chemistry

• Properties of iron:

  • Appearance: black solid
  • Behavior in water: sinks
  • Interaction with a magnet: attracted
  • Action with acid: liberates hydrogen gas
• Properties of sulphur:

  • Appearance: yellow solid
  • Behavior in water: most sinks, while a little floats
  • Interaction with a magnet: not attracted
• Properties of iron/sulphur mixture:

  • Interaction with a magnet: only iron is attracted
  • Chemical reaction: no reaction takes place; usually no heat change in making the mixture
• Properties of iron(II) sulphide:

  • Appearance: black or dark brown solid
  • Behavior in water: sinks
  • Interaction with a magnet: not attracted
  • Action with acid: gives toxic hydrogen sulphide gas
• Main differences between mixtures and compounds:

  • Mixtures: no chemical reaction takes place; constituent substances retain their own properties
  • Compounds: a chemical reaction takes place; heat is usually given out or absorbed when a compound forms
• Compounds:

  • Examples: water, carbon dioxide, common salt, sugar
  • Definition: a pure substance made up of two or more elements chemically combined together
• A mixture consists of two or more pure substances which have not chemically combined together
• An impure substance is always a mixture, while a pure substance is either an element or a compound
• Elements are pure substances that cannot be broken down into simpler substances by chemical methods
• When a substance undergoes a chemical change, it changes to one or more new substances
• The reaction between magnesium and oxygen to form magnesium oxide is a chemical change
• Physical changes do not produce new substances, like the melting of ice
• Substances like dry ice and iodine can change directly from the solid state to the gaseous state on heating, known as sublimation
• Physical properties of a substance can be determined without the substance changing into other substances
• Chemical properties describe the ability of a substance to react with other substances
• Physical properties include appearance, odour, taste, hardness, density, solubility, melting point, boiling point, malleability, and thermal conductivity
• Comect method


  • Detecting the odour of a
• Hazard warning label


  • Corrosive
• Do not eat or drink in the laboratory
• Never store any chemical solution
• Do not smell gases directly (Figure 1.9)
• Do not touch any chemicals and hot objects with bare hands
• Beware of burns
• Do not leave experiments unattended
• Return reagents and chemicals to appropriate places immediately after use, with their labels facing out
• Dispose of solid waste (e.g., broken glass, filter paper, copper sponge, etc.) in the waste bin, never in the sink
• Clean up all the spillage (on the floor or bench) at once. Clean the bench and wash hands after experiment
• Report all accidents and breakages to your teacher at once
• Hazardous chemicals


  Substances which may cause injury to people or damage to property
• Reasons chemicals may be hazardous

  • Corrosive
  • Toxic
  • Explosive
  • Flammable
  • Oxidizing
  • Harmful
  • Irritant
• Many hazardous chemicals may involve more than one hazard
• A bottle containing a hazardous chemical should bear the appropriate hazard warning label(s)
• Understanding the different types of hazardous chemicals

  1. Study the Handbook on Safety in Science Laboratories (2013)

  2. Match the type of hazardous chemicals with the meanings
• Hazardous types


  • Corrosive
  • Toxic
  • Explosive
  • Flammable
  • Oxidizing
  • Harmful
  • Irritant
• Meanings


  • Substances which may start a highly exothermic reaction when in contact with other substances, particularly easily oxidizable substances. It can create a fire risk
  • Substances which may easily catch fire if heated or comes into contact with a flame
  • Substances which if breathed in, or swallowed, or absorbed through skin may cause serious health risk or even death
  • Substances which can cause, by itself or its vapour, inflammation upon contact with the eyes, skin or respiratory system
  • Substances which may cause serious injuries upon contact with living tissues (e.g. the skin, eyes)
  • Substances which if breathed in, or swallowed or absorbed through the skin, may cause limited health risk
  • Substances which may explode if ignited in air or exposed to heat. A shock or friction may also start an explosion
• Find the hazardous nature of each of the following chemicals from Material Safety Data Sheets (MSDS)
• Chemicals


  • Chlorine
  • Hydrogen
  • Limewater (or calcium hydroxide solution)
  • Ethanol (also known as alcohol)
  • Propanone (also known as acetone)
  • Concentrated sulphuric acid
  • Sodium
  • Magnesium
  • Sulphur dioxide
• Physical properties


  Properties that can be determined without the substance changing into other substances
• Physical properties of substances

  • Appearance
  • Odour
  • Taste
  • Hardness
  • Density
  • Solubility
  • Melting point
  • Boiling point
  • Malleability
  • Electrical conductivity
  • Thermal conductivity
• Appearance


  What a substance looks like, such as its physical state (solid, liquid, or gas), its colour, whether it is shiny or dull, etc.