1. An Introduction to Volumetric Analysis
Experiment 1
An Introduction to Volumetric Analysis
Chemistry Department UCC 1st Year Practicals

2. Objectives Quantitative experimental work
Gain experience with calculations involving mole quantities, reaction ratios, molar concentrations, and reaction equations
Preparation of standard solutions, and standardisation of solutions of unknown concentration

3. Experimental
Preparation of a standard solution of sodium carbonate [Na2CO3]
Titration of Na2CO3 solution with hydrochloric acid
Na2CO3 + 2HCl  2NaCl + H2O + CO2
Titration of a strong acid with a strong base
NaOH + HCl  NaCl + H2O
Titration of a weak acid with a strong base
CH3COOH + NaOH  CH3COONa + H2O

4. Introduction Acid + Base  Salt + Water Acids have pH values of <7
Bases have pH values of >7
pH 7 is neutral
For acid/base titrations, indicators are used that display different colours at acidic and basic pH values

5. Indicators
Indicators are organic chemicals that change colour as the pH of a solution changes
Above a certain pH value they have one colour, but have another colour when the pH is below that value
Allow for the accurate determination of end points of acid/base reactions

6. Indicators
pH < 7
colourless
pH > 7
pink

7. Titration Curves

8. Calculations Mass = No. of moles x molecular mass
Molar conc. = No. of moles ÷ volume
Units Mass g
Molar concentration mol/L
Molar mass g/mol
Volume L

9. Calculations eg: 1H2SO4 + 2NaOH  Na2SO4 + 2H2O
M = molar concentration of solution (mol/L)
V = volume of solution
n = no. of moles of acid/base consumed, obtained from balanced equation (in example above, n=1 for the acid and n=2 for the base

10. Titrations Make sure the tap is closed when filling the burette
Swirl flask constantly
Perform one rough followed by two accurate titrations for each part b,c,d
Add solution from the burette one drop at a time when approaching end point

11. Experiment 1A
Make up 500 mL of a standard solution of sodium carbonate
This will be used in part B in titration against the HCl solution
There are a number of techniques to ensure that the solution is made up accurately

12. Experiment 1B ? 2HCl + Na2CO3  2NaCl + H2O + CO2
acid
2HCl + Na2CO3  2NaCl + H2O + CO2
4.5 indicator used to determine the end point of the reaction
Colour change of blue to pink ?
Both M2 and V2 known
base 2 1
Obtained from the burette

13. Experiment 1C
Given solution of fixed [HCl], can use this to determine the concentration of a solution of NaOH
4.5 indicator used to determine end point
Colour change of blue to pink
HCl + NaOH  NaCl + H2O

14. Experiment 1D CH3COOH + NaOH  CH3COONa + H2O
Acetic acid is a weak acid
Weak acid so less base required
Phenolphthalein used as indicator
Colour change of pink to colourless

15. Report Experimental observations Balanced reaction equations
Titration results
Calculations
Answer questions in the manual