Sulfur has 4 isotopes: sulfur-32 is 95.0%, sulfur-33 is 0.76%, sulfur-34 is 3.22%, and sulfur-36 is 0.89% abundant. calculate its average atomic mass. express your answer with five sig figs.

- Average atomic mass is 32.066.

Solution:- To calculate the average atomic mass the percentages of the isotopes are converted to decimals and multiplied by their respective isotopic masses. We do this for all the isotopes and take the sum as:

average atomic mass = 32(0.95)+33(0.0076)+34(0.0322)+36(0.0089)

= 30.4+0.2508+1.0948+0.3204

= 32.066

So, the atomic mass of sulfur is 32.066.

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when 25.0 ml of 0.700 mol/l naoh was mixed in a calorimeter with 25.0 ml of 0.700 mol/l hcl, both initially at 20.0 °c, the temperature increased to 22.1 °c. the heat capacity of the calorimeter is 279 j/°c.

the equation for the reaction is:

naoh + hcl → nacl + h₂o

moles of hcl = 0.0250 l hcl ×

0.700

mol hcl

1 l hcl = 0.0175 mol hcl

volume of solution = (25.0 + 25.0) ml = 50.0 ml

mass of solution = 50.0 ml soln ×

1.00

ml soln

= 50.0 g soln

δt=t2-t1

= (22.1 – 20.0) °c = 2.1 °c

the heats involved are

heat from neutralization + heat to warm solution + heat to warm calorimeter = 0

q1+q2+q3=0

nδh+mcδt+cδt=0

0.0175 mol ×

δh

+ 50.0 g × 4.184 j·g⁻¹°c⁻¹ × 2.1 °c + 279 j°c⁻¹ × 2.1 °c = 0

0.0175 mol ×

δh

+ 439.32 j + 585.9 j = 0

0.0175 mol ×

δh

= -1025.22 j

δh=1025.22j0.0175 mol= -58 600 j/mol = -58.6 kj/mol