Potassium has three naturally occurring isotopes. According to one source of data, Potassium-39 (mass 38.9637 amu) makes up 93.26%, potassium-40 (mass 39.9640 amu) makes up just 0.01%, and potassium-41 (mass 40.9618 amu) makes up 6.73%. What is the average atomic mass of potassium based on these relative abundances

Average atomic mass of potassium based on these relative abundances

Explanation:

The atomic mass of this element will be equal to the sum of product of its three isotopic masses and its fractional abundance

For isotope I -

Mass of Potassium-39 amu

Fractional abundance of Potassium-39 %

Mass of Potassium-40 amu

Fractional abundance of Potassium-40 %

Mass of Potassium-41 amu

Fractional abundance of Potassium-41 %

Average atomic mass of potassium based on these relative abundances

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

the temperature of the gas, in k, not celsius.