SmarterEd

Aussie Maths & Science Teachers: Save your time with SmarterEd

CHEMISTRY, M2 2005 HSC 25a

A student collected a 500 mL sample of water from a local creek for analysis. It was filtered and the filtrate evaporated to dryness. The following data were collected.

Calculate the percentage of total dissolved solids in the creek sample.  (2 marks)

Show Answers Only

Show Worked Solution

→ The dissolved solids in the creek sample are contained in the evaporating basin and the undissolved solids are contained in the filter paper.

→ Mass of undissolved solids in filter paper =

→ Mass of dissolved solids in evaporating basin =

→ Total Mass of solids =

→ Percentage of dissolved solids = of total solids in the creek sample

CHEMISTRY, M2 2009 HSC 22

The nitrogen content of bread was determined using the following procedure:

    • A sample of bread weighing 2.80 g was analysed.
    • The nitrogen in the sample was converted into ammonia.
    • The ammonia was collected in 50.0 mL of 0.125 mol L hydrochloric acid. All of the ammonia was neutralised, leaving an excess of hydrochloric acid.
    • The excess hydrochloric acid was titrated with 23.30 mL of 0.116 mol L sodium hydroxide solution.
  1. Write balanced equations for the TWO reactions involving hydrochloric acid.  (2 marks)

  2. Calculate the moles of excess hydrochloric acid.  (1 mark)

  3. Calculate the moles of ammonia.   (2 marks)

  4. Calculate the percentage by mass of nitrogen in the bread.  (2 marks)

Show Answers Only

a.   

b.   

c.   

d.   

Show Worked Solution

a.   


 

b.   
 

c.   


 

d.   

CHEMISTRY, M2 2010 HSC 31ai

A student collected a 250 mL sample of water from a local dam for analysis. The data collected are shown in the table.

The water was filtered and the filtrate evaporated to dryness.

Calculate the percentage of the total dissolved solids in the dam sample.  (2 marks)

Show Answers Only

0.46%

Show Worked Solution