C3- Quantitative chemistry

• What is the relative formula mass (Mr) of a compound?

  It is the sum of the relative atomic masses of all the atoms in the molecular formula.
• What does Ar stand for in chemistry?

  Ar stands for relative atomic mass.
• How do you find the relative formula mass of MgCl2?

  By adding the relative atomic mass of Mg (24) and twice the relative atomic mass of Cl (35.5), resulting in 95.
• How do you calculate the percentage mass of an element in a compound?

  Percentage mass = (Ar x number of atoms of that element / Mr of the compound) x 100.
• What is the relative atomic mass of Carbon?

  The relative atomic mass of Carbon is 12.
• What is the Avogadro constant?

  The Avogadro constant is (6.02 times 10 to the power of 23).
• What does one mole of atoms or molecules represent in grams?

  One mole has a mass in grams equal to its relative formula mass.
• What is the law of conservation of mass?

  No atoms are created or destroyed during a chemical reaction.
• What does a balanced chemical equation indicate?

  It indicates that the number of atoms of each element is the same on both sides of the equation.
• How do you calculate the total mass of products in a chemical reaction?

  The total mass of products equals the total mass of reactants.
• What happens in a closed system during a reaction?

  The total mass remains constant and follows the conservation of mass.
• What is the effect of an unsealed container on mass during a reaction?

  The mass will decrease if gases escape.
• What do the numbers in front of chemical formulas in a reaction represent?

  They indicate the number of moles of each substance involved in the reaction.
• How do you balance a chemical equation using moles?

  Divide the mass of each substance by its relative formula mass to find the number of moles.
• What is the limiting reactant in a chemical reaction?

  The limiting reactant is the substance that is completely consumed when the reaction stops.
• How does the amount of product formed relate to the limiting reactant?

  The amount of product formed is directly proportional to the amount of limiting reactant used.
• What is the volume occupied by one mole of any gas at room temperature and pressure?

  One mole occupies 24 dm³.
• How do you calculate concentration in a solution?

  Concentration = moles/volume in dm³.
• How do you convert concentration from moles to grams?

  Mass in grams = moles x molar mass.
• What does atom economy measure?

  Atom economy measures the percentage of reactants that form useful products.
• What does 100% atom economy indicate?

  It indicates that all atoms in the reactants have been converted into the desired product.
• Why is high atom economy beneficial?

  High atom economy leads to better profit and a reduced environmental impact.
• How do you calculate percentage yield?

  Percentage yield = (actual yield / predicted yield) x 100.
• What does a 100% yield mean?

  It means that all expected product was obtained from the reaction.
• Why are yields typically less than 100%?

  Yields are less than 100% due to side reactions, impurities, and reversibility of reactions.
• How can actual yield be increased?

  By optimizing the amounts of reactants used in the reaction.
• What happens when filtering a liquid in terms of yield?

  You nearly always lose a bit of liquid or solid during the process.
• What is the significance of transferring liquids between containers?

  Liquid is often lost during the transfer, affecting yield.
• What does the law of conservation of mass state?

  No atoms are lost or made in reactions
• What does it mean for a chemical equation to be balanced?

  Same number of atoms on both sides
• How is relative formula mass (Mr) calculated?

  Sum of relative atomic masses in formula
• What is the relative formula mass of HCl?

  $36.5$
• What must be true in a balanced chemical equation regarding Mr?

  Sum of Mr of reactants equals products
• What happens to mass when a gas is involved in a reaction?

  Mass may appear to change if gas escapes
• What should you check if a reaction shows a mass change?

  Whether a gas was released or not
• What is always present in measurements made in chemistry?

  Some uncertainty about the result
• What should you be prepared to do regarding uncertainty in measurements?

  Make estimations of uncertainty
• What is a limiting reactant in a chemical reaction?

  The reactant that is used up
• Why do you use one reactant in excess?

  To ensure all of the other reactant is used
• How does a limiting reactant affect product formation?

  It restricts the amount of product produced