Chemistry​​​​​​​​⚖️ _ Topic 3 - Qauntative Chemistry

• What is the value of the avogadro constant?

  6.02x1023
• What is a mole?

  One mole of a substance is the amount of it that contains an avogadro number of particles (6.02x1023 )
• The mass of one mole of atoms or molecules of any substance is exactly the same as the relative atomic mass (Ar) of an element or relative formula mass (Mr of a compound. In grams
• What equation can be used to calculate the number of moles in a substance by using mass and Mr / Ar ?
• What is the law of conservation of mass?

  During a chemical reaction, no atoms are created or destroyed
• During a chemical reaction, no atoms are created or destroyed so the mass of the products is the same as the mass of the reactants
• In a balanced symbol equation the combined relative formula mass of the reactants is the same as that of the {{c1::products
• Why might mass seem to increase after a reaction?
• Why might mass seem to decrease after a reaction?
• In a balanced chemical equation, the big numbers in front of the chemical formulas tell you the relative number of moles of each reactant and product
• How can you balance a chemical equation using the masses of the substances involved?


  Divide the mass of each substance by its Mr to find the number of molesDivide the nuber of moles of each substance by the smallest number of moles in the reactionIf any of the numbers are not whole numbers, multiply all the numbers by the same amount so that they all become whole numbersWritre the balanced symbol equation for the reaction by putting these numbers infront of the chemical formulas
• What is a limiting reactant?

  The reactant that is the one to be fully used up and stop a reactant. It limits the products formed
• The amount of product formed is directly proportional to the amount of limiting reactant
• How can you calculate the mass of a product using the mass of the limiting reactant?

  Write out the balanced equationWork out the Mr of the limiting reactant and the product you want to find the mass ofWork out how many moles there are of the limiting reactantUse the balanced equation to work out how many moles there will be of the productUse the number of moles, along with the relative formula mass of the product to calculate the mass
• How can you calculate the mass of a reactant using the mass of a product?

  Write out the balanced symbol equationCalculate the number of moles of the product using its mass and MrUse the balanced symbol equation to find out how many moles the reactant usesUse the moles and Mr to calculate its mass
• At the same temerature and pressure, equal numbers of moles of any gas will occupy the same volume For example, If two moles of oxygen occupies 50dm3 then two moles of chlorine gas will also occupy 50dm3 at the same temperature and pressure
• What equation is used to calculate the volume of a gas at room temp and pressure?
• What is concentration

  The amount of a substance in a certain volume
• Give the equation to work out concentration g/dm3
• What is a solute?

  A substance that is dissolved in a solvent to form a solution
• What is the equation to work out the mass of a solute in a solution?

  Mass of solute (g) = concentration (g/dm3 ) x volume (dm3 )
• How do you convert between cm3 and dm3 ?

  divide by 1000
• How do you convert between dm3 and cm3 ?

  multiply by 1000
• What is the equation to work out the concentration of a solution in mol/dm3 ?
• What is the equation used to convert between mol/dm3 and g/dm3

  mol/dm3 = g/dm3 / Mr
• What does the atom economy of a reaction tell you?

  The percentage of reactants that form useful products
• What is the equation for calculating atom economy?
• How do you calculate the perventage waste of a reaction?

  Substract the atom economy from 100
• What economic advantages does using a high atom economy have?

  They are more profitable because waste removal and raw materials are expensive
• What environmental advantages does high atom economy have?

  Reactions with a higer atom economy use fewer raw materials than reactions with low atom economies. They also produce less waste that could damage the environment. It is more sustainable
• What is the theoretical yield of a reaction?

  The amount you would get if everything in the reaction reacted perfectly and nothing was lost
• What is yield?

  The actual amount of product formed in a reaction
• What is the equation used to calculate the percentage yield?
• Give three reasons why a reaction may have under 100% percentage yield

  The reaction is reversibleProduct is lost when its seperated from the reactantsUnexpected reactions may be happening
• What is a reversible reaction?

  A reaction where the products of the reactions can react to form the reactants aswell
• How is product lost when its seperated from the reactants?

  When you filter for example, some liquid remains in the filter paper with the solid. Some solid will get left behind when you scrape it of the filter paper. These lead to a lower yield
• Give two examples of how unexpected reactions may be happening

  the reactants may react with gas in the airthe reactants may react with impurities in the reaction mixture
• Why do industrial reactions produce a lot more waste and are more expensive?

  They are done on a much bigger scale
• Give 5 factors that need to be considered before an industrial reaction is setup to ensure its econimical and environmentally sustainable

  Atom EconomyYieldRateEquilibrium positionUsefulness of by-products
• Why should industrial reactions have a high atom economy?

  Reactions with higher atom economies produce less waste and need less raw materials. This makes them cheaper and more sustainable to run