6/6/13 Week 9 May 2013 Home

I was meant to blog these results a week ago, but I only remembered now.
When conducting  more methanol tests to resolve the large spread 3 more results were achieved. 94.4, 94.3 and 94.3.

27/05/13 Week 7 May 2013 Home 5

Below is the final equipment list of the experiment after changes were made. One significant change was the decision to use a more accurate method of measuring. When comparing this equipment list to the last one this list shows the inclusion off three different sized pipettes. These pipettes were the method of a more accurate form of measuring liquid volumes. 

·        -300-500ml of pure Methanol

·       - 300-500ml of pure Ethanol

·       - 300-500ml of pure Butanol

·       - 25ml Pipette

·        -10ml Pipette

·       - 5ml Pipette

·        -3-4 Litres of distilled water

·      -2, 100ml glass graduated cylinder

·        -100ml glass beaker

·      -  Stirring Rod

·     -   Lab Coat

·     -   Safety Glasses

27/05/13 Week 7 May 2013 Home 4

Uncertainty, accuracy and precision

Uncertainty
You should become familiar with the principles of Accuracy and Precision, and the corresponding principles of uncertainty and error.
What is the difference between accuracy and precision? Perhaps this diagram can help.


In experimental work you may need to calculate using uncertainties. See this video for an introduction.

• When adding or subtracting measurements you add uncertainties
• When multiplying or dividing measurements you add percentage uncertainties

For example, when measuring a mass of 0.2g of a substance in a beaker a student measured a value of 0.210g as follows:
Mass of beaker = 101.400g
Mass of beaker plus substance = 101.601g
For each measurement the uncertainty would be +-0.0005 (half the smallest interval).
The mass of the object is 101.601-101.400 = 0.201g
The total uncertainty in mass of the object is 0.005 + 0.005 = +- 0.001g.
So we quote our answer as 0.201 +- 0.001
This expected value (0.2) is within the error range of this measurement (0.200 to 0.202) so it's completely accurate.

If the substance was dissolved in a measured 250mL of solution with a quoted uncertainty of +- 1.0mL, then the calculation of concentration in g/L would involve a division (Mass/Vol). This requires percentage uncertainties.
The percentage uncertainty in the mass is
0.001/0.201 x 100 = 0.498%
The percentage uncertainty in the volume is
1/250 x 100 = 0.40%
The concentration (g/L) is 0.201/0.250 = 0.804 g/L
The total percentage uncertainty in the answer is 0.498% + 0.40% = 0.90%
But 0.90% of 0.804 is 0.007 g/L
So our answer is
0.804 g/L +- 0.90%
or 0.804 g/L +- 0.007 g/L

You will sometimes hear the term "Error" used when referring to uncertainty but this really refers to the variation between your answer and the accepted or expected answer.

Instructions on how to calculate the error when measuring the liquids used in the experiment. Instruction are taken off the Chemistry  Class wikispaces.

27/05/13 Week 7 May 2013 Home 3

These are the results from the  second test. At room temperature there is no change in volume contraction, this suggests the contraction is an instantaneous action. There is contraction in both the both the temperature 2°C and 40°C. This type of information conflicts with the hypothesis. It is possible that there is a contraction in the 2°C test possibly due to water molecules arranging themselves together as they are close to the freezing point of water. The was minimal contraction in the 40°C which suggests evaporation could have occurred.  The results will be further analysed in the EEI write-up.

27/05/13 Week 7 May 2013 Home 2

What intermolecular forces are responsible for the volume contraction in alkanol and water mixtures?

What affects does the variable temperature have on volume contractions and in particular hydrogen bonding?

Above are the research questions that will be answered when performing  the EEI write-up using the information posted earlier in the blog.

http://ssccchemistry.wikispaces.com/file/view/water.pdf/423564640/water.pdf - Link for writing the introduction that has a great understanding of water taken from the class wiki spaces.

Above is information on the particle nature taken from the class textbook Chemitry in Use 1 which will be used to help answer the the second research question.

Below is some more information taken from the class text book to assist in the EEI write-up.

27/05/13 Week 7 May 2013 Home

Finalized version of the method to be included in the EEI write up:

There are two separate methods as there are two separate hypotheses.

Method 1

11.      Using a pipette measure  1/3  of 100ml methanol and pipette into a 100ml graduated cylinder.

22.      Using a pipette measure  2/3  of 100 ml distilled water and pipette into the same 100ml graduated cylinder.

33.      Stir using a stirring rod and wait for all air bubbles to settle.

44.      Record the volume displayed on the 100ml graduated cylinder.

55.      Repeat steps 1 to 4 another two times.

66.      Repeat steps 1 to 5 using ethanol.

77.      Repeat steps 1 to 5 using butanol.

88.      Using a pipette measure  1/4  of 100ml ethanol and pipette into a 100ml graduated cylinder.

99.      Using a pipette measure  3/4  of 100 ml distilled water and pipette into the same 100ml graduated cylinder.

110.   Stir using a stirring rod and wait for all air bubbles to settle.

111.   Record the volume displayed on the 100ml graduated cylinder.

112.   Repeat steps 8 to 11 another two times.

113.   Repeat steps 8 to 12 using ethanol.

114.   Repeat steps 8 to 12 using butanol.

115.   Using a pipette measure  1/5  of 100ml methanol and pipette into a 100ml graduated cylinder.

116.   Using a pipette measure  4/5  of 100 ml distilled water and pipette into the same 100ml graduated cylinder.

117.   Stir using a stirring rod and wait for all air bubbles to settle.

118.   Record the volume displayed on the 100ml graduated cylinder.

119.   Repeat steps 15 to 18 another two times

220.   Repeat steps 15 to 19 using ethanol.

221.   Repeat steps 15 to 19 using butanol.

Method 2

11.      Mix up the optimum ratio of methanol, ethanol and butanol.

22.      Record the contraction of each alkanol and water mixture.

33.      Place each mixture in water bath set to 40°C and leave for 24 hours.

44.      Record results.

55.      Repeat steps 1 to 4 two more times.

66.      Repeat steps 1 to 2.

77.      Place each mixture in a fridge set to 2°C and leave for 24 hours

88.      Record results.

99.      Repeat steps 6 to 9 two more times.

22/05/13 Week 6 May 2013 Period 2

The second test was conducted on temperature and these were the results.

The alcohol to water ratio used for the temperature test was 1 : 2

The first test was put in a fridge with a temperature of 2 degrees Celsius
The other test was put in the water bath at a temperature of 40 degrees Celsius

The original volume of the 2 degrees Celsius test was 95.1 ml and the volume after one day was 93ml

The original volume of the 40 degrees Celsius test was 95.1 ml and the volume after one day was 84.0ml

There was error involved in the 40 degree Celsius test, the beaker containing the liquids was not sealed with cling wrap and evaporation of substances occured.

A second test was conducted for the 40 degrees Celsius test, the results were as followed

The original volume was 95.5ml and the volume after one day was 92.8ml

The results both showed a contraction. to further justify these results a repeat was conducted and the results will be posted at a later date.