Science Exam

Mixtures

• Definition: A mixture is composed of two or more elements and/or compounds that are not chemically combined.

  • Types of Mixtures:

    • Homogeneous Mixtures: Uniform composition throughout (e.g., saltwater).

    • Heterogeneous Mixtures: Varying composition throughout (e.g., salad).

Properties of Mixtures

• Characteristics:

  • Made up of components that retain their individual properties.

  • Can be separated by physical processes unlike compounds which require chemical reactions.

  • Constituents can be mixed in any proportion by mass.

Examples of Mixtures

• Common examples include:

  • Air

  • Mineral Water

  • Alloys (e.g., brass, steel)

  • Sand and water

  • Dishwashing liquid

  • Orange juice with pulp

  • Fruit cocktail

  • Water and rice

  • Muddy water

Separation Techniques

• Mixtures can be separated using various techniques based on the physical properties of their constituents.

  • Filtration: Used to separate solids from liquids.

  • Distillation: Takes advantage of differences in boiling points to separate components.

  • Evaporation: Removes liquid from a solution to obtain solid solute.

  • Chromatography: Involves solvent separation on solid media, useful for separating colored substances.

Questions for Consideration

1. Why is it important to separate materials from a mixture?

2. What are the specific techniques used for separation?

Distinguishing Between Substances

• Elements: Cannot be broken down into simpler substances.

• Compounds: Pure substances formed from two or more elements chemically bonded together (e.g., H2O).

• Mixtures: Combinations of two or more substances where each retains its properties.

Classification of Examples

• Examples include:

  • Elements: Sulfur, Helium, Gold (

  • Compounds: Water, Sodium chloride, Sugar

  • Mixtures: Air, Pizza, Concrete

Solutions and Solubility

Definitions

• Solution: A homogeneous mixture of solute and solvent, where the solute is dissolved in the solvent.

  • Solute: Substance being dissolved.

  • Solvent: Substance doing the dissolving.

Concentration of Solutions

• The concentration of a solution is defined as the amount of solute present in a given volume of solvent.

  • Mass Percent: It tells the amount of solute in a solution, calculated by (mass of solute / total mass of solution) x 100.

Types of Solutions

• Dilute Solution: Small amount of solute.

• Concentrated Solution: Large amount of solute.

• Saturated Solution: Maximum solute dissolved in a solvent at a given temperature.

Chemical Change and Physical Change

Concepts

• Physical Change: Alters the form but not the chemical identity of a substance (e.g., melting ice, chopping vegetables).

• Chemical Change: Forms new substances through chemical reactions (e.g., burning, rusting).

Indicators of Chemical Change

1. Gas Production: Formation of gas bubbles indicates a chemical reaction (e.g., baking soda and vinegar).

2. Formation of Precipitate: An insoluble solid forms from a solution.

3. Color Change: Observable change in color, indicating a reaction.

4. Temperature Change: Changes in temperature during a reaction can hint at exothermic or endothermic processes.

The Law of Conservation of Mass

• The total mass of reactants equals the total mass of products in a chemical reaction; mass is neither created nor destroyed.

Applications and Examples of Chemical Reactions

• Various chemical reactions are utilized in daily life, such as:

  • Cooking, fermentation, photosynthesis.

Useful and Harmful Effects

• Chemical reactions can lead to both beneficial outcomes (e.g., digestion, industrial processes) and harmful effects (e.g., pollution, corrosion).

Concentration of Solutions

• The concentration of a solution is defined as the amount of solute present in a given volume of solvent.

• Concentration of Solutions The concentration of a solution is defined as the amount of solute present in a given volume of solvent. Mass Percent Concentration: Mass Percent is calculated by taking the mass of solute divided by the total mass of solution, then multiplying by one hundred. Total Mass of Solution: The mass of solution is the sum of the mass of solvent and the mass of solute.

The Law of Conservation of Mass

• The first person to articulate the law of conservation of mass was Antoine Lavoisier.

• The total mass of reactants equals the total mass of products in a chemical reaction; mass is neither created nor destroyed.

Indicators of Chemical Change

• Gas Production (Effervescence): The formation of gas bubbles indicates a chemical reaction.

  • Identification of Gas Formation: Tydrogen: When hydrogen gas is ignited and then a flame is brought near it, it will produce a distinctive 'pop' sound. This is due to the rapid combustion of hydrogen, which combines with oxygen in the air to form water vapor.

  • Oxygen: When a glowing splint (a piece of wood that is smoldering but not burning) is exposed to oxygen, it will reignite. This occurs because oxygen supports combustion, allowing the splint to burn more vigorously.

  Summary of Concepts

  •  Hydrogen Gas: Produces a pop sound upon combustion.

  •  Oxygen: Reignites a glowing splint.

  • Examples of Reactions Producing Gases:

    • Baking soda reacting with vinegar (produces carbon dioxide).

    • Zinc reacting with hydrochloric acid (produces hydrogen gas).

    • Decomposition of hydrogen peroxide (produces oxygen gas).

• Formation of Precipitate: An insoluble solid forms from a solution. Types of precipitates can include:

  • Examples of Precipitates:

    • Lead (II) iodide from a reaction between lead (II) nitrate and potassium iodide.

    • Calcium carbonate from the reaction of calcium chloride and sodium carbonate.

    • Silver chloride from the reaction between silver nitrate and sodium chloride.