1.5Chapter 1: The Particle Model and States of Matter

Investigating boiling points — Alhussan Chemistry - Stage 7 Revision Notes & Topical Questions

5 min read 8 parts Lesson 5 of 8 3 quizzes

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Lesson summary

1.5 Investigating boiling points — Experimental Heating Curves — Alhussan International Academy — Chemistry (Stages 7–9) notes: Plan an investigation into boiling point, interpret a heating curve and data tables, and explain why boiling point matters.Hypothesis = a possible expla…

Anomalous result
Prediction
Limitation
Improvements
Sloping line
Flat line at the boiling point

Part 1 of 5Making a hypothesis and collecting evidence

Hypothesis

Hypothesis a possible explanation that is based on evidence and can be tested further.

Rabia's hypothesisthe higher the altitude (height above sea level), the lower the boiling point of water.

Testable

Testable evidence can be collected,
- so Rabia asked relatives in other places to measure the boiling temperature of water and found altitudes on the Internet.
One measurement in Mumbai alone is not enough evidence.

Recording

Recording results go in a table so all the data are easy to see, then a line graph makes the pattern easier to spot.

Part 2 of 5Analysing the evidence

Place	Altitude (m)	Boiling temperature of water (°C)
Chennai or Mumbai, India	0	100
Jos, Nigeria	1200	96
Srinagar, India	1585	95
Leh, India	3524	88
Summit of Puncak Jaya, Indonesia	4884	83
Summit of Mount Everest, Nepal	about 8850	69

Pattern

Pattern as altitude increases, the boiling temperature of water decreases, which supports the hypothesis.

Anomalous result

Anomalous result one that does not fit the pattern.

The reading for Riyadh (40 °C at 610 m) was wrong because the air temperature was measured, not the boiling temperature,
- so it is left out and the reason given.

Prediction

Prediction reading the graph at 2400 m (Addis Ababa) gives a boiling temperature of about 93 °C.

Limitation

Limitation the investigation does not explain why boiling temperatures differ at different altitudes,
because lower air pressure at height lets water boil at a lower temperature.

Precision

Precision three pots boiled in Srinagar gave the same temperature each time, so the data are precise.

Improvements

Improvements repeat the experiment three times and use thermometers with a suitable range and small scale divisions.

Part 3 of 5Reading a heating curve

Reading a heating curve

Axes

Axes plot temperature on the y-axis against time on the x-axis.

Sloping line

Sloping line the temperature rises as energy from the heater makes particles move faster, so their average kinetic energy increases.

Flat line at the boiling point

Flat line at the boiling point the temperature does not change although heating continues.
The energy is used to separate the particles, not to speed them up.

Pure substances

Pure substances they have a sharp, fixed boiling point, for example 100 °C for water at normal atmospheric pressure,
while a mixture boils over a range of temperatures.

Method

Method find where the line becomes flat, read the temperature from the y-axis, and explain the flat line in terms of energy and particles.

Part 4 of 5Accuracy and reliability

Repeat the experiment and calculate a mean.

Sources of error

Sources of error reading the scale from the wrong angle, heat lost to the surroundings, and a thermometer touching the bottom of the beaker,
which is hotter than the liquid.
A lid or insulation reduces heat loss.

Variables

Variables the independent variable is time, the dependent variable is temperature and control variables include the volume of liquid and the heat source.

Part 5 of 5Why the boiling point matters

Identification

Identification boiling points are used to identify substances by comparing with data-book values.

Purity

Purity impurities, such as dissolved salt in water, raise the boiling point slightly.
A boiling point different from the data-book value suggests the sample is not pure.

Key terms

Term	Meaning
Hypothesis	A possible explanation based on evidence that can be tested further.
Anomalous result	A result that does not fit the pattern.
Altitude	Height above sea level.
Heating curve	A graph of temperature against time while a substance is heated.
Boiling point	The temperature at which a liquid boils.
Precise	Giving results that are close together when repeated.