Determining pH of identical strong and weak solutions
Uploaded by sukashini on Mar 16, 2004
Experiment: Determining pH of identical strong and weak solutions
Date: 31/10/03
Aim: Plan and perform a first-hand investigation to measure the pH of identical concentrations of strong and weak acids.
Equipment:
· Deionised water (H2O) · Tartaric Acid (C4H6O6)
· Citric Acid (C6H8O7) · Sulfuric Acid (H2SO4)
· Acetic Acid (CH3COOH) · Hydrochloric Acid (HCl)
· Ammonium Chloride (NH4Cl) · Tap Water (H2O)
· Nitric Acid (HNO3) · Probe
· Ferric chloride (FeCl3) · Wash bottle
· Sodium Chloride in tap water (NaCl) · Beakers
· Sodium Chloride in deionised water (NaCl) · Data logger
Method:
1) Make sure there is an equal molarity of each substance. In this case 0.1 moles/litre. Therefore there are 0.1 moles of each substance in solution.
2) Place each of the substances in a beaker.
3) Calibrate the data logger by using buffer zones of pH 4 and 10.
4) Place the probe into one beaker and click the start button on the data logger. Record the pH level of the substance.
5) Remove the probe and wash thoroughly using the wash bottle.
6) Repeat for all the other substances and record their pH’s.
7) Determine which solutions are strong and which are weak.
Results:
Substance pH Acidic, Basic or Neutral Strong or Weak
Citric Acid (C6H8O7) 2.4 Acidic Weak
Acetic Acid (CH3COOH) 3.0 Acidic Weak
Tartaric Acid (C4H6O6) 2.3 Acidic Weak
Nitric Acid (HNO3) 1.5 Acidic Strong
Hydrochloric Acid (HCl) 1.5 Acidic Strong
Sulfuric Acid (H2SO4) 1.4 Acidic Strong
Ferric chloride (FeCl3) 1.5 Acidic Strong
Ammonium Chloride (NH4Cl) 7.0 Neutral -
Sodium Chloride in deionised water (NaCl) 5.6 Acidic Very Weak
Sodium Chloride in tap water (NaCl) 7.2 Neutral -
Deionised water (H2O) 6.0 Neutral -
Tap Water (H2O) 7.0 Neutral -
Discussion:
By observing our results it can be seen that even though all solutions have the same concentration they can still be strong or week. It can be seen that all organic acids eg. Acetic acid, Citric acid and Tartaric acid are all weak acids whereas all inorganic acids such as Sulfuric acid, Nitric acid and Hydrochloric acids were strong. It was also discovered that ionic molecules could be acidic eg. Ferric Chloride. In the past it has been said that all ionic substances tend to be more neutral than acidic or basic. This has all been changed now and we have the Brønsted Lowry concept. With the Brønsted-Lowry concept we usually refer to a hydrogen ion as a proton. That is because a proton is all that is left when a hydrogen atom loses an electron to become an ion. Brønsted and Lowry independently came up with the idea that an acid is an acid because it provides or donates a proton to something else. When an acid reacts, the proton is transferred from one chemical to another. Note that in order for an acid to act like an acid, there needs to be something for it to react with. There needs to be something to take...