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What is the unknown white powder?

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Introduction

Neerav Shah IB Chemistry Qualitative Analysis Lab January 31, 2003 Problem: What is the unknown white poweder? (glucose, sodium chloride, sodium tetraborate, calcium chloride) Hypothesis: I think that the unknown substance is sodium tetraborate (borax). Background: Calcium chloride - stable reactivity / white colorless crystals / granules / irritant to body tissue / "not all health aspects have been fully investigated" / density = 0.835 / very soluble in alcohol Sodium Tetraborate (borax) - white, odorless crystals / powder / stable reactivity / density = 1.73 / "not all health aspects have been fully investigated" / melting point = 75 degrees Celsius / insoluble in alcohol / pH = 9.5 , 1g/16mL of water Sodium chloride - density = 2.17 / 1g/2.8mL of water / slightly soluble in alochol / pH = 7 / colorless / transparent / crystals / stable reactivity / "not all health aspects have been fully investigated" / slightly toxic Glucose - melting point = 83 degrees Celsius / 1g/1mL og water / ...read more.

Middle

* Compare the unknown with the rest of the substances * Next, using the formula d = g/L, calculate and record the density of each substance * Using the pH strips, figure out and record the pH of each substance and compare it with the unknown substance *To calculate the density of the unknown substance, a 1 molar solution of the unknown substance was given to us. This solution was used to calculate the pH and the conductivity of the unknown substance. We then evaporated the water to calculate the amount, in grams, of the unknown substance in 50mL of water. We could then use that to calculate density. Data: Grams: Calcium Chloride --> [ (110.98g) / (1 mol) ] (.05 moles) = 5.55g Sodium Tetraborate --> [ (381.42g) / (1 mol) ] (.05 moles) = 19.07g Sodium Chloride --> [ (58.44g) / (1 mol) ] (.05 moles) ...read more.

Conclusion

The final piece of data that reinforced this conclusion was that the conductivity of the sodium tetraborate (22 blinks) was closest to that of the unknown substance (19 blinks). Error was abundant in this experiment. However, it did not affect the final conclusion. Firstly, the unknown substance was hot when the indicator was put in. This could have altered the number of blinks that resulted. Also, any of the unknown substance that was stuck to the side of the beaker after evaporation could not be weighed. This probably resulted in a decreased actual mass. To correct these various sources of error, the following could be done: first, wait for the unknown substance to cool before taking any tests. This will avoid any variations in actual data that could have resulted from heat. To remove the second source of error, instead of weighing the substance itself, weigh an empty beaker, and then weigh the unknown substance inside the beaker, and finally subtract the mass of the beaker from the total mass. This will avoid any error in relation to substance stuck to the side. ...read more.

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