Module 1: Chapter 1 - PAG's

Question 1

PAG 1.1

What is the method for determining the composition of Copper(II) carbonate basic?

Answer 1

1. Set up the apparatus as shown in the diagram
2. Weigh approximately 1.5g of CuCO₃*Cu(OH)₂ (s). Record the exact mass
3. Add the solid to the conical flask and replace the bung
4. Using a 50cm³ measuring cylinder, measure out 50cm³ of 1.0 mol dm⁻³ H₂SO₄ (aq) (this is in excess)
5. Remove the bung from the conical flask and quickly add the acid to the flask, immediately replacing the bung afterwards
6. Collect the gas in the 250cm³ measuring cylinder and record the final volume of carbon dioxide.
7. Record all data in appropriate table
8. Calculate the amount of carbon dioxide in moles
9. Calculate the amount of CuCO₃ in moles
10. Calculate the amount of CuCO₃ in grams and deduce the % by mass in the original sample of CuCO₃*Cu(OH)₂

Question 2

PAG 1.1

What are 2 errors in the procedure for determining the composition of Copper(II) carbonate basic that may lead to innacuracies in the experimental value?

Answer 2

• When the stopper is off the conical flask, CO2 may escape
• CO2 is slightly soluble in water

Question 3

PAG 2.1 and 2.2

How do you prepare a standard solution of a carbonate?

Answer 3

1. Using a weighing boat, accurately measure a specific mass of the carbonate
2. Transfer the solid to a clean, dry 100cm³ beaker
3. Rinse the weighing boat with distilled water into the beaker
4. Add enough distilled water to the beaker and mix with a glass rod so that the carbonate is completely dissolved
5. Pour the solution down a glass rod, through the funnel into a 250 cm³ volumetric flask
6. Rinse the beaker, glass rod, and funnel with distilled water and include rinsings into the volumetric flask
7. Add distilled water until just under the mark. Add stopper and slowly invert several times to mix thoroughly
8. Make solution up to the mark, insert stopper and invert several times to mix thoroughly
9. Label the flask clearly with exact concentration of the solution

Question 4

PAG 2.1 and 2.2

How do you carry out a titration?

Answer 4

1. Transfer your standard solution to a beaker and label it
2. Use a pipette and a pipette filler to transfer exactly 25cm³ of the standard solution into the clean 250cm³ conical flask
3. Add 2-3 drops of phenolphtalein to indicator to the conical flask
4. Using the funnel, rinse then fill the burette with the acid up to the 0 mark
5. Carry out a rough titration by opening the tap and swirling the conical flask, when the colour change becomes persistent, add dropwise and wait for a permanent colour change
6. Record the end point and repeat using accurate titrations by adding rapidly until 5cm³ from the rough end point, then adding slow and dropwise to find an accurate end point
7. Repeat step 6 until you have 2 concordant results

Question 5

PAG 2.1

What is the method for determining the concentration of hydrochloric acid?

Answer 5

1. Prepare a standard solution of 0.1 mol dm⁻³ NaHCO₃ (2.1g of NaHCO₃) (method for preparing a standard solution)
2. Carry out a titration of the unknown concentration of HCl against the 0.1 mol dm⁻³ NaHCO₃ (method for carrying out a titration)
3. Calculate your mean titre using your concordant results
4. Calculate the amount in moles of NaHCO₃ present in the 25cm³ sample (not the origingal 250cm³)
5. Calculate the amount in moles of HCl present in the mean titre (using the mole ratio in the equation)
6. Calculate the concentration of HCl using the number of moles and mean titre

Question 6

PAG 2.2

What is the methof for determining the molar mass of an unknown acid?

Answer 6

1. Record the mass of the unknown acid provided
2. Prepare a standard solution of the unknown acid (method for preparing a standard solution)
3. Carry out a titration of the unknown acid against 0.1 mol dm⁻³ NaOH (aq) (method for carrying out titration)
4. Calculate your mean titre
5. Calculate the amount in moles of NaOH in the 25cm³ sample
6. Using the equation given, determine the amount in moles of the unknown acid in your mean titre
7. Calculate the concentration of the unknown acid and use this to determine the amount in moles in the orignal 250cm³ standard solution
8. Use the original mass recorded and the number of moles to determine the molar mass