Question

For each reaction, calculate the mass (in grams) of the product formed when 10.5 g of the underlined reactant completely reacts.

Assume that there is more than enough of the other reactant.

Part A

2K(s)+Cl2(g)−−−−−→2KCl(s)

Part B

2K(s)+Br2(l)−−−−−→2KBr(s)

Part C

4Cr(s)+3O2(g)−−−−−→2Cr2O3(s)

Part D

2Sr(s)−−−−−+O2(g)→2SrO(s)

Answer 1

A)
2K(s)+Cl2(g) →2KCl(s)

mass of Cl2= 10.5 g
Molar mass of Cl2 = 71 g/mol
Number of moles of Cl2 = mass / molar mass
                                                  = 10.5 / 71
                                                  =0.148 mol

1 mol of Cl2 forms forms 2 mol of KCl
So,
number of moles of KCl formed = 2* Number of moles of Cl2
                                                                 = 2*0.148
                                                                 =0.296 mol
Molar mass of KCl = 74.5 g/mol
mass of KCl = number of moles *molar mass
                         = 0.296*74.5
                         = 22 g
Answer: 22 g

b)
2K(s)+Br2(l)−−−−−→2KBr(s)

mass of Br2= 10.5 g
Molar mass of Br2 = 160 g/mol
Number of moles of Br2 = mass / molar mass
                                                  = 10.5 / 160
                                                  =0.0656 mol

1 mol of Br2 forms forms 2 mol of KBr
So,
number of moles of KBr formed = 2* Number of moles of Br2
                                                                 = 2*0.0656
                                                                 =0.1312 mol
Molar mass of KBr = 119 g/mol
mass of KBr = number of moles *molar mass
                         = 0.1312 *119
                         = 15.6 g
Answer: 15.6 g

c)
4Cr(s)+3O2(g)−−−−−→2Cr2O3(s)

mass of O2= 10.5 g
Molar mass of O2 = 32 g/mol
Number of moles of O2 = mass / molar mass
                                                  = 10.5 / 32
                                                  =0.328 mol

3 mol of O2 forms forms 2 mol of Cr2O3
So,
number of moles of Cr2O3 formed = (2/3)* Number of moles of O2
                                                                 = (2/3)*0.328
                                                                 =0.219 mol
Molar mass of Cr2O3 = 152 g/mol
mass of Cr2O3 = number of moles *molar mass
                         = 0.219 *152
                         = 33.2 g
Answer: 33.2 g

d)
2Sr(s)−−−−−+O2(g)→2SrO(s)

mass of Sr= 10.5 g
Molar mass of Sr = 87.62 g/mol
Number of moles of Sr = mass / molar mass
                                                  = 10.5 / 87.62
                                                  =0.12 mol

2 mol of Sr forms forms 2 mol of SrO
So,
number of moles of SrO formed = 0.12 mol
Molar mass of SrO = 103.62 g/mol
mass of Cr2O3 = number of moles *molar mass
                         = 0.12 *103.62
                         = 12.4 g
Answer: 12.4 g