272_Exp4BC

# Use this water to prepare both the titrant and

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Unformatted text preview: Henderson- Hasselbalch equation). In this experiment, you will use a primary standard (potassium hydrogen phthalate, KHP) to standardize a NaOH solution and then use that solution to titrate a polyprotic acid (phosphoric acid, with three titratable protons). You will follow the titration by measuring the pH (potentiometrically) after each addition of NaOH. Appendix 1: Interpolation of data Let’s say that your ½ equivalence point should occur at 30.20 mL and you did not collect a data point at 30.20 mL. However you did collect data at 30.00 mL and 31.00 mL. How do you determine the pH for the 30.20 mL point? The known data points are: (30.00, 9.86) and (31.00, 10.07). You must interpolate using the equation below to find the pH at 30.20 mL. (" X − x % + 1 *\$ ' ( y2 − y1 )- + y1 = Y )# x2 − x1 & , € )# 30.20 − 30.00 & , ((10.07 − 9.86). + 9.86 = 9.902 = 9.90 +% *\$ 31.00 − 30.00 ' - Possible quiz questions 1. Why does the NaOH solution have to be standardized? 2. The stockroom will sparge (displace the CO2 with N2 gas) the distilled water that we use for the preparation of the standard NaOH solution in order to remove excess CO2 from the solution. Why must the CO2 be removed? (Hint: Think about what happens when CO2 reacts with H2O.) 3. Calculate the concentration (in mol/L) of 30% by weight (30 g NaOH per 100 g of solution) NaOH solution. (The density of the 30% by weight solution is 1.33 g/mL). Show your work. 4. What volume of this 30% by weight solution is needed to make 250 m...
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