Rlab (version 1.1)

salt: The effect of salt on ice melting

Description

When salt comes into contact with ice, it tends to break apart into individual ions which then interact with the frozen water and disrupt hydrogen bonds that have formed between ice molecules. This lowers the melting temperature of ice, and it was hypothesized that the melting process would be hastened. The data set salt was collected during an experiment to determine whether varying the type and amount of salt applied to a specific amount of ice has an effect on the interval required to melt that ice.

Usage

data(salt)

source

Taken from a 1999 project by Wayde D. Johnson

Details

Background: The Effect of Salt on the Rate at Which Ice Melts In those sections of the country that experience winter as a time of snow and ice, salt is often spread on roadways in an attempt to counter the hazardous consequences of accumulated ice. Ice is formed when the relatively disordered molecules in liquid water reach a temperature of 32 degrees F (0 degrees C) and begin to "nucleate" or form solid ice crystals consisting of ordered water molecules. Salt, when in contact with ice, tends to break apart into individual ions (i.e. sodium and chloride) which then interact with the water and disrupt the hydrogen bonds that have formed between water molecules. Since no covalent bonds are broken or formed, the resulting chemical "solvation" is not considered to be a chemical reaction. However, the end result from the introduction of salt is that the ice crystals are disrupted and liquid water is achieved. The purpose of the current experiment is to study the effect of salt on the rate at which ice melts. More specifically, the experiment is being conducted to answer the following questions: 1. Does varying the amount of salt applied to a constant quantity of ice result in a change in the rate of melting? 2. Does the type of salt used have an effect on the melting rate? The first question is of interest as it relates to issues such as the cost of salt and the potential harmful effects of its use on pavement. If increasing the amount of salt applied to a given quantity of ice is not accompanied by an increase in melting rate, any application of salt beyond minimal amounts would constitute a waste of public money and possibly cause unnecessary damage to public roadways. It is hypothesized that the relationship between amount of salt used and the time required to completely melt a given quantity of ice is negative and significant. Likewise, the second question seeks to address the possibility that dissimilar forms of salt may produce different rates of melting. To answer this question, table salt and rock salt were included in the experimental design. Although both are chemically similar, rock salt consists of larger crystals than does the typical table salt bought in local supermarkets. Given the greater density and more efficient packing of NaCl molecules within the larger rock salt crystals, a specified volume of rock salt will likely contain a greater number of salt molecules than a similar volume of the less tightly packed table salt crystals. Therefor, it is hypothesized that rock salt will result in faster melting times than table salt. Materials Tap water 42 - 6 ounce plastic cups (paper cups tend to break at the seam as the contents freeze) Morton brand table salt Morton brand rock salt 1/2 cup measure Stop Watch Procedure To answer the questions posed above, a balanced 2 x 4 factorial design was employed with amount of salt identified as a factor consisting of four levels (i.e. no salt, 1/2 tsp, 1 tsp, 1 tbsp), and the other factor being type of salt with two levels (i.e. table salt, rock salt). Three replications were conducted within each cell for a total of 24 runs. A p-level of .05 was identified for statistical significance prior to the data collection phase of the project. Twenty-four small plastic cups were each labeled with a number designating type of salt, and a letter A-D indicating amount of salt. Each plastic cup was then filled with 4 ounces of tap water and placed in the freezer overnight (approximately 16 hours). Since salt could not be emptied into all of the ice cups simultaneously, the remaining 18 plastic cups were each labeled and then used to hold an amount and type of salt corresponding to one of the experimental conditions. After the ice cups had been removed from the freezer, each salt cup was quickly emptied into a corresponding ice cup with matching identification so as to minimize the time interval between the application of salt to the first and last cups. After the last cup of salt had been emptied into the appropriate ice cup, the stopwatch was started. Room temperature during the data collection phase was approximately 72 degrees Fahrenheit. The time was recorded for each cup when ice was no longer visible in that cup.