Amount of substance

What does percentage of atom economy tell you?

• How efficiently atoms in the reactants are used to make the desired products

• A high atom economy means most of the atoms from the starting materials end up in the final product with minimal waste

Equation for percentage atom economy

suggest why a conical flask is prefered to a beaker in titration?

• Less chance of losing liquid on swirling

Why does repeating the titration make the average titre more reliable?

• A single titration could be anomalous

Why does the water used for rinsing have no effect on the accuracy of the titration?

• Water is a reagent

How do you calculate percentage yield?

• Actual yield/theoretical yield times by a 100

What does avagadro’s constant tell you ?

• Number of particles in 1 mol of a substance

What is a titration?

• Allows you to determine the concentration of a solution

• Using a fixed volume of a solution with a known concentration

How do you carry out a titration?

• In this example we are using an acid (unknown solution) and an alkali

• Measure an accurate fixed volume of alkali→ using a pipette with a volume of 25cm³

• Rinse it with distilled water to remove unwanted chemicals

• This may leave water droplets that can dilute the solution, so rinse it again with the alkali.

• Put the alkali in a conical flask

• Must use an indicator in an acid base titration

• Add a few drops of indicator (indicators are weak acids so too much indicator can cause inaccurate results)

• Rinse the burette with the acid. Clamp it so its level. Use funnel to pour in acid to the 0 mark

• Place the conical flask on a white tile so colour change is more visible

• Slowly release the acid into the flask while swirling it

• Stop adding acid when there is a colour change to show end point

• Read level of acid left in the burette

• Subtracting the start volume by final volume=Titre (which is how much acid reacted with the alkali)

• Repeat titration until you have 2 concordant results - difference of 0.1 cm³

• Calculate mean of concordant results

What is the uncertainty on a burette?

• 0.05cm 3

When do you use the 2 indicators?

• For weak acid and strong base use phenolphthalein

• For strong acid and weak base use methyl orange

Why should there be no air bubbles in your burette?

• Air bubbles take up space that should be filled with solution

• Causing inaccurate volume readings

What is the analyte and what’s the titrant ?

• Analyte=unknown solution

• Titrant = known solution