AMOUNT OF SUBSTANCE Flashcards
Importance of high Percentage Yield
And how can percentage yield be increased
• Increases the amount of product that is made from the reactants
• Percentage yield can be increased by making improvements in experimental technique
Importance of high Atom Economy
And how can it be improved
Increases the mass of atoms in the reactants that are turned into products and
• Reduces the amount of waste by-products
• Atom economy can only be improved by finding a different reaction to produce the desired
product, which also produces fewer by-products
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Practical Aspects of Titrations procedure to make up a standard solution:
Stage 1: transfers known mass of solid
a) Weigh the sample bottle containing the solid on a (2 dp) balance b) Transfer to beaker* and reweigh sample bottle
c) Record the difference in mass
Stage 2: Dissolves in water
a) Add distilled / deionised water b) Stir (with a glass rod) or swirl c) Until all solid has dissolved
Stage 3: Transfer, washing and agitation
a) Transfer to volumetric / graduated flask using a funnel b) With washings
c) Make up to 250cm3 / mark with water
d) Shakes/inverts/mixe
Calculating Percentage error (equation)
Percentage error = Error of the equipment (x by how many times measured using that equipment ) /Amount measured x100%
Why is Removing any air bubbles from the burette important
Otherwise, the volume of the air bubble will be counted in the burette reading
Why is Removing the funnel that’s used to fill the burette important before starting the titration
Solution drops could fall from the funnel into the burette and affect the
burette reading
Why is During the titration, swirling the conical flask and rinsing the walls of the conical flask with distilled water important
Ensures all reactants mix and no reagent is left unreacted on sides of flask
Doesn’t change number of moles in conical flask so has no adverse effect on titration
The student identified use of the burette as the largest source of uncertainty in the experiment.
Using the same apparatus, suggest how the procedure could be improved to reduce the percentage uncertainty in using the burette.
Justify your suggested improvement.
Use a larger mass of solid OR use a more concentrated solution of MHCO3 OR less concentrated / more dilute solution of HCl OR more MHCO3
Justification: So a larger titre/reading will be needed OR larger volume of HCl
Q5.
In an experiment to determine the concentration of a solution of sodium hydroxide, 25.0 cm3 of 0.100 mol dm–3 hydrochloric acid were transferred to a conical flask. An indicator was added to the flask. The solution of sodium hydroxide was then added to the flask from a burette.
(a) State a suitable amount of indicator solution that should be added to the flask.
2-6 drops / 0.1-0.3 cm3
Accept ‘a few drops’
In an experiment to determine the concentration of a solution of sodium hydroxide, 25.0 cm3 of 0.100 mol dm–3 hydrochloric acid were transferred to a conical flask. An indicator was added to the flask. The solution of sodium hydroxide was then added to the flask from a burette.
State why it is important to fill the space below the tap in the burette with alkali before beginning the titration.
Incorrect volume recorded / space will fill during titration / produces larger titre value
Name of a potentials indicator in a titration and when should be used
Phenolphthalein - weak acid strong base
Methyl orange - strong acid weak base
The uncertainty in using the pipette in this experiment is ±0.06 cm3. Amount measured by pipette is 25cm3
Calculate the percentage uncertainty in using the pipette
% uncertainty = 0.06/25.0 x 100 = 0.24 %
what is Avogadro’s constant1
number of particles in a molecule
equation to workout number of particles
number of particles= Avogadro’s constant x moles
what is a dative bond
both of the electron in the shared pair of electrons is supplied from a single atom. represented using an arrow from lone electron pair. then treated as standard covalent bond
