Quantitative And Qualitative Analysis

Quantitative and Qualitative analysis
Ensuring accuracy in both quantitative and qualitative methods.
Accurate data collection is essential in maintaining the integrity of research. Working accurately greatly decreases the possibility of an error occurring in an experiment, provides a greater chance of producing expected results and provides knowledge gained only from proven results.
Quantitative methods generate numerical data or data that can be transformed into useable statistics. It is used to quantify attitudes, behaviours and other defined variables and to formulate facts and uncover patterns in research (Wyse S., 2011). Quantitative research is made using scientific methods such as experimental control, collection of empirical data, analysis of data and practicals such as titrations. Qualitative methods, on the other hand, are the examination, analysis and interpretation of observations for the purpose of discovering underlying meanings and patterns of relationships in a manner that does not involve mathematical models (Wikipedia, 2015).
GCSE Science (2014) states that accuracy is the degree of closeness a measurement of a quantity is to that quantity’s actual value. With quantitative methods, accuracy defines the limits of the errors. Ideally, a piece of apparatus (e.g. a burette in a titration) is both accurate and precise, with measurements generated close to the true value. To ensure accuracy in quantitative methods, apparatus must be calibrated, checked and analysed before use to certify that the instrument is fit for purpose. In addition, the investigator should be competent in using said apparatus and in carrying out the experiment as equipment could be misused, measurements misread and techniques performed incorrectly which results in the undermining of the accuracy and validity of a research study (Answersresearch.com, n.d.). Furthermore, repeat tests are commonly carried out and an average calculated to improve the accuracy of the results. Errors in measurement are random and by averaging multiple measurements taken, you can find a value that is consistent and statistically close to the actual (true) value. The more trials there are, the closer to this value they will become – this is due to the denominator that you use to calculate the mean increasing as the number of trials also increases. Another way of ensuring accuracy in quantitative methods is to use a lower concentration of a substance, microorganism or analyte.
Qualitative methods include flame and food testing. Accuracy in qualitative techniques is difficult to achieve and inaccuracies are usually caused by the investigator making a mistake or being unfamiliar with the experiment. For example, a flame test can be made accurate if the investigator is familiar with the expected results and knows that they are looking for (i.e. a green flame for Barium). Before carrying out such tests, equipment should be cleaned to avoid contamination. As well as this, contamination could occur due to impurities in compounds used and so pure compounds should be used to prevent this. Repeat tests are also a good way of ensuring accuracy in qualitative methods because the investigator can check to see if he/she is generating the same result each time. If they are not then an error has occurred somewhere in the method or with their technique. Control solutions may be used to compare results obtained from tests and allow clear identification of a change (e.g. a colour change). Standardisation of volumes of a solution will mean that the method is consistent and no variables have been changed – this results in a more reliable and fair test.

Evaluation of own techniques
To demonstrate good technique, competence and safe working practice in a quantitative analysis, we carried out a series of titrations of sodium carbonate and hydrochloric acid. I believe that, with each experiment, I became increasingly competent in carrying out titrations and making standard solutions. The method used (described in the accompanying lab notebook) was straightforward, allowing it to be easily followed. However, in some of the titrations the results obtained were not expected and problems with the method and technique were most likely the reason for this.
The apparatus used and the way it had been set up was effective and accurate. A 50 ml burette was used because it guarantees the smallest possible relative error and provides finer volumes. It also has a tap which enabled us to easily control the amount of hydrochloric acid released into the conical flask. This meant with each run we could decrease the amount of acid released and eventually reach the exact point at which the sodium hydroxide was neutralised. Any number of errors could have occurred during the titration, many of which are either human or equipment error. One possible source of error would have been the misuse of the burette or a faulty valve because I noticed that, as we opened and closed the tap or refilled the burette between runs, some acid escaped down the side of the burette or leaked out and dripped into the conical flask below. Consequently, the volume of solution used will not have been correct, affecting the overall result. This error could be minimalised in the future by first checking that the burette is not faulty and by careful calibration of the glassware carried out by the tutor beforehand. Additionally, it was hard to read the volume on the burette scale due to the height of the table it had been placed on. Thus, the measurement was read at an angle - looking from below, the volume seemed to be higher than it actually was and so the measurement was in error. Similar to before, this would affect the overall result as the volume used is the main value in calculating the titre. To make sure that this did not happen again, we could place the apparatus on a lower bench and at eye level. Such improvement would allow the volume to be read at eye level and would subsequently mean the measurement is more accurate.

http://www.gcsescience.com/hsw10.htm http://en.wikipedia.org/wiki/Quantitative_research http://www.snapsurveys.com/blog/what-is-the-difference-between-qualitative-research-and-quantitative-research/ http://www.answersresearch.com/article9.php As part of this unit we were required to carry out a quantitative analysis – a titration. According to Avogradro.co.uk (n.d.), the technique of titration is used to “find out accurately how much of a chemical substance is dissolved in a given volume of a solution, that is, the concentration of the solution”. Titrations use a particular set of apparatus (burette, pipette, scales and volumetric flask) with which volumes are measured to an accuracy of greater than 0.1cm3 (Avogadro.co.uk, n.d.). The accuracy of each measurement taken depended on the quality of the measuring apparatus and the skill of the investigator (BBC, n.d.). As a way of ensuring accuracy, each piece of equipment should be calibrated before use to prevent errors occurring from faults, e.g. incorrect readings on a scale. Furthermore, the investigator must be competent in carrying out the experiment because poor technique leads to misread/incorrect measurements, misuse of apparatus and greater errors. Another way that accuracy can be ensured in a titration is to use a lower concentration of solution. This is because there is less of a chance of missing the ‘endpoint’ with a lower concentration than a higher concentration. A reading is usually within ±0.5 when titrating a low concentration of solution and so the titre will be bigger - this, in turn, lowers the overall percentage error.

If the apparatus is faulty, or the scientist makes a mistake, the measurement may be inaccurate. The selection of appropriate instruments and clearly delineated instructions of their correct use reduce the likelihood of errors occurring (ori.hhs.gov, n.d.).

http://ori.hhs.gov/education/products/n_illinois_u/datamanagement/dctopic.html http://www.bbc.co.uk/schools/gcsebitesize/science/21c_pre_2011/materials/measuringpropertiesrev1.shtml