TABLE OF CONTENTS

INTRODUCTION

MATERIALS

METHOD

RESULTS

DISCUSSION

LINKS

Research Page

Amy Kiefer, Jessica Tierney

 

 

3 2 1 MELT DOWN!

 

 

Introduction (Table of Contents)

The definition of solubility is the amount of substance that will dissolve in a given amount of another substance (Webster 1936).  The rate of solubility is the amount of time it takes a substance to dissolve in another substance.  The substance, which dissolves, is the solute (Webster 1936).  The substance capable of or used in dissolving something is the solvent (Mebane 1985).  The sugar cube is the solute and the water is the solvent.

            Temperature increases the rate of solubility.  If you put salt into a tube of cold water some salt will dissolve, but if you then heat the tube more salt will dissolve in the warmer water (Ardley 1984).  As the temperature increases or decreases so will the rate of solubility, because heat can travel through solid objects faster (Walpole 1995).  We will graph the changes in the rate of solubility.

            When there is a greater amount of substance on one side of a mixture then the other side, a downhill transport occurs which is called diffusion (Duve 1984).  When a solution reaches its equilibrium diffusion stops.  Equilibrium is when there is a state of balance (Webster 1936).  So when there is a large amount of sugar cube at the bottom of the glass we know that the sugar cube has met its solubility (equilibrium).

            The purpose of the study is to find temperatures impact on the rate of solubility of a sugar cube.  From our resulting data we will create charts and graphs.

            Many aspects effect solubility: Temperature, pressure, and equilibrium of solute versus solvent (Ardley 1984).  So it would be in our best interest to manipulate these areas and find the optimal conditions for solubility.

            Temperature will be manipulated through the water temperature.  Since temperature flows through solid and liquid objects we can increase or decrease the temperature of the sugar cube (Walpole 1995).  As the temperate of the solute increases or decreases the rate of solubility will increase or decrease (Ardley 1984). 

            Our hypothesis is that a change in temperature will result in a change in solubility.   As we increase the temperature we believe that the solubility will also increase.  We are certain of this because when a substance is heated its molecules move faster, increasing the rate of solubility.  This theory is referred to as entropy.

MATERIALS (Table of Contents)

·        ruler

·        bowl

·        glass

·        syringe

·        sugar cubes

·        duct tape

·        timer (stop watch)

·        thermometer

·        water (hot and cold)

 

METHOD (Table of Contents)

 

In order to prove our hypothesis, that an increase in temperature causes an increase in solubility, we are going to dissolve sugar cubes using both hot water and cold water.  We hope to show that hot water will dissolve the sugar cube faster than the cold water.  We begin our experiment by setting up an apparatus.  This apparatus consists of a glass bowl in which an upside-down glass sits.  The base of this glass is therefore in the air, our sugar cube resting upon it.  The glass we choose to use is a wineglass because it has a small base, allowing room for the cube, yet preventing puddling.  The water should flow off the glass into the bowl.  This keeps sitting water from dissolving the cube and ruining data.  Next we connect a ruler to the side of the bowl.  This is to keep us from changing the length of the water flow. 

 

Following this we fill a syringe first with cold water.  Holding the syringe at the 8cm mark on the ruler, above the cube we started our timer.  At the same time we begin pushing the water out of the syringe at a constant rate until it is empty.  This syringe is filled with 60 ml of water each time, and the process is repeated 10 times.  From here we will repeat the whole process using hot water.  Our data for time varies only 3 seconds (each trial taking between 4 and 7 seconds) showing we are keeping the rate of water flow basically constant.

 

RESULTS (Table of Contents)

The actual experiment seems to be a success; the hot water is obviously melting the cube faster than the cold water.  However we still need to analyze our resulting data.  From here we put our collected data into two charts.  One chart, page 5, is the information yielded from the cold water trials and the other chart, page 6, is the information yielded from the hot water trials.  Each chart includes five things: the temperature of the water, the amount of time each trial takes, the percentage of the cube that dissolves, the dissolving rate, and the flow rate of the water.  These charts allow us to analyze the information from each experiment separately; they are shown below.  From here we put both the cold water and hot water data into one graph, page 7, in order to compare the two.  Our x-axis is the temperature of the water during a trial, and the y-axis is the amount of the sugar cube dissolved during that trial.  This graph shows us that the hotter temperatures have a faster dissolving rate.  To find the dissolving rate we take the percentage dissolved during the trial and divide it by the amount of time that trial takes.  The graph is shown below.  The next graph, page 8, shows, yet again, that hotter temperatures cause the cube to melt faster.  Our x-axis is temperature and our y-axis is percentage dissolved.  The last graph, page 9, shows that flow rate does not have a strong impact on the percent dissolved.  This leaves the main factor to be temperature.  Our x-axis is the flow rate and our y-axis is the percent dissolved.  In order to find the flow rate of each trial we take our 60-ml of water and divide it by the amount of time that trial takes. 

 

 

DISCUSSION (Table of Contents)

Our overall analyses of data, and the experiment in itself, show us that hotter temperatures do increase the rate of solubility of a sugar cube.  We used the process of trial and error in order to come up with a working apparatus and experiment.  We began using a completely different set up, and even a different solute altogether.  We started with sweet tarts and a contraption that looks like this.

 

 

However, how accurate our experiment and data collected from that experiment is, is another question all together.  Many variables in our project are not accurate because the are not monitored closely enough.  The first variable is time; data shows that our time uncertainty is 3 seconds.  This may seem as though we control the time pretty well, and as though it was basically constant.  On the contrary, since our longest time is only 7 seconds a 3-second difference doubles the amount of time the experiment lasts.  This tells us that in a future trial we need to have one set time.  Also our temperatures differ.  Yes we need two temperatures, a cold and a hot in order for the experiment to work, but we should have had one set cold temperature and one set hot temperature.  Our cold-water temperature stays at 70 degrees, which is good, but our hot-water temperature keeps dropping too quickly.  In order to keep the data more accurate and easier to compare we need to find a way to keep the hot water constant as well as the cold water.   In order for an experiment to be accurate there should only be one changing variable, we have two, the time and the temperature.  We need to decide whether our temperature or our time is going to be the changing variable not both.  Over all this experiment gives us a successful conclusion data-wise, but leaves more to be desired from the accuracy of the experiment itself.  In the future, along with keeping only one changing variable, other changes can be made to this experiment.  For example pressure can be added into consideration, along with diffusion and equilibrium.  However, our data supports our hypothesis showing that however limited the topic, we have a successful experiment.

This graph shows the correlation between temp. and dis. rate

data for graph above

 This graph shows %dis. with the water speed 

data for graph above

This graph shows the %dis. with temperature

data for graph above

LINKS (Table of Contents)

DATA LINK

http://library.thinkquest.org/2690/exper/exp23.htm - This is an similar experiment on solubility that you can perform on your own.

http://www.akucell.com/solu.htm - Shows temperatures impact on solubility with processed foods

http://www.acdlabs.com/products/phys_chem_lab/aqsol/ - ACD/Solubility determines the aqueous solubility at 25oC of organic compounds for pH values from 0.0 to 14.0 with a single step.

http://www.globe.gov/hq/charts/hydro/hydtemp1.htm - Things that water temperature effects

http://edie.cprost.sfu.ca/~rhlogan/sol_diff.html - What factors will affect solubility differences between compounds?