# 6/23/2014

Lab1: Introduction to Science

Diffusion through a Liquid

Purpose

Thepurpose of this experiment is to understand the effects oftemperature, surface area and concentration in the rate of reaction.

Pre-LabQuestions ( no pre-lab question)

Hypothesis

Hypothesis1: The decrease in the concentration of the solution will decreasethe rate of reaction.

Hypothesis2: The higher the surface area for reaction will result to higherrate of reaction.

Hypothesis3: The increase in temperature will also increase the rate ofreaction.

Data

Table 1:Reaction Rate Data and Observations

 Substance, Reaction # Variable Mass of the CaCO3 (g) (these should be close) Time of the reaction (sec) (start-stop) % Citric Acid Observations CaCO3Rock, #1 Saturated acid solution, iced 0.320 1220 60 Bubbles formed in very slow rate CaCO3Rock, #2 Diluted acid solution, room temp. 0.327 760 30 The bubbles are formed in normal rate CaCO3Powder, #3 Diluted acid solution, room temp. 0.326 15 30 Fastest reaction among the samples CaCO3Rock, #4 Saturated acid solution, room temp. 0.325 430 60 Bubbling is relatively quicker CaCO3Rock, #5 Saturated acid solution, heated 0.330 90 60 Fastest reaction among the rock samples

Observations

Inall of the samples performed, there are observations of bubblesforming from the bottom of the beaker and the test tubes whichescapes through the surface. It means that the reaction of calciumcarbonate and citric acid is occurring in the samples producing thecarbon dioxide gas. It is also observed that there is a difference inthe time for the bubbles to stop and the nature of these bubbles inthe different samples performed.

Calculations

Calculatethe rate (g/sec) of each of the reactions you observed.

• Reaction 1 (rock, iced, saturated solution):

Rate of reaction = (0.320 g / 1220 sec) = 2.63x 10-4g/sec

• Reaction 2 (rock, room temperature, diluted solution):

Rate of reaction = (0.327 g / 760 sec) = 4.30 x10-4g/sec

• Reaction 3 (powder, room temperature, diluted solution):

Rate of reaction = (0.326 g / 15 sec) = 2.17 x10-2g/sec

• Reaction 4 (rock, room temperature, saturated solution):

Rate of reaction = (0.325 g / 430 sec) = 7.56 x10-4g/sec

• Reaction 5 (rock, heated, saturated solution):

Rate of reaction = (0.330 g / 90 sec) = 3.67 x10-3g/sec

Conclusion

Inthe experiment, the effect of the three factors, namely temperature,concentration of the acid and the surface area on the rate of thereaction is analyzed. In this experiment, it is concluded that thetemperature decreases, the rate of reaction also decreases and viceversa. In the case of the concentration of the acid, the rate ofreaction is faster in the sample where the concentration is higher.In this observation, it is also concluded that the higher theconcentration of the acid means the rate of reaction will be faster.Lastly, it is also concluded that the rate of reaction is also fasterwhen the surface area of the solid exposed for reaction is larger.

Questions

Pre-labQuestions

1. Name five factors that can affect the rate of a reaction.

The main factors that could affect the rate of reaction are:

• Nature of the reactants – the reaction is characterized by its reactants

• Concentration of the solution – the concentration will also provide the amount of collision that would happen in the reaction

• Surface area in solids – the larger surface area will provide more collisions for the reaction to happen

• Temperature – the reacting particles will move faster in solutions with higher temperature thus creating more possibilities of collision for reaction

• Presence of Catalyst – the reaction is faster with the presence of catalyst.

1. In the opening paragraph example, it took more time to make sweet tea with cold water and sugar cubes than to sweeten hot tea with granular sugar. Why?

There are two factors to considerin the example of the first paragraph. First, with the use of sugarcubes, there is less surface area that is exposed for the reactantparticles in the solution to collide or react to. Basically, surfacearea is one of the factors that could affect the rate of the reactionto occur. In this case, the powder will dissolve faster in the teabecause it has more solid surface area for collision which controlsthe rate of reaction. Second, the difference between the hot waterand the cold water is that, the hot water could allow the particlesto move faster in the solution. In that sense, the reactants willcollide more that the collision occurring in the cold water thus thereaction would be faster in the hot water. The effects of the largersurface area and the collision effect of the hotter water is thereason why the rate of sweetening the tea is a lot faster using hotwater and granular sugar.

1. What is the primary factor that determines whether a reaction rate increases or decreases?

The primary factor that determineswhether the rate of reaction will increase or decrease is the rate ofcollision that results to the reaction. The collisions of thereacting molecules will trigger the reaction and the rate of reactionwill depends on the frequency of the collisions.

Post-labQuestions

1. All the reactions that you performed were chemically the same. You just varied several factors. What were the factors that were varied?

In the experiments, each of thereaction samples has different conditions which pertain to thefactors that could affect the rate of reaction. The reaction 1,reaction 5and reaction 5 are variations of temperature. The effect oftemperature is observed using the reaction rates in the case ofputting the solution in ice, the reaction at room temperature and thereaction while heating the solution. The variation of theconcentration is also characterized by the variation in the reaction2 and 4 where both of the solutions are at room temperature and theyare both using rock samples. However, the variation is usingdifferent concentration of the citric acid. The last variation thatis performed in the experiment is the surface area difference whichis observable in the reaction 2 and reaction 3. The variation is theuse of powder and the use of rock solid samples.

1. Which factor do you think made the biggest influence on the reactions? Why?

The biggest influence in the reaction time is the surface area of thesolid used in the reaction. In the sample reaction 3, there are twofactors to consider which is the surface area and the concentrationof the acid which is generally lower that the saturated acid.However, it is the fastest reaction to occur even if theconcentration of the acid is lower.

1. Out of the five different reactions, which reaction was the slowest? Was this what you expected? Why?

Reaction 1 takes the slowest reaction. This is also what I expectedbecause there is a general assumption that most of the reaction willhave double their reaction rate per 10 degree change in thetemperature. Although the temperature is not taken in the experiment,the change would be a large number since the involved medium is ice.

1. Why do you think marble statues require long periods of time to degrade in regions that are affected by acid rain?

Marble statues degrade usually fora long period of time due to the effects of temperature, surface areaand concentration. The only expose part of the marble statue for thereaction to acid to occur is the outside part which has relativelylow area compared to the powder form. The precipitation also occursat low temperature which slows down the reaction rate. And lastly,the concentration of the acid in the rain is relatively low.