chemistry - topic 8

• What is a pure substance in chemistry?

  A pure substance is a single element or compound, not mixed with any other substance.
• What is a formulation in chemistry?

  • A mixture designed as a useful product
  • Each chemical has a specific purpose
  • Made by mixing components in measured quantities
• What are some examples of formulations?

  Formulations include fuels, cleaning agents, paints, medicines, alloys, fertilizers, and foods.
• How does everyday language define a pure substance?


  In everyday language, a pure substance means it is unadulterated and in its natural state, such as pure milk.
• What do pure elements and compounds do at specific temperatures?

  Pure elements and compounds melt and boil at specific temperatures.
• How can melting point and boiling point data be used?

  Melting point and boiling point data can distinguish pure substances from mixtures.
• What happens to the temperature of a pure substance during melting?

  The temperature does not rise when the solid is melting because heat is absorbed to break the bonds between the solid particles.
• What does a melting point curve for a pure solid look like?


  A pure solid will melt at a fixed temperature, and the line will stay horizontal when it is melting.
• What does chromatography help to do?

  Chromatography can be used to separate mixtures and provide information to help identify substances.
• What are the two phases involved in chromatography?

  Chromatography involves a stationary phase (paper) and a mobile phase (solvent).

  
• How does the distance a compound moves in chromatography depend on its properties?


  The distance a substance moves depends on its attraction for the paper and its solubility in the solvent.

  
• What happens if a compound is more soluble in the solvent during chromatography?

  If a compound is more soluble in the solvent, it will move further up the paper.
• What is the first step in the chromatography practical method?

  Draw a pencil line 1 cm above the bottom of the paper and mark spots for each sample.
• Why is it important to keep the solvent level below the pencil line in chromatography?

  The solvent level must be below the pencil line to prevent dissolving the sample spots from the plate.
• What is the purpose of marking the solvent level in chromatography?

  Marking the solvent level helps to measure how far the solvent has moved.

  
• What is the formula for calculating Rf values in chromatography?

  The Rf value is calculated as $Rf =$$\frac{\text{distance moved by substance}}{\text{distance moved by solvent}}$.

  
• How do different compounds behave in chromatography?

  Different compounds have different Rf values in different solvents, which can help identify the compounds.
• What happens to a pure compound in chromatography?

  A pure compound will produce a single spot in all solvents.
• What do carbonates react with to produce carbon dioxide?

  Carbonates react with dilute acids to produce carbon dioxide.
• What is observed when carbon dioxide is produced from carbonates?

  Fizzing is observed when carbon dioxide is produced from carbonates.
• What precipitate is formed when halide ions react with silver nitrate?


  Halide ions produce silver halide precipitates with silver nitrate solution.
• What color precipitate does silver chloride produce?

  Silver chloride produces a white precipitate.
• What color precipitate does silver bromide produce?

  Silver bromide produces a cream precipitate.
• What color precipitate does silver iodide produce?

  Silver iodide produces a yellow precipitate.
• What precipitate is formed when sulfate ions react with barium chloride?

  Sulfate ions produce a white precipitate with barium chloride solution.
• What are the advantages of instrumental methods in chemistry?

  • Accurate
  • Sensitive
  • Rapid
  • Useful for small sample amounts
• What is flame emission spectroscopy used for?

  Flame emission spectroscopy is used to analyze metal ions in solutions.
• How does flame emission spectroscopy identify metal ions?

  The light given out is passed through a spectroscope to produce a line spectrum that can be analyzed.
• What is unique about each element's line spectra?


  Each element has its own unique line spectra (fingerprint).
• How can elements be identified using their emission spectra?


  Elements can be identified by matching the lines in their emission spectra.