Chapter 9C - Volumetric Analysis

Question 1

What is volumetric analysis?

Answer 1

• quantitative technique
• involves measuring volume of a solution of known concentration to determine the concentration of the analyte
• titration process

Question 2

What are the steps to volumetric analysis?

Answer 2

1. Preperation of a standard solution using a primary standard
2. Titration b/w standard solution & solution to be standardised
3. Titration b/w standardised solution & solution being analysed
4. Stochiometric calculations to determine the concentration of the solution being analysed

Question 3

Volumetric flask

Answer 3

• used for measuring a fixed volume (commonly 100 or 250mL)
• used to prepare a standard solution (known concentration)
• rinse with distilled water

Question 4

Pipette

Answer 4

• used for measuring a fixed volume (aliquot)
• commonly 20 or 25mL
• used to transfer a known volume of the solution being analysed to the conical flask
• rinse with the solution it is to contain

Question 5

Burette

Answer 5

• measure a variable volume (titre)
• holds up to 50mL
• usually contains the standard solution (known concentration)
• rinse w/ the solution it is to contain

Question 6

Concentration

Answer 6

• amount of solute in a specified volume of solvent/solution

Question 7

Conical flask

Answer 7

• used for holding the aliquot delivered from the pipette
• rinse w/ distilled water

Question 8

Molarity

Answer 8

• amount of substance (mol) per volume of solution (L)

Question 9

Percentage by mass

Answer 9

• %m/m
• mass of component (g) per 100g sample/solution

Question 10

Percentage by volume

Answer 10

• %v/v
• volume of solute (mL) per 100mL solution

Question 11

Percentage mass/volume

Answer 11

• %m/v
• mass of solute (g) per 100mL solution

Question 12

Parts per million (ppm)

Answer 12

• mass of solute (mg) per kg of solution
• mass of solute (mg) per L of solution

Question 13

What is a standard solution?

Answer 13

• solution w/ accurately known concentration
• prepared in volumetric flask
• prepared using a primary standard

Question 14

What is a primary standard?

Answer 14

• available in pure form
• has a known formula
• is stable enough to not react w/ atmosphere or decompose over time
• reasonably high molar mass to minimise weighting errors
• inexpensive

Question 15

Standardisation

Answer 15

A standard solution is used to standardise another solution

Question 16

What is a titration?

Answer 16

Involves adding one solution (oxidant/reductant) to another solution (oxidant/reductant) until the reaction b/w them is complete

Question 17

Equivalence Point

Answer 17

Point at which the ratio of oxidising agent to reducing agent present is equivalent to the stochiometric mole ratios in the equation

Question 18

End point

Answer 18

When the reaction solution changes colour (due to the indicator or one of the chemicals involved in the redox reaction)

Question 19

What are steps of the titration process?

Answer 19

1. Rinse & fill a pipette w/ the analyte. Transfer aliquot to a conical flask
2. Add several drops of a suitable indicator to the conical flask if the reaction is not self indicating
3. Rinse & fill a burette w/ standard solution. Record initial burette reading
4. Titrate analyte w/ known solution until endpoint reached. Record final burette reading and titre
5. Repeat until 3 concordant titres obtained

Question 20

What are concordant titres?

Answer 20

• 0.1mL b/w lowest & highest titre
• increases reliability/precision
• minimises effect of random errors

Question 21

What type of experimental errors are associated with volumetric analysis?

Answer 21

• rinsing errors
• indicator errors

Question 22

Why do rinsing errors need to be considered?

Answer 22

• lead to overestimations or underestimations of the final analyte concentration

Question 23

What happens if the pipette is rinsed with water?

Answer 23

• decrease reactant amount (in mol) in the aliquot delivered to the conical flask
• decreases size of titre
• underestimated concentration

Question 24

What happens if the pipette is rinsed with a more concentrated solution?

Answer 24

• increase reactant amount (in mol) in the aliquot delivered to the conical flask
• increases size of titre
• overestimated concentration

Question 25

What happens if the burette is rinsed with water?

Answer 25

* decrease concentration of the reactant in the burette * increase size of titre required to react w/ analyte * overestimated concentration

Question 26

What happens if the burette is rinsed with a more concentrated solution?

Answer 26

* increase concentration of the reactant in the burette * decrease size of titre required to react w/ analyte * underestimated concentration

Question 27

What happens if the conical flask is rinsed with the solution in the aliquot?

Answer 27

* increase the amount (mol) of reactant in the conical flask * increase the size of the titre * overestimated concentration

Question 28

What happens if the indicator end point is missed?

Answer 28

* Size of titre will be bigger than it should be * overestimated concentration