Because of this, I predict the rate that milk coagulates will increase proportionally to the increase in calcium chloride concentration, until the point where the optimum amount of calcium chloride had been added, at which point the rate that milk coagulates would no longer increase. This would be represented on a graph by a proportional diagonal line which would then level off.
The reason for my prediction is the fact that the higher the calcium concentration, the greater the ionic strength, destabilising the milk and bringing about coagulation. The +2 (Ca2+) charge on the calcium allows the coagulation of milk. This means that the substrate, milk, can bind more easily when the concentration of calcium ions is higher. The higher the charge, the faster the irreversible coagulation process occurs.
To summarise, the higher the calcium chloride concentration the faster flecks of curd will appear.
Preliminary Tests
Preliminary tests must be carried out to ensure that the right concentrations are being used to give visible and fair results. They would also ensure that the volumes and masses of substrates being used give good results.
Method:
IV: Concentration of calcium ions
DV: Rate of Coagulation of the milk
Constants: Temperature, PH, Sodium concentration, Concentrations of the substrate
After the successful conclusion of the Preliminary Tests, I would use from 0.0 mol to 1.00 mol calcium chloride. 0.00 mol is made up 2cm3 of distilled water with no calcium chloride and would be my control, essential to prove that the reaction would not just happen normally. I would make up different concentrations of calcium chloride by adding water to each amount of calcium chloride (0.00mol would be just water, 0.20mol would combine 0.4cm3 calcium chloride with 1.6cm3 of water and so on with all the solutions) resulting in 6 levels of concentration.
I would test each concentration 3 times. I would then take the first 6 test tubes and add 10cm3 of milk. To each of these I would add a solution of 1.0 mol dm-3 of sodium citrate in order to get rid of all calcium ions that are already present.
I would then put all the test tubes in a water bath at 37°C to ensure a constant body temperature, before adding 1cm3 of rennin and the calcium chloride solutions. With a pipette, I would immediately put three drops of each concentration onto a slide and, observing under a microscope, log in the results table how long it takes for curd to start to appear.
Fair Test:
The most important factor in ensuring a fair test is to make sure that there is no change in those aspects that should remain constant.
Temperature: should be kept at 37°C as this is near the optimum temperature when there are the most collisions with the substrate and the enzymes active site. (Rennin works most effectively at 40°C, but a small increase in temperature beyond this could result in the enzyme becoming denatured.)
PH: during the experiment the PH is to be kept at 7 as it is neutral. (The optimum PH for rennin is 1 or 2, but as long as the PH is constant the experiment would be fair.)
Substrate Concentration: must be constant to ensure that each time there is equal chance for the substrate to come into contact with the enzymes active site.
Sodium Citrate Solution Concentration: must be constant – if a very small amount was added to one sample then it would be possible for not all the calcium ions to be removed, affecting the results.
Reliability:
To make the test as reliable as possible, and to get the most accurate results, I would repeat the test with each concentration of calcium ions three times. To plot a graph I would take the mean average rate for each concentration (add the results and divide by 3, the number of tests for each concentration). By doing this my results should be reliable. If any individual result varies greatly from the average, an anomaly may have occurred, and I would repeat the test until consistent results were achieved.
Results/precision:
Results would be measured in seconds to 2 decimal places, as this is fine enough to give an accurate result while being possible to measure.
Results chart:
I would then plot these results onto a line graph so that I could more easily see if there was a relationship between the concentration of calcium chloride and time taken for flecks of curd to appear.
Risk assessment:
To conduct the experiment as safely as possible everyone involved would wear goggles at all times to avoid any irritant substance getting into anyone’s eyes. In addition, all long hair must be tied back so not to get in the way, any spillages must be wiped up as soon as possible so that they are not later rubbed upon the skin, and any substance that dose make contact must be washed immediatelys.
Hazard Cards:
Number 19: calcium chloride
IRRITANT, dangerous with water, wash off skin
References:
