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Questions and Answers
What defines a pure substance scientifically?
What defines a pure substance scientifically?
In everyday terms, the word 'pure' implies the absence of added substances.
In everyday terms, the word 'pure' implies the absence of added substances.
True
How can melting points be used to determine if a substance is pure?
How can melting points be used to determine if a substance is pure?
A pure substance has a sharp melting point, while impure substances melt over a range of temperatures.
The average mass of an atom of an element is compared to _____ of an atom of carbon-12.
The average mass of an atom of an element is compared to _____ of an atom of carbon-12.
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Match the following terms with their definitions:
Match the following terms with their definitions:
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What is the empirical formula for the compound C4H10?
What is the empirical formula for the compound C4H10?
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Alloys are typically softer and weaker than pure metals.
Alloys are typically softer and weaker than pure metals.
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What is the relative formula mass of Ca(OH)2?
What is the relative formula mass of Ca(OH)2?
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What type of ions form ionic bonds?
What type of ions form ionic bonds?
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Ionic compounds conduct electricity in their solid state.
Ionic compounds conduct electricity in their solid state.
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What holds ionic compounds together?
What holds ionic compounds together?
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Covalent bonds form when two non-metals ___ a pair of electrons.
Covalent bonds form when two non-metals ___ a pair of electrons.
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Why do simple molecules have low boiling points?
Why do simple molecules have low boiling points?
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Match the type of bonding to its characteristic:
Match the type of bonding to its characteristic:
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Metallic bonds allow metals to be brittle.
Metallic bonds allow metals to be brittle.
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What is the electron configuration of an atom with a full outer shell?
What is the electron configuration of an atom with a full outer shell?
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Mendeleev arranged elements by increasing atomic ___ initially.
Mendeleev arranged elements by increasing atomic ___ initially.
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What is the structure of diamond?
What is the structure of diamond?
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Graphene is used in electronics due to its high strength and conductivity.
Graphene is used in electronics due to its high strength and conductivity.
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What happens to energy during condensing and freezing?
What happens to energy during condensing and freezing?
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Nanoparticles are ___ to ___ nanometers across.
Nanoparticles are ___ to ___ nanometers across.
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Which of the following best describes fullerenes?
Which of the following best describes fullerenes?
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What is a property of graphite that allows it to conduct electricity?
What is a property of graphite that allows it to conduct electricity?
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Which of the following is an example of a formulation of a mixture?
Which of the following is an example of a formulation of a mixture?
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Filtration can be used to separate soluble salts from a solution.
Filtration can be used to separate soluble salts from a solution.
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What is the primary purpose of crystallisation in separating substances?
What is the primary purpose of crystallisation in separating substances?
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Fractional distillation is commonly used to separate _____ due to its boiling point properties.
Fractional distillation is commonly used to separate _____ due to its boiling point properties.
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Match the following chromatography types with their descriptions:
Match the following chromatography types with their descriptions:
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What does the Rf value represent in chromatography?
What does the Rf value represent in chromatography?
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Positive ions are formed when non-metals gain electrons.
Positive ions are formed when non-metals gain electrons.
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What chemical equation represents the reaction between magnesium and oxygen?
What chemical equation represents the reaction between magnesium and oxygen?
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Metals are typically found on the _____ side of the periodic table.
Metals are typically found on the _____ side of the periodic table.
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What process is used to separate a mixture of volatile liquids?
What process is used to separate a mixture of volatile liquids?
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Chromatography can be used to identify mixtures by showing multiple spots on the chromatogram.
Chromatography can be used to identify mixtures by showing multiple spots on the chromatogram.
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Describe the difference between a covalent bond and an ionic bond.
Describe the difference between a covalent bond and an ionic bond.
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In chromatography, the stationary phase for thin layer chromatography is a thin layer of _____ on an unreactive surface.
In chromatography, the stationary phase for thin layer chromatography is a thin layer of _____ on an unreactive surface.
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Which type of chromatography uses a solid carrier to transport substances?
Which type of chromatography uses a solid carrier to transport substances?
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Elements in the same group of the periodic table have the same number of outer electrons.
Elements in the same group of the periodic table have the same number of outer electrons.
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Study Notes
Pure Substances and Mixtures
- A pure substance, scientifically, is composed of a single element or compound.
- Everyday usage of "pure" implies nothing is added, but scientifically, milk, for instance, contains a mixture.
- Pure substances have a sharp, precise melting point.
- Impure substances melt over a range of temperatures.
Identifying Pure Substances Using Melting Points
- A pure substance exhibits a definite, precise melting point.
- Mixtures melt across a range of temperatures, due to different components melting at various points.
Measuring Temperature
- Thermometers and temperature probes are used to measure temperature.
- Temperature probes give more precision, recording to 2 decimal places.
Relative Atomic Mass
- The average mass of an atom of an element compared to 1/12 the mass of a carbon-12 atom.
Relative Formula Mass
- The weighted average mass of the formula units in relation to 1/12 the mass of a carbon-12 atom.
Relative Molecular Mass
- The average mass of a molecule compared to 1/12 the mass of a carbon-12 atom.
Calculating Relative Formula Mass
- Add the relative atomic masses of each element in the formula.
Calculating the Relative Formula Mass of Ca(OH)2
- Ca(OH)2's relative formula mass is calculated as 40 + 2(16 + 1) = 74.
Empirical Formula
- The simplest whole-number ratio of atoms in a compound.
Molecular Formula
- The actual number of atoms of each element in a compound.
Empirical Formulae of CH4 and C4H10
- CH4: Already the simplest whole-number ratio, so the empirical formula is CH4
- C4H10: Simplifying the ratio gives C2H5
Molecular and Empirical Formulae of C2H4Br2
- Molecular formula: C2H4Br2
- Empirical formula: CH2Br
Alloys
- Mixtures of two or more metals.
Advantages of Alloys over Pure Metals
- Alloys often exhibit more desirable properties, such as increased hardness and strength.
- The different sizes of atoms in alloys distort the layers of the material, restricting movement and improving the material's strength.
Formulations of Mixtures
- Formulations are mixtures containing exact quantities of substances.
- These quantities are optimized to achieve the best properties for a specific purpose.
Examples of Formulations
- Sunscreen
- Medicine
- Perfume
- Drinks
Separating Insoluble Salts (Filtration)
- Filter paper in a funnel over a flask to separate solids from liquids.
- Pour the mixture through the funnel; wash remaining solids with distilled water to collect any remaining salt.
- Remove filter paper and evaporate water from the residue to obtain the salt.
Separating Soluble Salts (Crystallisation)
- Heat a solution gently to increase its concentration.
- Remove the solution from heat and allow it to cool slowly.
- Crystals will form as water evaporates.
Simple Distillation
- Used to separate miscible liquids with different boiling points.
Separating Ethanol from Water (Simple Distillation)
- Place mixture in a flask connected to a condenser with a collecting flask.
- Maintain a temperature gradient in the condenser by circulating cool water.
- Water will not evaporate due to its higher boiling point. Heat will evaporate the ethanol, which will then condense and collect.
Fractional Distillation (Crude Oil)
- Used to separate crude oil by boiling point differences.
- Vapours rise through a fractionating column with a temperature gradient.
- Different hydrocarbons condense at different fractions according to their boiling points.
Chromatography
- Separates mixtures of soluble substances by their different affinities for a stationary and mobile phase.
Paper Chromatography Phases
- Stationary phase: Paper
- Mobile phase: Solvent
Thin-Layer Chromatography (TLC) Phases
- Stationary phase: Thin layer of inert substance on a surface.
- Mobile phase: Solvent
Performing Paper/TLC Chromatography
- Draw a pencil line a few centimeters from the bottom of the stationary phase.
- Spot the mixture to be tested on the baseline.
- Place the stationary phase in a beaker with solvent, ensuring the solvent level is below the pencil line.
- The solvent will travel up the paper, separating substances.
Using Pencil in Chromatography
- Pencil is insoluble and won't affect the chromatography's results.
- Ink is soluble and can interfere with the results.
Rf Value
- Ratio of distance travelled by solute to the distance travelled by the solvent.
Calculating the Rf Value
- Rf = Distance travelled by substance / Distance travelled by solvent
Gas Chromatography (GC) Use
- Separates mixtures of volatile liquids.
Gas Chromatography Phases
- Stationary phase: Solid/liquid on a solid support.
- Mobile phase: Inert carrier gas.
Gas Chromatography Separation
- Substances travel through a column at different speeds.
- Retention time (time to reach the detector) identifies them.
Using Chromatography to Determine Purity
- Pure substances show one spot/peak.
- Impure substances show multiple spots/peaks.
Metals in the Periodic Table
- Found on the left side of the periodic table.
- React to form positive ions.
Non-Metals in the Periodic Table
- Found on the top right of the periodic table.
- React to form negative ions.
General properties of Metals
- Shiny
- Good conductors
- Dense
- Malleable and ductile
- High melting and boiling points
General properties of Non-metals
- Dull appearance
- Poor conductors
- Lower density than metals
- Low melting and boiling points
- Brittle
Metal Reaction with Oxygen
- Metal oxide is formed.
Ion Formation
- Positive ions (cations) are formed when a metal loses electrons.
- Negative ions (anions) are formed when a non-metal gains electrons.
Magnesium and Oxygen Reaction
- 2Mg + O2 → 2MgO
Periodic Table Arrangement of Elements
- Ordered by increasing atomic number.
- Elements in the same group have similar properties.
Similarity of Properties in the Same Group
- Elements have the same number of outer shell electrons, influencing reactions.
Periodic Table Period/Row
- Period number indicates the number of electron shells possessed by the elements in that row.
Periodic Table Group/Column
- Group number indicates the number of outer shell electrons.
Covalent vs. Ionic Bonds
- Covalent: Non-metals share electrons.
- Ionic: Metal loses electrons to non-metal creating oppositely charged ions.
Ionic Compound Bonding
- Electrostatic attraction between positive and negative ions.
Ionic Compound Properties (High Melting/Boiling Points)
- Strong electrostatic forces require significant energy to overcome during melting/boiling.
Ionic Compound Conductivity
- Conduct electricity when molten or dissolved (aqueous), as the ions are free to move and carry charge.
Bonding in Simple Molecules
- Covalent bonds form from electron sharing between non-metals.
Simple Molecules (Low Boiling Points)
- Weak intermolecular forces between molecules,requiring less energy for boiling.
- The covalent bonds within the molecules remain intact.
Simple Molecules and Electricity Conductance
- Simple molecules do not conduct electricity as they lack an overall charge.
Simple Molecule Boiling Point Change with Size
- Stronger intermolecular forces lead to higher boiling points with increasing molecular size.
Giant Covalent Structures (Bonding)
- Many strong covalent bonds connecting atoms in a large network.
Giant Covalent Structures (Melting Points)
- High melting points because breaking covalent bonds requires lots of energy.
Polymer Bonding
- Covalent bonds within the polymer's structure.
Polymer Solids
- Strong intermolecular forces, holding large polymer molecules together in a solid form.
Metallic Bonding
- Metal atoms form a giant structure of positive ions in a sea of delocalized electrons.
Metallic Conductivity
- Delocalized electrons moving through the structure carry charge for conductivity.
Metallic Malleability
- Layers of atoms in uniform arrangement can slide easily past each other.
Metallic Melting Points
- Strong metallic bonds, resulting in relatively high melting points requiring large amounts of energy to overcome the attraction.
Dot and Cross Diagrams Limitation
- Do not show the 3D arrangement of atoms within the molecule.
Ball and Stick Models
- Show the 3D shape of the molecule and the bonds between atoms, but do not represent electrons.
Highest Electron Configuration (Three Shells)
- 2, 8, 8.
Most Desirable Electron Configuration
- Full outer shell, typically 8 electrons.
Noble Gas Reactivity
- Stable full outer shell configurations make them unreactive.
Reactive Element (Example)
- An element with 2, 8, 1 electrons configuration can easily lose one electron to attain a stable configuration.
Mendeleev's Periodic Table
- Ordered elements by increasing atomic mass, adjusting to place elements with similar properties in the same group.
- Left gaps for undiscovered elements predicting their properties.
Modern Periodic Table vs. Mendeleev's Table
- Modern table is organized by increasing atomic number.
Carbon Bonding
- Carbon can form four covalent bonds.
Organic Compounds
- Compounds containing carbon covalently bonded to other atoms.
Diverse Organic Compounds
- Carbon's ability to form chains, rings, and families of similar compounds results in diverse organic compounds.
Graphite Structure
- Carbon atoms arranged in hexagonal layers with one delocalized electron per carbon atom.
Graphite Properties
- Soft/slippery layers allow for sliding, conducting electricity due to delocalized electrons.
Diamond Structure
- Each carbon atom is bonded to four other carbon atoms, forming a giant tetrahedral structure with no delocalized electrons.
Diamond Properties
- Very hard and high melting point due to strong covalent bonds.
- Does not conduct electricity.
Fullerene
- Molecule of carbon with a closed tube or hollow ball shape.
Examples of Fullerenes
- Graphene, C60 (buckminsterfullerene).
Fullerene Properties and Uses
- Large surface area for catalyst trapping.
- Hollow structure for targeted drug delivery.
Graphene in Electronics
- Strong, conductive, and only one atom thick, making it useful in electronics.
Energy Transfer in State Changes
- Energy is transferred from the surroundings during condensation and freezing.
- Energy is transferred to the substance during evaporation and melting.
Substance State at a Temperature
- Substance A (-174°C): Liquid
- Substance B (-7°C): Solid
Atom vs. Substance Properties
- Individual atoms don't have the same characteristics as the material they form. Physical properties depend on bonding and the structure of the substance.
Nanoparticle Size
- 1–100 nanometers across, larger than typical atoms but smaller than most particles.
Surface Area to Volume Ratio
- Nanoparticles have a much higher surface area to volume ratio compared to larger particles.
Nanoparticle Reactivity
- High surface area to volume ratio leads to a higher number of accessible reaction sites, increasing reactivity.
Nanoparticles as Catalysts
- High surface area to volume ratio maximizes reaction sites for catalysis.
Surface Area to Volume Ratio Calculation
- Surface area to volume ratio = surface area ÷ volume.
Nanotubes in Electrical Circuits
- Lightweight, conductive, and small enough for use in computer circuits.
Nanoparticles in Sunscreen
- Use high surface area to volume ratio to block UV light without creating white marks..
Nanoparticle Risks
- Limited understanding of their long-term risks.
- Potential for harmful effects if they are able to enter the bloodstream.
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Description
Test your knowledge on the concepts of pure substances and mixtures, including their definitions, characteristics, and the significance of melting points. Learn how to differentiate between pure substances and mixtures scientifically, as well as understand the role of relative atomic and formula masses in chemistry.
