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16.2Unit 8: Chemical reactions and neutralisation

Investigating acids and alkalis — Cambridge Checkpoint Science 0893 Revision Notes & Topical Questions

5 min read 9 parts Lesson 2 of 5 1 quiz

📚 Cambridge Checkpoint Science 0893 Hub / Topical Revision
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Lesson summary

16.2 Investigating acids and alkalis — CHECKPOINT (CHEMISTRY) notes: Use indicators and the pH scale and plan a fair test about acids and alkalis.pH — a number scale from 0 to 14 that shows how acidic or alkaline a solution is.Acids are below 7.Pure water and neutral solutions ar…

  • Universal indicator
  • Independent variable
  • Control variables
  • Anomalous result
  • Conclusion
  • Reliability

Section 1 of 9The pH scale

pH
  • pH a number scale from 0 to 14 that shows how acidic or alkaline a solution is.
  • Acids are below 7.
  • Pure water and neutral solutions are exactly 7.
  • Alkalis are above 7.
Strength
  • Strength the further from 7, the stronger the acid or alkali.

Section 2 of 9Indicators

IndicatorIn acidIn neutralIn alkali
LitmusRedPurpleBlue
Universal indicatorRed / orange / yellowGreenBlue / purple
Methyl orangeRedOrangeYellow
PhenolphthaleinColourlessColourlessPink
  • Universal indicator
    • gives a range of colours so that the pH value can be estimated.

Section 3 of 9Variables in a fair test

Independent variable
  • Independent variable the factor you change, such as the type of antacid.
Dependent variable
  • Dependent variable the factor you measure, such as the volume of acid neutralised.
Control variables
  • Control variables the factors kept the same, such as the volume and strength of acid and the temperature.

Section 4 of 9Investigating how antacids neutralise acid

1
Ask a question and make a prediction.
2
Measure the same volume of dilute acid into each beaker and add universal indicator.
3
Add a measured amount of one antacid at a time and stir.
4
Record the amount needed to reach a green colour.
5
Repeat for each antacid and repeat each test three times.
6
Calculate the mean for each antacid.

Section 5 of 9Recording and presenting results

Table
  • Table records the independent variable in the first column and repeats and the mean in the next columns.
Bar chart
  • Bar chart is used when the independent variable is a category such as the type of antacid.
Anomalous result
  • Anomalous result a result that does not fit the pattern and should be repeated or left out of the mean.

Section 6 of 9Drawing conclusions

Conclusion
  • Conclusion a statement that follows only from the results.
Reliability
  • Reliability repeating the test and getting similar results makes the findings more reliable.

Section 7 of 9Safety

Eye protection
  • Eye protection goggles are worn when using acids and alkalis.
Small volumes
  • Small volumes using small amounts of dilute solutions reduces risk.

Section 8 of 9Key terms

TermMeaning
VariableA factor that can change in an investigation.
Independent variableThe variable you change.
Dependent variableThe variable you measure.
Control variableA variable kept the same.
IndicatorA substance that changes colour in acids and alkalis.
MeanThe average of repeated results.

Section 9 of 9Exam technique

1
Changing more than one variable at once — only the independent variable may change.
2
Saying pH 7 is acidic — pH 7 is neutral.
3
Using a line graph for categories — use a bar chart.
4
Including anomalous results in the mean without checking.

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