KEY
1. Write the number of significant figures in the following measurements:422 cm 3
6.02 g 30.825 m 3
0.0043 g 2
1.310 x 1022 atoms 4
7000 mL 1
0.0000003 cm 3
6001 sec 4
2. Name these:
NaFSodium floride
CuClO2
Copper chlorite
Fe2(SO3)3
Iron(III) sulfite
N2O4
Dinitrogen tetroxide
Ca(HCO3)2
Calcium bicarbonate
3. Calculate the percent abundance of two isotopes of a fictional element, georgium, if it has an average atomic mass of 291.23 amu. (Go-290 : 289.86 amu; Go-292 : 292.07 amu)
Percentage of Go-290 =x Percentage of Go-292=y x+y=1
Average atomic mass =291.23 amu = 289.86x +292.07y y=1-x291.23 =289.86x +292.07(1-x)
(292.07-289.86)x = 292.07-291.232.21x=0.84 x=0.38 y=1-x=1-0.38 =0.62
38% Go-290 32% Go-2924. When 0.115 g of a hydrocarbon is burned, 0.379 g of CO2 and 0.1035 g of H2O are produced. What is the empirical formula of the hydrocarbon?(molecular mass of CO2 = 44 g/mol; H2O=18 g/mol)
Hydrocarbon CxHy
nC = 0.379g CO2 x 1 mol CO2 /44 g x 1mol C /1 mol CO2 =0.09
nH = 0.135g H2O x 1 mol H2O / 18g x 2mol H / 1mol H2O = 0.12C0.09 H0.12 both parts divided by 0.09 CH1.33 multiplied by 3 C3H4
5. Express the following numbers in scientific notation:
0.00000000066 6.6 x10-10356 3.56 x102
47,764 4.78 x 10
0.096 9.6 x 10-2
6. Indicate the number of protons, neutrons and electrons in an element with atomic number of 38 and mass number of 84.
Atomic number = numbers of protons =38
and if the element has no charge = numbers of electrons= numbers of protons =38Mass number = numbers of protons+ numbers of neutrons
84 = 38 + numbers of neutronsnumbers of neutrons = 84-38 = 52
7. The density of ammonia gas under certain conditions is 0.625 g/L. Calculate its density in g/cm3.0.625 g/L x 1L/1dm3 x 1 dm3/1000 cm3 = 6.25 x 10-4 g/cm3
8. Carry out the following arithmetic operations to the correct number of significant figures: