105a postlab1

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University of Southern California *

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105

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Chemistry

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Jan 9, 2024

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docx

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Uploaded by ColonelEnergySeaUrchin26

Data Trial 1: pipet density = sample + beaker − beaker volume Density for 2% NaCl: 85.4 − 80.2 5.2 = 1 g / cm 3 Average density for water: 1.234 + 0.8 + 0.966 + 1.126 4 = 1.0315 Standard deviation for DI density: √ ( 1.234 − 1.0315 ) 2 +( 0.8 − 1.0315 ) 2 +( 0.966 − 1.0315 ) 2 +( 1.126 − 1.0315 ) 2 4 = 0.1895776 %error(accuracy) for water= ¿ averagevalue − truevalue ∨ ¿ truevalue ¿ ×100% = 1.0315 − 1 1 ×100%=3.15% Trial2: buret

Average DI water density: 0.9955g/cm3 Standard deviation for water density: 0.0198 %error(accuracy) for water= ¿ averagevalue − truevalue ∨ ¿ truevalue ¿ ×100% = 1 − 0.9955 1 ×100%=0.45% Percent error in buret trial is smaller, so buret is more accurate than pipet. Graph Trial 1 Linest equation

y = -0.0006x + 1.0665 Unknown B density: 1.01923g/cm3 x= 1.01923 − 1.0665 − 0.0006 = ¿ 78g/cm3 (invalid data) buret Trial 2 LINESTequation Unknown B density: 1.01923g/cm3

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X= 1.01923 − 0.9925 0.0088 = ¿ 3.0375% Error propogation: 1.01923 − 0.9925 ± 0.0175 0.0088 ± 0.00357 ± √ 0.0175 2 + 0.00357 2 =0.134 X= ¿ 1.01923 − 0.9925 0.0088 = ¿ 3.0375 ± 0.134 ¿ % So unknown B is 3.0375 ± 0.134% NaClsolution Discussion Buret gives better results than pipet. In my results, on buret matches the expected results. from the buret trial, we can see that as percent concentration increases, density increases. But in pipet trial, I got a negative trend and my measured density for unknown b is 78g/cm3, which is completely wrong and cannot be used in the following calculation. This might happen because I couldn’t hold the balloon when I used the pipet to transfer the solution. I always squeezed some liquid out before I transferred the liquid into the beaker. Therefore the volume I got for in the pipet trial might be wrong. Therefore buret is more accurate. Also buret is much more precise than the pipet (standard deviation value: 0.0198 compared to 0.19, around ten times smaller than the pipet)

I think one source of error in my experiment is that when I was using a pipet to transfer the solution, I found it hard to transfer the exact amount I recorded because I always squeezed some liquids out of the pipet. Also, some liquid may be left in the container so the volume might be less than I recorded. What’s more when I was reading the buret reading I didn’t level my eyes with the marking. I was standing so that I was looking down at the liquid level. To sum up, the greater the solute density, the greater the density because NaCl is heavier than the H2O molecule. My Lineast equation results intersect with the density of water. In buret trial, 1g/cm3 (the density of water) is within 0.992517 ± 0.01749 , and in my pipet trial, 1g/cm3 is also within 1.0665 ± 0.0935261.