Using Mass in Chemical Equations

What phrase describes the idea that matter can

neither be created nor destroyed as part

of a chemical reaction

• Because the reaction would create an explosion

• Because conservation of mass only applies to endothermic reactions

• Because this equation hasn't been balanced

• Because several of the compounds involved are gases

• 48 RAM

• 38 RAM

• 108 RAM

• 76 RAM

Which of the following is the symbol for

Relative Formula Mass?

• F_r

• F_m

• M_f

• M_r

Using equations and

finding the formula mass (M_r)

of a compound:

Step one will be to:

• Count the number of atoms of each element in a compound

• Count the number of elements of each atom in a compound

• Count all atoms from all compounds on one side of an equation

• Cound the letters in a chemical formula

You are finding the M_r of FeS (fools gold)

and know that

RAM of Fe is 56

RAM of S is 32

will you...

• Multiply

  56 x 32

  for M_r of

  1792

• Add 56 and 32 (88)

  then x 2

  (no. of atoms in compound)

  for M_r of 176

• Just add 56 and 32, because there is only one atom of each,

  for M_r of 88

• Doesn't apply - we don't know the reactants so can't make the calculation

The formula for Ammonium Sulphate, a fertiliser, is

(NH₄)₂ SO₄

How many oxygens would you count

when deriving the formula mass?

The formula for Ammonium Sulphate, a fertiliser, is

(NH₄)₂ SO₄

How many nitrogens would you count

when deriving the formula mass?

The formula for Ammonium Sulphate, a fertiliser, is

(NH₄)₂ SO₄

How many hydrogens would you count

when deriving the formula mass?