hard water Analysis Guided Inquiry Lab CaCl2 + Na2CO3 > CaCO3 + 2 Na + 2 Cl Purpose: Determine the amount of ions, specifically calicum, that are present in multiple samples of water by adding another chemical to create a reaction to percipitate the calcium out of the water into a measureable solid Materials: balance (. 001g), 100ml beakers, graduated cylinder, drying oven, Na2CO3 (sodium carbonate), stir rod, scoopula, DI water, watch glasses, filter paper, ring stand, funnel, water samples with CaCl2 (calcium chloride) Procedure:1. Measure out a 20ml sample of each A, B, and C hard waters 2.
Place samples in separate beakers 3. Add . 500g of sodium carbonate to each water sample beaker (absolute maximum concentration is considered to be 180 mmole, so this amount of sodium carbonate will allow for such a number, if present) 4. Thoroughly stir until all precipitate has been formed 5. One sample at a time, place filter paper in funnel on ring stand and pour liquid and precipitate into filter paper (RECORD MASS OF EACH FILTER PAPER) 6.
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Place each sample of collected precipitate in filter paper on individual watch glass 7. Place each sample of precipitate in oven on watch glass for 10 minutes, remove, break up solid, allow 5 more minutes for complete drying 8. Mass each sample on filter paper Sample Volume Na2CO3 added Mass of Filter Paper Mass of Precipitate A 20. 0 ml .500g 1. 277g .198g B 20. 0 ml .500g 1. 273g .289g C 20. 0 ml .500g 1. 240g .082g Observations: white, milky-like, solid substance formed when sodium carbonate added to hard water sample, thin in consistency Calculations:(Mass of Substance / MM of CaCO3) / . 020 Liters * 1000. = milimoles of Ca2+ Sample A (. 198g / 100. 09g) / . 020 Liters * 1000. = 98. 9 mmol of Ca2+ Should be 90 mmole Sample B (. 289g / 100. 09g) / . 020 Liters * 1000. = 144 mmol of Ca2+ Should be 135 mmole Sample C (. 082g / 100. 09g) / . 020 Liters * 1000. = 41. 0 mmol of Ca2+ Should be 30 mmole Conclusion and Error Analysis: At the conclusion of this lab each sample was found to be above the expected value for the outcome of the measurement of the calcium present in each hard water sample.
It was found to be a relatively consistent factor over the expected value over, 11 mmole for two and 9 mmole for the other, all falling closely in amount over expected. The amount of calcium in each sample being 98. 9 mmole, 144 mmole, and 41. 0 mmole to A, B, and C, respectively. Due to this relatively consistent over expected value, it is expected that there was already calcium present in the water used to prepare the samples before calcium chloride was added for the intended purpose of making it a hardwater sample, which it most likely already was. If this is true, because there was already calcium present in the water, there would be more, therefore, more precipitate would be formed than expected, resulting in the 9+ mmole in each calculation. A way to solve this problem from occurring is to be very precise in the amount of calcium chloride added to each sample. As well as ensuring the water being used to create the samples does not have calcium present in it already.
