Investigating acids and alkalis
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Summary
Investigating acids and alkalis
In a nutshell
By adding powdered calcium hydroxide or calcium oxide to a fixed volume of dilute hydrochloric acid , the aim is to see how the changes as powdered alkali is added to the acid.
Equations
Word equation | Symbol equation |
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Equipment list
The following equipment list is used to conduct an experiment to evaluate the relationship between adding alkali to an acidic solution and pH.
Equipment | Use |
| Measuring cylinder | To measure the amount of dilute hydrochloric acid |
| Beaker | Where the solution is contained |
| Glass rod | Stirrer when adding powdered alkali and dabbing solution onto universal indicator paper |
| Universal indicator paper | Measure pH of solution |
| Spatula | Transfer of powdered alkali to the beaker |
| Hydrochloric acid solution | Solution to which base is added |
| Calcium oxide / hydroxide powder | Added to solution to elicit a change in pH |
Experiment: Adding powdered calcium hydroxide to hydrochloric acid solution and investigating the changes of pH
Experimental variables
Independent variables are variables which can be changed. Dependent variables are changed and are measured. Control variables are kept constant and do not change.
| Independent variable | |
| Dependent variable | |
| Control variable | |
Safety precautions
When performing experiments, it is very important you consider safety precautions. This is so you and others do not get hurt.
Hazard | RISK | SAFETY MEASURE |
| Hydrochloric acid | Causes serious eye damage | Wear gloves |
| Hydrochloric acid | Causes skin irritation | Wear safety gloves |
| Hydrochloric acid | Acid is corrosive and damages the skin and clothes | Use dilute acid |
| Calcium hydroxide powder | Causes skin irritation | Wear gloves |
| Calcium hydroxide powder | Causes serious eye damage | Wear safety goggles |
| Calcium hydroxide powder | Can cause respiratory irritation | Avoid making dust, make sure room is well ventilated |
Method
These are the instructions on how to complete the experiment.
| 1. | Use a measuring cylinder to add a specified amount of dilute hydrochloric acid to a beaker. |
| 2. | Dip a clean glass rod into the solution, transfer a drop of solution from the glass rod to a piece of universal indicator paper and place it on a white tile. Wait , then estimate the pH on the indicator paper by comparing it to the pH scale. Record the estimated pH. |
| 3. | Add a level spatula of calcium hydroxide powder to the solution in the beaker. |
| 4. | Stir thoroughly using a glass rod and record the pH of the mixture as done in step 2. |
| 5. | Repeat steps 3 and 4 until the pH no longer changes. |
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Analysis
Record the results in a table as follows:
Number of spatulas | pH |
| | - |
| | - |
Plot a graph to show the pH on the vertical () axis and the number of spatulas on the horizontal () axis. Make sure to use the appropriate scale so that the plotted area takes up at least .
Conclusion
Your graph should show an increase in pH until a certain point where adding is powdered alkali does not affect the pH.
Evaluation
Once you have completed the experiment it will be important to understand the shape of the graph and why the pH increase with the addition of alkali.
FAQs - Frequently Asked Questions
How do I plot the graph of the pH and number of spatulas?
Plot a graph to show the pH on the vertical (Y) axis and the number of spatulas on the horizontal (X) axis.
How do you find the pH of the solution?
Estimate the pH on the indicator paper by comparing it to the pH scale.
What equipment is required for an acids and alkalis practical?
The equipment required for this practical is: measuring cylinder, beaker, glass rod, universal indicator paper, spatula, hydrochloric acid and calcium hydroxide powder.