Understanding Dissolving, Solutions, and Mixtures

Dissolving

• A solute is a substance that dissolves.
• A solvent is a substance that dissolves a solute.
• A solution is a mixture of two or more substances (solute) dissolved in a solvent.
• Dissolving is the process where a solute is added into a solvent and disappears; also known as dissolution.
• A solution is a homogeneous mixture with evenly distributed solute.
• Mixtures are materials made by physically combining two or more substances, not chemically.
• Solutions are clear and transparent.
• Solutions do not scatter light beams.
• Solution components cannot be separated by simple filtration.
• A mixture with these traits is a true solution.
• Suspension is a heterogeneous mixture where solid particles spread throughout a liquid without dissolving, settling and are visible e.g., flour in water, sand and mud in water.
• Colloid mixtures contains one or more substances dispersed as relatively large solid or liquid particles and remains dispersed without settling due to gravity e.g., milk, blood, or ice cream.
• Colloids scatter light but are not true solutions.
• The mass of a solution equals the total mass of the solute plus the solvent.

Types of Solutions and Examples

• Solutions are categorized into three types based on the physical state of the solvent
• Solid solutions have a solid solvent
  • Examples: Copper dissolved in gold (alloys) and Mercury with sodium (amalgam)
• Liquid solutions have a liquid solvent
  • Examples: Sodium chloride/Ethyl alcohol/Carbon dioxide dissolved in water (soda water)
• Gaseous solutions have a gas solvent
  • Example: Water vapor in air (cloud) and Mixture of Helium-Oxygen gases

Solutions and Solubility

• A concentrated solution has a large amount of solute in a solvent e.g., orange juice or dark color tea.
• A dilute solution is one with a small amount of solute in a large amount of solvent e.g., light color solution.
• Dilution involves adding a solvent to a solution to lower the concentration of the solute.
• Dilution does not change the amount of solute, but it changes the solvent volume and concentration.
• A saturated solution contains the maximum amount of solute that can dissolve at a given temperature
• No more solute can dissolve in a saturated solution at that temperature; achieved by continually dissolving the solute.
• An unsaturated solution contains less than the maximum amount of solute that can dissolve.
• A supersaturated solution contains more than the maximum amount of solute that can dissolve at a given temperature.
• Substance in supersaturated solution > amount of solute in saturated solution.
• A soluble solid dissolves in a solvent such as water.
• An insoluble solid does not dissolve in a solvent e.g., Water is insoluble.
• Solubility is the maximum amount of a substance that can dissolve in a given amount of water at a specific temperature to form a saturated solution.
• For example, 40g of sodium chloride in 100g of water at room temperature creates a saturated solution; the solubility is 40 g / 100g of water.
• Different substances have different solubilities
• To compare solutes, measure how much each dissolves in the same amount of solvent.
• Most solutes dissolve faster and more easily in hot water.

Factors Affecting Solubility

• Temperature of the solvent.
• Pressure.
• Molecular size of a solute.
• Type and strength of chemical bonds (intermolecular force).
• Solubility of most solutes in solid and liquid states increases with temperature, except calcium hydroxide.
• Solubility decreases as temperature rises.
• Solubility of solids and liquids is directly proportional to the temperature of the solvent.
• A larger mass of a solute in the solid-state dissolves in hot water than in cold water.
• Gas solubility rises with pressure; it is directly proportional to pressure.
• Pressure does not has no effect on solid and liquid solutes.
• As molecular size increases, solubility decreases, making them inversely proportional.
• Stronger intermolecular forces between solvent and solute molecules increases solubility in the solvent.

Calculating Solubility

• At 20°C, 204g of sugar dissolves in 100g of water.
• At 20°C, 408g of sugar dissolves in 200g of water (200g / 100 g x 204 g = 408g).
• At 20°C, 102g of sugar dissolves in 50g of water (50g / 100g x 204 g = 102 g).
• At 20°C, 510g of sugar dissolves in 250g of water (250g/100g x 204 g = 510g).
• At 80°C, 2040g of sugar dissolves in 250g of water (510 x 4 = 2040g).
• With a solubility of 30 g of solid in 100 g of water at 30°C, the maximum amount of solid to dissolve in 25g water at 30°C is 7.5g (25g/ 100g x 30 = 7.5g).
• At 30°C, 5g of solid can dissolve in 16.67g of water (5g/30g x 100g = 16.67g).
• Mass of solution equals mass of solid + mass of water (30 g + 100g = 130g).
• On evaporation, 120g of a solution will yield 27.69g of solid (120g/130g x 30g = 27.69g).

Solubility Curve

• A graph showing the relationship between temperature and solubility is a solubility curve.
• The x-axis is temperature.
• The y-axis is solubility.
• Plot points of intersection of temperature and solubility and join them.
• Solubility curves determine solubility at a temperature.
• Solubility curves compare substance solubility at the same temperature.
• Solubility curves show how solubility changes with temperature.
• Solubility curves indicate solubility trends for different substances.

Other Solvents

• Common Solvents and Their Uses
  • Water: Universal solvent, making solution
  • Ethanol: Solvent for perfumes and paint varnish.
  • Methanol: Solvent for cleaning paint brush.
  • Acetone: Nail polish remover.
  • Toluene: Stain remover

Planning a Solubility Investigation

• The variable you change is the independent variable.
• The variable you measure is the dependent variable.
• The variables you keep constant are the control variables.
• On a graph, the independent variable is on the horizontal axis, and the dependent variable is on the vertical axis.

Paper Chromatography

• Paper chromatography separates and analyzes mixtures of soluble substances based on their solubility.
• Paper chromatography separates mixed colored inks, food dyes, hair dyes, and plant pigments.
• Solvents like water or alcohol are used as the mobile phase.
• Paper, made of cellulose (a glucose polymer), is the stationary phase.
• The final image is a chromatogram.
• The more soluble substances travel farther from the baseline, carried by the solvent over varying distances.

Atoms

• Atoms are building blocks of matter
• Atoms of a specific element are identical, but atoms of different elements vary.
• Atoms consist of protons, neutrons, and electrons.
• Protons and neutrons form the atom's nucleus while electrons move around it.
• Protons and neutrons have much more mass than electrons.
• Atoms are mostly empty space.
• Atomic Number: number of protons in an atom
• Mass Number: total number of protons and neutrons in the nucleus.
• Protons are positive, neutrons have no charge, and electrons are negative.
• Charge of Particles
  • Proton: Positive (+)
  • Neutron: No net charge
  • Electron: Negative (-)
• Electrostatic attraction between protons and electrons holds the atom together.
• Atoms are electrically neutral because they have equal protons and electrons.

Atomic Models Through History

• J.J. Thomson's model features electrons scattered throughout the atom.
• J.J. Thomson discovered the electron.
• Rutherford discovered the proton in 1909 and the nucleus in 1911.
• Rutherford's experiment was the gold foil experiment.
• James Chadwick proved neutrons exist in 1932, working with Rutherford and Thompson.
• Bohr's atomic model is the current standard.

• Thomson: Electrons scattered in a positive sphere.
• Rutherford: Electrons orbit nucleus in shells
• Bohr: Electrons orbit nucleus in fixed paths
• Thomson: Uniform positive charge.
• Rutherford: Positive charge in nucleus.
• Bohr: Positive charge in nucleus.
• Thomson: Uniformly distributed mass.
• Rutherford: Mass in nucleus.
• Bohr: Mass in nucleus.
• Thomson, Rutherford, and Bohr models depict a neutral atom.

Purity in Elements

• Elements are pure when all atoms are identical.
• Pure gold consists only of gold atoms, whereas gold alloys contain metals like copper or silver.
• A carat measures gold purity.
• Pure gold is 24 carat; 18 and 9 carat golds are alloys.
• Greater the gold content, the higher the purity. 18-carat gold consists of 18 parts gold and 6 parts other metals out of 24.
• Purity percentage: (carat of gold / 24) x 100
• 18-carat gold is 75% pure (18/24 x 100).
• 925 mark shows 925 parts silver per 1000 in a silver ring.

Climate Zones

• Each climate zone has unique characteristics
• Polar: Very cold and dry year-round.
• Temperate: Cold winters and mild summers.
• Arid: Hot and dry year-round.
• Tropical: Hot and wet year-round.
• Mediterranean: Mild winters and hot, dry summers.
• Mountains/tundra/taiga: Very cold year-round.

Climate and Ice Ages

• Ice Age: A period marked by widespread glaciers and ice sheets, resulting in colder temperatures; Earth's climate cycles between glacial and interglacial periods.
• Interglacial Period: Permanent ice is limited to the North and South Poles.
• Glacial Period: Ice spreads far from the poles.
• Past climate evidence: Boulders, fossils of cold-adapted species, and pollen in peat bogs show past climate.
• Auger used for peat bog samples.
• Deeper peat layers are older, while upper layers are younger.

Atmosphere and Climate

• The atmosphere is a layer of gas above the Earth's surface with five major layers: troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
• Troposphere is the weather layer.
• Stratosphere, also known as the ozone layer, filters UV radiation.
• Volcanoes emit water vapor and sulfur dioxide.
• Calcium carbonate (CaCO3) comprises animal shells and limestone.
• Fossils are preserved remains in sediments.
• Fossil fuels are hydrocarbons from dead plants and animals, extracted and burned as fuel.
• Fossils are analyzed via radiometric carbon dating.

Atmospheric Changes

• Atmospheric change means changes in the composition of Earth’s atmosphere from natural processes (volcanic eruptions) and human activity (emissions and deforestation).
• Burning fossil fuels combines carbon with oxygen to produce carbon dioxide.
• Carbon + oxygen makes carbon dioxide.
• Heating calcium carbonate decomposes it into calcium oxide and carbon dioxide.

Atmospheric Change and Climate

• Greenhouse gases trap heat in the atmosphere.
• Increased greenhouse gas increases heat and causes global warming.
• Global warming results from increased greenhouse gases, such as carbon dioxide.
• Causes of global warming are volcanoes, burning fossil fuels, deforestation, industry emissions, and nitrogen fertilizers.
• Carbon footprint measures greenhouse gases in the atmosphere.
• Renewable resources are replenished in a lifetime and include wind, tidal, and solar power.
• Non-renewable resources cannot be replaced once used and include coal, petroleum, and natural gas.
• Solar energy can be converted to electricity using photovoltaic cells.
• Bioplastics made from biomass reduce reliance on fossil fuels and single-use plastics.
• Biogas, a mixture of gasses made through anaerobic decomposition of organic matter, consists mainly of methane, water vapor, carbon nitrogen dioxide gas.