What happens when we add salt to boiling water? 

*Note- This dataset was collected by real students, but students can easily collect their own data for this activity and use the same questions with their own dataset. Learn about working with your own data in DataClassroom here.

Introduction

Solutions are homogeneous mixtures of solute and solvent. The solvent is the most abundant substance in a solution. In a liquid solution, the solvent does the dissolving.  The solute is the other substance in a solution. In a liquid solution, the solute is dissolved.  It is possible for a solution to have more than one solute - in fact, air is an example of a gaseous solution with multiple solutes - but a solution can have only one solvent.

The boiling point of a substance is the temperature at which the liquid form of that substance transitions to the gaseous state.  When a substance boils, the particles gain enough energy to overcome their attractions to one another and escape as a gas. When an ionic substance boils, ionic bonds break and individual ions enter the gaseous state. When a covalent substance boils, intermolecular attractive forces (IMAFs) break and individual molecules enter the gaseous state.

The Dataset

The dataset in this virtual lab activity was collected by real students. The students created salt water solutions of five different concentrations, heated each solution to a boil, and recorded the boiling points of each solution. The dataset includes data from three different student groups.

In your analysis, you’ll examine the collected data of three different groups (A-C) that measured the boiling points of five different aqueous solutions of sodium chloride. You’ll use this data to create a graph and carry out some calculations designed to verify the experimental boiling point elevation factor (Kb) of water.

Variables

Student Group - This categorical variable indicates which of the three student groups recorded the observation.

Solution Concentration (molal, m) - This numeric variable is the solution concentration for each observation.

Boiling Point (°C) - This numeric variable is recording the temperature for each observation.

The Activity

1. This lab requires you to use NaCl solutions of various concentrations. Determine the correct amount of NaCl (in grams) needed to prepare 200. mL of each of the following solutions.

Note:

1. 1 mL of water has a mass of 1 g

2. molality (m) = moles of solute/kg of solvent

   
   

a) 0.0 m NaCl solution

b) 0.5 m NaCl solution

c) 1.0 m NaCl solution

d) 1.5 m NaCl solution

e) 2.0 m NaCl solution

2. Next, you’ll set up your graph using the dataset. Click on the Graph tab at the top of the screen to switch to graph view. Be sure that the Scatter/Box/Bar or Categorical Bubble icon is selected. Click the Show buttons beneath the variable names to show the independent variable on the X-axis and the dependent variable on the Y-axis of the graph. Next, click on the Show button under the Group column and select the Z axis (on the right side panel). This will show each group’s data with its own color. Finally, check the Regression Line box.

3. Determine the slope of the regression line from your graph. Don’t forget units!

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