An Investigation Into The Neutralisation Of Acids

Neutralisation is when you make a acidic or alkaline substance neutral by adding the other to it. Whatever the substance, when you neutralise it, a salt is always formed. I will be trying to find out the stronger out of a variety of Acids and place them into a rank order from strongest to weakest using neutralisation.

Research

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Acids is the name given to substances that have a pH value lower than 7. As the pH gets lower, the more acidic the substance gets. Acids react with most metals to produce hydrogen and form a salt. The salt forms because the metal takes the place of the hydrogen in the acid e.g. Sodium Nitrate.

Acids are caused by the amount of H+ (hydrogen) ions contained, the more H+ ions then the lower pH and the stronger the acid is. This is because there are more H+ ions to react. Different acids have different H+ concentrations so if you have two acids of the same concentration it does not mean they will be the same strength.

Alkalis refer to substances that have a pH over 7 and soluble in water. Alkalis are similar to acids but have OH- (hydroxide) ions instead.

Neutral substances have a pH of exactly 7. Distilled water is neutral.

Apparatus

I will need the following for my experiments:

* Beaker

* Test Tubes and Rack

* Datameter

o pH probe

o Temp. probe

* Universal Indicator

* Measuring Cylinder

* Stopwatch

* Goggles

Chemicals

The chemicals I will use in my experiment are as follows:

Acids- Sulphuric 1.0M H2SO4

Hydrochloric 1.0M HCl

Ethanoic 1.0M CH3COOH

Nitric 1.0M HNO3

Alkalis- Sodium Hydroxide 1.0M NaOH

Method

I will put 30cm3 of NaOH into a beaker, as this is a reasonable amount suitable to use in the laboratory, and record its starting temperature (should be room temperature) and pH and add a few drops of Universal Indicator so I can monitor the pH change visually. At intervals of 20 seconds, chosen to allow the acid and alkali enough time to react, I will add 5cm3 of an acid to the NaOH until the total acid added exceeds 30cm3. The reason I use 5cm3 is because that should be a small enough fraction of the total amount of NaOH so I can monitor its progress. For each addition of acid I will record the pH and temperature in a table.

Equations

Sulphuric

Sodium Hydroxide + Sulphuric Acid –> Sodium Sulphate + Water

2NaOH (aq) + H2SO4 (aq) –> Na2SO4 (aq) + 2H2O (l)

2Na+ + 2OH- +2H+ + SO42- –> 2Na+ + SO42- + 2H20

2OH- +2H+ –> 2H20

2 : 1 : 1 : 2

2NaOH (aq) + H2SO4 (aq) –> Na2SO4 (aq) + 2H2O (l)

15cm3 7.5cm3 7.5cm3 15cm3

0.015m 0.0075m 0.0075m 0.015m

Hydrochloric

Sodium Hydroxide + Hydrochloric Acid –> Sodium Chloride + Water

NaOH (aq) + HCl (aq) –> NaCl (aq) + H2O (l)

Na+ + OH- +H+ + Cl- –> Na+ + Cl- + H20

OH- +H+ –> H20

1 : 1 : 1 : 1

NaOH (aq) + HCl (aq) –> NaCl (aq) + H2O (l)

15cm3 15cm3 15cm3 15cm3

0.015m 0.015m 0.015m 0.015m

Nitric

Sodium Hydroxide + Nitric Acid –> Sodium Nitrate + Water

NaOH (aq) + HNO3 (aq) –> Na NO3 (aq) + H2O (l)

Na+ + OH- +H+ + NO3- –> Na+ + NO3- + H20

OH- +H+ –> H20

1 : 1 : 1 : 1

NaOH (aq) + HNO3 (aq) –> NaNO3 (aq) + H2O (l)

15cm3 15cm3 15cm3 15cm3

0.015m 0.015m 0.015m 0.015m

Ethanoic

Sodium Hydroxide + Ethanoic Acid –> Sodium Ethanoate + Water

NaOH (aq) + CH3COOH (aq) –> NaCH3COO (aq) + H2O (l)

Na+ + OH- +H+ + CH3COO- –> Na+ + CH3COO- + H20

OH- +H+ –> H20

1 : 1 : 1 : 1

NaOH (aq) + CH3COOH (aq) –> NaCH3COO (aq) + H2O (l)

15cm3 15cm3 15cm3 15cm3

0.015m 0.015m 0.015m 0.015m

Prediction

I predict that my results will show the order of acids to be as follows (strongest to weakest):

* Sulphuric Acid

* Nitric Acid

* Hydrochloric Acid

* Ethanoic Acid

Results

Sulphuric

0

5

10

15

20

25

30

Temp

21.4

24.7

26.4

26.2

25.5

25.0

24.7

pH

12.8

10.5

4.9

1.7

1.5

1.5

1.4

Colour

Purple

Blue

Orange

Red

Red

Red

Red

Hydrochloric

0

5

10

15

20

25

30

Temp

21.1

22.7

24.8

25.7

25.5

25.3

24.9

pH

12.7

12.8

12.5

2.7

1.2

1.2

1.1

Colour

Purple

Purple

Purple

Orange

Red

Red

Red

Nitric

0

5

10

15

20

25

30

Temp

23.0

25.4

26.7

28.1

28.1

28.0

27.5

pH

12.8

12.8

12.7

11.6

1.4

1.2

1.0

Colour

Purple

Purple

Purple

Blue

Red

Red

Red

Ethanoic

0

5

10

15

20

25

30

Temp

23.3

26.1

27.4

28.1

28.5

28.2

28.1

pH

12.8

12.9

12.8

10.8

5.6

5.1

4.8

Colour

Purple

Purple

Purple

Blue

Yellow

Yellow

Orange

Analysis

From the graphs I have discovered that if I draw a line across from 7 on the pH scale to where it meets the pH line, then draw a vertical line down to the axis I can see how much acid it takes to neutralise the alkali. From this I can now put the acids into a rank order:

Rank

Acid

pH

Volume needed

1

Sulphuric

7

8 cm3

2

Hydrochloric

7

12.3 cm3

3

Nitric

7

17 cm3

4

Ethanoic

7

18.5 cm3

Because it took less of Sulphuric Acid to neutralise the Sodium Hydroxide than any other this is the strongest acid. Ethanoic Acid is the least strongest because it took the most to neutralise the alkali.

This did not match what my equations said above but allowing for experimental error, I can say that I came quite close to what the values should be.

Also from the graphs I can see that the peak of the highest temperature is not at the point of neutralisation for any of the acids. This proves there must have been something wrong as heat is given off all until the point of neutralisation, as that is when all of the ions are used up in the reaction so no more heat is produced.

Evaluation

I believe that my experiment was conducted quite precisely but there are still quite a few things that could possibly vary the results, such as:

* I could have put a lid on the beaker to stop any heat from escaping

* I should have stirred the mixture between adding acid to allow all reactions to take place

* I could have used smaller amounts of acid and/or a longer time span to get more precise results

* As the readings on the Datameter kept changing up and down I had to choose one to write down so this may not be precise

* I could have measured the acid/alkali more precisely by using better apparatus instead of plastic measuring tubes as these tend not to be too accurate and always have some left in the bottom after tipping into the beaker

* All starting temperatures should have been the same

* The polystyrene cup could have had some residue on it from previous experiments which would dramatically alter my results