Lab 4

Question 1

What was this lab about?

Answer 1

Quantitative volumetric analysis - the acetic acid content of vinegar.

Question 2

Why is chemical analysis important?

Answer 2

Food, pharmaceuticals, chemical manufacturing, pollution control, require routine product analysis.

Question 3

What is titration and what did we titrate?

Answer 3

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.

Question 4

What is NaOH?

Answer 4

Sodium Hydroxide

Question 5

What is an acid?

Answer 5

A proton donor.

Question 6

What is a base?

Answer 6

A proton acceptor.

Question 7

What defines an acid-base reaction?

Answer 7

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.

Question 8

What is a neutralization reaction?

Answer 8

Another name for an acid-base reaction.

Question 9

What are spectator ions?

Answer 9

Ions that do not participate in the reaction.

Question 10

What is the net ionic equation?

Answer 10

The equation derived by writing a complete ionic equation and then elimination the spectator ions.

Question 11

What is the equivalence point?

Answer 11

When all of the acetic acid present initially in the vinegar had been consumed by reaction with the added base, the NaOH.

Question 12

What is phenolphthalein?

Answer 12

An acid-base indicator, colourless in acidic solution and pink in basic solution.

Question 13

What is an acidic solution?

Answer 13

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.

Question 14

What is a basic solution?

Answer 14

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.

Question 15

What is a primary standard?

Answer 15

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.

Question 16

What is benzoic acid?

Answer 16

C6H5COOH. Ring of C6, H5, with an attached carboxyl group.

Question 17

What is phthalic acid?

Answer 17

KC8H5O4. Ring with two carboxyl groups.

Question 18

Why is it difficult to weigh out an exact weight of NaOH?

Answer 18

NaOH rapidly absorbs water vapour and CO2 from the atmosphere.

Question 19

How do we weigh out NaOH?

Answer 19

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

Question 20

How to find moles of NaOH.

Answer 20

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).

Question 21

How is vinegar produced?

Answer 21

By bacterial oxidation of a dilute aqueous solution of ethanol (ethyl alcohol).

Question 22

What is the acetic acid concentration of regular vinegar and what is the concentration of pickling vinegar?

Answer 22

5% and 7%, respectively, by volume in water.

Question 23

What is the chemical formula for acetic acid?

Answer 23

CH3COOH

Question 24

What is the overall reaction for the titration of sodium hydroxide with acetic acid?

Answer 24

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.

Question 25

What is the equation for Molarity?

Answer 25

M = mol/V
mol = M*V
V = mole/M

Question 26

How do you find the mass (g) of acetic acid?

Answer 26

Mass (g) = moles x molar mass (in g/mol)

Question 27

How do you find the mass of the vinegar?

Answer 27

Assume that its density is 1.00 g/mL. d = m/v

Question 28

How do you find percent by mass?

Answer 28

Mass of acetic acid/mass of vinegar * 100

Question 29

What is an aliquot?

Answer 29

A portion of a larger whole, especially a sample taken for chemical analysis or other treatment.

Question 30

How do you calculate percent difference?

Answer 30

larger value- smaller value/smaller value * 100

Question 31

How do you calculate average?

Answer 31

All amounts added divided by the number of amounts.

Question 32

How do you find absolute error?

Answer 32

|measured value - true value|

Question 33

How do you find percent error?

Answer 33

Absolute error / true value x 100

Question 34

What is acceptable agreement?

Answer 34

When trials are within 1% of each other. When multiple trials are done, one value is usually closer to the true value than the others. Instead of guessing which trial is closer to the unknown true value, taking the average of these values is a safer bet.

Question 35

What is precision?

Answer 35

The variability in the values of repeated measures.

Question 36

What is accuracy?

Answer 36

How close a measured value is to the true value.