quantitative chem

• What is the law of conservation of mass?

  That no atoms are lost or made during a chemical reaction so that the mass of the products equals the mass of the reactants
• What is the relative formula mass (Mr) of a compound?

  The sum of the relative atomic masses of the atoms in the numbers shown in the formula
• What is the relationship between the sum of the relative formula masses of the reactant and the sum of the relative formula masses of the products in a balanced symbol equation?

  They are equal
• Why do some reactions appear to involve a mass change?

  Because one of the reactant or products is a gas and its mass has not been taken into account
• What is uncertainty in a measurement?

  The interval within which the true value of a quantity can be expected to lie.
• What two ways can you determine the uncertainty in a measurement?

  By considering the resolution of the measuring instrument and from the range of a set of repeat results
• What is the resolution of a measuring instrument?

  The smallest change in a quantity that gives a change in the reading that can be seen
• How can you use the resolution of a measuring instrument to estimate the uncertainty in a measurement?

  The uncertainty of a measuring instrument is estimated as plus or minus (±) half the smallest scale division
• How can you estimate the uncertainty in a measurement form a set of repeated results?

  The uncertainty is ± half the range
• What is the symbol for the mole??

  Mol
• What is the mass of one mole of a substance?

  The mass of one mole of a substance in grams is numerically equal to its relative formula mass
• What is the number of atoms, molecules or ions in a mole of a given substance equal to?

  The Avogadro constant. The value for the Avogadro constant is 6.02 x 10 to the power of 23 per mole
• What is the equation that connects moles, mass and relative formula mass?

  Moles = mass in g/relative molecular mass (Mr)
• What is meant by a reactant being in excess in a reaction between two reactants?

  There is more of one reactant so that all of the other reactant is used up
• What is a limiting reactant?

  The reactant that is completely used up in a reaction (it limits the amount of product)
• What units are the concentration of a solution measured in?

  Mass per given volume of solution; e.g. grams per dm3 (g/dm3) or moles per dm3 (mol/ dm3)
• Give three reasons why in a reaction the calculated amount of product is not always produced

  The reaction may not go to completion because it is reversible, some of the product may be lost when it is separated from the reaction mixture or some of the reactants may react in ways different to the expected reaction
• What is the amount of product made called?

  The yield
• How do you calculate percentage yield?

  Mass of product actually made/Maximum theoretical mass of product x 100
• What is atom economy?

  The measure of the amount of starting materials that end up as useful products
• Why is it important to use reactions with high atom economy?

  For sustainable development and for economic reasons
• How do you calculate the percentage atom economy of a reaction?

  Relative formula mass of desired product from equation/Sum of relative formula masses of reactants from equation x 100
• What do equal amounts in moles of gases occupy?

  The same volume under the same conditions of temperature and pressure
• What is the volume of one mole of any gas at room temperature and pressure?

  24 dm3
• What is room temperature and pressure?

  20°C and 1 atmosphere