Comprehensive Study Notes on Scientific Skills, Matter, Chemical Reactions, and Forces Between Particles

Scientific Skills: Line Graphs

Summary of Important Points About Line Graphs:

• Identify Variables:
  • Independent Variable: Deliberately changed or manipulated (x-axis).
  • Dependent Variable: Changes with the independent variable and is measured (y-axis).
• Heading/Title:
  • "Graph representing ___ (y-value) versus ___ (x-value)".
• Label Axes:
  • Clearly label axes with units of measurement.
• Determine the Variable Range:
  • Subtract the lowest data value from the highest data value for each variable (y and x).
• Determine the Scale of the Graph:
  • Calculate the range for each axis:
    • y-axis: \frac{\text{y-axis range}}{\text{Number of lines on the y-axis}}, round to a convenient number.
    • x-axis: \frac{\text{x-axis range}}{\text{Number of lines on the x-axis}}, round to a convenient number.
  • Note: Graphs should pass through the origin, so the range should be calculated from zero to the maximum of each quantity.
• Plot the Data Points:
  • Plot each set of data values (coordinates) on the graph.
• Draw the Graph:
  • Draw a curve or line that best fits the plotted data points; do not connect the dots.
• State the Relationship Between Variables:
  • Straight Line Through the Origin:
    • The dependent variable (y-variable) is directly proportional to the independent variable (x-variable).
    • \frac{y}{x} = \text{a constant}
  • Curved Line (or line not through the origin):
    • As the x-variable increases or decreases, the y-variable increases or decreases.

Examples

Electromagnet Experiment:

• Experiment: Various numbers of wire coils were wound around a nail connected to a battery, making an electromagnet. The number of pins each electromagnet could pick up was counted.
• Data Table:
  • Number of coils in the electromagnet vs. Number of pins picked up:
    • 0 coils: 0 pins
    • 25 coils: 1 pin
    • 50 coils: 2 pins
    • 100 coils: 4 pins
    • 200 coils: 9 pins
    • 400 coils: 15 pins
• Graph Title: Graph showing number of pins picked up against number of coils.
• Relationship: The number of pins picked up is directly proportional to the number of coils of the electromagnet.

Spring Stretch Experiment

• Experiment: Various masses were hung on a spring, and the distance that this made the spring stretch was measured in each case.
• Data Table:
  • Mass hung on spring (kg) vs. Distance spring stretches (cm):
    • 1 kg: 3 cm
    • 2 kg: 6 cm
    • 3 kg: 9 cm
    • 4 kg: 12 cm
    • 5 kg: 15 cm
• State the relationship from your graph

Syringe Experiment

• Experiment: Mass loaded on a closed syringe (kg) vs. Volume of air (cm3)
• Data Table:
  • Mass loaded on a closed syringe (kg) vs. Volume of air (cm3):
    • 1 kg: 15 cm3
    • 2 kg: 8 cm3
    • 3 kg: 5 cm3
    • 4 kg: 4 cm3
    • 5 kg: 3 cm3
• State the relationship from your graph

Distance and Time Experiment

• Experiment: How the distance increases with increasing time
• Data Table:
  • Time (s) vs. Distance (m):
    • 3 s: 9 m
    • 5 s: 15 m
    • 15 s: 45 m
    • 30 s: 90 m
    • 50 s: 150 m
• State the relationship from your graph

Diameter and Circumference Experiment

• Data Table:
  • Diameter (mm) vs. Circumference (mm):
    • 3 mm: 9 mm
    • 10 mm: 31 mm
    • 18 mm: 57 mm
    • 25 mm: 79 mm
    • 40 mm: 126 mm
• State the relationship from your graph

Gradient of a Straight Line

• Gradient (slope) shows how steep or inclined the line is to the horizontal.
• Formula: \text{Gradient} = \frac{\text{change in y-value}}{\text{change in x-value}}
• Example Gradients:
  • Graph 1: Gradient = \frac{5}{5} = 1
  • Graph 2: Gradient = \frac{7}{3} = 2.5
  • Graph 3: Gradient = \frac{4}{5} = 0.8
• Ranking Steepness (Descending Order):
  1. Graph 2
  2. Graph 1
  3. Graph 3

Coordinates

• Coordinates are expressed as (x-value, y-value).
• The first number is the x-coordinate, and the second number is the y-coordinate.

Gradient Using Two Points (Coordinates)

• Gradient Formula: m = \frac{y2 - y1}{x2 - x1}
• Where (x1, y1) and (x2, y2) are two points on the line.

Analyzing Graphs

Graph Analysis Examples

• Graph 1: Height dropped (m) vs. Time squared (s^2)
  • Suitable Heading.
  • Identify the independent variable.
  • State the relationship from the graph.
  • Use the graph to calculate the gradient. Show the two points you have used on the graph.
  • Complete the table of results below using the graph above.
• Graph 2: Graph representing time against distance.
  • Correct the heading if incoorect.
  • Calculate the gradient of the graph.
  • State the relationship between distance and time.
• Graph 3: Plant growth, Height (m) vs. Time (days)
  • Give a suitable heading for the graph above.
  • Write an investigative question for this experiment.
  • Identify the dependent variable.
  • Is the height directly proportional to time? Explain your answer.
  • Calculate the gradient of the graph above. Show the two points you have used on the graph.
• Graph 4: Density of aluminium, Mass (g) vs. Volume (mL)
  • Give a suitable heading.
  • Draw a best fit line on the graph above.
  • State the relationship between mass and volume using the graph.
  • If the mass is 100 g, what is the volume?
• Graph 5: Circumference in cm vs. Diameter in cm
  • Give a suitable heading.
  • Extend the best fit line on your graph through the origin.
  • Using the graph above, state the relationship between circumference and diameter.
  • If the diameter is 15 cm, what is the circumference? Give your answer in mm.
  • Calculate the gradient of the graph above. Show the two points you have used on the graph.

Matter and Materials: Classification of Matter

• Matter: Anything that has mass and occupies space.
• Classification: Matter can be either a mixture or a pure substance.
  • Mixtures: Can be physically separated. Composition is not uniform (Heterogeneous) or uniform (Homogeneous).
    • Homogeneous Mixtures (Solutions): E.g., Sugar/Salt solution.
    • Heterogeneous Mixtures: E.g., Italian dressing, polluted river.
  • Pure Substances: Cannot be physically separated.
    • Compounds: Can be broken down into simpler parts by chemical means. Examples: Table salt (NaCl), Water (H2O).
    • Elements: Cannot be broken down into simpler parts by chemical means. Examples: Helium gas (He), Iron (Fe).
• Colloids: A mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance.
• Suspensions: A heterogeneous mixture in which solid particles do not dissolve but are suspended throughout the bulk.

Pure Substances

• (a) Elements:
  • Cannot be broken down into simpler substances by chemical means.
  • Examples: Atoms (Ne, He), Diatomic elements (H2, N2, O2), Solid metals (Cu, Li).
• (b) Compounds:
  • Composed of two or more elements in a specific ratio.
  • Can be broken down into simpler substances by chemical means.
  • Examples: Water, Ammonia, Carbon dioxide, Methane

Mixtures

• Contain two or more substances which are NOT chemically bonded.
• Can be separated by physical means (evaporation, filtration, magnets, etc.).
• Components are not in a specific ratio.
• Components retain their own physical properties.
• (a) Homogeneous Mixtures:
  • Uniform appearance, composition, and phase throughout.
  • Solutions are examples (liquids mixing completely, salt in water).
• (b) Heterogeneous Mixtures:
  • Consist of visibly different substances or phases.
  • Suspensions and emulsions are examples (sand in water, oil mixed with iron filings).

Atoms

• Smallest particles from which all matter is made.
• Components:
  • Neutrons: Neutral charge, found in the nucleus.
  • Protons: Positive charge, found in the nucleus.
  • Electrons: Negative charge, space around the nucleus.
• Atoms are neutral: number of electrons = number of protons.

Pure Materials

• Elements:
  • Consist of one kind of atom.
  • Found on the Periodic Table.
  • Cannot be broken down into simpler materials.
• Compounds:
  • Form when two or more different atoms chemically bond.
  • Can be broken down into simpler materials.
  • Are not found on the Periodic Table.
  • Have different properties than the elements they are made of.
  • Atoms are bonded in a specific ratio.

Mixtures

• Components are not in a specific ratio.
• Components retain their properties.
• Components can be separated by physical methods.
• A decomposition reaction is a chemical reaction that breaks up a compound into simpler products. Energy is required for that.

Chemical Reactions

• Definition: A process in which one or more reactants are converted to one or more products. A chemical change involving rearrangement of atoms.
• Product properties differ from reactants.
• Represented by word equations or chemical symbols.
  • Example: Hydrogen + oxygen → water or 2H2(g) + O2(g) → 2H_2O(l)
• Transition process of reactants to products is indicated by an arrow (→).
• Energy is needed to break chemical bonds in reactants, and energy is released when products form.

Types of Chemical Reactions:

• (a) Combination/Synthesis: Two or more reactants combine to form a single product.
• (b) Decomposition: A single reactant breaks down into two or more products.
• (c) Displacement: One element replaces another in a compound.
• Phase Symbols:
  • (s) - solid, (l) - liquid, (g) - gas, (aq) - aqueous solution

Naming Binary Compounds

• Binary compounds consist of two different elements bonded.
• Periodic Table predicts possible compounds.
• Metals form positive ions; non-metals form negative ions.
• Noble gases do not form ions.
• Consider sodium and chlorine forming sodium chloride: 2Na + Cl_2 → 2NaCl

Forces Between Particles

• Particles in molecules are held together by forces of attraction/repulsion.
• Intramolecular Forces: Binding forces between atoms in a molecule.
• Intermolecular Forces: Binding forces between molecules.

Types of Particles

• Atoms: Atoms of noble gasses (He)
• Ions: Charged atoms (Cl-, Na+).
• Molecules: Formed when non-metal atoms bond chemically (CO2).
• Formula Unit: Formed when a metal ion and non-metal ion bond (NaCl).

Intramolecular and Intermolecular Forces

• Intramolecular Forces: Forces between atoms in a molecule.
• Intermolecular Forces: Weak forces of attraction between molecules and atoms of noble gases.

Electrostatic Forces (Ionic Bonds)

• Strong attraction between metal ions and non-metal ions in an ionic compound.

Molecular Compounds

• Intramolecular bond: bond between atoms in a molecule
• Intermolecular forces: forces of attraction between molecules

Impact of Heating Water:

• Intermolecular forces weaken.
• Intramolecular bonds are NOT broken.
• Molecules move further apart; phase change occurs (liquid to gas).
• Physical change: H2O (liquid) --------> H2O (gas)

Electrolysis of Water:

• Intramolecular bonds between hydrogen and oxygen break.
• New products form (hydrogen gas and oxygen gas).
• Chemical change: H2O (liquid) → H2 (gas) + O_2 (gas)

Ionic Compounds

• Ionic bond: Large electrostatic force between metal ions (Cu2+) and non-metal ions (Cl-) in an ionic compound (CuCl2).

Conductivity of Ionic Compounds

• Ions can conduct electricity ONLY if the ions can MOVE
• Molten: the ions can move.
• Dissolved: the ions can move.