Hard Water Analysis

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. 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