Lab 4 Flashcards
(36 cards)
What was this lab about?
Quantitative volumetric analysis - the acetic acid content of vinegar.
Why is chemical analysis important?
Food, pharmaceuticals, chemical manufacturing, pollution control, require routine product analysis.
What is titration and what did we titrate?
A titration is a technique where a solution of known concentration is used to determine the concentration of an unknown solution. Typically, the titrant (the know solution) is added from a buret to a known quantity of the analyte (the unknown solution) until the reaction is complete. In this case, we titrated 2.00 ml of vinegar with about 23.00 ml of NaOH.
What is NaOH?
Sodium Hydroxide
What is an acid?
A proton donor.
What is a base?
A proton acceptor.
What defines an acid-base reaction?
A reaction which involved the transfer of protons from the acid to the base, producing a product called a salt. Many salts will be ionic compounds consisting of a cation derived from a base and an anion derived from an acid.
What is a neutralization reaction?
Another name for an acid-base reaction.
What are spectator ions?
Ions that do not participate in the reaction.
What is the net ionic equation?
The equation derived by writing a complete ionic equation and then elimination the spectator ions.
What is the equivalence point?
When all of the acetic acid present initially in the vinegar had been consumed by reaction with the added base, the NaOH.
What is phenolphthalein?
An acid-base indicator, colourless in acidic solution and pink in basic solution.
What is an acidic solution?
An acid is a substance that donates hydrogen ions. Because of this, when an acid is dissolved in water, the balance between hydrogen ions and hydroxide ions is shifted. Now there are more hydrogen ions than hydroxide ions in the solution. This kind of solution is acidic.
What is a basic solution?
A base is a substance that accepts hydrogen ions. When a base is dissolved in water, the balance between hydrogen ions and hydroxide ions shifts the opposite way. Because the base “soaks up” hydrogen ions, the result is a solution with more hydroxide ions than hydrogen ions. This kind of solution is alkaline.
What is a primary standard?
A solid that is very pure and very dry. It meets the specifications for purity of the National Bureau of Standards. Examples are benzoic acid or potassium hydrogen phthalate.
What is benzoic acid?
C6H5COOH. Ring of C6, H5, with an attached carboxyl group.
What is phthalic acid?
KC8H5O4. Ring with two carboxyl groups.
Why is it difficult to weigh out an exact weight of NaOH?
NaOH rapidly absorbs water vapour and CO2 from the atmosphere.
How do we weigh out NaOH?
Prepare aqueous solution of base that is approximately the concentration desired
Determine the volume of an aqueous solution of the base required to neutralize a known number of moles of an acid
Moles of acid come from volumetric primary standard
How to find moles of NaOH.
NaOH reacts with acid in 1:1 ratio. So, moles NaOH = moles acid. Moles acid = grams * (1/molar mass). Moles NaOH is equal to M*V, molarity * volume. So, (grams of acid/molar mass of acid) = (Molarity) * (volume).
How is vinegar produced?
By bacterial oxidation of a dilute aqueous solution of ethanol (ethyl alcohol).
What is the acetic acid concentration of regular vinegar and what is the concentration of pickling vinegar?
5% and 7%, respectively, by volume in water.
What is the chemical formula for acetic acid?
CH3COOH
What is the overall reaction for the titration of sodium hydroxide with acetic acid?
CH3COOH (aq) + NaOH (aq) –> CH3COO-Na+ (aq) + H2O (l)
or
acid + base –> salt + water
1:1 ratio, so at the equivalence point, the moles of acetic acid is equal to the moles of NaOH. The phenolphthalein indicates the equivalence point.
