1.2 - Amount Of Substance Flashcards
In a titration question, what do you do if there are more than 2 concordant results?
Include them all.
What is the technique to doing back titrations?
There are always 2 equations. You’ll have an excess of something, let’s call it B, reacting with the thing you’re trying to find, A. Then you react what’s left of B with something else, C. You’re given C. Use stoichiometry to find the how much of the left over B reacted. You’ll also be given the original excess B. So you do original - left over to find how much of B reacted. Therefore, you can use that to find how much of A reacted.
Can you us pv = nrt to find moles of solid?
No. Only gas.
What is a standard solution?
Known concentration.
What effect would air bubbles in the burette have on the titre reading in a titration?
Larger titre reading.
What’s the benefit of using a conical flask compared to a beaker?
Easier to swirl mixture in conical flask without spilling the contents.
Why shouldn’t you use universal indicator?
Colour change is gradual. No specific end point.
What colours are phenolphthalein and methyl orange in acid and alkali?
Phenolphthalein is colourless in acid and pink in alkali.
Methyl orange is red in acid and yellow in alkali.
Why is actual yield usually lower than theoretical yield?
Reaction is incomplete. Reactants lost during transfer between containers. Some product escape as gas.
What’s the formula for atom economy.
Mr of desired product/ Mr of reactants
X 100
A waste tank has volume 25000. It’s full of phosphoric acid by adding phosphorus(v) oxide to water. A 25cm^3 sample of this solution required 21.2cm^3 of 0.5 mol dm^-3 sodium hydroxide solution for complete reaction. Calculate the mass in kg of phosphorus oxide that was added to the water in the waste tank.
H3PO4 + 3NaOH -> Na3PO4 + 3H2O
6H2O + P4O10 -> 4H3PO4
251kg
