Chemistry EEI – “The effect of propanol on the rate of solubility of potassium nitrate"
The relationship between solubility and temperature can be shown by a solubility curve. A solubility curve is a graphic representation of changing temperatures of the solubility of given substances in a certain solvent. Solubility measures how many grams of a substance which will dissolve in a certain volume of solution. It depends on the solute (in this case- potassium nitrate) and the solvent (propanol and water). Solubility can be measured in mass per volume which is how you calculate density.
On a solubility curve, the lines indicate the concentration of a saturated solution - the maximum amount of solute that will dissolve at that specific temperature. The molar concentration of the substance can also be calculated.
Solubility curves, like Figure 1. shown here, tell us what mass of solute will dissolve in 100g (or 100mL) of water over a range of temperatures.
Dissociation is when ionic compounds dissolve to produce ions (anions & cations) which are then separated from each other. Ionic compounds dissociate when they dissolve in water because the solution conducts electricity. Potassium Nitrate (KNO3) is a highly ionic compound and dissolves in water (polar solvent) to give potassium cations and nitrate anions, which are solubilised by water molecules (for potassium, the partially negatively charged oxygen atoms from water molecules stabilise the ion in aqueous solution, whereas for the nitrate anion, the partially positively charged hydrogen atoms from water stabilise it). The strong ionic bonds hold the compound in an ionic lattice which gives KNO3 its crystalline structure. The ionic bonds give KNO3 high melting and boiling temperatures. KNO3 is soluble in water, despite and the solubility is increased by heating to high temperatures. Potassium nitrate is a polar molecule where electrons are both lost and gained. One atom of oxygen gains an electron, while potassium and nitrogen lose an electron. Figure 1. Example of a solubility curve
The purpose of this experiment is to investigate the effect of different amounts of propanol which effect the solubility of potassium nitrate (KNO3), when placed in a solution of water and propanol.
Aim: To investigate how the solubility of potassium nitrate is affected by increasing amounts of propanol
Hypothesis: The highest amount of propanol placed in the solution will affect the rate of solubility of potassium nitrate by increasing it
Temperature of crystallisation
Apparatus & Materials Required:
Chemicals (including solutions)
· 6.5g potassium nitrate
· 2 x large test tubes
· 1 x Burette
· 1 x Boss head
· 1 x 250mL beaker
· 1 x electronic balance
· Bunsen burner
· Datalogger temperature probe
· Gauze mat
· Safety mat
Method: (change to...