Chemistry Experiment

Question

I am performing an experiment and I need to determine whether an unknown sample (Sample A) of a chemical matches another known sample containing:

- 0.51 g sucrose

- 0.67 g sand

- 0. 43 g sodium carbonate

- 0.34 g rice grains

 

What tests can I perform on the unknown sample to see if it matches the sample above? 

Answer 1

To determine if your unknown sample matches the known sample containing sucrose, sand, sodium carbonate, and rice grains, you can perform several tests to identify and quantify the components. Here’s a step-by-step approach:

1. Physical Examination

1. Visual Inspection: Compare the appearance of the unknown sample to the known sample. Look for similarities in color, texture, and granularity.

2. Solubility Tests

1. Sucrose Test:
2. Procedure: Dissolve a small portion of the sample in water.
3. Observation: Sucrose will dissolve completely in water, forming a clear solution.
4. Sodium Carbonate Test:
5. Procedure: Test the aqueous solution with an acid (e.g., hydrochloric acid).
6. Observation: Sodium carbonate will react with acid, producing carbon dioxide gas (bubbles) and water.
7. Sand and Rice Grains Test:
8. Procedure: Filter the solution to separate the insoluble residues.
9. Observation: Sand and rice grains will remain as residues and not dissolve.

3. Chemical Tests

1. Sodium Carbonate Presence:
2. Procedure: Test the aqueous solution with phenolphthalein or a similar indicator.
3. Observation: Sodium carbonate will make the solution alkaline (turn pink with phenolphthalein).
4. Sucrose Presence:
5. Procedure: Use a test for reducing sugars, such as Benedict's test. Sucrose is a non-reducing sugar, so it should not react with Benedict's reagent unless hydrolyzed first.
6. Observation: Sucrose, without hydrolysis, will not give a positive test. For a confirming test, perform an acid hydrolysis to convert sucrose into glucose and fructose.

4. Density/Gravity Separation

1. Procedure: Perform a density or gravity separation test.
2. Observation: Sand will settle due to its higher density compared to other components.

5. Microscopy

1. Procedure: Examine the sample under a microscope.
2. Observation: Distinguish between sand grains, rice grains, and the overall texture of the sample.

6. Quantitative Analysis

1. Weigh the Components:
2. Procedure: After separation, weigh the amounts of each component.
3. Observation: Compare the weights with the known amounts of sucrose, sand, sodium carbonate, and rice grains.

7. Additional Tests

1. Rice Grains Test:
2. Procedure: Boil the sample in water and examine the residues.
3. Observation: Rice grains will not dissolve and should be identifiable after boiling.
4. Chromatography:
5. Procedure: Perform thin-layer chromatography (TLC) on an aqueous extract to identify the presence of sucrose and other components.

By conducting these tests, you can identify the individual components of your unknown sample and compare them with the known sample’s composition.