Given four unlabeled compounds and four labels (potassium sulfate, potassium carbonate, chromium sulfate, and cobalt bromide) is there a simple test that will allow correct labelling of each compound?
I take we are looking for a simple school lab type test?
If only allowed one reagent then consider the following properties:
cobalt (II) bromide is green (the hydrate is is a reddy violet colour)
chromium (III) sulfate (usually a hydrate) is violet
potassium sulfate is white, colourless solution in water.
potassium carbonate is white, colourless solution in water and evolves CO2 with acid.
Post your answer if you want to check it.
Dr Russ
The question states two of the compounds are white solids and the other two are green solutions.
I had already found out that the two potassium compounds are white solids and cobalt bromide is green. I couln't find out the colour of chromium sulfate (but had assumed it was green because of the question), so thank you for that. What would turn a solution of chromium sulfate green?
I had worked out all of your clues, but I just don't know the answer.
I am studying Yr 12 Chemistry, but have not done Yr 11. Is there something I should have learnt but haven't yet?
To determine the correct labeling of each compound, we can perform a simple test based on the properties of the compounds provided. Here's how you can do it:
1. Take one of the unlabeled compounds and dissolve it in water to form a solution.
2. Add a few drops of a solution of cobalt (II) bromide to the test tube containing the unknown compound. If the solution turns green, then the compound is cobalt (II) bromide. Label it accordingly.
3. If the solution does not turn green, discard the solution and repeat steps 1 and 2 with another unlabeled compound.
4. For the remaining compounds, dissolve each one separately in water and perform the following tests:
a. Add a few drops of hydrochloric acid to one of the solutions. If bubbles of carbon dioxide gas are evolved, then the compound is potassium carbonate. Label it accordingly.
b. If no bubbles are evolved, add a few drops of barium chloride solution to the solution. If a white precipitate forms, then the compound is potassium sulfate. Label it accordingly.
5. The remaining compound is chromium (III) sulfate. It should be a violet-colored solution when dissolved in water. Label it accordingly.
By systematically performing these tests, you can correctly label each of the four compounds based on their distinctive properties.
Regarding your question about what would turn a solution of chromium sulfate green, it is important to note that chromium (III) sulfate is usually violet in color when dissolved in water. However, under specific conditions, it can undergo a reaction and form a complex with other substances that may give it a green color. Without further information or specific reactions, it's difficult to determine the exact conditions required for the solution to turn green.
In terms of your chemistry studies, it's possible that you haven't covered specific reactions or complex formation involving chromium (III) sulfate yet, as it might be part of the curriculum in Year 11. However, it's always good to do additional research or ask your teacher for more information to expand your understanding of the topic.