Calculating m1- the mass of sodium carbonate needed, m1.
To find the mass of sodium carbonate (Na2CO3) we need to find its molecular mass.
To calculate the molecular mass of Sodium Carbonate = Na2CO3
Making a 0.1 M (mol dm-3) solution of sodium carbonate in 1000 cm3
A 1 M (mol dm-3) solution of sodium carbonate (Na2CO3 ) means: -106 g of sodium carbonate is dissolved in a cubic decimetre (1000 cm3).
To make 0.1 M, we need to dissolve 10.6g of sodium carbonate in 1000 cm3 of distilled water.
We did not use 1000cm3 of water we used 250cm3 of water, so to make 0.1 M, we need to dissolve 10.6/4=2.65g of sodium carbonate in 250 cm3 of distilled water.
I now have a sodium carbonate solution of 0.1 m.
Results
I have prepared in this experiment a standard solution of 0.1mol dm-3 of sodium carbonate. I made 250cm3 of sodium carbonate, which was then used in my titration experiment to work out the concentration of hydrochloric acid.
Experiment2
Finding out the concentration of hydrochloric acid by neutralising the standard solution of 0.1 M sodium carbonate prepared in experiment 1.
Titrations are quantitative (they can be used to work out the exact concentration of a chemical).
When chemists analyse samples of substances, they are interested in:
What chemicals are present in the sample, and carry out a qualitative analysis
The concentrations of chemicals in the sample, and carry out a quantitative analysis.
Aim
To calculate the unknown concentration of hydrochloric acid by carrying out a titration
Equation
The equation for this reaction is:
Acid + base ⇨ salt + water + carbon dioxide
Hydrochloric + sodium ⇨ sodium + water + carbon
acid + carbonate chloride dioxide
2HCl + Na2CO3 ⇨ 2NaCl + H2O + CO2
2 moles of hydrochloric acid (N1) react with 1 mole of sodium carbonate (N2)
Safety
Wear goggles
Hydrochloric acid is corrosive
Sodium carbonate is irritant.
Volumetric analysis
Volumetric analysis is used to find the concentration of an unknown solution. The method uses a titration in which an acid is added to a base, until there is just enough of the acid to neutralise the base. An indicator tells when exactly the right volume of solution has been added to achieve neutralisation. When the concentration of the acidic and basic complexes of the indicator is equal, the indicator is said to be at its end point. The amount of acid it takes to neutralise the base is recorded.
The concentrations of one of the two solutions must be known, and the volumes of both must be measured.
You can use a standard solution of a base to find out the concentration of a solution of an acid. You have to find out what volume of the acid solution of unknown concentration is needed to neutralise a known volume, usually 25.0cm3, of the standard solution of a base.
Method
Use a pipette to deliver 25.0cm3 (V2) of the alkali solution into a clean conical flask Add a few drops of indicator. (The alkali solution in this experiment is the standard solution you made up of 0.1M Sodium Carbonate (M2) )
Wash the burette with a little of the acid solution. Allow the solution to run into the tip of the burette. Read the burette (from the bottom of the meniscus) and record this ‘initial volume of acid’ in the results table)
Arrange the apparatus as shown on page 6. Run the acid solution from the burette drop by drop. Use your left hand to open the tap and your right hand to swirl the conical flask (unless you are left-handed). Stop when the indicator just changes colour. This is the 'end-point' of the titration.
Read the burette again and record this ‘final volume of acid’ in the results table. Subtract the initial value from the final value to find the volume of acid used. This 'titre' is the volume of acid needed to neutralise 25.0cm3 of alkali.
Repeat the titration at least 2 more times. Obtain an average titre. From this volume, you can calculate the unknown concentration of acid (M1)by rearranging the formula
We use volumetric analysis to find out the concentration of a solution that is un-known.
The name of the method used to add acid to a base is titration.
We are trying to find the concentration of hydrochloric acid.
The name of the standard solution we made in the first experiment is sodium carbonate.
We are adding 25cm3 of alkali to the conical flask in step1.
The alkali is 0.1 m concentration.
We know this because we made the solution ourselves.
Adding an acid to a base to make a salt + water (+ carbon dioxide) is an example of a neutralisation reaction.
We need to use an indicator to find out the exact point when the solution is at neutral.
When an indicator reaches its end, this means the indicator can no longer show the acidity of the solution.
What must be known in order to carry out volumetric analysis?
Methyl Orange~ this is a more accurate way of recording pH rather than using a universal indicator.
I need to calculate the concentration of hydrochloric acid, by rearranging the formulae from:
(M1 x V1) / N1 = (M2 x V2) / N2
To:
(M1) = (M2 * V2) *N1/ (N2 * V1)
M1=concentration of hydrochloric acid (HCl)
M2=concentration of sodium carbonate (Na2CO3)
V1=average volume of acid used
V2=volume of Na2CO3 used
N1= number of moles of hydrochloric acid used in reaction
N2= number of moles of sodium carbonate used in reaction
Results
M1=concentration of hydrochloric acid (HCl) =
M2=concentration of sodium carbonate (Na2CO3) = 0.1 M
V1=average volume of acid used = 25.4333cm3
V2=volume of Na2CO3 used = 25cm3
N1= number of moles of hydrochloric acid used in reaction
= 2
N2= number of moles of sodium hydroxide used in reaction
= 1
(M1) = (M2 * V2) * (N1/ (N2 * V1))
M1= (0.1*25) * (2 / (1*25.43))
M1= (2.5) * (2 / (25.43))
M1= (2.5) * (2 / (25.43))
M1= (2.5) * (0.07864)
M1= 2.5*0.07864
M1=0.1966 Mol dm-3
M1=0.2 Mol dm-3
The unknown concentration of the hydrochloric acid is 0.2-mol dm-3
Evaluation
The unknown concentration of hydrochloric acid was 0.2-mol dm-3. The accuracy of my calculation was quite good, as my predictions never went above 25.6 (first 25.6, second 25.4, third 25.3).
Problems with experiment
For some of the results I did not turn off the tape at the exact time that it changed colour, which would make it not a far test.
There were some problems that were not my fault; such as I could not turn off the tape some times, which made it difficult to get a correct reading.
I also may not have filled the burette to exactly 50cm3, which means that it would have taken more solution to get to the correct reading.
When I put the 50cm3 of solution into the burette I could not clearly see the line, and I may have not read off the reading from the meniscus line.
I did not stop pouring out the solution at exactly the same time it changed colour, and so this would make readings out.
To get even better results I could do more of the same experiment and overall get the class average.
A known mass of the primary standard is dissolved in distilled water……
…… and the volume of the solution is made up to a known volume.
Use a pipette filler to suck up the liquid into the pipette
Allow liquid to run slowly down to the graduation mark
Run the liquid into a conical flask
Touch the side of the flask with the tip of the pipette.
by
keesha_andre (student)
