Titration (Acid – Base Reaction)

In the calculation assume that 1mL of cloudy ammonia solution has a mass of 1 g)

The solutions that contain ammonia have to be stopped because they can evaporate easily.

Ammonia was chose because it also contain some actual mass (approx. 5%)

The concentration of HCl has to remain the same throughout the whole experiment

The concentration of HCl was calculated to be able to calculate ammonia concentration.

METHOD:

. All the equipment were prepared and set.

2. Na2CO3 was weighted (2.653) and data was recorded.

3. Na2CO3 was dissolved in 100ml tap water.

4. The solution was tipped into the volumetric flask.

5. Water was added to make the solution reach 250ml mark.

6. The solution was mixed and tipped into a large beaker.

7. 25ml of the solution was pipetted into the 250 conical flasks

8. Step 7 was repeated again 2 more times to make 3 conical flasks with equal amount of 25ml dissolved Na2CO3 solution in them.

9. 3 drops of methyl orange indicator were added to each flask.

0. The burette was cleaned by HCl

1. The burette was filled with HCl to the zero mark.

2. The solution in the conical flasks was carefully and slowly titrated by HCl in the burette till they reach the point that the colors change (the end point).

3. The data were recorded and the average number of moles of acid was calculated.

4. The concentration of acid was calculated and recorded. (0.213)

5. Na2CO3 was discarded.

6. 10ml of commercial household ammonia (NH3) was pipetted and poured into the volumetric flask.

7. Ammonia (NH3) was diluted with water to make it reaches the mark.

8. The diluted solution was mixed thoroughly.

9. 25ml of the diluted solution was pipetted into the 250 conical flasks.

20. Two drops of methyl orange were added into diluted solution.

21. The burette was cleaned by HCl.

22. The burette was filled with HCl to the zero mark.

23. The diluted solution was titrated with HCl in the burette till they reach the point that the colors change (the end point).

24. steps 19-23 were repeated 2 more times to get average end point

25. average endpoint was calculated and recorded

26. The equation for the reaction between ammonia and HCl was written.

27. Number of moles of NH3 solution was calculated and recorded(1.16511 * 10-3)

28. The concentration of NH3 solution was calculated and recorded(0.0466044)

29. The concentration of undiluted NH3 solution was calculated and recorded(1.16511)

30. The concentration ammonia in g / L in 1000mL solution was calculated and recorded (40.77885)

31. The mass of ammonia per 100g of solution was calculated and recorded (4.07%)

Data:

The Na2CO3 obtained in the patty pan was 2.653 grams

The end point when dissolved Na2CO3titrated by diluted HCl were

The end point when diluted ammonia titrated by diluted HCl were

23.5 mL

5.5

23.5 mL

5.5

24.5 mL

5.4

---------------average endpoint

used in calculation = 23.5

---------------average endpoint

used in calculation = 5.47

Analysis:

FIND THE CONCENTRATION OF ACID HCl

Na2CO3 + 2HCl --> 2NaCl + H2O + CO2

Number of moles = mass / molar mass

2.503 * 10-3 = 0.2653 / 105.986

(0.2653 was used because it's only 1/10 of the whole Na2CO3 in petty pan)

The number of moles = 2.503 * 10-3

So the concentration of HCl is

Concentration = number of moles / volume

0.21302 = (2.503 * 10-3 * 2) / 23.5 * 10 -3

(Number of moles has to times by 2 due to the stoichiometry equation)

The concentration of HCl is 0.21302 mol / L

FIND THE CONCENTRATION OF UNDILUTED AMMONIA

NH3 + HCl --> NH4Cl

Number of moles HCl = volume times by concentration (from above)

.16511 * 10-3 = 5.47 * 10-3 * 0.213

The number of moles HCl reacted = 1.16511 * 10-3

From the stoichiometry equation above N (HCl) = N (NH3)

So the number of moles NH3 = 1.16511 * 10-3

So the number of moles NH3 in full 250 mL solution = = 1.16511 * 10-3 times by 10

Number of moles NH3 in 250 mL solution = 0.0116511

The concentration of 250 mL NH3 solution = number of moles / volume

0.0466044 = 0.0116511 / 0.25

(250mL change to litre = 0.25 L)

The concentration of 250 mL NH3 solution = 0.0466044 mol / L

Concentration1 multiply by Volume1 = Concentration2 multiply by Volume2

0.0466044 * 250 = Concentration2 * 10

Concentration of undiluted ammonia = 1.16511 mol / L

FIND THE MASS OF AMMONIA PER 100 GRAMS OF SOLUTION

Concentration in g/L ammonia in 1L of solution =Concentration of undiluted ammonia * molar mass

40.77885 = 1.16511 * 35

(Molar mass = 35 because the molar mass on the bottle is NH4OH)

Concentration in g/L ammonia in 1L of solution = 40.77885

From above 40.77885 -------------------- 1000 grams

Change to 100 grams ------------- 40.77885 / 10

00 grams ---------------------------- 4.077885

The % w/w of ammonia in the sample = 4.07 % (3 sig.)

Questions:

. The original ammonia solution was diluted for the analysis to make it suitable for the experiment because the concentration of HCl according to the result of experiment was 0.21302 mol / L and the concentration of undiluted ammonia according to the result of experiment was 1.16511 mol / L. The undiluted ammonia has a very high concentration if compared to the HCl so it has to be diluted for the better reaction in the experiment

2. The cloudy ammonia and the diluted solution should not be left unstopped because the ammonia solutions can easily evaporate in the air and that's made the result inaccurate, as it should be i.e. the concentration might change.

3. All the glassware has to be rinsed out because there might be some solution or particle left in them that can react with the solutions and make them change their status or react strangely.

4. The titration volume would have been less if H2SO4 had been used instead of HCl because of its stoichiometry equation

shows that it needs more ammonia and less of acid used.

Errors:

. The equipment used in the experiment weren't clean enough

- May cause an inaccurate result, inaccurate solution

- Can be avoided by clean all the equipment used and clean by the acid where it's possible.

2. The solid Na2CO3 didn't completely dissolve

- May cause an inaccurate result, concentration, volume

- Can be avoided by stir the solution by using the stirring rod until it's completely dissolve ( no solid particles left in the solution)

3. The solution sometimes spill out of the container

- May cause an inaccurate volume, result, concentration

- Can be avoided by be very careful throughout the experiment

4. Ammonia evaporated

- May cause an inaccurate result, volume, solution, concentration

- Can be avoided by place the lid over the ammonia container

5. Human reactions when do the titration with the partner.

- May cause an inaccurate data, result, volume of acid

- Can be avoided by work alone

6. When using apparatus to transfer the solution, some particles or liquids still left in the container

- May cause inaccurate result, may change to status of solution

- Can be avoided by checking the container for the left over every times and wash them one or two times with the solution before the actual solution.

7. When using the burette some bubbles might be in it.

- May cause inaccurate result, measurement, volume

- Can be avoided by use the burette carefully and slowly and also check before pour into the container.

8. The eye level when measuring the liquid solutions

- May cause inaccurate result, measurement, volume

- Can be avoided by carefully measure them with the eye level (mentioned above in the background)

9. During the titration there might be some liquid drops left in the beak of burette

- May cause inaccurate result, end point, volume

- Can be avoided by always wash the beak by the distill water to get the right amount of acid needed to neutralize.

0. Round-up calculations

- May cause inaccurate result, data, calculation

- Can be avoided by using the exact number throughout the calculation

1. Some tap water was used

- May cause inaccurate solution because tap water in not purely H2O and contain some other particle or elements

- Can be avoided by using the distill water.

2. The concentration of the concentrations may change during the experiment because some error made throughout the experiment.

- May cause inaccurate result, concentration, calculation

- Can be avoided by carefully work through each step.

3. Parallax errors may occur when measure the volume of the solution because the wrong eyes level

- May cause inaccurate result, measurement

- Can be avoided by carefully measure them and also use meniscus reading.