Mrs. smith is demonstrating a chemical change for her class. she places 15 grams of baking soda into a beaker. next she adds 15 grams of vinegar to the same beaker. when the two compounds make contact, they bubble and fizz a great deal. she places the beaker on the balance and notes that the mass of the solution in the beaker is less than the expected 30 grams. why is the mass of the solution in the beaker less than 30 grams? a) the balance was not working correctly. b) the gas that was released changed the mass. c) mass is always lost in a chemical reaction. d) the new products have less mass than the original reactants.

B) The gas that was released changed the mass.

Explanation:

In the acid base reaction of vinegar and sodium bicarbonate, sodium acetate, water and carbon dioxide are formed.

 → ↑

Carbon dioxide is released from the beaker in the form of gas (as can be seen in the previous reaction), which is due to the loss of mass observed. This compound is responsible for the formation of bubbles in the reaction.

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

water at room temperature is flowing through a pipe with pressure taps located 10 ft apart along one section of the pipe, which are connected to a mercury (s=13.6) manometer.