17. (a) Give the meaning of the term empirical formula (b) Analysis of 3.150 g o

Question

17. (a) Give the meaning of the term empirical formula (b) Analysis of 3.150 g of compound X showed that it contained 0.769 g of calcium and 0.539 g of nitrogen; the remainder was oxygen. Calculate the empirical formula of X. 18. The metal lead reacts with warm dilute nitric acid to produce leadll) nitrate, nitrogen monoxide and water according to the following equation. 3Pb(s) 8HNo,(aq) 3Pb(NC)2(aq) 2NO(g) 4H2O(l) + + + (a) In an experiment, an 8.14 g sample of lead reacted completely with a 2.00 mol dm solution of nitric acid. Calculate the volume, in dm2, of nitric acid required for complete reaction.

Explanation / Answer

Q17

a)

Empirical formula is the least coefficient formula, that is, the simplified version which keeps ratios between atoms of the compound

b)

For X:

mol of Ca = mass/MW = 0.769/40 = 0.019225

mol of N = mass/MW = 0.539/14 = 0.0385

mol of O = (3.15-0.769-0.539) / 16 = 0.1151

ratio

0.1151/0.0385 = 3

0.1151/0.019225 = 6

then

Ca6N3O

Q18

a)

m = 8.14 g of lead

M = 2 HNO#

find nitric acid volume for reaction:

mol of lead = mass/MW = 8.14/207.2 = 0.0392

3 mol of lead = 8 mol of acid

mol of acid in smaple = 8/3*0.0392 = 0.1045

M = mol/V

V = mol/M

V = (0.1045)/2

V = 0.05225 L = 52.25 mL

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