During an investigation, a scientist burned 48 g of magnesium strip. After the reaction, the total mass of the product formed was found to be 80 g. Does the law of conservation of mass hold true in this case? Use complete sentences to justify your answer based on numerical calculations.

Answer

yes

Explanation:

the law of conservation of mass hold true in this case burning magnesium strip is explained by this equation 2 Mg (s) + O2 (g) -> MgO (s)So the lighter magnesium, after reacting with oxygen in air, forms the heavier magnesium oxide. molar mass of magnesium and magnesium oxide are 24g and 40g respectively. So the same ratio 24:40 (i.e. 3:5) is maintained in the given masses of 48g and 80g, which means mass is conserved in the reacion.

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