2. Describe how we would prepare 1.000L of 0.10 M NaOH from a stock solution tha

Question

2. Describe how we would prepare 1.000L of 0.10 M NaOH from a stock solution that is 2.5M NaOH.

3.

(a) What is the percentage of sodium in Na2CO3? Report answer to 3 significant figures.

(b) How many grams of a 3.50 g sample of Na2CO3 is sodium? Report anwer to 3 significant figures.

(c) How many grams of Na2CO3 should be added to a 1000mL volumetric flask to make 1.00L of 0.400 M Na2CO3? We may assume that distilled water is added to the volumetric flask to bring it to the mark after the Na2CO3 is added and that the solution is mixed well.

(d) What would be the molarity of a solution of Na2CO3 if it was diluted twice, as follows:

     i) 10.00mL of the 0.400 M solution of Na2CO3 prepared in "c" was added to a 100.00 mL volumetric flask and the flask was diluted to the mark with distilled water

and then

    i i) the solution in the 100.00 mL volumetric flask was further diluted by placing 1.00 mL of it in another 100.00 mL volumetric flask and diluting it to the mark with distilled water?

4. Define and give a specific example for each of the following:

1) Parallax

2) Electroanalytical method

3) TC marking on glassware

5. Give 4 or more considerations when planning a quantitative analysis.

Explanation / Answer

2.    V1 X S1 = V2 X S2; V1 X 2.5 M = 1000 ML X 0.1 M , V1 = 40 ML OF THE STOCK HAS TO BE DILUTED TO 1000 ML .

Na2CO3 = 106 MOL WT.

2Na = 23 x 2 = 56 ; % OF Na . = 56/106 x 100 = 52.83%; b ) 3.5 g of NaCO3 = 52.83/100 X 3.5 = 1.85 g OF Na. c) 106 g in 1000 ml = 1M, SO FOR 0.4 M = 106 X 0.4 = 42.4 g should be dissolved in 1 L OF solvent.

d) 10 ml x 0.4 M = 100 ML X S2, SO S2 = 0.04 M,

1ML OF IT , SO 1 ML X 0.04 M = 100 ML X S2, SO S2 = 0.0004 M = 0.4 mM

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