Acid or Base? Investigation

Acid or Base?
Aim:

To check different solutions electrolyte strength and seeing if the solution is an acid, base or neutral.

Equipment:

• test tubes
• beakers

0.100 mol L-1 of the following solutions:

• ammonium chloride
• ammonium acetate
• potassium nitrate
• sodium carbonate
• sodium acetate
• sodium bicarbonate
• sodium sulfate
• hydrochloric acid
• sodium hydroxide
• acetic acid
• limewater
• DC power source
• 2 electrical conducting metal rods
• ammeter
• pH indicator

Method:

1. place 10 ml of each solution in separate test tubes
2. place 3 drops of the pH indicator in each of the test tubes
3. mix every test tube gently
4. leave the test tubes to rest for a couple of minutes
5. observe the colour of the indicator
6. compare the colour to the pH table
7. record the data
8. place 50 ml of every solution in separate beakers
9. connect the DC power source so that positive and negative create a complete circuit with the ammeter and the solution
10. place the rods inside on beaker on the edges so that the rods don’t touch each other
11. turn on power source and read the value on the ammeter
12. record the data from the ammeter
13. clean and dry rod before placing it in the next beaker

Safety Tips:

• have safety glasses on at all times
• have the DC voltage at 6V
• do not touch the solutions
• do not drink the solutions
• do not directly inhale the solutions
• wash hands if solution spills on you
• tell teacher ASAP
• do not touch both the rods together as they will spark
• if the ammeter indicates a reading too far to the right, break the power source

Observations and Results:

Solution	pH Level	Acid or Base	Electrolyte Strength in mA
Ammonium Chloride	6	Weak Acid	30
Ammonium Acetate	7	Neutral	25
Potassium Nitrate	7	Neutral	30
Sodium Carbonate	10	Base	40
Sodium Acetate	8 - 9	Weak Base	15
Sodium Bicarbonate	9 - 10	Base	20
Sodium Sulfate	8	Weak Base	35
Hydrochloric Acid	2	Strong Acid	150
Sodium Hydroxide	11	Strong Base	70
Acetic Acid	3 - 4	Weak Acid	5
Limewater	11	Strong Base	20

Discussion:

From the results table above we can see that stronger bases and acids are better electrical conductors. We know this as the strong bases and acids completely ionise. Therefore, creating a passage for the electricity to move through. Also from the table we can see that the weaker bases and acids are not as good as the strong bases and acids in conducting electricity. This is because the weaker bases and acids only partially ionises. This means that the solution has some ions but most of it still stays in molecular form. As there are much less ions to carry the electrical energy, means that it is not as good as a strong base or acid. For example in a solution of hydrochloric acid, it completely ionises to hydrogen ions and chloride ions.

HCl → H+ + Cl-

However in a acetic acid solution only some of the molecules ionise.

CH3COOH ⇆ H+ + CH3COO-

In a 1 mole per litre situation, the hydrochloric acid completely ionises meaning that the whole 1 mole of hydrochloric acid become hydrogen and chloride ions. However, for acetic acid in the same situation, only 0.004 mole of it ionises into hydrogen and acetate ions. The difference between the 1 mole and 0.004 mole means that the 1 mole which is the hydrochloric acid is a better electrical conductor.

Also from the results we can see that some neutral solutions conduct electricity. Because a solution is neutral does not mean that it will not conduct. As both the neutral solutions ionise, it allows the electricity to flow through. This means that for the solution to ionise it should be either a strong base, strong acid or an ionic compound.

A problem within the results is the electrolyte strength for limewater. From the indicator and formula it has to be a strong base. However its conductivity showed to be weaker than most weak bases. This is probably because of error in the experiment while test were being conducted. It should have the same electrolyte strength as sodium hydroxide.

Another problem within this experiment was the supply of the pH indicator table. It did not cover the full range of pH levels. For example, the once the pH indicator was added to the hydrochloric acid, it was more red compared to the lowest pH level of the table which was 3. For this reason this created a small confusion because the acetic acid had a reading of 3 which seemed to be a strong acid as it was right at the bottom of the pH table.

Conclusion:

To conclude, were able to get the electrolyte strength and pH level of each solution with the aid of a DC power source and a pH indicator. The results above are quite reliable with a few exceptions as they were all tested twice. Assumptions such as contamination will have to be taken into consideration as it is practically impossible to not contaminate a solution as some of the solution may not wash of the rods.