chemical calculation ✩

• What is a mole in chemistry?

  A mole is a concept used to count molecules, atoms, or anything extremely small.
• Why do scientists want to know how many atoms are in the universe?

  To understand the composition and scale of matter in the universe.
• Who proposed the idea that equal volumes of gases at the same temperature and pressure contain an equal number of particles?

  (Lorenzo Romano Amedeo Carlo) Avogadro.
• What was the initial reception of Avogadro's idea by most scientists?

  Most scientists viewed it as purely hypothetical and did not accept the idea of the atom.
• In what year was Avogadro proven correct about his hypothesis?

  By late 1860.
• What is Avogadro's number?

  Avogadro's number is $6.02 \times 10^{23}$.
• How many gas particles are in a balloon at zero degrees Celsius and one atmosphere of pressure?

  There are precisely $6.02 \times 10^{23}$ gas particles.
• Why might the example of gas particles be misleading when thinking about the size of atoms?

  Because gases take up a lot of space due to the high kinetic energy of the gas particles.
• How many molecules of water are in 18.01 grams of water?

  There are $6.02 \times 10^{23}$ molecules of water.
• What is the significance of the number 18.01 in relation to water?

  It represents the mass of one mole of water in grams.
• What is the second name for Avogadro's number?

  The mole.
• How do chemists use the mole in their work?

  Chemists use the mole to refer to quantities at the magnitude of $6.02 \times 10^{23}$.
• Why do students find it hard to understand the concept of a mole?

  Because they have difficulty picturing the size of a mole or $6.02 \times 10^{23}$.
• What are some analogies used to explain the size of a mole?

  • A mole of donuts would cover the Earth to a depth of 8 kilometers.
  • A mole of basketballs could create a new planet the size of Earth.
  • A mole of pennies spent at a million dollars a second would leave you with over 99.99% of your money at age 100.
• How do you buy items like grapes or deli meat in a grocery store?

  You buy them by weight or quantity, similar to how chemists use moles.
• How does the mole relate to other familiar quantities like a dozen or a gross?

  The mole is a specific quantity that represents $6.02 \times 10^{23}$, similar to how a dozen represents 12.
• What is the story of the mole in chemistry?

  • The mole is a concept for counting small particles.
  • Avogadro proposed that equal volumes of gases contain equal particles.
  • Avogadro's number is $6.02 \times 10^{23}$.
  • The mole is used to refer to quantities at this magnitude.
  • Analogies help illustrate the size of a mole.
• What is the unit used to measure the amount of chemical that we have?

  Mole
• How many particles are in 1 mole of any substance according to Avogadro's Constant?

  1. 6.02 x 10²³ particles
• If you have 1 mole of carbon dioxide, how many particles do you have?

  1. 6.02 x 10²³ particles of carbon dioxide
• Why is Avogadro's Constant specifically 6.02 x 10²³?

  Because the mass of 6.02 x 10²³ particles of any substance equals that substance’s relative atomic or formula mass in grams
• What is the relative atomic mass of carbon?

  12
• How much would 1 mole of carbon dioxide weigh?

  Exactly 12 grams
• What is the formula to calculate the number of moles in a sample?

  Number of moles = mass of that element or compound ÷ Mr
• If you know the number of moles and the relative mass, how can you find the mass of a compound?

  Mass of that element or compound = Mr × the number of moles in a sample
• What should you remember when using the formula for calculating moles?

  It doesn't matter if it says Mr rather than Ar; use the Ar of the element if it's a single element
• How can chemical equations be interpreted in terms of moles?

  • Chemical equations can be thought of in terms of moles.
  • Moles in equations represent ratios of reactants and products.
• the mole


  it is the relative atomic/ formula mass in grams
• What is one of the most important concepts in chemistry?

  The idea of conservation of mass
• What does the conservation of mass mean in a chemical reaction?

  Mass is always conserved, meaning no atoms are created or destroyed
• In the reaction of sodium and chlorine, how many sodium chlorides are formed if there are two chlorine atoms?

  Two sodium chlorides
• How do you balance a chemical equation using the conservation of mass principle?

  You ensure the number of atoms of each element is the same on both sides of the equation
• What is the total relative formula mass of the reactants in the sodium and chlorine reaction?

  117
• How do you calculate the total relative formula mass of the products in the sodium and chlorine reaction?

  By adding the relative formula masses of the products, which also equals 117
• If 2.3 grams of sodium reacts with 3.5 grams of chlorine gas, what is the mass of sodium chloride produced?

  1. 8 grams
• What happens to the mass during a chemical reaction when gases are involved?

  The mass might seem to change because gases can escape into the air
• What is the effect of heating magnesium in air during its reaction with oxygen?


  The product, magnesium oxide, weighs more than the magnesium alone
• Why might the scales not measure the total mass during a reaction involving gases?

  Because the gas can escape into the air and not be accounted for
• How does conducting a reaction in a sealed container affect the measurement of mass?

  The mass of reactants and products will balance perfectly since all gases are contained
• What happens when calcium carbonate decomposes in an open system?

  The weight of the products appears to decrease because carbon dioxide gas escapes