter is one of the many distinct forms in which matter can exist. We observe four states of matter in everyday life: solid, liquid, gas and plasma. Apart from these, there are more states of matter which we do not see in our everyday life.
SQ 1.21
Why are the three primary states of matter different from each other?
Answer
The solid, liquid and gaseous states are different from each other due to the different strength of intermolecular forces, the arrangement of particles and the distance between the particles.
SQ 1.22
Why are gases easily compressible and have low densities?
Answer
In gases, molecules are very widely apart with no order whatsoever and very weak intermolecular forces. All these features make gases easily compressible. Their densities are obviously very low.
SQ 1.23
Why are liquids not easily compressible?
Answer
Liquids have molecules which are closely attached but moving randomly, and there exist significant intermolecular forces between their molecules. Liquids are therefore not easily compressible and their densities are higher than those of gases.
SQ 1.24
Why are solids rigid and almost incompressible?
Answer
Particles in solids are closely packed and have very strong interatomic or intermolecular attractions. The particles remain fixed at their positions where they can oscillate about their mean positions. Solids are therefore relatively incompressible and rigid. In crystalline solids, particles are perfectly arranged and strongly bonded, which makes them almost incompressible.
SQ 1.25
Why do solids not need a container to be stored?
Answer
Solids have a definite shape and a fixed volume. They are the only state of matter which does not need any container to be stored.
SQ 1.26
What is plasma? Where is it found?
Answer
Plasma is not a generally seen form of matter. It 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.
SQ 1.27
What are intermediate states of matter? Give examples.
Answer
Matter also exists in intermediate states, where liquid meets gas and liquid meets solid, for example supercritical fluids, liquid crystals and graphene.
SQ 1.28
What are supercritical fluids?
Answer
Supercritical fluids are highly compressed states which show both properties of gases and liquids. Chemical reactions which may not be carried out in conventional solvents may possibly be carried out in supercritical carbon dioxide.
SQ 1.29
What are liquid crystals? Give their uses.
Answer
Liquid crystal is a state of matter whose properties are between those of conventional liquids and those of crystalline solids. Liquid crystals are used in display devices including computer monitors, clocks, watches and navigation systems.
SQ 1.30
What is graphene?
Answer
Graphene is an example of a two-dimensional crystal, a single layer of carbon atoms arranged in a hexagonal pattern. Graphene is a tough, flexible and light material with a high resistance.
SQ 1.31
What are exotic states of matter?
Answer
States of matter that are not commonly encountered are called exotic states of matter. Examples are dark matter, Bose-Einstein condensate, nuclear matter and quantum spin liquid.
Elements, compounds and mixtures
SQ 1.32
Define an element. Give examples.
Answer
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 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, magnesium, calcium, carbon, nitrogen, oxygen, chlorine, copper, gold, mercury and bromine.
SQ 1.33
In which physical state are most elements found?
Answer
Elements exist in all three forms, solid, liquid and gas, but most of the elements found in this world exist in solid form. Liquid and gaseous elements are very few in number compared with solids.
SQ 1.34
Define a compound. Give examples.
Answer
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 or coordination complexes, and inorganic or organic.
Examples: water, ammonia, methane, carbon dioxide, sodium carbonate, potassium chloride, starch and proteins.
SQ 1.35
Define a mixture. Differentiate between homogeneous and heterogeneous mixtures.
Answer
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 of mixtures.
| Homogeneous mixture | Heterogeneous mixture |
|---|
| Concentration is uniform throughout. | Concentration of its constituents is different in different parts. |
| A solution of salt in water. | A sample of rock (granite, mica, limestone). |
SQ 1.36
In what ratio by weight are hydrogen and oxygen present in water?
Answer
In a compound the atoms combine in a fixed ratio by weight. In water (H₂O), hydrogen and oxygen are present in a fixed ratio of 1 : 8 by weight.
SQ 1.37
How can a compound be broken into its elements? Give an example.
Answer
It is possible to break a compound into its constituent elements by a chemical reaction. For example, ammonia can be converted back to nitrogen and hydrogen by a suitable chemical reaction.
SQ 1.38
How are the components of a mixture separated?
Answer
The components of a mixture are not chemically bound together and they can be separated by physical methods, such as filtration, evaporation, distillation and crystallisation. Each component retains its identity and specific properties.
SQ 1.39
In what form do gaseous elements and noble gases exist?
Answer
Gaseous elements exist in the form of independent molecules, for example nitrogen (N₂), oxygen (O₂) and chlorine (Cl₂). Noble gases, however, exist as monatomic molecules, for example helium (He) and argon (Ar).
SQ 1.40
Which was the first element created in the laboratory?
Answer
Many elements are found in nature but some are artificial. Technetium was the first element created by scientists in the laboratory.
Allotropy
SQ 1.41
Define allotropy. Give examples.
Answer
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.
Oxygen exists as oxygen (O₂) and ozone (O₃); carbon as diamond, graphite and buckminster fullerene; sulphur as rhombic and monoclinic.
SQ 1.42
Name the allotropic forms of sulphur. Which is more stable?
Answer
Element sulphur exists in two crystalline allotropic forms, rhombic and monoclinic; the former (rhombic) is more stable than the latter.
SQ 1.43
Describe the structure and properties of buckminster fullerene.
Answer
Buckminster fullerene (C₆₀) consists of spheres made of atoms arranged in pentagons and hexagons. Fullerenes are stable at high temperatures and high pressures. Being covalent, they are soluble in organic solvents. The molecule is not charged, has no boundaries and has no unpaired electrons; it has a cage-like structure. C₆₀ has a low melting point, is soft and cannot conduct electricity.
SQ 1.44
How does diamond differ from graphite in structure?
Answer
Diamond has a giant macromolecular structure in which every carbon is bonded to four others, whereas graphite has a layered structure of hexagonal rings of carbon.
Solutions, colloids and suspensions
SQ 1.45
Define a true solution. Give examples.
Answer
A solution is such a mixture in which solute particles are completely homogenised in the solvent, e.g. dissolution of sodium chloride or copper sulphate in water. The solute particles cannot be seen by the naked eye. If the solution is filtered, these particles pass through the pores of filter paper leaving no residue. Such a solution is called a true solution.
SQ 1.46
Define a suspension. Give an example.
Answer
A suspension is a mixture in which solute particles do not dissolve in the solvent. We can actually see these particles. If a suspension is kept for some time, these particles settle down, and on filtering they cannot pass through the pores of filter paper and are collected as a residue. A mixture of chalk in water is an example.
SQ 1.47
Define a colloidal solution. Give examples.
Answer
In a colloidal solution the solute particles do not homogenise with the solvent. These particles are a little bigger than the solute particles 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 filter paper. Starch solution and white of an egg are common examples.
SQ 1.48
How are mixtures related to our everyday lives?
Answer
Mixtures are closely related to our everyday lives. The air we breathe, the foods we consume, the fluids in our body and solids like steel are all either homogeneous or heterogeneous mixtures.
Saturated solutions and solubility
SQ 1.49
Define an unsaturated solution and a saturated solution.
Answer
A solution which can dissolve more amount of a solute at a particular temperature is called an unsaturated solution.
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.
SQ 1.50
How will you prepare a saturated solution of sugar?
Answer
Take about 100 g of water in a beaker, add 5 g of table sugar and stir; it dissolves. Add another 5 g; this also dissolves (unsaturated solution). Continue adding sugar: dissolution becomes more difficult, and a stage comes when no more sugar will dissolve and any more settles at the bottom. The solution is now saturated at that temperature.
SQ 1.51
Define solubility.
Answer
The solubility of a solute is the amount of solute which can dissolve in 100 g of a solvent at a particular temperature.
SQ 1.52
Why is table sugar more soluble in water than sodium chloride?
Answer
At 20 °C, 36 g of sodium chloride dissolves in 100 g of water but 203.9 g of table sugar dissolves. This is because sugar molecules are larger than salt ions, so more water molecules can surround a single sugar molecule, causing it to dissolve in larger amounts.
SQ 1.53
How does temperature affect solubility? Give examples.
Answer
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.
- Increases: potassium nitrate (KNO₃), silver nitrate (AgNO₃), potassium chloride (KCl), copper sulphate, sodium nitrate.
- Does not increase appreciably: sodium chloride.
- Decreases: lithium carbonate (Li₂CO₃), calcium chromate (CaCrO₄), calcium hydroxide, and gases.
SQ 1.54
Why are soda water bottles stored in the refrigerator?
Answer
Generally the solubility of gases decreases with increase in temperature. Carbon dioxide gas is more soluble in water at low temperature, so soda water bottles are stored in the refrigerator to keep carbon dioxide dissolved for a longer period of time.
SQ 1.55
What happens when a saturated solution of sugar is heated and more sugar is added?
Answer
By heating the solution, the quantity of sugar dissolved in water increases, i.e. the solubility of sugar increases with temperature, so the added sugar dissolves.
