Chem Pre-Lab Essay

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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
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The number of moles of ascorbic acid neutralized in the experiment is given by multiplying the moles of NaOH used (0.00235128 mol) by the unit conversion coefficient (1 mol ascorbic acid/1 mol NaOH). molascorbic acid = molNaOH(1 mol ascorbic acid/1 mol NaOH)
= (0.00235128 mol NaOH)(1 mol ascorbic acid/1 mol NaOH) molascorbic acid = 0.00235128 mol
Rounding this off to 3 significant figures gives: molascorbic acid = 0.00235 mol

(e) How many grams of ascorbic acid is this?
The mass of ascorbic acid neutralized is given by multiplying the calculated moles of ascorbic acid used (0.00235128 mol) with the molas mass of ascorbic acid (176.1 g/mol). massascorbic acid = (mol ascorbic acid)(molar mass ascorbic acid)
= (0.00235128 mol)(176.1 g/mol) massascorbic acid =0.414060408 g
Rounding this off to 3 significant figures gives: massascorbic acid = 0.414 g

(f) What is the mass percent ascorbic acid in the sample?
The mass percent of ascorbic acid in the sample is given by dividing the calculated mass of ascorbic acid (0.414060408 g) by the calculated mass of the sample (0.5500 g) and multiplying the quotient by 100%. mass percentascorbic acid = (massascorbic acid/masssample)100%
= 100% x (0.414060408 g)/(0.5500 g) mass percentascorbic acid = 75.3
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