C3 - Quantitative Chemistry

• What does the law of conservation of mass state?

  No atoms are lost or gained during a chemical reaction.
• How does the mass of products compare to the mass of reactants in a chemical reaction?

  The mass of the products is the same as the mass of the reactants.
• Why might some reactions appear to give a change in mass?

  This is because a gas may have escaped from the reaction container.
• What is relative atomic mass (Ar)?

  The average mass of an atom of an element compared to Carbon-12.
• What is relative formula mass (Mr)?

  The sum of all the atomic masses of the atoms in a formula.
• How is uncertainty defined in measurements?

  It is the interval within which the true value can be expected to lie.
• If a temperature is measured as 25°C with an uncertainty of ±2°C, what is the range of the true value?

  The true value lies between 23°C and 27°C.
• What is a mole in chemistry?

  A measurement for the amount of a chemical, equivalent to the mass of $6.02 \times 10^{23}$ atoms of an element.
• What is the symbol for mole?

  The symbol is mol.
• What does a balanced equation represent in a chemical reaction?

  It shows the number of moles that react.
• In the equation Mg + 2HCl -> MgCl2 + H2, how many moles of hydrochloric acid react with one mole of magnesium?

  Two moles of hydrochloric acid react.
• What is a limiting reactant?

  The reactant that is completely used up in a chemical reaction.
• What is an excess reactant?

  The reactant that is not completely used up in a chemical reaction.
• How is concentration defined in chemistry?

  A measure of the number of particles of a chemical in a volume.
• What is the unit for measuring concentration?

  Concentration can be measured in g/dm³.
• What is a decimeter cubed (dm³)?

  A measurement of volume that contains 1000 cm³.
• What are the key concepts related to the law of conservation of mass?

  • No atoms are lost or gained during a chemical reaction.
  • Mass of products equals mass of reactants.
  • Apparent mass change may occur due to gas escape.
• What are the definitions of relative atomic mass and relative formula mass?

  • Relative atomic mass (Ar): Average mass of an atom compared to Carbon-12.
  • Relative formula mass (Mr): Sum of atomic masses in a formula.
• What are the definitions of limiting reactant and excess reactant?

  • Limiting reactant: Completely used up in a reaction.
  • Excess reactant: Not completely used up in a reaction.
• What are the definitions of concentration and decimeter cubed?

  • Concentration: Measure of particles in a volume (g/dm³).
  • Decimeter cubed (dm³): Volume measurement containing 1000 cm³.