FlashCards for ATP

Q. What is the difference between qualitative and quantitative data?

Qualitative: non-numeric data collected through observation.

Quantitative: data that can be measured.

Q. Give examples of qualitative data.

- Colour of a solution

- Observations of precipitates

- pH when using an acid-alkali indicator

Q. Give examples of quantitative data.

- Height

- Temperature

- Mass

- Age

Q. What are anomalies?

Data that does not fit the trend.

Q. Why does repeating an experiment increase the accuracy?

Gaining more data allows easy identification of anomalies, which can be removed, making the results more accurate.

Q. Why is it important that all observations are written down during an experiment?

Observations help explain the reactions occurring in an experiment, and they are used to draw conclusions.

Q. What is an estimation? Why are they used in experiments?

Estimates are rough calculations of values. They are useful in experiments because they quickly show if there is a general relationship between variables.

Q. How are approximations used during a titration?

The point at which neutralisation occurs is estimated when a trial titre is completed. This shows the approximate volume of solution that needs to be added from the burette. As a result, the burette solution can be added dropwise close to the end point in future titrations, increasing accuracy.

Q. How is the mean titre calculated after a titration?

2 concordant results are used (within 0.1 cm3 of each other). The rough trial should not be included in this calculation. Mean = Sum of results / Number of results.

Q. What are the median and mode of a set of data?

Median: the middle value when all values are placed in numerical order.

Mode: the most common value in the data.

Q. What is interpolation?

If the value being measured does not fall exactly on a scale division, you can interpolate and estimate a more precise reading.

Q. How many significant figures should calculated results be given to?

The same number of significant figures as (or one more than) the least accurate measured quantity.

Q. How are the independent and dependent variables laid out in a table?

The independent variable is always in the first column, with the dependent variable in the next column.

Q. When plotting a graph, what key points should be remembered?

- Draw in pencil

- Must fill at least half the available space

- Appropriate scale must be used

- Label axes (including units)

- Plot each point as a cross

- Draw a ring around outliers

- Line/curve of best fit

Q. Why are graphs often used to display data?

They clearly show patterns and trends in the data and make anomalous results easy to spot.

Q. When graphing results, on which axis do the independent and dependent variables go?

Dependent variable - y-axis

Independent variable - x-axis

Q. How can an anomalous result be identified from a scatter diagram?

The anomalous data value will fall outside the trend of all the other data values and will not lie on or near the line of best fit.

Q. What information should be included ina conclusion?

- Hypothesis

- Whether or not  the data supports the original hypothesis

- Scientific knowledge to explain the shapes/trends of graphs and data

- Evaluation of the results

- Relevant improvements

Q. How might the range of intervals used in an experiment be changed to allow more valid conclusions to be drawn?

If the trend is difficult to see, broader or narrower intervals can be used. If there is little change across the data, the intervals should be broadened to investigate a larger range of values. If there is lots of quick, abrupt changes across the data, intervals should be narrowed to see the trend in more detail.

Q. Solution is known to be an alcohol. How can you distinguish whether it is a primary, secondary or tertiary alcohol?

Add acidified potassium dichromate. For primary and secondary alcohols, the solution will turn from orange to green. For tertiary alchols the solution will remain orange. To distinguish between primary and secondary alcohols, test the product of the above reaction with Tollens' reagent. If a silver mirror is formed, then the original solution was a primary alcohol, else a secondary alcohol.

Q. Which qualitative test can be used to distinguish an aldehyde from a ketone?

- Add Tollens' reagent. A silver mirror formed on the test tube for an aldehyde. No change for ketone.

- Add Fehling's reagent. A blue solution turns brick-red for an aldehyde. No change for ketone.