A group of students prepared 500 cm³ of a 0.05 M standard solution of sodium carbonate, using anhydrous sodium carbonate (Na₂CO₃), which is a primary standard. The required mass of the carbonate was weighed accurately on a clock glass. It was then dissolved in deionised water in beaker A. The solution was transferred to flask B and made up accurately to the 500 cm³ mark with deionised water. (a) Explain the underlined term. (b) Give one property of anhydrous sodium carbonate that allows it to be used as a primary standard. (c) Name the type of flask labelled B in the diagram. (d) Outline how you would have ensured that all of the solution in the beaker was transferred to flask B? (e) Describe the procedure for bringing the solution in flask B accurately to the 500 cm³ mark. What further step should be taken before the solution is ready for use? (f) It was found by titration that exactly 17.85 cm³ of a hydrochloric acid (HCl) solution neutralised 25.0 cm³ of this 0.05 M sodium carbonate solution. The equation for the titration reaction is: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂ Find, correct to two decimal places, the concentration of the hydrochloric acid solution (i) in moles per litre. (ii) in grams per litre.

Leaving Cert Chemistry Experiments - All: A group of students prepared 500

A group of students prepared 500 cm³ of a 0.05 M standard solution of sodium carbonate, using anhydrous sodium carbonate (Na₂CO₃), which is a primary standard - Leaving Cert Chemistry - Question 2 - 2013

Question 2

A group of students prepared 500 cm³ of a 0.05 M standard solution of sodium carbonate, using anhydrous sodium carbonate (Na₂CO₃), which is a primary standard. The r... show full transcript

Worked Solution & Example Answer:A group of students prepared 500 cm³ of a 0.05 M standard solution of sodium carbonate, using anhydrous sodium carbonate (Na₂CO₃), which is a primary standard - Leaving Cert Chemistry - Question 2 - 2013

Step 1

Explain the underlined term.

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Answer

A standard solution is a solution of known concentration that is used in titrations. It contains a precise quantity of solute dissolved in a specific volume of solvent, allowing for accurate comparison during analyses.

Step 2

Give one property of anhydrous sodium carbonate that allows it to be used as a primary standard.

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Answer

Anhydrous sodium carbonate is stable and does not absorb moisture from the air, making it suitable for accurately measuring mass without affecting its concentration.

Step 3

Name the type of flask labelled B in the diagram.

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Answer

Volumetric flask.

Step 4

Outline how you would have ensured that all of the solution in the beaker was transferred to flask B.

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Answer

To ensure all the solution was transferred, the beaker should be rinsed with a small amount of deionised water and the rinsings added to the volumetric flask. Additionally, a glass rod can be used to assist in guiding the liquid transfer.

Step 5

Describe the procedure for bringing the solution in flask B accurately to the 500 cm³ mark. What further step should be taken before the solution is ready for use?

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Answer

To accurately bring the solution in flask B to the 500 cm³ mark, fill the flask carefully with deionised water until the bottom of the meniscus aligns with the 500 cm³ line at eye level. Then, invert the flask several times to ensure thorough mixing before using the solution.

Step 6

Find, correct to two decimal places, the concentration of the hydrochloric acid solution in moles per litre.

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Answer

To find the molarity (M) of the hydrochloric acid solution:

Using the formula:

$M = \frac{C_1V_1}{C_2V_2}$

Where:

$C_1 = 0.05$ (molarity of sodium carbonate)
$V_1 = 25.0$ cm³ (volume of sodium carbonate)
$V_2 = 17.85$ cm³ (volume of hydrochloric acid)

Substituting the values:

$M = \frac{0.05 \times 25.0}{17.85} \approx 0.07$

Therefore, the concentration of the hydrochloric acid is approximately $0.14$ moles per litre.

Step 7

Find, correct to two decimal places, the concentration of the hydrochloric acid solution in grams per litre.

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Answer

To convert the molarity of HCl to grams per litre:

Using the molar mass of HCl, which is approximately 36.5 g/mol:

$\text{grams/L} = M \times \text{molar mass}$

Thus:

$\text{grams/L} = 0.14 \times 36.5 \approx 5.11$

Therefore, the concentration of the hydrochloric acid solution is approximately $5.11$ grams per litre.

A group of students prepared 500 cm³ of a 0.05 M standard solution of sodium carbonate, using anhydrous sodium carbonate (Na₂CO₃), which is a primary standard - Leaving Cert Chemistry - Question 2 - 2013

Worked Solution & Example Answer:A group of students prepared 500 cm³ of a 0.05 M standard solution of sodium carbonate, using anhydrous sodium carbonate (Na₂CO₃), which is a primary standard - Leaving Cert Chemistry - Question 2 - 2013

Explain the underlined term.

Give one property of anhydrous sodium carbonate that allows it to be used as a primary standard.

Name the type of flask labelled B in the diagram.

Outline how you would have ensured that all of the solution in the beaker was transferred to flask B.

Describe the procedure for bringing the solution in flask B accurately to the 500 cm³ mark. What further step should be taken before the solution is ready for use?

Find, correct to two decimal places, the concentration of the hydrochloric acid solution in moles per litre.

Find, correct to two decimal places, the concentration of the hydrochloric acid solution in grams per litre.

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