Moles

• Avogadro’s constant=6.023x10(23)
• Mass=moles x Mr (when finding mass/moles of a compound)
• Mass=moles x Ar (when finding the moles/mass of an element)
• 1dm^3


  =1000cm^3
• Moles= volume x concentration
• Moles of solute required to make 550cm^3 of 0.5mol/dm^3?

  550cm^3=0.55dm^3 —> 0.6x0.55=0.33 mol
• Concentration when 0.73g of HCl dissolve in 400cm^3 of water?

  Mr (HCl)= (1x1)+(1x35.5)=36.5/mol

  mol= 0.73/36.5=0.02 mol

  0.02/0.4=0.05mol/dm^3
• Concentration when 12.045g of HCl is dissolved in 300cm^3 of water?

  Mr=36.5g/mol

  12.045/36.5=0.33 mol

  0.33/0.3=1.1 mol/dm^3
• Why might the mass of a product be decreasing or increasing?

  -One of the reactants may be a gas that is abundant in air and bonded with it ,changing the overall mass depending on whether this reactant leaves the container of the reaction.

  -the reactants may have not properly reacted with each other.
• What is a limiting reactant?

  The reactant that is used up first in a reaction
• What does it mean when reactants are referred as being in excess?

  The limiting reactant has used up all of its energy and the other reactants ,still producing a reaction of the product are in excess.
• How can we calculate the mass of a reactant that produces the known mass of a product?

  Find the Mr of both the reactant and product.Find the number of moles of the reactant with a known mass and then use this to find the number of moles of the reactant you are calculating the mass of.Finally ,use the number of moles and Mr to calculate the mass.