C3 Quantitative Chemistry

• What is the law of conservation of mass?

  No atoms are lost or made during a chemical reaction, so the mass of products equals the mass of reactants.
• In the reaction of magnesium and oxygen, what are the reactants and products?

  The reactants are magnesium and oxygen, and the product is magnesium oxide.
• How would you calculate the missing mass in a chemical reaction?

  Add the masses of the reactants to find the total mass, which must equal the total mass of the products.
• Why is it important to balance chemical equations?

  To ensure that the number of atoms of each element is the same on both sides of the equation.
• What must be true about the total mass of reactants and products in a chemical reaction?

  The total mass of the reactants must equal the total mass of the products.
• How would you balance the equation Mg + O$_2$ → MgO?


  By adjusting the coefficients to 2Mg + O$_2$ → 2MgO.
• What is the rule regarding changing formulae when balancing equations?

  You cannot change the formulae; you can only add numbers in front of them.
• What happens if there is a small number in a formula when balancing equations?

  You multiply the large number by the small number to account for all atoms.
• What is the relative atomic mass (RAM) of carbon?

  12
• How is relative formula mass (RFM) calculated?

  By summing the relative atomic masses of all atoms in the formula.
• What is the relative formula mass of H$_2$O?


  $H_2O: 2(1) +$$16 =$$18$
• How does RFM relate to the conservation of mass?

  In a balanced equation, the sum of the RFM of reactants equals the sum of the RFM of products.
• What is the percentage mass of sodium in sodium carbonate (Na$_2$CO$_3$)?


  43%
• How do you calculate the percentage mass of an element in a compound?

  Divide the mass of the element by the total mass of the compound and multiply by 100.
• What is the percentage mass of oxygen in water (H$_2$O)?


  89%
• How can you determine if a chemical reaction is taking place?

  By observing signs such as popping, fizzing, gas release, color change, or heat changes.
• What tool is used to measure the volume of a gas in a reaction?

  A gas syringe.
• Why might some reactions appear to involve a change in mass?

  Because a reactant or product is a gas and its mass has not been accounted for.
• How would you measure the mass of a gas produced in a reaction?

  By using a balance before and after the reaction to see the mass change.
• What is the significance of balancing equations in relation to mass changes?

  It ensures that mass is conserved and accounted for in the reaction.
• What is the objective of measuring the mass or volume of a gas?

  To describe a method for measuring a mass or volume of a gas.
• Why do some reactions appear to involve a change in mass?

  Because a reactant or product is a gas and its mass has not been taken into account.
• What are some indicators that a chemical reaction is taking place?

  Popping, fizzing, gas given off, color change, smell, precipitation, heat given off, reaction gets colder.
• What is a gas syringe used for?

  To measure the volume of gas produced in a reaction.
• How does a gas syringe work during a reaction?

  The gas travels into the syringe and moves the plunger, allowing the volume to be read off the syringe.
• What happens to the mass when magnesium reacts with hydrochloric acid?

  The overall mass decreases because hydrogen gas escapes if the reaction vessel is not sealed.
• What is the balanced equation for the reaction of magnesium with hydrochloric acid?

  Mg (s) + HCl (aq) → MgCl₂ (aq) + H₂ (g)
• What should you do after burning magnesium in air before reweighing?

  Leave it to cool for at least 10 minutes.
• What are non-enclosed systems in chemical reactions?

  Reactions that take place in apparatus that are not perfectly sealed, allowing gases to enter and escape.
• What is the definition of uncertainty in measurements?

  Uncertainty refers to the doubt that exists about the result of a measurement.
• How can you express the uncertainty of a measuring cylinder?

  By stating the uncertainty value printed on it, such as ±0.5 mL.
• How do you calculate the range of a set of measurements?

  Range = highest measurement - lowest measurement.
• What is the relationship between moles and the number of particles?

  One mole contains \(6.02 \times 10^{23}\) particles (atoms, molecules, or ions).
• What is Avogadro's constant?

  Avogadro's constant is \(6.02 \times 10^{23}\) atoms per mole.
• How do you calculate the number of moles from a given mass?

  Number of moles = mass (g) / molar mass (g/mol).
• What is the mass of one mole of carbon in grams?

  12 g.
• How many atoms are in 2 moles of gold?

  2 x \(6.02 \times 10^{23}\) = \(1.204 \times 10^{24}\) atoms.
• How do you find the mass of a substance using its moles and molar mass?

  Mass (g) = number of moles × molar mass (g/mol).
• What is the molar mass of water (H₂O)?

  18 g/mol.
• How do you calculate the mass of 0.36 moles of ethanoic acid (CH₃COOH)?

  Mass = 0.36 moles × 60 g/mol = 21.6 g.