YR9 sci chemistry

• What type of change is a change of state?

  Physical change
• Why is fractional distillation used?

  To separate different liquids from a mixture based on their boiling points
• What is an example of a mixture that can be separated by fractional distillation?

  Ethanol and water
• How does fractional distillation work?

  It works because different substances have different boiling points
• What is simple distillation used for?

  Separation of a liquid from a mixture
• What is the process involved in simple distillation?

  Evaporation followed by condensation
• What defines a mixture?

  A mixture consists of two or more elements or compounds not chemically combined
• What happens to the chemical properties of substances in a mixture?

  The chemical properties of each substance remain unchanged
• What is filtration used for?

  Separation of an insoluble solid from a liquid
• What is crystallization used for?

  Separation of a soluble solid from a liquid by evaporation
• What are the characteristics of physical changes?

  • No new substance is made
  • The change is easily reversible
• What are the characteristics of chemical changes?

  • A chemical reaction occurs
  • New products are formed
  • The change is often not easily reversed
• What are some indicators of a chemical reaction?

  Change of colour, temperature, state, or production of gas bubbles
• What are the properties of solids, liquids, and gases?

  Solids:

  • Particles are tightly packed
  • Vibrate about fixed positions

  
  

  Liquids:

  • Particles are closely packed
  • Take the shape of the container

  
  

  Gases:

  • Particles are far apart
  • Move randomly
  • Take the shape of the container
  • No fixed volume
  • Highly compressible

  
• How can you predict the state of a substance based on its melting and boiling points?

  Anything below the melting point is a solid, and anything above the boiling point is a gas

  
• What is a pure substance characterized by in terms of melting point?

  A sharp melting point
• What does chromatography separate based on?

  The distance substances move depends on their attraction for the paper and their solubility in the solvent

  
• What are the stages of water treatment to make it potable?

  1. Sedimentation: Allowing particles and impurities to settle
  2. Filtration: Removing insoluble substances
  3. Chlorination: Adding chlorine to kill bacteria

  
• What is the difference between potable water and pure water?

  Potable water is safe to drink but contains mineral ions, while pure water is 100% water with no dissolved substances

  
• What are the steps in the chromatography practical?

  1. Draw a pencil line 1cm above the bottom of the paper
  2. Add tiny drops of each substance on the line
  3. Add solvent to the beaker with a lid
  4. Place paper in the beaker ensuring solvent level is below the pencil line
  5. Remove paper when solvent reaches 1cm from the top and mark the solvent level
  6. Calculate the Rf values

  
• What is desalination?


  Desalination is the process of turning seawater into potable water
• What are the steps involved in desalination by distillation?

  1. Salt water is boiled
  2. Water evaporates and turns into steam, leaving salts behind
  3. Steam passes through a condenser
  4. Water vapor condenses and pure water is collected

  
• What is the mass number of an atom?

  Number of protons plus neutrons
• What is the atomic number of an atom?

  Number of protons or number of electrons
• How do you calculate the number of neutrons in an atom?

  Mass number minus atomic number
• What are isotopes?


  Atoms of the same element with the same number of protons but different number of neutrons
• What is relative atomic mass?

  It is an average value that takes into account the abundance of isotopes
• How do you calculate the relative atomic mass of sulfur with two isotopes?

  Relative atomic mass = (32 x 97) + (35 x 3) = 32.09
• Who discovered the nuclear model of the atom?

  Rutherford
• What did Niels Bohr improve about the nuclear model?

  He stated that electrons orbit the nucleus at different distances, called shells or energy levels
• Who discovered the neutron?

  James Chadwick
• What were the key developments in the atomic model from 1808 to 1932?

  • 1808: Dalton proposed atoms as indivisible spheres
  • 1897-1900: Discovery of electrons led to the plum pudding model
  • 1911: Rutherford proposed the nuclear model
  • 1913: Bohr improved the model with shells
  • 1932: Chadwick discovered the neutron

  
• How are elements arranged in the modern periodic table?

  • Arranged in increasing atomic number
  • Rows are called periods
  • Columns are called groups

  
• What was Mendeleev's contribution to the periodic table?

  • Arranged elements by relative atomic mass
  • Grouped elements with similar chemical properties
  • Left gaps for undiscovered elements
• Why did Mendeleev swap the positions of iodine and tellurium?

  To align iodine with elements that have similar chemical properties
• What are the similarities and differences between Mendeleev's periodic table and the modern periodic table?

  Similarities:

  • Both arrange elements into groups/periods
  • Elements with similar properties are in the same group

  
  

  Differences:

  • Mendeleev's table was arranged by relative atomic mass
  • Mendeleev's table had gaps and fewer elements
  • Mendeleev's table did not include noble gases

  
• What is the electronic configuration of Aluminium?

  1. 8.3
• How many shells of electrons does Aluminium have?

  Three shells of electrons
• In which group is Aluminium found?

  Group 3