Can anyone help with Unit 6 Sample Work Conservation of Mass
lesson 11
im not on that yet but here is for the test:
1. Why are open systems inappropriate for studying the conservation of mass?
-Matter may be lost to or gained from the surroundings.
2. A student claims that the reaction of hydrogen and oxygen to form hydrogen peroxide is evidence supporting the claim that mass is conserved in a reaction. The chemical equation the student uses for the reaction is shown.
H2 + O2 → H2O2
Does this evidence support the claim? Why or why not?
-Yes, it supports the claim because the equation is balanced.
3. A student records the masses of two reactants (baking soda and vinegar), and then mixes them. The reactants bubble and foam, forming a paste. The student measures the mass again, and the final mass is slightly less than the sum of the initial masses. Considering that mass is supposed to be conserved, which statement is a possible explanation for this "loss" of mass?
-The bubbling indicates a gas was formed, so some atoms formed gas; therefore, mass was transferred to the atmosphere.
4. Which quantity is used to define 1 atomic mass unit?
-one-twelfth the mass of a neutral carbon atom
5. Use the equation to answer the question.
FeCl3 + 3NH4OH → Fe(OH)3 + 3NH4Cl
Which statement about the equation is correct?
-Mass is conserved because the number of each atom in the reactants equals the number of each atom in the products.
6. The atomic mass of nickel (Ni) is 58.693 amu, and the atomic mass of chlorine (Cl) is 35.45 amu. Which molar mass is correct for nickel chloride (NiCl2)
-129.59 g/mol
7. When the products of a reaction are known, which fact can be deduced about the reactants?
-the number of atoms in the reactants
8. Iron combines with oxygen to produce rust according to the following reaction.
4Fe + 3O2 → rust
Based on the law of conservation of mass, which could be the product of the reaction?
-2Fe2O3
9. Calcium carbonate (CaCO3) can undergo a chemical reaction to produce calcium oxide (CaO) and carbon dioxide (CO2). Which possible masses of calcium oxide and carbon dioxide can form when 200 g of calcium carbonate undergoes this chemical reaction?
-112 g CaO and 88 g CO2
10. Use the chemical equation to answer the question.
2HCl(aq) + Zn(s) → ZnCl2(aq) + H2(g)
The molar mass of hydrogen (H) is 1 g/mol, the molar mass of chlorine (Cl) is 35 g/mol, and the molar mass of zinc (Zn) is 65 g/mol. When 130 grams of zinc react completely in hydrochloric acid (HCl), how much is the total mass of the products?
-274 g
11. Propane reacts with oxygen to produce carbon dioxide and water according to the following equation.
C3H8 + 5O2 → 3CO2 + 4H2O
Which ratio of components is correct?
-`For every 3 moles of carbon dioxide produced, 5 moles of oxygen react.
12. Elements A and B react according to the following equation.
4A + B2 →2A2B
The molar mass of A is 12 g/mol. The molar mass of B is 4 g/mol. The molar mass of A2B is 28 g/mol. When the goal of the reaction is to produce 112 g of the product, how many grams of reactant A should be present initially?
-96
13. The molar mass of BF3 is 67.81 g/mol. How many molecules of BF3 are there in 2 g?
-1.776×1022
14. Can the law of conservation of mass be applied when cooking? In one to two sentences, explain why or why not.
- yes the law of conservation holds that mass can not be destroyed but can only take on different forms. So if 5 g of water becomes a gas it becomes 5 g of water vapor. The mass of the liquid water is simply transferred into the mass of the newly formed water vapor.
15. The molar mass of ammonium acetate is 77.083 g/mol. A student uses 0.100 mol of ammonium acetate in a chemical reaction. The student claims that the reaction uses (0.100 mol)(77.083 g/mol)=7.71 g(0.100 mol)(77.083 g/mol)=7.71 g of ammonium acetate, which has (7.71)(6.022×1023)=4.64×1024(7.71)(6.022×1023)=4.64×1024 molecules.
In one to two sentences, explain the mistake that the student made and determine the correct number of molecules of ammonium acetate used in the reaction.
-the mistake here is the fact the student turned the moles back into mass and then multiplied the mass by Avogadro's number (6.02 x ), which gave him a false answer. To get the correct answer, he had to multiply the number of moles of ammonium acetate by Avogadro's number for the number of molecules.
Number of molecules = Moles times avogadro's number
Number of molecules = 0.100 times (6.02times10^23)
Number of molecules = 6.02 times 10^22
The correct number of molecules of ammonium acetate used in the reaction is 6.02 x mo