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.

18/05/2013 Week 6 Sunday Home

Results updated:

Ratio	Methanol				Ethanol			Butanol
1:2	94.7	95.9	95.2		94.5	94.3	94.9	95.8	96.9	96.9	96.0	96.2
1:3	97.9	98.3	98.1	96.9	97.4	97.5	97.1	96.9	96.8	96.8
	96.9	97.8	97.8	97.7
1:4	97.1	96.8	97.0		97.1	97.2	97.0	97.0	97.1	97.2

Now that the results for the first section of the report have been recorded and tabulated I am ready to begin testing the second hypothesis regarding temperature.

In conclusion the results convey that the higher the amount of alcohol in the ratio the higher the volume contraction.

15/05/2013 Week 5 Wednesday Home 2

After further understanding of research question and hydrogen bonds, a flaw has arisen in my one of my assumptions earlier on in my blog under the post titled 1/05/2013 Week 3 Wednesday Home.

Under this post in the 6th paragraph I stated that:

I hypothesise this as volume contraction is a direct result of hydrogen bonding from the Oxygen molecule bonding to the Hydrogen's  connected to the carbon chains of the alkanols, when these hydrogen bonds occur they ultimately surround and compress the alkanol molecule. As alkanol carbon chains get larger e.g. methanol, ethanol, propanol etc... There are more readily available hydrogen's available to bond, therefore a more complex alkanol should result in a large volume contraction.

 I took the liberty of constructing a diagram to assist in the explanation. Paragraph 6  has suggested the bond indicated between Ethanol and Water in the diagram above, however a for a bond to become a hydrogen bond it can only be bonded  to an O, N or F atom in one molecule becoming attached to an O, N, or F atom in a different molecule. The problem here is that the Hydrogen is bonded to a Carbon and an Oxygen.

The correct bond is indicated in the diagram above and shows hydrogen being bonded to two oxygen molecules. This bond is bonding to the alcohol group of the alkanol and not the carbon chain. The correct assumption written in the blog post: 1/05/2013 Week 3 Wednesday Home is:

I hypothesise this as volume contraction is a direct result of hydrogen bonding from the Oxygen molecule bonding to the Hydrogen's connected to the alcohol group of the alkanols, when these hydrogen bonds occur; they ultimately surround and compress the alkanol molecule. As alkanol carbon chains get larger e.g. methanol, ethanol, propanol etc... There are more readily available hydrogen's available to bond, therefore a more complex alkanol should result in a large volume contraction.

15/05/2013 Week 5 Wednesday Home

Results updated:

Ratio	Methanol				Ethanol			Butanol
1:2	94.7	95.9	95.2		94.5	94.3	94.9	95.8
1:3	97.9	98.3	98.1	96.9	97.4	97.5	97.1	96.9
	96.9	97.8	97.8	97.7
1:4	97.1	96.8	97.0		97.0	97.2	97.0	97.0

Physical observations of the butanol mixtures in all three ratios were different to all physical observation previous. In the previous the Methanol and Ethanol tests, it was clear that there was alcohol mixed through out the water and the water appeared cloudy.

In the Butanol tests the contraction was present yet there was no clear mixutre of the two compounds. The water and alkanol clearly separated from each other. To see whether they will mix over time I left all three tests separate covered and will check them tomorrow.

It apparent so far that the longer the alkanol chain has a affect of the diffuseness gradient.

12/05/2012 Week 5 Sunday Home 2

HYDROGEN BONDS

The third and strongest type of inter molecular force is a hydrogen bond

A hydrogen bond is a  type of intermolecular force that involves a hydrogen atom bonded to an O, N or F atom in one molecule becoming attached to an O, N, or F atom in a different molecule. (I will insert the textbook reference after)

O, N and F atoms have very strong electron-attracting powers— they are the three most electronegative elements. This means that the bonding electrons O-H, N-H and F-H bonds are strongly attracted to the H atom becoming positively charge. In addition, the small size of the the H atom means that two adjacent molecules can get closer together: the positive H atom, bonded to the O, N or F atom in one molecule, forms a strong attractive intermolecular force. (I will insert the textbook reference after)

Ethanol - Water with hydrogen bonding:

Various molecules may mix and dissolve in each other if they have approximately the same type of polarity. In the case of water and ethanol, this is the situation. The hydrogen of the -OH group on alcohol is polar as it is in the water molecule.

Therefore, the hydrogen of the -OH group on the ethanol may hydrogen bond to an oxygen of a water molecule (shown) or to an oxygen of an alcohol (not shown).

(http://www.elmhurst.edu/~chm/vchembook/162othermolecules.html)

Hydrogen bonding in alcohols

 An alcohol is an organic molecule containing an -O-H group.

Any molecule which has a hydrogen atom attached directly to an oxygen or a nitrogen is capable of hydrogen bonding. Such molecules will always have higher boiling points than similarly sized molecules which don't have an -O-H or an -N-H group. The hydrogen bonding makes the molecules "stickier", and more heat is necessary to separate them.

Ethanol, CH3CH2-O-H, and methoxymethane, CH3-O-CH3, both have the same molecular formula, C2H6O.

They have the same number of electrons, and a similar length to the molecule. The van der Waals attractions (both dispersion forces and dipole-dipole attractions) in each will be much the same.

However, ethanol has a hydrogen atom attached directly to an oxygen - and that oxygen still has exactly the same two lone pairs as in a water molecule. Hydrogen bonding can occur between ethanol molecules, although not as effectively as in water. The hydrogen bonding is limited by the fact that there is only one hydrogen in each ethanol molecule with sufficient + charge.

In methoxymethane, the lone pairs on the oxygen are still there, but the hydrogens aren't sufficiently + for hydrogen bonds to form. Except in some rather unusual cases, the hydrogen atom has to be attached directly to the very electronegative element for hydrogen bonding to occur. (http://www.chemguide.co.uk/atoms/bonding/hbond.html)

12/05/2013 Week 5 Sunday Home

Results so far on the experiment

Ratio	Methanol				Ethanol			Butanol
1:2	94.7	95.9	95.2		94.5	94.3	94.9
1:3	97.9	98.3	98.1	96.9
	96.9	97.8	97.8	97.7
1:4	97.1	96.8	97.0

These are the rough results so far, all measurements are in ml. There were more than three tests conducted for methanol , ratio 1:3, because there were not consistent results that followed a patter as the ratio increased.

So far the results show that the more alcohol in the ratio, the larger the contraction.

1/05/2013 Week 3 Wednesday Home 2

Method Draft

1. Measure appropriate of alkanol into graduated cylinder and pour into a 100mL beaker.

2. Measure the correct ratio of water to alkanol (1:2, 1:3 and 1:4) into a graduated cylinder and pour into the  beaker containing the alkanol.

3. Wait 10 seconds and record the volume contraction

4. Repeat 3 times 

5. Repeat steps 1-4 with a different alkanol

For the second part of the EEI

The second method for the next part of the EEI will be drafted up later.

1/05/2013 Week 3 Wednesday Home

A similar experiment was was undergone by Dmitri Mendeleev (Analytical and Bioanalytical Chemistry, 2009, V 395 (1) 2009, p7-8)) where ratios of volume contraction through water and alcohol were tested and he felt that a ratio of 1:3 ethanol to water resulted in the best contraction. A report of some of his work can be found here.

http://seniorchem.com/mendeleyev_vodka.pdf

With this information in mind the first part of my EEI will conduct an experiment to test the validity of this statement by Mendeleev. Earlier on I talked about a possible hypothesis where I stated the higher the water ratio is to alcohol, the larger the resulting contraction will be, this hypothesis alone will not be the sole research question into my EEI, however I will have several hypotheses/research questions that I will investigate.

The first section of my EEI will test Mendeleev's research by testing the following ratios, 1:2, 1:3 and 1:4 (I will not be testing 1:1 as I feel the contraction will be minimal when compared to other ratios). I will be doing 3 repeats of each individual test resulting in 9 overall tests to have a wide spread of data and ensure accuracy. This first section of my EEI will be a relatively short one as this initial experiment will not take long.

I decided upon the separate alcohol and water mixture to equal 100mL. Mendeleev during his experiment found this perfect ration only through the volume contraction of ethanol as pure ethanol is pure alcohol and  very common. I will be taking this one step further and testing the following alkanols; methanol, ethanol and propanol resulting in a total of 27 tests including repeats once all alcohols are tested. From this information I will be able to analyse how the volume contraction affects different alcohols at different rations and determine whether the ratio of 1:3 is optimal for all three alcohols or whether their chemical structure and hydrogen bonding effects the overall volume contraction. 

I hypothesise that the optimal ratio for volume contraction will 1:3 for all alkanols and that as the molecular complexity of each alkanol increases the volume contraction will be larger.

I hypothesise this as volume contraction is a direct result of hydrogen bonding from the Oxygen  molecule bonding to the Hydrogen's  connected to the carbon chains of the alkanols, when these hydrogen bonds occur they ultimately surround and compress the alkanol molecule. As alkanol carbon chains get larger e.g. methanol, ethanol, propanol etc.. there are more readily available hydrogen's available to bond, therefore a more complex alkanol should result in a large volume contraction.

If all is said and done I will further test the validity of the volume contraction by testing how well it performs under temperature changes. I have researched how hydrogen bonds are effect by temperature and an increase in temperature results in molecules moving fast therefore effecting the hydrogen bonds. 

I hypothesise that an increase in temperature will result in a reduction in volume contraction.

I hypothesise this because the increased temperature should have faster moving molecules which should result in weaker hydrogen bonds. Weaker hydrogen bonds suggest that a smaller contraction will occur as they will not compress the alkanol as much.

Overall these tests should provide a lot of depth hydrogen bonding and inter molecular forces.