Quantitative chemistry

• What is the relative atomic mass symbol?

  Ar
• What does the relative atomic mass of an element compare to?

  The mass of its atoms compared to a carbon-12 atom
• Where can the Ar values for elements be found?

  In the periodic table
• Why does relative atomic mass have no units?

  Because it is a measure of relative mass
• What is the process for calculating relative formula mass (Mr)?

  1. Count the number of atoms of each element in the formula.
  2. Add the Ar values for all the atoms of each element present.
• What is the formula for carbon dioxide?

  CO2
• How do you calculate the Mr of CO2 using its atomic masses?

  Mr of CO2 = 12 + 16 + 16 = 44
• What is another way to express the calculation of Mr for CO2?

  Mr of CO2 = (1 × 12) + (2 × 16) = 44
• What is the symbol for relative formula mass?

  Mr
• How are the relative formula masses of ionic compounds calculated?

  In the same way as molecules, from the numbers shown in the formula
• What does the law of conservation of mass state?

  No atoms are lost or made in a chemical reaction
• What happens to atoms during a chemical reaction according to the law of conservation of mass?

  Atoms join together in different ways to form products
• Why is the number of atoms of each element the same on both sides of a balanced symbol equation?

  Because of the law of conservation of mass
• What is the relationship between the total mass of products and reactants in a chemical reaction?

  The total mass of products equals the total mass of reactants
• How can the mass of one substance in a reaction be calculated?

  If the masses of the other substances are known
• How much calcium carbonate is made from 28 grams of calcium oxide and 22 grams of carbon dioxide?

  50 grams
• How do you find the amount of calcium carbonate from the masses of calcium oxide and carbon dioxide?

  Add 28 grams of calcium oxide and 22 grams of carbon dioxide
• What is the total mass of magnesium oxide formed from 48 grams of magnesium and an unknown amount of oxygen that totals 80 grams?


  80 grams
• How do you find the mass of oxygen when given the mass of magnesium oxide and magnesium?

  Subtract 48 grams of magnesium from 80 grams of magnesium oxide
• How much oxygen remains when 48 grams of magnesium reacts to form magnesium oxide weighing 80 grams?

  32 grams
• What is a closed system in the context of chemical reactions?

  A system where no substances can enter or leave
• What happens to the total mass in a closed system during a reaction?

  The total mass stays the same
• What is a non-enclosed system?

  A system where substances can enter or leave
• What happens to the total mass when a gas escapes from a non-enclosed system?

  The total mass appears to decrease
• What happens to the total mass when a gas is gained in a non-enclosed system?

  The total mass appears to increase
• What is uncertainty in chemical measurements?

  It is the doubt about the accuracy of a measurement
• What are two causes of uncertainty in chemical measurements?

  Judging thermometer readings and timing reactions
• How is uncertainty estimated from measuring instruments?

  By considering the resolution of the instruments
• What is the resolution of a measuring instrument?

  The smallest change in a quantity that gives a change in the reading
• How is uncertainty estimated for a thermometer with a resolution of 1.0°C?

  ± 0.5°C
• How is uncertainty estimated for a digital measuring instrument?

  Half the last digit shown on its display
• How is uncertainty estimated from a set of repeat measurements?

  ± half the range
• How can uncertainty be shown on a graph?

  By plotting vertical lines joining repeat readings
• What is a solution and how is it formed?

  • A solution forms when a solute dissolves in a solvent.
  • The concentration measures how 'crowded' the solute particles are.
• What is the concentration of a solution a measure of?

  How 'crowded' the solute particles are
• How is concentration calculated?

  Concentration = mass of dissolved solute (g) / volume of solution (dm³)
• What is the concentration of a solution if 8 g of sodium hydroxide is dissolved in 2 dm³ of water?

  4 g/dm³
• What are the volume units used in concentration calculations?

  • cm³ or ml (both describe the same volume)
  • Volumes must be in dm³ for concentration calculations.
• How do you convert cm³ to dm³?

  Divide by 1000
• What is the concentration formula in terms of mass and volume?

  Concentration = mass of solute in grams divided by volume in dm³