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CHEMISTRY, M5 2023 HSC 34

When 125 mL of a magnesium nitrate solution is mixed with 175 mL of a 1.50 mol L sodium fluoride solution, 0.6231 g of magnesium fluoride (MM = 62.31 g mol) precipitates. The of magnesium fluoride is 5.16 × 10.

Calculate the equilibrium concentration of magnesium ions in this solution.  (5 marks)

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♦ Mean mark 45%.

CHEMISTRY, M5 EQ-Bank 24

When a sample of solid silver chloride is added to a mol L−1 sodium chloride solution, only some of the silver chloride dissolves.

Calculate the equilibrium concentration of silver ions in the resulting solution, given that the of silver chloride is .   (3 marks)

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CHEMISTRY, M5 2022 HSC 31

Silver ions form the following complex with ammonia solution.

The equilibrium constant is at 25°C.

  1. In order to determine the free concentration in an aqueous ammonia solution, a student carried out a precipitation titration with as the titrant.
  2. Evaluate the suitability of this method.   (3 marks)
  1. If 0.010% of the total silver ions in solution are present as at equilibrium, calculate the equilibrium concentration of aqueous ammonia in this solution.   (4 marks)
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a.  The method is not suitable. 

→ Adding would cause the ions to precipitate with the ions to form

→ As a result, this would decrease , and disturb the equilibrium.

→ According to Le Chatelier’s Principle, the equilibrium will shift to the right in an attempt to counteract the change and increase .

→ As a result, would shift to the left and increase .
 

b.   

Substitute (1) into

 
 

 
Therefore, the concentration of at equilibrium is 0.025 mol L¯1.

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a.  The method is not suitable. 

→ Adding would cause the ions to precipitate with the ions to form

→ As a result, this would decrease , and disturb the equilibrium.

→ According to Le Chatelier’s Principle, the equilibrium will shift to the right in an attempt to counteract the change and increase .

→ As a result, would shift to the left and increase .


♦ Mean mark (a) 40%.

b.   

Substitute (1) into

 
 

 
Therefore, the concentration of at equilibrium is 0.025 mol L¯1.


♦ Mean mark (b) 40%.

CHEMISTRY, M5 2022 HSC 17 MC

A 2.0 g sample of silver carbonate (MM = 275.81 g mol ¯1) was added to 100.0 mL of water in a beaker. The solubility of silver carbonate at this temperature is mol L ¯1. It was then diluted by adding another 100.0 mL of water.

What is the ratio of the concentration of silver ions in solution before and after dilution?

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The maximum moles of that can be dissolved in 100.0 mL is:

 

 
The number of moles of silver carbonate added to the water is:

 
 

 
→ Thus, the moles of   added is more than the maximum moles of able to be dissolved. i.e. the solution would be saturated before and after dilution.

→ As a result, the solution would have the same concentration before and after, thus, the ratio is 1:1.


♦♦♦ Mean mark 15%.