Question

MANUALLY prepare a density/molality calibration plot from the following MgCl2(aq) data. Clearly label the axes on the  

plot, and draw a smooth, linear curve through the data.

          density (g/mL)         MgCl2 molality (nsolute/1 kg H2O)

1.0070.100       Gross mass of beaker and solution:    81.7982 g

1.0220.300       Tare mass of beaker:       55.6732 g

1.0360.500

1.0500.700       Net mass of unknown solution: _____g

1.0650.900       Pipet volume: 25.00 mL

- Calculate the density of Mg(Cl)2(aq) solution of unknown concentration from the above data.

- Determinate the molality of the unknown from the density and the plot. Clearly show this on the plot.

- Calculate the mass % and the Molarity (nsolute/1 L of solution) of MgCl2 in the unknown. Do your calculations on

          the back and write your answers here.            

Answer 1

ANSWER:

1) Calibration curve

• For the calibration curve we plot density (y-axis) vs. molality (x-axis) and we add the trendlne to the graph:

• From calibration curve we get the following equation:

or

2) Density of Mg(Cl)₂ solution of unknown concentration

• The volume of solution is 25.00 mL
• The mass of solution is

• And the density of Mg(Cl)₂ solution of unknown concentration is

3) Molality of the unknown concentration

• Using the plot we get:

• From the plot, the molality of unknown solution is 0.630 m
• We also can use the trendline obtained from calibration curve

4) Mass percent and molarity of the solution

• For this solution, in 1 Kg of water we have 0.625 moles of MgCl₂. And the mass of MgCl₂ (94.211 g/mol) is

• The mass of solution is

• The volume of solution is

• Then, the mass percent of solution is

• And the molarity is