Acid Test- How to Spot Minerals Separately

What is an Acid Test?

An Acid test is a chemical or metallurgical process where acids are used to identify the quality of material present in rock and mineral samples.

Table of contents

• Examples Of Acid Test
• Apparatus And Ingredients Required For Acid Test
• Experiment For Acid Test
• Result Of Acid Test
• FAQs

Examples of Acid Test

The rocks containing carbonate minerals are identified by the acid test. In this process, a drop of dilute (5-10%) hydrochloric acid is placed on a rock or mineral and watched for bubbles of carbon dioxide gas released. The bubbles signal the presence of carbonate minerals present in the rock and mineral.

An Acid test is also used for the gold test, any gold-coloured item rubbed on a black stone leaves a visible mark, this mark is tested by applying aqua fortis (nitric acid), which dissolves the mark of all gold-coloured items except gold. If the remaining mark is tested with aqua regia (1:3 ratio of nitric acid and hydrochloric acid) it dissolves.

Let us see how minerals change when we put acid on them

Apparatus And Ingredients Required To Perform The Test

Below are the equipment and materials required to conduct the acid test to spot minerals separately.

1. The mineral sample set viz. lodestone, azurite, rose quartz, amethyst, calcite, pyrite, talc (8 Nos).
2. Vinegar (one bottle).
3. Steel nail
4. Paper and Pencil
5. Magnifying glass
6. Eyedropper
7. Paper towel
8. Cup(Non-reactive metal)

How To Perform The Experiment

Let us understand the different steps that need to be followed to successfully carry out the acid test to spot the minerals separately. Below eight steps will guide you to experiment.

Step 1: Make columns under various headings on the piece of paper with words like Fizz, Sample and Powder.

Step 2: On the left edge of the paper with the sample heading, write down the name of mineral samples like pyrite, calcite etc.

Step 3: Pour a little vinegar ( Vinegar typically contains 5–8% acetic acid by volume) into the cup provide which you can take later with an eyedropper.

Step 4: Keep the mineral sample of your choice on the paper towel and use the eyedropper to pour a drop of vinegar (acid drop) on it.

Step 5: Look at the mineral closely and see the outcome of the chemical reaction like the vinegar fizzling. If it is, write Yes under the column of fizz or else write No.

Step 6: If the vinegar didn’t give the intended outcome of fizzing, use a steel nail and scratch the mineral sample. If there is no impact on the mineral, write the mineral being “too hard “under the column named powder. If in case the scratch produces some mineral powder, put a drop of vinegar on the mineral powder.

Step 7: With the magnifying glass, see whether the mineral is fizzing or not and write the outcome being a yes or no under the powder column

Step 8: Follow the same pattern for every other mineral sample.

Results of the acid test

Let us first look at the results of minerals which have calcium carbonate in them. Such minerals will fizz in the first attempt. If there are minerals with close bonding at the molecular level with calcium carbonate as the main component, they need to be powdered to check the difference between minerals. This is one of the easiest ways where one could spot the differences between these minerals.

Carbonate minerals are unstable in contact with acid. When acid begins to effervesce (fizz) on a specimen, a reaction similar to the one shown below is taking place.

CaCO₃ + CH₃COOH → Ca(CH₃COO)₂ + H₂O + CO₂

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