easy chemistry .please help

2009-09-08 7:52 am

1.)The density of a sample of an unknown solid is 19.1 g/cm3. Convert this density to to units of lb/ft3.

2.)A compound that contains only carbon, hydrogen, and oxygen is 45.3 % C and 9.43 % H by mass.
What is the empirical formula of the substance?

Enter the correct subscript for each atom using the smallest whole number.

3)Determine the mass percent of iron in FeO to four significant figures.

Use the following atomic masses: Fe, 55.85 amu; O, 16.00 amu

回答 (1)

老爺子

2009-09-08 10:53 pm

✔ 最佳答案

1.)The density of a sample of an unknown solid is 19.1 g /cm3. Convert this density to to units of lb/ft3.

1 ft3 = 28317 cm3
1 lb = 453.59 g

19.1 g /cm3
= ( 19.1 g /cm3) x ( 28317 cm3/ft3) / ( 353.59 g /lb)
= 1530 lb/ft3

2.)A compound that contains only carbon, hydrogen, and oxygen is 45.3 % C and 9.43 % H by mass. What is the empirical formula of the substance?
Enter the correct subscript for each atom using the smallest whole number.

Mole ratio C : H : O
= 45.3/12 : 9.43/1 : (100 – 45.3 – 9.43)/16
= 3.78 : 9.43 : 2.83
= 1.34 : 3.33 : 1
= 4 : 10 : 3

The empirical formula of the substance = C4H10O3

3)Determine the mass percent of iron in FeO to four significant figures. Use the following atomic masses: Fe, 55.85 amu; O, 16.00 amu

Mass of one formula unit of FeO = 55.85 + 16.00 = 71.85 amu
Mass of Fe in one formula unit of FeO = 55.85 amu
Mass per cent of Fe in FeO = (55.85/71.85) x 100% = 77.73%

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