Amixture of mgcl2 and nacl has an initial mass of 0.4015 g. excess agno3(aq) was added and 1.032 g of precipitate, agcl(s), was recovered. how many moles of mgcl2 were in the original mixture?

8.909*10^-4 moles

Explanation:

The mixture contains MgCl and NaCl with a total mass of 0.4015 g. The mass of precipitate AgCl(aq) is 1.032 g and it has a molar mass of 143.32 g/mol. Therefore, the moles of the precipitate is:

n = 1.032/143.32 = 7.2007*10^-3 moles

Molar mass of NaCl = 58.44 g/mol and the molar mass of MgCl is 95.21 g/mol. Let the mass (g) of MgCl  in the original mixture be 'x'. Thus:

7.2007*10^-3 = (0.4015-x)/58.44 + 2x/95.21

(7.2007*10^-3)*58.44*95.21 = 95.21(0.4015-x) + 2x(58.44)

40.06505 = 38.227 -95.21x + 116.88x

40.06505 - 38.227 = -95.21x + 116.88x

1.83805 = 21.67x

x = 1.83805/21.67 = 0.0848 g

moles of MgCl = 0.0848g/95.21 g/mol = 8.909*10^-4 moles

most historians agree that gabriel mouton, the vicar of st. paul’s church in lyons, france, is the “founding father” of the metric system. he proposed a decimal system of measurement in 1670. mouton based it on the length of one minute of arc of a great circle of the earth (now called a nautical mile, 1852 meters). he also proposed the swing-length of a pendulum with a frequency of one beat per second as the unit of length (about 25 cm). a pendulum beating with this length would have been fairly easy to produce, thus facilitating the widespread distribution of uniform standards. over the years, his work was revised, improved, and extended by a number of french scientists.

the political sponsor of weights and measures reform in the french revolutionary national assembly was the bishop of autun, better known as talleyrand. under his auspices, the french academy appointed several committees to carry out the work of developing a usable system of weights and measures for france. one of the committees recommended a decimalized measurement system based upon a length equal to one ten-millionth of the length of a quadrant of the earth’s meridian (i.e., one ten-millionth of the distance between the equator and the north pole).