Asample of cesium is 75.00% cs-133, 20.00% cs-132, and 5.000% c$-134. what is the
average atomic mass of cesium? round your answer to four significant figures.
a
132 amu
b
132.8 amu
c
132.9 amu
d
133 amu

C) 132.9 amu

Explanation:

Data Given:

Abundance of Cs-133 = 75 % = 0.75

mass of Cs-133 = 133 amu

Abundance of Cs-132 = 20 % = 0.20

mass of Cs-132 = 132 amu

Abundance of Cs-134 = 5 % = 0.05

mass of Cs-134 = 134 amu

Average atomic mass of cesium = ?

Solution:

formula used to check average atomic mass is as under

                  Average atomic mass = m₁A₁ + m₂A₂ + m₃A₃

Where

m₁ , m₂ and m₃ = mass of isotope 1 , 2 and 3 respectively

A₁ , A₂ and A₃= abundance or fraction of isotope 1, 2 and 3 respectively

Put values in above formula

Average atomic mass = (133 amu)(0.75) + (132 amu)(0.20)+(134 amu)(0.05)

    Average atomic mass = 99.75 + 26.4 + 6.7

    Average atomic mass = 132.85 amu

So

Round to four significant figures

Average atomic mass of Cs = 132.9 amu

option C is correct

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2