Chem Pre-Lab

Topics: Sodium hydroxide, Concentration, Acid Pages: 3 (635 words) Published: February 7, 2011
Pre-Laboratory Assignment
1.What are the hazards associated with sodium hydroxide (NaOH) solution? Sodium hydroxide solutions, especially in high concentrations, are toxic and corrosive.

2.(a)What buret reading should you record when the liquid level is as shown in Figure 2? In Figure 2, the lower meniscus lies below the 3 mL line and 4 minor gradations that signify 0.1 values. Estimating the uncertain digit to be 0.04 mL, the reading we record for this particular buret is 3.44 mL.

(b)How will you recognize the end point of your titration? We know that that the end point of the titration is reached when, after drop after careful drop of NaOH, the solution in the flask retains its pale pink color while swirling for about 30 seconds (as opposed to the pink color simply disappearing as the base mixes into the solution).

3.A student collected the following data in the laboratory. mass of flask, g52.87
mass of flask and sample, g53.42
concentration of NaOH solution, M0.101
initial buret reading, mL0.50
final buret reading, mL23.78

(a)What is the mass, in grams, of the sample?
The mass of the sample is given by the mass of flask (52.87 g) subtracted from the mass of flask and sample (53.42 g). masssample = massfs – massf = (53. 42 – 52.87) g
masssample = 0.5500 g

(b)What volume, in liters, of NaOH solution was used in the titration? The volume of NaOH solution used in the titration is given by the initial buret reading subtracted (0.50 mL) from the final buret reading (23.78 mL). VNaOH = Vf – Vi = (23.78 – 0.50) mL

VNaOH = 23.28 mL
However, since we are looking for the volume in liters, and 1 L = 1000mL: VNaOH = (23.28 mL)(1 L/1000 mL)
VNaOH = 0. 02328 L.

(c)How many moles of NaOH solution were used in the titration? The number of moles of NaOH solution used in the titration is given by multiplying the volume of NaOH used in the solution (0. 02328 L) with the concentration of NaOH (0.101 M). It should also be noted that...
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