SSCE HSC Chemistry Using Quantitative Analysis: Describe steps A, B and C includ

Question

Describe steps A, B and C including correct techniques, equipment and appropriate calculations. Determine the concentration of the hydrochloric acid.

**Preparation of Standard Solution (Step A)**
To prepare a 500 mL solution of 0.100 mol L⁻¹ sodium carbonate, you will need:
- Sodium carbonate (Na₂CO₃)
- A volumetric flask (500 mL)
- A balance
- Distilled water

Procedure:
1. Calculate the mass of sodium carbonate required:
   
   $$	ext{Mass} = 	ext{Molarity} 	imes 	ext{Volume} 	imes 	ext{Molar mass}$$
   
   Where:
   - Molarity = 0.100 mol L⁻¹
   - Volume = 0.500 L
   - Molar mass of Na₂CO₃ = 105.99 g/mol
   
   Thus, the mass required is:
   
   $$	ext{Mass} = 0.100 	imes 0.500 	imes 105.99 = 5.2995 	ext{ g}$$
   
2. Weigh out approximately 5.3 g of sodium carbonate on the balance.
3. Transfer the sodium carbonate into the 500 mL volumetric flask and dissolve it in a small amount of distilled water. Swirl to mix.
4. Fill the volumetric flask to the 500 mL mark with distilled water, ensuring thorough mixing.

**Performing the Titration (Step B)**
The titration involves adding the hydrochloric acid of unknown concentration to the sodium carbonate standard solution until neutralization is reached.
- You'll need:
   - Burette
   - Pipette (25 mL)
   - Conical flask
   - Indicator (e.g., phenolphthalein)

Procedure:
1. Rinse the burette with hydrochloric acid, then fill it with the acid solution.
2. Using a pipette, measure 25.0 mL of the sodium carbonate solution and transfer it to a conical flask.
3. Add a few drops of phenolphthalein indicator to the conical flask.
4. Slowly titrate the hydrochloric acid from the burette into the sodium carbonate solution, swirling until the endpoint is reached (color change).
5. Record the volume of hydrochloric acid used. Repeat for consistent results and calculate the average titration volume, which is given as 21.4 mL.

**Calculating Concentration (Step C)**
Using the average volume from the titration:
1. Write the balanced equation for the reaction:
   
   $$	ext{Na}_2	ext{CO}_3 + 2	ext{HCl} ightarrow 2	ext{NaCl} + 	ext{H}_2	ext{O} + 	ext{CO}_2$$
   
2. Determine the number of moles of sodium carbonate used:
   
   $$	ext{Moles of } 	ext{Na}_2	ext{CO}_3 = 	ext{Molarity} 	imes 	ext{Volume} = 0.100 	imes 0.025 = 0.00250 	ext{ moles}$$
   
3. From the equation, 1 mole of sodium carbonate reacts with 2 moles of hydrochloric acid, hence:
   
   $$	ext{Moles of HCl} = 2 	imes 0.00250 = 0.00500 	ext{ moles}$$
   
4. Calculate the concentration of hydrochloric acid:
   
   $$	ext{Concentration} = rac{	ext{Moles}}{	ext{Volume}}$$
   
   Converting 21.4 mL to liters (0.0214 L):
   
   $$	ext{Concentration} = rac{0.00500}{0.0214} 	ext{ mol L}^{-1} 	imes 1000 = 0.233 	ext{ mol L}^{-1}$$

Thus, the concentration of the hydrochloric acid is approximately 0.233 mol L⁻¹.

Describe steps A, B and C including correct techniques, equipment and appropriate calculations - HSC - SSCE Chemistry - Question 28 - 2010 - Paper 1

Worked Solution & Example Answer:Describe steps A, B and C including correct techniques, equipment and appropriate calculations - HSC - SSCE Chemistry - Question 28 - 2010 - Paper 1

Preparation of Standard Solution (Step A)

Performing the Titration (Step B)

Calculating Concentration (Step C)

Join the SSCE students using SimpleStudy...