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Unit 2: Dissolving, solubility and chromatography

Planning a solubility investigation — HIA International - Grade 7 Revision Notes & Topical Questions

5 min read 8 parts Lesson 4 of 5 3 quizzes

📚 HIA International - Grade 7 Hub / Topical Revision
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Lesson summary

2.3 Planning a solubility investigation — HIA INTERNATIONAL notes: Plan a fair test of how temperature affects the amount of salt that dissolves, identifying the variables.Variable = something that can change and affect results.Independent variable = the variable you change.Depen…

  • Control variables
  • Volume of water
  • Temperature control
  • Equipment and method
  • Results table
  • Graph axes

Section 1 of 8Variables in an investigation

Variable
Variable something that can change and affect results.
Independent variable
Independent variable the variable you change.
Dependent variable
Dependent variable the variable you measure, which depends on the independent variable.
Control variables
Control variables the variables you keep the same to make the test fair.

Section 2 of 8Variables in the salt and temperature investigation

Independent variable
  • Independent variable the temperature of the water.
Dependent variable
  • Dependent variable the number of spatulas of salt that dissolve.
Control variables
  • Control variables the volume of water (50 cm3), the type of salt, the size of the spatula and the amount of stirring.
Volume of water
  • Volume of water if it is not kept the same, more water would dissolve more salt and the test would not be fair.

Section 3 of 8Planning decisions

Volume of water
  • Volume of water decide on one volume and keep it fixed.
Temperature control
  • Temperature control decide how to change and keep the water at each temperature while adding salt.
Range
Range the highest and lowest temperatures used, chosen to be practical.
Interval
Interval the gap between temperatures, for example 10 °C or 5 °C.
Safety
  • Safety carry out a risk assessment for hot water and equipment.
Equipment and method
  • Equipment and method write a full step-by-step method before starting.

Section 4 of 8Results table and graph

Results table
  • Results table choose the columns, headings with units, and number of readings.
Repeats
  • Repeats repeat the tests to check results.
Graph axes
  • Graph axes the independent variable always goes on the horizontal axis and the dependent variable on the vertical axis.
Graph label
  • Graph label the vertical axis would read number of spatulas of salt dissolved.

Section 5 of 8Method for the investigation

1
Measure 50 cm3 of water into a beaker and bring it to the first temperature.
2
Add salt one spatula at a time, stirring after each, until no more dissolves.
3
Record the number of spatulas.
4
Repeat at each temperature from 20 °C to 80 °C.
5
Plot a graph and write a conclusion.

Section 6 of 8Evaluating the investigation

Accuracy
  • Accuracy check whether the equipment and measurements were precise.
Improvements
  • Improvements measure the mass of salt, repeat readings and use a water bath.
Other salts
  • Other salts copper sulfate or lead chloride would give different amounts because each salt has its own solubility.

Section 7 of 8Key terms

TermMeaning
Independent variableThe variable that is changed.
Dependent variableThe variable that is measured.
Control variableA variable kept the same.
RangeThe highest and lowest values used.
IntervalThe gap between values.
AccurateClose to the true value.
ReliableGiving similar results when repeated.
Risk assessmentIdentifying hazards and how to reduce them.

Section 8 of 8Exam technique

1
Changing more than one variable — the test is no longer fair.
2
Putting the independent variable on the vertical axis — it goes on the horizontal axis.
3
Confusing range and interval — range is the highest and lowest values, interval is the gap.
4
Forgetting to keep the volume of water the same.

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