QChem

• What methods can be used to measure the mass or volume of reactants or products?


  • Collect products in a gas syringe
  • Use a scale or balance to measure mass
• What should you look for when measuring liquid in a burette or graduated cylinder?


  The bottom of the meniscus
• Why is there a degree of uncertainty in measurements?


  Because of the difficulty in determining exact liquid levels
• How is concentration calculated?

  Concentration = amount / volume
• What are the units for concentration, amount, and volume?

  Concentration: moles per decimeter cubed, amount: moles, volume: decimeters cubed
• What does the new style of exams emphasize?

  Wordy questions that incorporate multiple skills
• What is the formula for hydrochloric acid?

  HCl
• What is the formula for magnesium?

  Mg
• What products are formed when a metal reacts with an acid?


  Salts and hydrogen gas
• What is the formula for magnesium chloride?


  MgCl2
• Why does magnesium chloride have the formula MgCl2?


  Because magnesium has a 2+ charge and chlorine has a 1- charge
• What steps are involved in balancing a chemical equation?


  1. Write the unbalanced equation
  2. List the number of each atom on both sides
  3. Adjust coefficients to balance the atoms
  4. Rewrite the balanced equation neatly
• How do you balance the equation for the reaction of hydrochloric acid and magnesium?


  By adding coefficients to ensure equal numbers of each atom on both sides
• What is the relative atomic mass (AR) of hydrogen?


  1
• What is the relative atomic mass (AR) of oxygen?


  16
• How do you calculate the relative formula mass (MR) of a compound?


  By adding the relative atomic masses of all atoms in the formula
• What is the formula to calculate moles?


  Moles = mass / MR
• What is Avogadro's number?


  1. 02 x 10^23
• What is the balanced equation for the decomposition of hydrogen peroxide?


  2 H2O2 → 2 H2O + O2
• How do you find the mass of oxygen produced from a given mass of hydrogen peroxide?


  Use a ratio based on the balanced equation
• What is the mass of hydrogen peroxide if it decomposes to produce 32 grams of oxygen?


  68 grams
• How do you calculate the mass of oxygen produced from 40.8 grams of hydrogen peroxide?


  By using the ratio from the balanced equation
• What is the concept of limiting reactants?


  It is the reactant that is completely consumed first, stopping the reaction
• How do you calculate percentage yield?


  Percentage yield = (actual yield / theoretical yield) x 100
• What is atom economy?


  It is the ratio of the molar mass of desired products to the molar mass of reactants
• What are the steps involved in carrying out a titration?


  1. Use a pipette to measure 25 cm³ of alkali into a conical flask
  2. Add an indicator
  3. Fill the burette with acid of known concentration
  4. Record the initial burette reading
  5. Slowly add acid while swirling until the first permanent color change
  6. Record the final burette reading
  7. Repeat until consistent titers are obtained
• How do you calculate the number of moles of acid in a titration?


  By finding the number of hydrogen ions involved in the reaction
• What volume does one mole of gas occupy at standard conditions?


  24 decimeters cubed
• What types of calculations are included in the quantitative chemistry topic?


  • Balancing equations
  • Titration calculations
  • Bond enthalpy calculations
  • Molar mass calculations