quantitative chemistry

• What does the conservation of mass state?

  Atoms cannot be created or destroyed
• What happens to atoms in a chemical reaction according to the conservation of mass?

  Atoms are rearranged into new substances
• What must be true about the mass at the start and end of a reaction?

  The mass must be the same
• Why might the mass appear to change in some reactions?

  Gas may be produced and lost
• What is produced when sodium reacts with water?

  Sodium hydroxide and hydrogen
• Why is the mass of sodium and water greater than sodium hydroxide after the reaction?

  Hydrogen atoms are lost as gas
• What happens to mass when sodium reacts with chlorine?

  The mass appears to increase
• Why does the mass increase when sodium reacts with chlorine?

  Gaseous chlorine atoms are added
• What is the process for balancing symbol equations?

  1. Ensure equal number of each atom on both sides
  2. Adjust coefficients to balance the equation
• What is the unbalanced equation for the reaction of hydrogen and oxygen?

  H₂ + O₂ - H₂O
• How many hydrogen atoms are on each side of the unbalanced equation H₂ + O₂ - H₂O?

  Two hydrogen atoms on each side
• How many oxygen atoms are in the reactants of the unbalanced equation H₂ + O₂ - H₂O?

  Two oxygen atoms in the reactants
• What is the balanced equation for the reaction of hydrogen and oxygen?

  2H₂ + O₂ - 2H₂O
• How many hydrogen and oxygen atoms are present in the balanced equation 2H₂ + O₂ - 2H₂O?

  Four hydrogen and two oxygen atoms
• What steps do you follow to calculate the mass of a product from a given mass of a reactant?

  1. Balance the symbol equation
  2. Calculate moles of known substance
  3. Use balanced equation to find moles of unknown
  4. Calculate mass of unknown substance
• What steps do you follow to balance an equation?

  1. Work out the mr of all substances
  2. Calculate moles in each substance
  3. Convert to a whole number ratio
  4. Balance the symbol equation
• What are the state symbols for solid, liquid, gas, and aqueous?

  (s), (l), (g), (aq)
• What does mr stand for in chemistry?

  Formula mass
• How is the formula mass calculated?

  Sum of relative atomic masses of atoms
• What is the Avogadro constant?

  6.02x10²³ particles per mole
• How many grams of water correspond to one mole?

  18 grams of water
• How do you calculate moles from mass?

  Moles = mass / mr
• What is the ratio of hydrogen to oxygen in their reaction?

  2:1 ratio of molecules
• If you have 10 molecules of oxygen, how many molecules of hydrogen do you need?

  20 molecules of hydrogen
• If you have 1 mole of oxygen, how many moles of hydrogen do you need?

  2 moles of hydrogen
• If you have 1.75 moles of oxygen, how many moles of hydrogen do you need?

  3.5 moles of hydrogen
• What are excess and limiting reactants?

  • Excess reactant: leftover after reaction
  • Limiting reactant: runs out first in reaction
• How do you determine which reactant is limiting?

  1. Write the balanced symbol equation
  2. Pick a reactant and its quantity
  3. Use the ratio from the balanced equation
  4. Compare to the given quantity
  5. Identify excess and limiting reactants
• What is concentration in chemistry?

  Amount of solute in solvent volume
• What is the unit of concentration?

  g/dm³
• How is concentration calculated?

  Concentration = mass / volume
• How is volume converted from cm³ to dm³?

  Volume (dm) = volume (cm) / 1000
• What does high and low concentration mean?

  • High concentration: lots of solute in little solution
  • Low concentration: little solute in lots of solution