Method
First, you need to get a pipette and measure out 25.0cm3 of water and put it into a conical flask
- Then you need to weigh out 1.000g of sodium carbonate and dissolve it in the water, stirring for 10 seconds so results are comparable.
- Filter out the excess.
- You then need to get a burette and fill it with soap over the zero mark and then open the tap so it goes back to zero with the meniscus on the mark.
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Put the conical flask under the burette and put in 1.0cm3 of soap solution into the water, put the bung on and shake it for 10 seconds, again to make the results comparable.
- Repeat step 5 until a permanent lather is created, at which point, you know the water has been softened. Record the volume of soap you need to create this lather.
- Repeat this experiment except each time, instead of putting just 1g of sodium carbonate in the water, put 2.000g, then 3.000g, then 4.000g etc. Do this until you get up to 6.000g of sodium carbonate then stop. You also need to repeat the experiment two or three times to avoid rogue results, which could be misleading and out of proportion to the other results.
The key factors in this experiment are:
- Amount of sodium carbonate-change
- Amount of water-constant
- Concentration of soap solution-controllable & variable
- Water type (source) / hardness- controllable & variable
- Temperature-uncontrollable & variable
- Shaking intensity-controllable to a certain degree
Reactions and equations
The calcium and ions in the water and the magnesium ions react with (sodium) carbonate ions.
Calcium ions + Carbonate ions Calcium Carbonate
(From hard water) + (From sodium
Carbonate)
Ca2+ (aq) + CO32- (aq) CaCO3 (s)
Another name for sodium carbonate is washing soda, because it was used for washing up when all of it was done using soap. This method of softening is called precipitation. The sodium carbonate removes the calcium ions from the water as a precipitate of calcium carbonate.
Calcium ions + Stearate ions Calcium Stearate
(From hard water) + (From soap) (scum)
Ca2+(aq) + 2St-(aq) CaSt2(s)
Another way of removing the hardness from the water is to add soap. Sodium stearate is the soap we are going to use since it is quite common in soap. Sodium stearate dissolves in water, but calcium stearate is insoluble. So when you add the soap to the hard water, which possesses calcium ions, calcium stearate (the precipitate) forms. This is scum.
The equations above are the ionic equations, which only include the ions that are reacting, and leave out the “spectator” ions. The full equations are shown below, which include the “spectator” ions.
Sodium Carbonate + Calcium Chloride Sodium Chloride + Calcium Carbonate
Na2Co3 + CaCl2 2NaCl + CaCo3
Sodium Stearate + Calcium Chloride Sodium Chloride + Calcium Stearate
2NaSt + CaCl2 2NaCl + CaSt2
To make results as accurate as possible, I will, use a burette and pipette, which are very precise measuring, instruments to measure volumes of liquid. The weighing scale is also very precise and I will take readings up to three decimal places. I will also use the average mass and volume of soap and sodium carbonate. Below is a sketch graph prediction, which is what I think is going to happen in this experiment.
Preliminary Experiments
These are preliminary results, which were experiments I did earlier on.
The above table (with the exception of the last two results) shows how much soap was needed to create a permanent lather without sodium carbonate. When we did use sodium carbonate, (0.5000g) the water needed 4.0cm3 of soap solution to create a permanent lather and when we added 2.000g of sodium carbonate it only needed 3.0cm3 of soap solution to create a permanent lather. This shows that the more sodium carbonate you add, the less soap is needed, which means the water is softer.
Sketch Graph Prediction
Volume of soap
(cm3)
Mass of Sodium Carbonate (g)
In effect, this graph shows that the higher the amount of sodium carbonate in the water, the less soap needed to create a permanent lather. This theoretically works because the sodium carbonate softens the water by removing the calcium ions which cause the hardness and the more you add, the softer the water gets, which means that it is easier to create a permanent lather which is what the sketch graph shows.
The aim of this experiment is to investigate the effect of sodium carbonate on hard water and my prediction is that sodium carbonate will soften the water, which makes it easier for the soap to create a permanent lather.
