Volumetric analysis

Prepared by;Punia TurimanFor Chemistry HL Year 1 2011/13

Solution

A homogeneous mixture formed from a solute and a solvent.

Solute : substance that dissolves in solvent

Solvent : liquid present in excess in which dispersion occurs

How to express concentration?

gdm-3 Mass of solute in g1 dm3 of solution

e.g. Calc. the conc. of a

0.0400 moldm-3 solution of sodium

carbonate, Na2CO3, in gdm-3.

Moldm-3

No.of mole of solute1 dm3 of solution

e.gCalc. the molarity of 0.4 moles of NaOH in

500 cm3 of water.

How to prepare a solution? Question : Calculate the mass of NaOH needed to

prepare a solution of 250.0 cm3 of 0.500 M solution?

Answer : n = mV/1000 = 250.0 (0.5000) = 0.1250 mol 1000 Mass of NaOH = n x Mr = 0.1250 x (22.99 + 16.00 + 1.01)

= 4.999g

Question on molarity

A solution is made containing 2.38g of MgCl2

in 500 cm3 of solution.

a) What is the conc. of MgCl2 in this solution?

b) What is the conc. of the chloride in this solution?

Mixing two solutions

100cm3

of 0.500M HCl

400cm3 of 2.00M HCl

Newconc.of HCl??

Dilution

100 cm3

of 0.1moldm-

3 NaOH

Diluted in 400 cm3

of pure water

New conc.??

Titration

A titration is a lab procedure where a measured volume of one solution (burette) is added to a known volume & concentration (flask) of another solution until the reaction is complete.

Standard solution

A standard is a solution of precisely known concentration

It must be available in a highly pure state

It must be stable in air It must dissolve easily in water It should have a fairly high relative

molecular wt It should under go a complete and

rapid reaction

Question

25 cm3 of NaOH aq. required 28 cm3 of 1M H2SO4 aq. for complete neutralization.

Write a balanced eqn. for the rxn. How many moles of the acid were used to neutralize

the NaOH? How many moles of the alkali were neutralized? How many moles of the alkali are there in 25 cm3 of

solution? What is the molarity of the sodium hydroxide?

Enrichment question

27.82g of hydrated sodium carbonate crystals, Na2CO3.xH2O were dissolved in water and made up to 1.000 dm3. 25.00cm3 of this solution were neutralized by 48.80 cm3 of HCl of concentration 0.1000 moldm-3.

Write eqn. btw. Na2CO3 and HCl Calc. the conc.of Na2CO3 neutralized by HCl Determine mass of Na2CO3 neutralized by HCl and

hence the mass of Na2CO3 present in 1.000dm3 of soln. Calc. mass of water in the hydrated crystal and hence

fine the value of x. (IBO2004)

Try ALL questions. Practice makes

perfect.