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: According to the law of conservation of mass, mass can neither be created nor be destroyed. Thus the mass of products has to be equal to the mass of reactants. The number of atoms of each element has to be same on reactant and product side. Thus chemical equations are balanced.

But in the given reaction, one of the products is gas and it escapes. Thus the mass of products is not equal to the mass of reactants and is less than 30 grams ( sum of masses of reactants).

catya your not at all which answer i've seen you do this on another question!

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2