preliminary chemistry - module 1 summary notes PDF

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MODULE 1: PROPERTIES AND STRUCTURE OF MATTER

PROPERTIES OF MATTER: How do the properties of substances help us to classify and separate them? Explore homogenous mixtures and heterogenous mixtures through practical investigations: - Using separation techniques based on physical properties 1 Define the terms matter, pure substances and mixtures   

Matter is anything that has mass and occupies space. It can be classified as pure substance (element or compound) or mixture (homogenous or heterogenous). Pure substance is sample of matter with both definite, constant composition and distinct chemical properties. Mixtures are two or more pure substances physically combined together. It does not have definite composition and proportion of each substance can vary. Physical properties of mixtures can be changed, unlike compounds.

2 Identify the differences between elements and compounds Elements    

Elements are composed of one type of atom. Most non-metallic elements form discrete molecules with definite number of atoms. Sulfur forms a discrete molecule of 8 atoms. Some non-metallic elements are monatomic (noble gases). Noble gases are generally chemically inert. Some non-metallic atoms form covalent networks or giant molecules. Carbon forms covalent networks of diamond and graphite, and giant molecule of graphene.

Compounds  

Compounds contain two or more atoms of different elements chemically bonded together in definite proportions. Atoms in compounds can form molecules – a network of atoms. Molecule is group of two or more atoms chemically bonded together.

3 Apply the term ‘homogenous’ and ‘heterogenous’ to mixtures Mixtures  

Homogenous mixture has uniform composition; any sample of mixture is identical to any other sample. A solution is homogenous. Heterogenous mixture has composition that varies within mixture. Different components of mixture can be seen.

Suspensions and Colloids   

Substance mixed with solvent does not always dissolve to form solution; it can form suspension or colloid. Suspension is heterogenous mixture and has distinguishable parts. It forms when substance does not dissolve significantly. Red blood cells in plasma. Colloid is mixture of particles that consist of smaller clusters of ions or molecules. It is evenly dispersed throughout solvent. Milk is colloid of fat in water.

4 Define the terms ‘physical property’ and ‘chemical property’    

Physical property describes features that can be observed or measured without changing the composition of matter; the element. Colour, density. Physical change is a change in a substance’s appearance without changing its chemical composition. Chemical property relate to how easily element undergoes chemical change. It can only be observed during a chemical reaction; changing chemical composition of substance. Acidity/basicity, flammability. Chemical change is a process where one or more substances are changed into new substances; involves rearrangement of atoms.

5 Perform a series of first hand investigations to determine the physical properties that enable mixtures to be separated using the following separation techniques; magnetic separation, filtration, evaporation, distillation, fractional distillation     

Magnetic separation, process of passing mixture through magnetic field to separate magnetic and non-magnetic components. (Iron filings & sand mixture) Filtration, process of separating undissolved solid from liquid or gas by passing mixture through filter. (Sand & water mixture) Evaporation, process of separating dissolved solid from solution by vaporising liquid. (Copper sulfate & water mixture) Distillation, process of separating liquid component of solution by boiling solution and condensing resulting vapour back to liquid. (Copper sulfate & water mixture) Fractional distillation, process of separating liquid component of a solution by boiling solution and condensing the resulting vapour back to liquid, separating the mixture into fractions. (Ethanol & water mixture)

Filtration 

It is useful to isolate one of the components (chemicals) from mixture, based on physical properties. Physical properties of substances in mixture are different. In recycling, magnetic properties are considered in order to separate iron from non-magnetic metals.



Filter is a physical barrier that trap solid components while allowing fluid components to pass through in a mixture. Filtrate is the fluid that passes. Does not completely separate solid from mixture as some fluid remain in solids and smaller particles of solids can pass through filter to the filtrate.

 

For homogenous fluid mixture, often possible to add reagents or change T to make one of mixture’s components change state to solid and be separated.

Evaporation      

Small fraction of any liquid is present as vapour. Liquid that easily becomes vapour is volatile (changes state easily); evaporation occurs quicker for volatile liquids. BP is measure of liquid’s volatility and more volatile liquids have lower BP. In open container, vapour move away from liquid’s surface; liquid becoming vapour and soon evaporated. Evaporation can be accelerated by methods like warming mixture or increasing SA over which evaporation occurs. If homogenous mixture is solution where one component is not volatile, evaporation can be used to separate liquid from solid. As liquid evaporates, mixture becomes increasingly concentrated and solid may precipitate from solution. Some solids precipitate as crystals in crystallisation; smaller crystals form when solvent evaporates quickly, larger crystals form when solvent evaporates slowly.

Distillation  

In homogenous mixture of two liquids where one is substantially more volatile, distillation can be used. Composition of vapour is richer in volatile component. Vapours can be collected and condensed to liquid mixture richer in volatile component and distillation can be repeated to further enrich more volatile component. Composition of liquid and vapour later becomes same, so components cannot be separated further by distillation. For mixture of liquids, vapour produced are rarely of one pure component but are mixture.

6 Students design, plan and conduct first-hand investigations to separate: a. Salt from water (homogenous) 1) 2) 3) 4)

Set up as shown in diagram. Weigh evaporating basin on electronic balance and record in results. Wear safety goggles and evaporate water using heating flame. Allow apparatus to cool. Allow salt in evaporating basin to crystallise. Weigh evaporating basin on electronic balance and record in results.

b. Oil from water (heterogenous) 1) 2) 3) 4)

Weigh separating funnel on electronic balance and record in results. Pour mixture in separating funnel and set up as shown in diagram. Open stopcock. Close stopcock once water has been separated from oil. Weigh separating funnel on electronic balance and record in results.

7 Explain the difference between quantitative and qualitative analysis and give examples of each   

Analytical chemistry is science of obtaining information about composition and structure of matter. There are two branches. Quantitative analysis identifies amount of element or compound present and is expressed in numerical value in appropriate units. Mass, concentration or relative abundance of the components of a sample. Qualitative analysis identifies elements and compound present in a sample of unknown material, based on chemical/physical properties. Colour of a sample or malleability of a metal are examples.

8 Write the correct method to weigh 100mL of a solution of sand, salt and water in a 250mL beaker using an electronic balance 1) 2) 3) 4) 5) 6)

Turn on electronic balance. Allow electronic balance to display 0g. Place 250mL beaker on electronic balance. Wait for electronic balance to stabilise and record results. Press tare/on button. Pour 100mL solution. Wait for electronic balance to stabilise and record results.

- Calculating percentage composition by weight of component and/or compounds 9 Perform a first-hand investigation to determine the percentage composition of sand, salt, water mixture and ethanol & water using a given method

Sand, Salt, Water Mixture 1) Weigh beaker on electronic balance and record in results. 2) Pour mixture into beaker. Weigh beaker containing mixture on electronic balance and record in results. 3) Weigh filter paper on electronic balance and record in results. Set up as shown in diagram. 4) Pour mixture into filtering funnel and rinse excess sand using wash bottle. 5) Remove wet filter paper from funnel onto watch glass after sand has been filtered from saltwater mixture. 6) Place watch glass holding filter paper and sand to dry in sunlight. 7) Weigh evaporating basin on electronic balance and record in results. 8) Set up as shown in diagram. 9) Weigh evaporating basin on electronic balance and record in results. 10)Wear safety goggles and evaporate water using heating flame. Allow apparatus to cool. 11) Allow salt in evaporating basin to crystallise. Weigh evaporating basin on electronic balance and record in results. Ethanol and Water Solution

Percentage Composition of Compounds 

Composition of elements in chemical compound or composition of a mixture can be described using percentage composition by mass, which gives mass of each element that would be found in 100g sample of the compound.

percentage composition by mass of element=

mass of element X 100 mass of compound

10 Recall the difference between physical and chemical properties Difference   

Physical property is any characteristic that can be determined without changing substance’s chemical identity. Chemical property is any characteristic that can be determined only by changing substance’s molecular structure. Physical property may involve physical change, but not chemical change. When chemical change or reaction occurs, observed characteristics are chemical properties.

Physical Properties and Changes in State 

Physical state is easiest to observe; most common physical states of matter are solid, liquid and gas.

  

Physical changes can occur within any state. May alter physical properties of substance, but not chemical nature. Reversible and occurs gradually within state of matter. Mixing; each component retains individual chemical properties and no new substance is formed. Heating causes physical change; adding heat lead to substance expand in V + lower density, removing heat leads to reduction in V + increased density. With sufficient heat, substances may undergo phase transition; physical properties can change drastically in phase transition.

Solids, Liquids and Gases     





Particle model is effective model for understanding differences between solid, liquid and gas. Liquids and gases have no fixed shape; fluids. In this model, particle size cannot be reduced by compression or division. They are in constant motion and attracted to each other, some strongly and some weakly. T affects particle movement in substance; vibrations and particle motion. Increased T; increased movement and distance between particles. Particle model explains change of state; vibrations and motion of particles opposing force of attraction between particles. However, does not include measure of forces between particles and so cannot predict T at state change. Solid expands when heated as particles move more, becoming further apart. Movements become so energetic that forces of attraction cannot hold particles in place; solid melts to liquid. When cooled, motion of particles cannot overcome forces of attraction between them; liquid freezes to solid. Liquid is heated, particles on surface move energetically with sufficient energy to overcome forces of attraction; liquid particles escaping and forming gas. As gas cools, motion of particles cannot overcome forces of attraction between particles; gas particles stick and condense back to liquid. Sublimation is change of state from solid to gas, skipping liquid phase. Occurs when heating substance in solid phase causes all forces of attraction between particles to be overcome. When P is sufficiently low like in a vacuum, common materials that normally melt to liquid sublime to gas.

Property Particle Packing Compressibl e Shape Mixing & Diffusion Pressure on Container Density Description

Solids Particles close packed

Liquids Particles loose packed

Gases Particles far apart

No – space to push

No – space to push

Yes – space to push

Fixed – particles held together No – particles in fixed position No

Not Fixed – particles can slide over each other Yes – particles can change direction Some

High Incompressible and fixed shape. Strong attraction between particles which keeps particles together. Particles vibrate in fixed position and more vigorously with heat, but do not shift position. Particles remain in contact but distance increases, with greater movement.

Fairly High Incompressible and adapt shape of container. Weaker attraction between particles which remain closely packed. Particles may shift positions and move past each other.

Not Fixed – particles move in all directions Yes – particles move in all directions Yes – particles impact container Low Compressible and take shape of container. Weak attraction between particles and particles not packed closely. Particles move faster and impact sides of container with more force and frequency; with greater movement.

11 Identify on a periodic table the position of: noble gases, metals, non-metals, metalloids, transition metals     

Noble gases: group 18 (VIII) Metals: Generally, on the left Non-Metals: (C to Rn staircase, H) Metalloids: (B to At, 12221) Transition Metals: (middle rectangle block)

Classify the element based on their properties and position in the periodic table through their: - Physical properties - Chemical properties 12 Perform a first-hand investigation and use secondary sources to classify elements as metals/non-metals (including copper, zinc, magnesium, tin, sulfur, carbon) based on their position in the periodic table and their physical properties including: a. b. c. d. e. f.

State at 25 Malleability & ductility Electrical & thermal conductivity MP & BP Solubility in water Density

State at Mailability/Ductility Electrical/Thermal MP & 25 Conductivity BP degrees Copper Solid O O MP1085, BP-2572 Zinc Solid O O MP-420, BP-907 Magnesium Solid O O MP-650, BP-1110 Tin Solid O O MP-232, BP-2602 Sulfur Solid X X MP-113, BP-445 Carbon Solid X O MP3974, BP-3974 And their chemical properties including: g. Reaction with acids/bases h. Reaction with water i. Reaction with oxygen

Copper Zinc

Reaction with HCl (acid) X O

Reaction with NaOH (base) X X

Reaction with water X X

Solubility Density in Water X

9.0

O

7.1

O

1.7

X

7.3

O

2.1

X

2.3

Magnesiu m Tin Sulfur Carbon

O (exothermic)

X

O

X X X

X O X

X X X

Properties   

Same group elements generally have similar physical and chemical properties although each element possesses individual characteristics. Period numbers give indication of electronic configuration of an element. In same period, elements same number of occupied electron shells. Difference between properties of metals and non-metals is related to number of valence electrons.

Metals   

Most elements are metals. Most are combined with other elements, extracted and processed to achieve pure elemental form. Some found as pure elements like gold. Alloys are physical mixture of metal with small amount of some other element. Properties of the mixture can be different from properties of the components. Properties of an alloy can vary depending on formation process. Alloy of iron and carbon is steel. Typically, metals are: -

Lustrous (shiny) Malleable (formed into shaped without breakage) Ductile (drawn into wire) Dense (heavy for their V) High BP High MP (solid at room T) High tensile strength (stretched without breaking) Good conductors of electricity and heat

Non-metals  

Next largest group of elements. Has greater variety in physical properties than metals. Typically, non-metals are: - Non-malleable - Non-ductile - Dull and non-lustrous - Not as dense - Lower BP and MP - Poor conductors of electricity - Poor conductors of heat

Metalloids   

Third and smallest group. Semi conductivity is ability to moderately conduct electricity. Has some metallic and non-metallic properties. Many tend to shine like metals but brittle like non-metals.

Investigate the nomenclature of inorganic substances using International Union of Pure and Applied Chemistry (IUPAC) naming conventions

13 Define the terms inorganic ions, polyatomic ions and valency and write the chemical formula for basic inorganic compounds including the following: hydroxides, sulfates, carbonates, nitrates, phosphates, acetates, sulphides, oxides, chlorides, fluorides, bromides, group I & II elements, ammonium compounds, aluminium compounds   

Inorganic substances are chemicals that do not consist of carbon. Polyatomic ions are a charged entity composed of two or more atoms bonded together. Valency refers to ability of an atom or a group of chemically bonded atoms to form chemical bonds with other atoms or groups of atoms; measure of combining power. Ammonium (NH4+)

Sulfate (SO42-)

Sulfite (SO32-)

Aluminium (Al3+)

Acetate (CH3COO-)

Nitrite (NO2-)

Sulfide (S2-)

Nitride (N3-)

Carbonate (CO32-)

Phosphate (PO43-)

Oxide (O2-)

Phosphide (P3-)

Hydroxide (OH-)

Cyanide (CN-)

Chloride Bromide (Br -) (Cl-)

Nitrate (NO3-)

Hydrogen carbonate (HCO3-)

Carbide (C4-)

Fluoride (F-)

ATOMIC STRUCTURE AND ATOMIC MASS: Why are the atoms of elements different from one another? Investigate the basic structure of stable and unstable isotopes by examining: - Their position in the periodic table - Distribution of electrons, protons and neutrons in the atom - Representation of the symbol, atomic number and mass number 1 Draw an atom and label protons, neutrons and electrons and define the term nucleons Nucleus   

Nucleus is made of two subatomic particles. Collectively term is nucleons; proton and neutrons. Nucleus of an atom is 10,000 – 100,000 times smaller than the size of atom but contributes to 99.97% of atom’s mass. Atomic nuclei are very dense. Neutrons are needed to maintain compact nucleus as positively-charged proton repel.

Electrons   

All atoms have positively charged nucleus surrounded by larger cloud of negatively charged electrons. Cloud gives atom its size and V. Electrostatic attraction is when negative particles attract positive particles. Electrons are bound to nucleus by electrostatic attraction. Electron’s mass is about 1800 times smaller than proton/neutron and contributes little to mass of atom.

2 Explain the term ‘isotope’ and draw a table to show the number of protons, neutrons, electrons, atomic number and atomic mass for a range of elements and their isotopes.  