Elements, Compounds, and Mixtures Chp.3

Question 1

two types of matter

Answer 1

pure (elements and compounds)

impure (mixtures)

Question 2

elements (5)

Answer 2

• basic unit of matter
• made up of only one kind of atom
• classified into metals, non-metals, metalloids, noble gases
• cannot be broken down into two or more simpler substances by any means
• pure substance

Question 3

Compound (4)

Answer 3

• formed by the combination of two or more different elements

-Elements are combined chemically in a fixed proportion

• it can be broken down into its constituent elements by chemical means
• pure substance

Question 4

mixture (4)

Answer 4

formed by the combination of two or more elements, compounds, or both

• Substances are mechanically mixed in any proportion
• retains the property of its constituent elements/compounds
• impure substance

Question 5

atom (2)

Answer 5

Basic unit of an element

smallest particle of an element which may or may exist independently

Question 6

division of an atom (5)

Answer 6

protons are positively charged particles

neutrons are particles carrying no charge

electrons are negatively charged particles

nucleus is located in the center of the atom and contains protons and neutrons

electrons revolve around the nucleus in orbits

Question 7

what is the modern periodic table?

Answer 7

is it the tabular arrangement of elements in order of increasing atomic number

Question 8

Examples of strong metals (name 3)

Answer 8

lithium

beryllium

sodium

calcium

pottasium

Question 9

give an example of a weak metal

Answer 9

aluminum

Question 10

give 7 characteristics of metals (+ exceptions)

Answer 10

• have luster/shine
• have high melting and boiling points
• have high density
• are malleable (can be beaten into thin sheets)
• are ductile (can be drawn into wires)
• good conductors of heat and electricity
• monoatomic (only one type of atom)

(Exceptions: mercury is a liquid at room temp, zinc in non-malleable beyond certain temps_

Question 11

give 7 characteristics of non-metals (+ exceptions)

Answer 11

• do not have luster, don’t shine
• have low melting and boiling points
• have low density
• are non-malleable
• are non-ductile
• poor conductors of heat and electricity
• mono/diatomic (one or two types of atoms)

(exceptions: iodine is lustrous, graphite is lustrous and conducts electricity)

Question 12

metalloids (3)

Answer 12

• are elements which show properties of both metals and non-metals
• are chemically reactive
• contain one type of atom (monoatomic)

Question 13

noble gases (3)

Answer 13

• occur in traces in the atmosphere in gaseous state
• are chemically inert/inactive
• contain one type of atom (monoatomic)

Question 14

what is a molecule? (2)

Answer 14

atoms of the same element or different elements combine to form a molecule

smallest particle of a substance that can normally exist independently and can retain the physical and chemical properties of the substance

Question 15

types of elements (3)

Answer 15

monoatomic (single atom retains all the properties of a chemical mixture) - He, Na

diatomic (they are molecules that contain two atoms of the same type) H2, O2, N2

polyatomic (molecules which contain more than three types of atoms of the same type) - O3, P4, S8

Question 16

what is atomicity

Answer 16

the number of atoms of an element that join together forming a molecule of that element is known as the atomicity

Question 17

molecules of a compound

Answer 17

molecules of elements containing two or more atoms of different kinds are called molecules of compounds

Question 18

define compound

Answer 18

a pure substance made up of two or more different elements combined chemically in a fixed proportion

Question 19

characteristics of compounds (5)

Answer 19

• Components in a compound are in a definite proportion
• particles in a compound are of one kind
• compounds have a definite set of properties
• elements in a compound do not retain their original properties
• components in a compound can be separated by chemical means only

Question 20

define a mixture (2)

Answer 20

• a mixture is made up of two or more substances, elements, compounds or both, mechanically mixed together in any (random) proportion

a mixture retains the properties of its constituent elements or compounds

Question 21

give example of a mixture which is:

element + element

compound + compound

element/s + compound

Answer 21

Cu + Zn = brass

Nacl + H2O (water) = salt solution

S + C + KNO3 = gun powder

Question 22

what is a homogenous mixture (3)

Answer 22

• the constituents are uniformly mixed
• properties and composition remain same throughout the mixture

-ex. Brass, air, salt solution, alcohol solution

Question 23

what is a heterogenous mixture (3)

Answer 23

• the constituents are not uniformly mixed
• properties and composition vary throughout the mixture
• iron + Sulphur, oil + water, sand + water

Question 24

4 types of separation techniques for a solid - solid mixture

Answer 24

sublimation

magnetic separation

solvent extraction

fractional crystallization

Question 25

principle of sublimation

Answer 25

based on - sublimable solid sublimes on heating, leaving behind the other (NH4CL and NaCl)

Question 26

principle of magnetic separation

Answer 26

based on-magnetic solids attracted by a magnet, leaving behind the non-magnetic solid (Fe and S)

Question 27

principle of solvent extraction

Answer 27

based on - soluble solids dissolves in a solvent, leaving behind the other (Sulphur and charcoal)

Question 28

4 types of separation techniques for a solid - liquid mixture

Answer 28

filtration sedimentation evaporation distillation

Question 29

principle of fractional crystallisation

Answer 29

based on - difference in solubility of the solids in a particular solvent (KNO3 and KCLO3)

Question 30

principle of filtration

Answer 30

based on - insoluble solid being filtered out using filter paper (ex. CaCO3 and h2O)

Question 31

principle of sedimentation

Answer 31

based on - insoluble solid settling down due to sedimentation (Sand and water)

Question 32

principle of evaporation

Answer 32

based on - evaporation of liquid component leaving behind the solid (NaCl and Water)

Question 33

principle of distillation

Answer 33

based on - liquid component collects in receiver after condensation and solid remains behind

Question 34

2 methods of separating a liquid-liquid mixture

Answer 34

- separating funnel (difference in densities of the two liquids) - fractional distillation (difference in boiling points of the two liquids)

Question 35

1 method of separating a liquid-gas mixture

Answer 35

- Boiling the mixture ( decrease in solubility of a gas in liquid) ex. in water with the increase in temperature of the liquid, carbon dioxide escapes out from the water

Question 36

2 methods of separating a gas-gas mixture

Answer 36

- diffusion (passage of gases through porous partition) (ex. hydrogen and oxygen) - Solubility in solvent (solubility of the gas in the solvent i.e water) (ex. hydrogen chloride and nitrogen)

Question 37

2 methods to separate complex mixtures

Answer 37

- chromatography (to separate the mixture of different solid constituents in a liquid constituent) - centrifugation (separation of mixtures using a centrifugal force - force exerted by a revolving object)

Question 38

what is centrifugal force

Answer 38

a revolving object exerts a force away from the centre of rotation called centrifugal force

Question 39

define chromatography

Answer 39

the process of separation of complex mixtures based on the difference in absorption of the solid constituents (e.g dyes on the surface of an adsorbent medium)

Question 40

centrifugation

Answer 40

it is the process of seperation of complex mixtures based on the separation of a more dense component (e.g cream from a less dense component e.g milk)