CHEMISTRY · Stage 8 · Chapter 8: Pure Substances and Solutions
Chemistry 8.9 Investigating temperature and solubility — Writing Up an Investigation
5 min read 7 parts Lesson 9 of 10
Lesson summary
8.9 Investigating temperature and solubility — Writing Up an Investigation — Alhussan International Academy — Chemistry (Stages 7–9) notes: Present evidence, write conclusions and evaluate an investigation of how temperature affects solubility.Observations — jottings such as "at …
- Results table
- Anomalous result
- Line graph
- Basic conclusion
- Detailed conclusion
- Explanation
Part 1 of 7Recording data
- Observations — jottings such as "at 0 °C, 7 g dissolved" are organised into a table to make patterns easier to spot and a graph easier to draw.
- Results table — write the independent variable (water temperature, °C) in the left column and the dependent variable (mass dissolved, g) in the right column.
- Include units in the column headings.
- Repeats — record repeated trials where possible and calculate means.
Part 2 of 7Analysing the evidence
- Pattern — as temperature increases, so does the mass of sodium carbonate that dissolves, so the prediction was correct.
- Anomalous result = a result that does not fit the pattern.
- In Hani's data the result at 10 °C was anomalous because the water was hotter than 10 °C when the reading was taken.
- State whether an anomalous result was included, and ignore it when drawing the line of best fit.
Part 3 of 7Bar chart or line graph
1Bar chart2 points
— draw one when the independent variable is categoric or discrete.
- Categoric variables are described by words.
- Discrete variables are numbers with no in-between values.
2Line graph1 point
— draw one when both variables are continuous.
- A continuous variable can have any numerical value.
Part 4 of 7Drawing a line graph
- Label the x-axis with the name and units of the independent variable.
- Label the y-axis with the name and units of the dependent variable.
- Choose a scale for each axis that uses most of the grid.
- Write evenly spaced values on the lines of each axis.
- Plot the points accurately.
- Draw a line of best fit to show the pattern, which can be a straight line or a smooth curve, ignoring anomalous results.
- Graph use — the graph can be used to predict values between the plotted points, such as the solubility at 35 °C.
Part 5 of 7Writing a conclusion
- Basic conclusionthe solubility of sodium carbonate increases with temperature, and the prediction was correct.
- Detailed conclusioninclude figures, for example solubility increases steadily from about 7 g/100 g of water at 0 °C to about 50 g/100 g at 50 °C.
- Explanationif a reason for the pattern is known, include it, for example that particles have more energy at higher temperatures and break up the solid more effectively.
- Link to the aimthe conclusion answers the aim using the evidence and says whether the prediction or hypothesis was supported.
Part 6 of 7Evaluating the investigation
- Limitation — Hani did not find the solubility at temperatures above 50 °C.
- Improvements — increase the range by taking readings at 60 °C and 70 °C.
- Repeat the anomalous reading at 10 °C.
- Repeat all readings to make the results more reliable.
- Quality of data — comment on whether repeats were close together, whether there were anomalies and whether the method was fair.
- Other limitations — judging when the solid has just stopped dissolving is subjective, and the temperature falls as the mixture cools in the air.
- Use a water bath, smaller steps of solute and more temperatures.
- Further work — test another solute.
Part 7 of 7Report structure and wording
- Order of a reportaim, hypothesis, variables, apparatus and method, results, analysis, conclusion and evaluation.
- Hypothesis a testable prediction with a scientific reason.
- Method wordinguse the passive voice and past tense.
- Key wordsreliable means similar results when repeated, accurate means close to the true value, and precise means finely measured.
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