Calculate the number of moles of the indicated sub- stance in each of the following samples. a. 41.5 g of mgcl2 b. 135 mg of li2o c. 1.21 kg of cr d. 62.5 g of h2so4 e. 42.7 g of c6h6 f. 135 g of h2o2

A: 0.436 moles MgCl2

B: 0.00452 moles Li2O

C: 23.3 moles Cr

D: 0.637 moles H2SO4

E: 0.547 moles C6H6

F: 3.97 moles H2O2

Explanation:

A: Calculate the number of moles of 41.5 grams of MgCl2

Molar mass of MgCl2 = 95.21 g/mol

Moles MgCl2 = 41.5 grams / 95.21 g/mol = 0.436 moles

B: Calculate the number of moles of 135 mg of Li2O

 Molar mass of Li2O = 29.88 g/mol

Moles Li2O = 0.135 grams / 29.88 g/mol = 0.00452 moles

C: Calculate the number of moles of 1.21 kg of Cr

  Molar mass of Cr = 52.0 g/mol

Moles Cr = 1210 grams / 52.0 g/mol = 23.3 moles

D: Calculate the number of moles of 62.5 grams of H2SO4

  Molar mass of H2SO4 = 98.08 g/mol

Moles H2SO4 = 62.5 grams / 98.08 g/mol = 0.637 moles

E: Calculate the number of moles of 42.7 grams of C6H6

  Molar mass of C6H6 = 78.11 g/mol

Moles C6H6 = 42.7 grams / 78.11 g/mol = 0.547 moles

F: Calculate the number of moles of 135 grams of H2O2

  Molar mass of H2O2 = 34.01 g/mol

Moles H2O2 = 135 grams / 34.01 g/mol = 3.97 moles

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6