For both reactions I shall collect the gas in a gas syringe, and compare the amounts of gas released. When metal reacts with acid, carbon dioxide is released. I will use acids of equal molarity, and the same mass of magnesium carbonate. I predict that the H2SO4 will produce twice the volume of gas in comparison to HCl, as this will demonstrate the dibasity of Sulphuric Acid.
Safety
Sulphuric Acid is corrosive and therefore goggles must we worn at all times. If spillages occur, these should be washed liberally with cold water. Sulphuric Acid can burn skin and eyes, so lab coats and gloves should be worn. In case of contact with eyes, immediately flush eyes with plenty of water for at least 15 minutes. If swallowed drink plenty of water and seek medical help. Also follow standard laboratory safety such as removing lose clothing and tying hair away from face.
Fair Test
Titration – to ensure a fair test in my titration, I will use the same amounts of acid the same in each titration, and measure the variation in alkali needed to neutralise the acid. I will use a pipette and burette because they are the most accurate equipment available, being accurate to +/- 0.05cm3. Before filling the burette and pipette I shall rinse them first with distilled water and then with the chemical to be used. This will allow me to take more accurate readings from the equipment and reduce the possible error margin. I shall rinse the burette and pipette also with the solution to be used to ensure no dilutions in my experiment, which could lead to inaccuracy.
Gas Collection – to ensure a fair test in the gas collection, I shall use equal masses of Magnesium Carbonate in both collections, and measure the varying amount of Carbon Dioxide released. I will use a gas syringe to collect the carbon dioxide because I think that this I more accurate than upwards delivery – carbon dioxide is soluble in water and this could affect my results.
For both experiments, I shall also use the largest values possible as this will reduce the percentage error in my practical to give me more reliable results.
Titration Method
Apparatus: Sodium Hydroxide (1.0 molar), Sulphuric Acid (1.0 molar), Hydrochloric Acid (1.0 molar), 50 cm 3 pipette, burette, phenolphthalein indicator, white tile, clamp stand, boss, distilled water dispensers, pipette filler, 4 × 100cm3 beakers, 2 × 100cm3 conical flasks, plastic filter funnel.
- Perform pre-tests to determine the colour change of the indicator at the end point of the titration and the colour of phenolphthalein in acids and alkalis.
- Prepare the equipment as follows:
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Burette – rinse with distilled water followed by the solution to be used, NaOH as not to dilute the solution with water.
- Run solution through and invert the burette to ensure no air bubbles.
- Fill the burette with NaOH using a filter funnel, and remove the funnel. Record the volume of solution within the burette to 0.05 ml.
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Pipette – rinse the pipette several times by sucking and releasing the solution to be used, HCl or H2SO4, using a pipette filler, (suck up solution to above the measured mark)
- Using pipette filler, fill pipette with until the meniscus is slightly above the mark.
- Take the pipette out of the solution to ensure no atmospheric pressure and allow the liquid to run out slowly until the meniscus is level with the mark.
- Touch the side of the flask with the tip of the pipette but allow any residue to remain in the pipette.
- Add 3-4 drops of the indicator phenolphthalein to the solution in the conical flask (no more as indicators are weak acids and so can have an effect on the titration)
- Use a white tile to help identify the colour change at the end point.
- Run the solution from the burette whilst swirling, stop as soon as the indicator colour changes.
- Record the volume of the rough titration.
- Repeat the titration carefully and drop wise until the colour is about to change, then add half a drop at a time.
- When the faintest detectable colour change can be noted, record the final volume to within 0.05 ml.
- Repeat the titration to get three accurate titrations within 0.1 ml of each other.
Gas Collection
Apparatus: Hydrochloric Acid (1 molar), Sulphuric Acid (1 molar), Magnesium Carbonate, 6 conical flasks, gas valves and bungs, gas syringe with delivery tube, Clamp stand and boss.
- Set up the experiment as shown.
-
React 0.34g MgCO3 with 100ml HCl for at least 10 minutes or until the reaction is complete.
-
Record the volume of CO2 produced.
- Repeat three times, ensuring that the gas syringe is always set at zero before the experiment is set.
-
Repeat with H2SO4to allow the comparison of results.
Quantities
Titration
From my research I know that the maximum volume of Sodium Hydroxide will be needed in the titration with Hydrochloric Acid. The burette I will be using can measure accurately up to 50cm3. I from my calculations, this amount will be used to neutralise 50cm3 of acid. For the reaction with Sulphuric Acid, twice the volume of NaOH shall be needed to neutralise the acid. Therefore, I shall use only 25cm3 acid for both titrations, as I know that 50cm3 NaOH is the maximum volume I will need. The advantage of using the largest volumes possible is that the percentage error is reduced, and my experiments will therefore me more accurate.
Gas Collection
H2SO4(aq) + MgCO3(s) → MgSO4(aq) + H2O(l) + CO2(g)
This is the reaction that I predicted would release the most carbon dioxide. I therefore had to work out what the maximum amount of product I could use within the practical limits of my apparatus.
Max volume gas released – 100cm3
No. moles = actual volume ÷ 24
= (100÷1000) ÷ 24
= 0.004 moles CO2
Molar ratio MgCO3: CO2 =1:1
Therefore 0.004 moles MgCO3
Mr MgCO3 = 24+12+ (16 x 3)
=84
Actual Mass = number of moles x mass 1 mole
= 0.004 x 84
0.34g Magnesium Carbonate to be used.
The Sulphuric Acid must also be present in excess to ensure the reaction goes to completion, and so I will therefore use 0.1 mole H2SO4.
Volume = number of moles ÷ concentration
= 0.01 ÷1 = 0.01 dm-3, or 100 cm-3
2HCl(aq) + MgCO3(s) → MgCl2(aq) + H2O(l) + CO2(g)
For my second reaction, I shall use the same mass of Magnesium Carbonate, and provided the acid is still in excess, the same volume of Hydrochloric Acid, to ensure a fair test.
Mass MgCO3 to be used = 0.34g
Molar ratio HCl: CO2 = 2:1
Therefore 0.004 x 2 moles HCl to be used.
To allow the acid to be present in excess, I shall use 0.01 mole of Hydrochloric Acid.
Therefore, volume = number of moles x concentration
=0.01 × 1
=100cm3
Specimen Calculations
Titration using Sodium Hydroxide and Hydrochloric Acid
HCl(aq) + NaOH(aq) → NaCl(aq) + H20(l)
Volume HCl used: 25 ml or 0.025 dm-3
Number of moles HCl = concentration (mol dm-3) × volume (dm-3)
= 1m× 0.025 dm-3
= 0.025 moles HCl
Molar ratio NaOH: HCl = 1: 1
Therefore 0.025×1= 0.025 moles NaOH
Volume NaOH = number of moles × concentration (mol dm-3)
= 0.025 × 1
=0.025 dm-3
This shows that an equal volume of Sodium Hydroxide is needed to neutralise the Hydrochloric acid, indicating that for every OH- ion in the NaOH, one H+ ion was released from the Hydrochloric Acid to form H2O, a neutral molecule. This shows that Hydrochloric Acid is monoprotic, as it releases one Hydrogen ion when it is reacted in an aqueous solution.
Titration using Sodium Hydroxide and Sulphuric Acid
H2SO4 (aq)+2 NaOH(aq) → Na2SO4(aq) +2H2O(l)
Volume H2SO4 used: 25 ml or 0.025 dm-3
Number of moles H2SO4 = concentration (mol dm-3) × volume (dm-3)
= 1m× 0.025 dm-3
= 0.025 moles H2SO4
Molar ration NaOH: H2SO4 = 2: 1
Therefore 0.025÷2 = 0.0125 moles NaOH
Volume NaOH = number of moles × concentration (mol dm-3)
=0.0125× 1 = 0.0125 dm-3
This shows that only half the volume of Sodium Hydroxide was needed to neutralise the Sulphuric Acid, indicating that for every OH- ion in the NaOH, two H+ were released from the Sulphuric Acid, demonstrating its dibasity, as for every mole of Sulphuric Acid reacting in solution; two moles of Hydrogen ions were released.
Gas Collection
2HCl(aq) + MgCO3(s) → MgCl2(aq) + H2O(l) + CO2(g)
Number of moles MgCO3 = actual mass ÷ mass 1 mole
Mr MgCO3 = 84
= 0.34 ÷ 84
= 0.004 moles
Molar ration HCl: CO2 = 2: 1
Therefore 0.004 ÷ 2 = 0.002 moles CO2
Volume = number of moles x 24
= 0.002 × 24
= 0.048 dm-3 or 48cm3
H2SO4(aq) + MgCO3(s) → MgSO4(aq) + H2O(l) + CO2(g)
Number of moles MgCO3 = actual mass ÷ mass 1 mole
Mr MgCO3 = 84
= 0.34 ÷ 84
= 0.004 moles
Molar ratio H2SO4: CO2 = 1: 1
Therefore 0.004 moles CO2
Volume = number of moles × 24
= 0.004 × 24
=0.096 dm-3 or 96cm3
When a metal carbonate reacts with acid, carbon dioxide is released. These results show that when Magnesium Carbonate reacts with Sulphuric Acid, twice the volume of Carbon Dioxide is produced in comparison to its reaction with Hydrochloric Acid. This shows that, as we know HCl to be a monobasic acid, Sulphuric Acid is dibasic, as it produced double the volume of gas as a result of its two Hyrdogen ions that are released.
Bibliography
- ‘Chemistry’ – Chris Conoley and Phil Hills (p. 332)
Collins Educational 1998
- Steven Doherty – Atoms, Molecules and Stoichiometry
- Cambridge University Press 2000
‘Chemistry’ Brian Ratcliff