Salt Solutions: Preparation, Density, and Concentration Relationships

Calculations To Do Before Lab Part 1: Calculate mass of NaCl needed to make 1.00L of a 1.000M solution. – Molarity is moles per liter Part 2: Calculate the volumes needed to prepare the diluted solutions. – Use equation: C 1 V 1 = C 2 V 2 (shown in lab book)

Part 1 Weigh out the mass of NaCl you calculated Use funnel to add it to a 1L volumetric flask Add enough water to fill the flask ~half full Swirl until the solute has dissolved Add water until the meniscus is at the neck of the flask Use wash bottle to add water until the bottom of the meniscus is at the line – Be careful not to overshoot, otherwise you will have to start over This is your “stock solution”

Part 2 Use the stock solution to make the following solutions: – Solution 2: 100mL of 0.50M NaCl sol’n from stock solution – Solution 3: 100mL of 0.25M NaCl sol’n from sol’n 2 – Solution 4: 100mL of 0.125M NaCl sol’n from sol’n 3

Part 3 Pour 50mL of the NaCl stock solution into a 50mL graduated cylinder Use the hydrometer to determine the specific gravity Record the value Repeat for each NaCl sol’n Determine the specific gravity of 50mL of DI water – Record and also record the room temperature

Unknown Obtain an unknown salt solution Follow the same procedure, and determine its specific gravity.

Calculate the Densities Calculate the densities of the four NaCl solutions. Use the equation provided on previous slide. Also calculate the density of your unknown

Plot Your Results Use excel to plot your data – Density vs Molarity – When place into excel place data as so: Highlight the data you input – “insert”  “scatter”  “scatter with only markers” (no line!!) – Then a graph should appear – Label the axis's, title, and add a trend line “layout”  “trendline”  “more trendline options”  “display equation on chart” AND “display R squared value on chart” X axis (Molarity) Y axis (Density) ####

Use Your Graph After you print out your graph: Physically, on your graph locate the density of your unknown solution on the y-axis (place a circle/dot). – Draw a line, with a straight edge, from that point to the trend line. – Then draw a line from the point on the trend line to the x- axis. – (Shown in lab book) Then use the equation, calculated from the trend line, to calculate the molarity of your unknown solution. – Describe which way is most accurate, compare the values.