How does the amount of dissolved NaCl in water effect the volume of one drop? Aim: This experiment plans to measure the volume of one drop of water and compare it the volume of one drop of sodium chloride solution. What will be attempted by this experiment is to measure the volume of one drop of distilled water by measuring a control and comparing it the volume of one drop of distilled water with dissolved NaCl. This will be done by using a burette for dropping the distilled water and a electrolyte solution. Hypothesis: I hypothesise that the volume of one drop of water will decrease as the concentration of NaCl increases.
I believe this is due to the type of intermolecular bonding present and the different densities of salty and pure water. Water is held together by the strongest intermolecular force called hydrogen bonding. This bonding is then replaced by ion-dipole when salt is dissolved in the water which is a weaker intermolecular force compared to hydrogen bonding. “Generally speaking, Hydrogen bonding is stronger (20-40 KJ/mol) than ion-dipole (10-20 KJ/mol)” (“Chemicalforums”) . The water is then not held together as tightly and less force is needed to separate one drop from the main body of water. It would therefore be expected that the volume of the drop would be less as the gravitational force on a substance is directly proportional to its mass, shown by the equation below . F=(G〖m_1 m〗_(2 ))/r^2
m_1=mass of object 1. Which in this case is constant as it refers to the mass of the earth. m_2=mass of object 2. Which is the mass of the drop r^2= the distance between the objects.
F= gravitational force
Therefore if the force to separate the water is less the gravitational force needed for a drop of water to fall would be less, this then means the mass of the drop would then be less as all other variables are kept constant. Also due to the fact that salty water is more dense than pure water it would mean that the volume of one drop of salty needed to overcome intermolecular forces would be less as salty water has a higher mass per volume ratio. Apparatus used
Apparatus Range Accuracy
Burette 1-50 ml ± 0.01cm³
Electronic Scale 0.01-600 g± 0.01 g
Measuring cylinder 5-50 ml± 0.25 cm³
Funnel with funnel paper
Independent VariableDependent Variable
Concentration of NaCl will be altered by changing the amount of NaCl (g) added to 50 cm³ of distilled water.The volume of one drop of water measured in cm³. Control Variables
How will it be controlled?Why will it be controlled? Same equipment usedBy using the same burette To ensure that the equipment does not change or effect the volume of the drops of water. Different burettes can have slightly different drop sizes and to minimize that change the same burette should be used for all tests. Temperature By using water baths to control the temperature of the water added to the burette. Temperature may have its own effect on the drop sizes of water and so it should be kept constant to ensure that all changes in volume of drop sizes is due to the independent variable. Type of Salt Use the same type of salt in all trials. To ensure that different impurities in the salt that may dissolve in to the water do not affect the volume of one drop the same type of salt should be used. Refined iodized table salt is preferred as it is 99.5% pure and the amount of impurities is minimum. However any type of salt can be used as long as it is kept constant. Type of water Always use distilled water.Water from different sources may have impurities which could affect the total mass of the water and could affect the volume of one drop of water. Using distilled water would make sure no impurities would affect the volume of one drop.
Measure out 30 ml of distilled water using a graduated cylinder into a 100ml beaker
Add 5 grams of salt to the beaker in step 1 and stir
Prepare 30ml solutions following step 1 and 2 with 0, 10, 15, and 20 grams of salt
Add the salt solution to a burette and record initial reading
Place a beaker on top of an electronic scale and tare
Open the burette to a point where water drops at a slow rate into the beaker
Count the amount of drops until the mass of the water in the beaker reaches 5 grams and take the final reading from the burette
Repeat with the different salt solution prepared in step 3
Repeat from step 1, two more time so an average can be calculated. Calculations
(Final Reading-Initial Reading)/(The amount of drops )=The volume of one drop (cm³)
Albert. “Ion Dipole Dipole vs. Hydrogen Bonding.” Chemicalforums.com. Mitch André Garcia, 23 Sept. 2011. Web. 27 Jan. 2013. . Chang, Muncel. “Salt Water vs. Fresh Water.” About.com. N.p., 19 Sept. 2000. Web. 27 Jan. 2013.