Exam specific answers (amount of substance)

Question 1

a student is required to make up 250cm^3 of a solution containing a known mass of MHCO3. the student is provided with a sample bottle containing the MHCO3. describe the method, including practical details, that the student should use to prepare the solution. (6)

Answer 1

stage 1:
weigh the sample bottle on a 2 dp place balance
transfer all the solid to a beaker and reweigh the bottle
record the difference in gas to get the mass of the solid

stage 2:
add distilled water
stir with a glass rod
until all the solid has dissolved

stage 3:
transfer solution to a volumetric flask
with washings (rinse beaker thoroughly into flask)
add water up to 250cm^3 mark
mix by gently inverting bottle

Question 2

what is the importance of percentage yield? (1)

Answer 2

getting as much product as possible in the reaction/ for an efficient conversion of reactants to products

Question 3

what is the importance of percentage atom economy? (1)

Answer 3

maximising the mass of reactants that end up in the desired product/ minimising the amount of by-products