Hey guys,
Would a colour change in an indicator when performing an acid-base titration be quantitative or qualitative? I think it's qualitative but my teacher said it was a 'quantitative estimate' since your estimating the approximate pH of the solution based on the colour of the indicator.
thanks
Im not sure about this, but I would say that the colour change itself is qualitative data (if you were to record that the colour changed from blue to red for example) but If you were recording the volume of titre at the colour change, then that would be quantitative data.
This is becuase qualitative data deals with decriptions/characteristics while quantitative data deals with numerical values
Hey guys, just a question about addition reactions
Let's say you react ethene (C2H4) with hydrogen bromide (HBr).
When the addition reaction occurs, do each of the atoms in the small molecule you are reacting (in this case HBr) always bond to a different carbon?
So in this case, H would bond to one C atom and Br would bond to the other C atom?
Or could they both bond to the same C atom?
They would bond to different Carbons. Carbon atoms will form 4 single bonds/1 double bond and 2 single bonds/1 triple bond and 1 single bond generally. If H and Br from hydrogen bromide were to both be added onto the same carbon from ethene, you would have a carbon with 3 single H-C bonds, 1 C-Br bond and a C-C bond (to the other carbon) making a total of 5 single bonds on that carbon, while you will also have another carbon with 3 single bonds (2 C-H bonds and a C-C bond). This just doesn't happen - it doesn't follow the rules of how carbon likes to bond.
Instead each atom from HBr will be added to another Carbon atom so that you have 2 carbons which each make 4 single bonds with other atoms.
These are some questions from the jacaranda textbook (I don't have the solutions) that I am struggling to answer. It would be great if you could help me out.
1) List two procedures that could adversely impact on the internal validity of an experiment.
- if factors other than the independent variable are not controlled and influence the dependent variable (eg. in an experiment to determine the effect of the length of hydrocarbon chain on its retention time in HPLC, if the temperature/pressure/length of column is not controlled, results will be inconclusive)
- if you want to measure a temperature change of 0.1șC, but use a thermometer with an uncertainty of ±2șC, you will not be able to measure the dependent variable accurately
2) Is it essential that the results of an experiment can be replicated in order for the experiment to be considered
reliable? Explain your answer
- yes, because reliability is the ability of another researcher to repeat your experiment by following the same method and obtain the same results, so in order to be reliable, results must be replicable.
3) Explain, how an experiment can be reliable but not valid, and why an experiment that is valid must also be reliable.
- an experiment can yield the same results when it is repeated but the results might be consistently affected by an uncontrolled variable in the same way, so an exclusive relationship between the independent variable and dependent variable cannot be identified.
- if the results are not reliable, they must be influenced by random or systematic errors which affect their repeatability, and also reduce the accuracy of the experiment which reduces the validity.
4) Give an example of a strength and a weakness of quantitative and qualitative data.
- quantitative:
- strength: measurable, more objective than qualitative data
- weakness: its accuracy and precision can be compromised by sources of error, can be difficult to obtain for some experiments
- Qualitative:
- Strength: consists of descriptive observations of results, provides more depth and detail than quantitative results, open to interpretation
- weakness: subjective, less reliable
Thank you so much.
1. Internal Validity refers to the ability of the experimental design to accurately identify the effect of the IV on the DV
Both of your examples here do talk about potential aspects of an experimental design that does reduce its ability to accurately identify the effect of the IV on the DV, as such I think they are good responses.
2. Reliability isn't neccasarily the ability of another researcher to obtain the same data (this is an aspect of it though). Reliability refers to the ability of an experimental design to produce consistant data - this might be in the context of the same experimenter conducting the experiment multiple times, or by other experimenters conducting the experiment. Reliable experiments will produce precise (tightly grouped) data.
I think you would get the marks for what you have written though - its just that its probably best to refine your definition of reliability since VCAA does talk about it also in the context of repeating the same experiment/using large sample sizes (not reccasarily just others doing the experiment)
3. Rather than just saying that the experiment may be reliable but not valid due to uncontrolled varaiable, its probably best to identify systematic errors as the specific source of this inaccuracy of the experiment (systematic errors are things like incorrectly calibrated scales which will consistanly provide inaccurate results across all trials). Also rather than saying 'exclusive', I would personally write' accurate'.
Note that in your second point, systematic errors do not effect reliability - they still return reliable results as they have the same impact across all trials. Rather, if an experiment is unreliable, it indicares the presence of random errors which (like you said) reduced the accuracy of the relationship between the IV and the DV, thus reducing the validty of the experiment
4. I think these are mostly good responses. However, for the strength of qualitative data, your first point is not a strength but more of a description of what it is, and your last point is actually a weakness, not a strength - the strengths of qualitative data is that it can (like you said) provide additional depth to results, and may allow for data collection where quantitative aproaches are impractical (i.e. noting the nature of a color change during a reaction). For the weaknesses of qualitative data, its lower reliability is due to its subjectivitiy (something that you might want to explain) since it might rely on the experimenters own interpretation of an event which may change from experimenter to experimenter and may not actually be accurate - I wouldn't put reliability and subjectivity as seperate weaknesses.
Hope this helps and good luck with chem!