amount of substance

• What is the unit of volume in the gas equation?

  m3 - divide cm3 by a million
• How do you convert mg to g

  divide by a 1000
• Limiting reagants:


  1)create a table organised in: moles start,change and end for each of the substances

  2)Calculate the moles from the info given

  3) calculate the limiting reactant-the first reactant reacts with second reactant with(reactant of first x coefficient of the second reactant).if it is less if it is limiting but if it is more it is in excess and the first is limiting.

  4) minus the limiting from start moles and multiply it to the product needed to find out its moles.
• Back titrations calculations


  1.Write out full equations for both reactions

  2. Identify the key substance involved in both reactions as a reactant

  3. How much of key substance(in moles) in the second reaction?

  4.How much of key substance (in moles) in the first reaction? minus inital from final to get how much reacted.

  5. How much of substance questions asks for -use the key substance and the mole ratio
• Back titration with titre

  1 find mean titre

  2. moles of key substance using volume of mean titre

  3. amount of what sample is used multiply it if it makes up a bigger solution.

  4. continue doing the calculation they've asked for.
• How do you calculate percentage by mass?

  mass of element/compound mr x 100
• What are the two types of yield to consider during a reaction and their definitions?

  Theoretical yield:The maximum amount of product we could get. Actual yield:Amount of product we actually get.
• both yields can be in mass or moles.
• What is the equation for percentage yield?

  Percentage yield=actual yield/theoretical x 100
• How to find theoretical yield if actual yield is given?

  1)Find limiting reagent and calculate its moles using the mole ratio.If youre calculating the yield in mass then multiply by Mr.
• Why do very few reactions have a percentage yield of 100%?

  -Raw materials may not be pure -Some of the products may be left behind in the apparatus -The reaction may not have completely finished. -Some of the reactants may give some unexpected products.
• What is % atom economy?

  Shows how many of the atoms used in the reaction becomes the desired product(the rest goes to waste).
• A high percentage atom economy means a lower proportion of waste products.
• How to calculate % atom economy?

  1)Find Mr of desired product(told in question) and multiply by its coefficients. 2)Find Mr of all reactants/products ( as their mr is the same) and multiply by its coefficients.

  3)input into the atom economy equation
• What's the equation for atom economy?

  %atom economy=Mr of desired product/total products or reactants x 100