Mercury can be obtained by reacting mercury(II) sulfide with
calcium oxide. How many grams of mercury(II) sulfide are
needed to produce 26.0 g of Cas?
4HgS(s) + 4CaO(s) — 411g() + 3CaS(s) + Caso.

111.68 g

Explanation:

Given data:

Mass of HgS needed = ?

Mass of CaS produced = 26.0 g

Solution:

Chemical equation;

4HgS + 4CaO  →     4Hg + 3CaS + CaSO₄

Number of moles of CaS:

Number of moles = mass/molar mass

Number of moles = 26 g/ 72.143 g/mol

Number of moles = 0.36 mol

Now we will compare the moles of HgS with CaS.

                 CaS             :             HgS

                   3                :               4

                   0.36           :              4/3×0.36 = 0.48 mol

Mass of HgS:

Mass = number of moles × molar mass

Mass = 0.48 mol × 232.66 g/mol

Mass = 111.68 g

yes

explanation:

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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