Transcript Grade 8 Review For Exam

Grade 8 Review For Exam
June 2015
Topics on June 2015 Exam
The Material World
The Living World
The Earth and Space
The Technological World
Properties
Ecology
Characteristics of the Earth
Mechanical Engineering
Mass
Species
Types of rocks
Types of motion
Volume
Population
Atmosphere
Effects of a force
Diversity of Life Forms
Geological and Geophysical Phenomena
Physical and behavioural Adaptation
Renewable and non-renewable energy
resources
Temperature
States of matter
Acidity/alkalinity
Characteristic properties
Changes
Evolution
Life–Sustaining Processes
Conservation of matter
Plant and animal cells
Mixtures
Cellular components visible under a
microscope
Separation of mixtures
Physical changes
Chemical changes
Organization
Atom
Molecule
Osmosis and diffusion
Photosynthesis and respiration
Survival of species
Asexual and sexual reproduction
Reproductive mechanisms in plants
Reproductive organs
Gametes
Fertilization
Astronomical Phenomena
Simple machines
System
Basic mechanical functions (links guiding
controls)
Motion transmission systems
Motion transformation systems
Cycles of day and night
Materials
Material Resources
States of Matter
• Matter occurs in three states:
1. Solid
2. Liquid
3. Gas
• A change in temperature will cause a
substance to change state.
Acidity Vs. Alkalinity
• Acids and bases are 2 groups of important
chemicals with the following characteristics:
Acids
Bases
Sour
Bitter
No distinct feel
Slippery
Turn blue litmus red
Turn red litmus blue
pH < 7
pH > 7
Acids Vs. Bases
Characteristic Vs. Non-Characteristic
• Characteristic properties are so specific that
they help you identify a substance. They are
often unique to that substance.
– Ex: density, melting point, boiling point
• Non-characteristic properties are general and
do not help you identify a substance.
– Ex: color, shape, mass, volume, texture
What are Mixtures?
• The atoms & molecules sometimes combine
without undergoing a chemical reaction.
Instead, they form a mixture.
• A mixture is made up of at least 2 different
substances which can always be isolated using
physical separation techniques (no chemical
bonds broken).
• Solutions are an important type of mixture.
Ex: Air, tap water, steel
• A solution is a liquid homogeneous mixture
containing dissolved substances. Cannot be
separated by filtering, but can by boiling.
• Homogeneous = component substances
cannot be distinguished, even with the aid of
a magnifying instrument.
• In contrast, a heterogeneous mixture would
be one in which the individual components
can be distinguished.
Separation of Mixtures
There are several ways to separate mixtures:
• Physical removal – pick parts out with fingers
or tweezers. Ex: In a salad, pick out the
onions.
• Use a magnet. Ex: Separating iron from sand.
How it works: The magnet sticks to the iron
but not to the sand.
• Filtering (filtration) -used to separate a solid
(or suspension) from a liquid. How it works:
The liquid (& anything dissolved in the liquid)
passes through holes in the filter paper but
the solid particles are too big and get stuck.
– Example: Separating dirt from salty water.
• Evaporation can be used to separate a
dissolved SOLUTE (the substance dissolved)
from a SOLUTION.
– Ex: Evaporate water off a salt water solution.
• Distillation = boiling, collecting the steam &
condensing it. Ex: to purify alcohol
• Sedimentation = particles in suspension in a
fluid will tend to settle on a surface if the
suspension is left, undisturbed.
– Ex: Used in water filtration plants to get rid of grit
in water.
Definitions
• Atom: The smallest part of a chemical element; the
basic building block of matter.
• Element: A pure substance considered not to be
divisible into smaller parts.
– H, He, Li, Be, etc.
• Molecule: a group of two or more chemically bonded
atoms. The smallest part of a substance that displays
the characteristic properties of that substance.
– Ex: H2O, O2 , N2
• Compound: A pure substance containing at least 2
different elements that are chemically bonded.
– Ex: NaCl, H2SO4
What Do Atoms Look Like?
What is in each box?
Finding p+, n, and e- for each Element:
• Protons = the atomic number
• Electrons = protons if the atom is neutral
• Neutrons = atomic mass minus # protons
(because mass = neutrons + protons only, electrons
are negligible)
Law of Conservation of Matter
• Matter is neither created nor destroyed, it simply
gets transformed into something different.
– i.e., if
reactants → products
Then
1. Mass of reactants = mass of products
2. Total # of atoms of reactants = total # of atoms of products
3. Total # of each kind of atom of reactants = total # of each
kind of atom of product
Physical Changes
• Alters neither nature nor characteristic
properties of matter. The atoms and
molecules of the substance do not change.
Chemical Changes
• Alter the nature & characteristic properties of
matter. The bonds between atoms are
rearranged.
Signs of a Chemical Change
1) Change in color (not a change in shade as
light red to dark red, but a total change in
color as red to blue)
2) You see bubbles of gas – it fizzes
3) A solution turns cloudy & a solid falls to the
bottom (precipitate forms)
4) Heat or light is given off or taken in (i.e.,
something gets hot or cold)
5) Electricity is produced (i.e., in a battery)
Chemical Changes
-You usually cannot reverse a chemical change.
Ex: you cannot “unburn” paper
-Alter the number of electrons in an atom
Earth & Space
Rocks
• Rocks are heterogeneous solids composed of
many minerals (minerals have well defined
properties whereas rocks have physical and
chemical properties that are not strictly defined)
• Rocks are formed by different processes:
– Rocks that are formed by water pressure are called
sedimentary
– Rocks that are formed by volcanic activity are called
igneous
– Metamorphic rock are rocks that have been
transformed by high temperatures & pressure.
3 Types of Rocks
• Igneous rocks are formed when magma cools and
solidifies. Ex: granite
• Sedimentary rocks are formed by the
accumulation and compaction of debris under
bodies of water. Ex: sandstone, limestone
• Metamorphic rocks are former igneous or
sedimentary rocks that have been transformed by
the heat or pressure. Ex: limestone turns into
marble or granite into gneiss
Igneous Rocks
Basalt
Pumice
Sedimentary Rocks
Black Limestone
Shale
Sandstone
Metamorphic Rocks
Slate
Marble
Schist
Gneiss
Gneiss
The Atmosphere
- Is the layer of air surrounding Earth
-extends more than 10 000 km above Earth, but
99% of its mass is concentrated in first 30 km.
- Is made up of gases essential to life:
- a screen blocking out dangerous sun rays (UV)
- ensures stable climate on Earth by retaining heat
- includes O2, essential for cellular respiration &
CO2, necessary for photosynthesis in plants
- Gravity pulls particles in atmosphere to Earth
Composition of the Atmosphere
- Air = mixture of gases that make up the
atmosphere
- Is made up of following gases:
• 78% N2
• 21% O2
• 1% other gases (Water vapor, Ar, CO2, Ne,
He, CH4, Kr, H2, N2O, Xe, O3, CFCs)
- Also contains suspended solid & liquid particulate
matter which comes from Earth’s surface (Dust,
pollen, soot, smoke, droplets, etc.) & mixes with
air.
5 Layers of the Atmosphere
Exosphere
5 Main Layers of Atmosphere
1.
Exosphere (500 km & more)
- Is practically empty
- Impossible to gauge temp with thermometer
- Most telecommunication satellites here
2.
Thermosphere (80–500 km)
- Absorbs most of sun’s rays (is hottest layer – up to 1800oC)
- Meteors (& other celestial bodies) burn up here
- Polar auroras usually here
3.
Mesosphere (50-80 km)
- Coldest layer (-80oC in upper reaches)
- Contains very few air particles (would suffocate in few mins.)
4.
Stratosphere (15-50 km)
- Where sun’s UV rays absorbed in ozone layer
- Temperatures increase with altitude because of ozone layer
- Air particles increasingly rare at higher altitudes
5.
Troposphere ( 0-15 km)
- Most meteorological phenomena (clouds, storms) here
- Higher the altitude, the lower the temp. (drops 6.5oC every 1000m)
Exosphere
Renewable & Non-renewable Energy
Resources
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•
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•
•
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Hydro energy - R
Wind energy - R
Solar energy - R
Geothermal energy - R
Nuclear energy - NR
Fossil fuel energy - NR
Biomass & biofuels - NR
Battery & hydrogen energy - NR
Day and Night
• One side of the Earth faces the Sun and is lit up (daytime) and the other is in
darkness because it is facing away from the Sun (nighttime).
• The Earth rotates on its axis once every 24 hours, so any given spot
experiences daytime and nighttime.
Phases of the Moon
• By observing the Moon over a period of several weeks, you
notice that the Moon rises and sets at different times each
night, and that there is a regular progression through lunar
phases.
• In one month, the Moon progresses through one lunar
cycle and will vary between being a completely dark new
moon and a fully illuminated full moon .
• The lunar phases are caused because the orbit of the
Moon around the Earth will vary the Moon’s position in
relation to the Sun.
• Half of the Moon is always lit by the Sun, but the portion
that we see will change depending on where the Moon is in
its orbit.