density?

[Dencology]

---

Members don't see this ad.

.41. A sample of gold weighing 38.6 g was added
to a graduated cylinder containing 23.00 mL
of water. The volume of the water plus the
gold was 25.00 mL. What is the density of
gold?
A. 0.0518 g mL-1
B. 2.00 g mL -1
C. 19.3 g mL -1
D. 38.6 g mL -1
E. 1540 g mL -1

i think ans. is B.

. .43. For the reaction between A and B to form C it
is found that when one combines 0.6 moles of
A with 0.6 moles of B, all of the B reacts, 0.2
moles of A remain UNREACTED and 0.4
moles of C are produced. What is the
balanced equation for this reaction?
A. A + 2B C
B. A + 3B 2C
C. 3A + 3B 2C
D. 3A + 2B 3C
E. 2A + 3B 2C

. .44. If the mass percent of oxygen in a nitrogenoxygen
compound is known, given the mass
percent of oxygen, all of the following are
needed to determine the molecular formula of
a nitrogen-oxygen compound EXCEPT one.
Which one is this EXCEPTION?
A. Atomic mass of nitrogen
B. Atomic mass of oxygen
C. Avogadro's number
D. Empirical formula
E. Molar mass of the compound

.C, cold be the ans.?

49. The molar volume of copper (63.5 gmol–1)
at 25oC is 7.09 cm3 mol–1. Which of the
following is the density of copper at 25oC in
g cm3?
A. (63.5)/(7.09)
B. (63.5)(7.09)
C. (7.09)/(63.5)
D. 7.09
E. ((63.5)/(7.09))(25)

.

.

 

[zuma35]

I say C

D=M/V

M=38.6g
V=(Total Volume)-(Volume of Water)=(25ml-23ml)=2ml

D=(38.6)/2= 19.3

 

[Sea of ASH]

I say C

D=M/V

M=38.6g
V=(Total Volume)-(Volume of Water)=(25ml-23ml)=2ml

D=(38.6)/2= 19.3

👍


43) E
44) E
49) A

 

[Dencology]

can you explain why you got E, E for 43 and 44?

 

[waystinthyme]

43. For the reaction between A and B to form C it
is found that when one combines 0.6 moles of
A with 0.6 moles of B, all of the B reacts, 0.2
moles of A remain UNREACTED and 0.4
moles of C are produced. What is the
balanced equation for this reaction?
A. A + 2B C
B. A + 3B 2C
C. 3A + 3B 2C
D. 3A + 2B 3C
E. 2A + 3B 2C

first, from the problem we can assume that B is the limiting reagent...since all of B is used up, and some of A still remains.

you start with 0.6 moles of A and B, but finish with 0.2 moles of A and 0 moles of B, therefore 0.4 moles of A are used up in the reaction. therefore, it takes 0.4 moles of A to react with 0.6 moles of B...or in other words, 2 moles of A to react with 3 moles of B.

we are also told, that 0.4 moles of C are produced. since 0.4 moles of A are used up, and 0.4 moles of C are produced, they must be present in the same amount. we found earlier that there are 2 moles of A reacting with 3 moles of B, so there must be 2 moles of C produced.

Answer E is correct...

EDIT: on second thought, i'm not 100% sure about this, since some of A is left over after all of B is consumed. can someone else confirm?

..44. If the mass percent of oxygen in a nitrogenoxygen.
.compound is known, given the mass.
.percent of oxygen, all of the following are.
.needed to determine the molecular formula of.
.a nitrogen-oxygen compound EXCEPT one..
.Which one is this EXCEPTION?.
.A. Atomic mass of nitrogen.
.B. Atomic mass of oxygen.
.C. Avogadro's number.
.D. Empirical formula.
.E. Molar mass of the compound.

C, cold be the ans.?
.

.

for this question i got C.

of course you'll need the atomic mass of nitrogen/oxygen, so A and B are out.

you will also need the molar mass of the compound, to find out how many grams the mass percent correlates to, so E is out.

since the molecular formula is a multiple of the empirical formula, it would be helpful to have the empirical formula of the compound as well.

you don't need avogandro's number, because you aren't trying to find the number of particles of either compound in any of the steps to solve the problem.

if this is unclear, you can try working out a sample problem, and see which steps you go through to solve for the correct answer.

-waystinthyme.

 

[Sea of ASH]

i read the question wrong, once again .waystinthyme is right
.