An unknown compound weighting 1.0 g contains table barium sulfate copper sulfate

Question

An unknown compound weighting 1.0 g contains table barium sulfate copper sulfate? After separating them you find that the solution 0.25 g barium sulfate. Based on these results what is the percent of sodium sulfate in the unknown calorimetric experiment is performed by adding a 100.00 g bar of an unknown metal with a temperature of 100 degree C into a perfectly insulate containing 20 g of water initially at 25 degree C. After letting the temperature stabilize the final temperature of the water is 32 degree C a. What is the heat absorbed by the water? b. What is the heat capacity of the metal? Compare and contrast precession and accuracy. Calculate the percent error depending on the following values. Theoretical gas constant value: 0.084 Experimental value: 0.042 What are the four indications of a chemical reaction that are seen upon the addition of reagents?

Explanation / Answer

1. Weight of unknown compound = 1 gm

weight of Barium Sulfate in unknown compound = 0.25 gm

weight of Copper sulfate in unknown compound = weight of unknown compound - weight of Barium sulfate in unknown compound = 1 - 0.25 = 0.75 gm

Percentage of Copper Sulphate in unknown compound = (weight of Copper sulfate in unknown compound / weight of unknown compound) x 100 = (0.75/1) x100 = 75%

2. Mass of bar of unknown metal = 100 gm

Temperature of bar = 100 degree celsius

Mass of water = 20 gm

Temperature of water = 25 degree celsius

After addition of bar into water, the final temperature of resulting mix of bar and water = 32 degree celsius

Heat capacity of water per gram of water = 4.18 J/g.0C

Heat absorbed by water = mass of water x heat capacity of water per 1 gm of water x (final temperature - initial temperature) = 20 x 4.18 x (32-25) = 585.2 J

In this case, heat absorbed by water = heat lost by metal bar

Heat lost by metal bar of unknown metal = mass of bar x heat capacity of bar (unknown metal) per gram x (Initial temperature - Final temperature)

585.2 = 100 x Cp x (100 - 32) = 0.0860 J/ g. 0C

Heat capacity of metal bar (or it can be referred directly as unknown metal) = 0.0860 J/ g. 0C  

3. Accuracy refers to the closeness of a measured value to a standard or known value. For example, if weight measured for a substance is 3.2 kg, but the actual or known weight is 10 kg, then the measurement is not accurate. In this case, the measurement is not close to the known value.

Precision refers to the closeness of two or more measurements to each other. Similar to the example above, if the substance is weighed for 5 trials or 5 times, and value obtained is 3.2 kg each time, then it can be said that measurement is very precise but since the actual weight is 10 kg it can be said that precision is independent of accuracy and measurement can be precise but inaccurate. You can also be accurate but imprecise.

For example, for an experiment on an average, the measurements for a given substance are close to the known value, but the measurements are far from each other, then thee is accuracy but without precision.

4. Percent error - |[(experimental value - theoretical value)/(theoretical value)]| x 100 = [(0.042-0.084)/(0.084)] x 100 = 50%

5. Four indications of a chemical reactions that are seen upon addition of reagent are: a) Change in color b) Change in temperature c) Formation of gas bubble d) Formation of precipitate

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