chem question - answer them if u think ur smart; (2 Viewers)

[gebey]

HERE :

SOME SIMPLE CHEM QUESTION:

1. Identify the ions present in an aqueous LiOH solution.

2. How many moles of oxygen are there in 10.46g SO<SUB>2</SUB> ?

3. What is the percent by mass of nitrogen N<SUB>2</SUB>O<SUB>3</SUB> ?

4. A compound has 40.9% Carbon, 4.58% Hydrogen and 54.5% Oxygen. The molecular mass was found to be 88.1. What is the molecular formula ?

5. What mass of magnesium sulfate must be dissolved in water to prepare 810 mL of 0.420 M MgSO<SUB>4</SUB> solution ?

6. What volume of 0.330 M HCl solution would be required to prepare 520 mL of 0.00790 M HCl solution ?

7. Select the spectator ions for the following reaction.

AgNO<SUB>3</SUB>(aq) + NaCl(aq)

AgCl(s) + NaNO<SUB>3</SUB>(aq)​

<TABLE cellSpacing=0 cellPadding=4 width="95%" bgColor=#9999ff border=3><TBODY><TR><TD class=questitem width="5%" bgColor=#9999ff>A</TD><TD class=questitem><BASEFONT>Ag<SUP>+</SUP>(aq), Cl<SUP>-</SUP>(aq) </BASEFONT></TD></TR><TR><TD class=questitem width="5%" bgColor=#9999ff><CENTER><INPUT type=submit value=" B " name=R6Y2B></CENTER></TD><TD class=questitem><BASEFONT>Na<SUP>+</SUP>(aq), NO<SUB>3</SUB><SUP>-</SUP>(aq) </BASEFONT></TD></TR><TR><TD class=questitem width="5%" bgColor=#9999ff><CENTER><INPUT type=submit value=" C " name=R632C></CENTER></TD><TD class=questitem><BASEFONT>Ag<SUP>+</SUP>(aq), NO<SUB>3</SUB><SUP>-</SUP>(aq) </BASEFONT></TD></TR><TR><TD class=questitem width="5%" bgColor=#9999ff><CENTER><INPUT type=submit value=" D " name=R642D></CENTER></TD><TD class=questitem><BASEFONT>Na<SUP>+</SUP>(aq), Cl<SUP>-</SUP>(aq) </BASEFONT></TD></TR></TBODY></TABLE>

8. When balanced, the coefficient of O<SUB>2</SUB> in the following equation is:

__ C<SUB>2</SUB>H<SUB>4</SUB> + __ O<SUB>2</SUB>

__ CO<SUB>2</SUB> + __ H<SUB>2</SUB>O
​

9. What is the theoretical yield of vanadium that can be produced by the reaction of 40.0 g of V<SUB>2</SUB>O<SUB>5</SUB> with 40.0 g of calcium, based on the following chemical reaction?
​

V<SUB>2</SUB>O<SUB>5</SUB>(s) + 5Ca(l)

2V(l) + 5CaO(s)
​

10. If Hg and 2.30g O<SUB>2</SUB> are obtained from heating 65.0g HgO, what is the mass percent yield of O<SUB>2</SUB> ? Hint work out the stoichiometry of the reaction first.​

 

[Alfred_rulz]

1. Identify the ions present in an aqueous LiOH solution.

Li+ and OH-

2. How many moles of oxygen are there in 10.46g SO2 ?

S=32.07 and O=32 add up to total 64.07
there is 5.22g of O2
Therefore (5.22/32)= 0.16 moles of Oxygen Gas
Therefore 0.16 x 2 = 0.32 moles of oxygen atom (The question is not clear...)

3. What is the percent by mass of nitrogen N2O3 ?

N2=28.02 and )3=48
Total mass is 76.02
(28.02/76.02) x 100 = 36.86%

4. A compound has 40.9% Carbon, 4.58% Hydrogen and 54.5% Oxygen. The molecular mass was found to be 88.1. What is the molecular formula ?

C-48.9%, H-4.58%, O-54.5%
C-0.409 x 88.1 = 36.0329g of Carbon
H-0.0458x88.1= 4.03g of Hydrogen
O - 0.545 x 88.1 = 48.01g of Oxygen

therefore 3 carbon, 4 hydrogen and 3 oxygen

Hence C3H4O3

5. What mass of magnesium sulfate must be dissolved in water to prepare 810 mL of 0.420 M MgSO4 solution ?

1mol/120.38g:0.42mol/xg
xg=50.5596g

810ml/xg:1000ml/50.5596g
xg=40.95g

6. What volume of 0.330 M HCl solution would be required to prepare 520 mL of 0.00790 M HCl solution ?

0.0079mol/1000ml:x mol/520ml
x mol = 0.004108 mol

1000ml/0.33mol:x ml/0.004108mol
x ml= 12.45ml

They are relatively easy... but very good for revision!

 

[saiandkid]

in the question like Q2, is the oxygen refers to oxygen gas or oxygen atom?

 

[xiao1985]

in the question like Q2, is the oxygen refers to oxygen gas or oxygen atom?

i would say O atom

@alfred: good response... except i believe q2, it should be O atom, not O2 ... so answer should be double that...

and the remaining q's

7. Select the spectator ions for the following reaction.

AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)

Ag+(aq), Cl-(aq)
Na+(aq), NO3-(aq)
Ag+(aq), NO3-(aq)
Na+(aq), Cl-(aq)


8. When balanced, the coefficient of O2 in the following equation is:

C2H4 + 3 O2 ---> 2 CO2 + 2 H2O


9. What is the theoretical yield of vanadium that can be produced by the reaction of 40.0 g of V2O5 with 40.0 g of calcium, based on the following chemical reaction?

V2O5(s) + 5Ca(l) 2V(l) + 5CaO(s)

V2O5: MW: 50.94 x 2 + 16 x 5 = 181.88 g mol -1
moles of V2O5: 0.2199 moles
ie yield: 0.4398 moles of V = 22.40g


10. If Hg and 2.30g O2 are obtained from heating 65.0g HgO, what is the mass percent yield of O2 ? Hint work out the stoichiometry of the reaction first.

2 Hg + O2 -> 2 HgO

65 g of HgO (MW: 200.6 + 16 = 216.6 g mol-1) = 0.3 mol

2.3 g of O2 (MW: 32 g mol-1) = 0.0719 mole
yield = 24%

 

[Aerlinn]

I seem to have gotten 0.326 mol of O atoms in Q2. Mehbe we're all interpreting it differently :/

 

[xiao1985]

I seem to have gotten 0.326 mol of O atoms in Q2. Mehbe we're all interpreting it differently :/

i agree with you

cf comment

 

[Soul Searcher]

1. Identify the ions present in an aqueous LiOH solution.

Li+, OH-

2. How many moles of oxygen are there in 10.46g SO2 ?

MM (total)= 64
32:32
so, m(O2) = 5.23g
n=m/MM
so, n(O2) = 5.23g/16g/mol = .326875mol O2

3. What is the percent by mass of nitrogen N2O3 ?

MM(total) = 76
N2 = 28
O3 = 48
so, % (N2) = 28/76 =38.8%


4. A compound has 40.9% Carbon, 4.58% Hydrogen and 54.5% Oxygen. The molecular mass was found to be 88.1. What is the molecular formula ?


O: 88.1 x .545 = 48.0145
48/16 = 3
So, 3 O atoms

C: 88.1 x .409 = 36
36/12 = 3
so, 3 C atoms

H: 88.1 x .0458= 4
4/1 = 4
so, 4 H atoms

Therefore, C3H4O3

5. What mass of magnesium sulfate must be dissolved in water to prepare 810 mL of 0.420 M MgSO4 solution ?

C=n/V(L)
o.420 = n/0.810
n=.3402
n=m/MM
.3402 = m/120.4
m=40.96g

6. What volume of 0.330 M HCl solution would be required to prepare 520 mL of 0.00790 M HCl solution ?

C1V1=C2V2
0.330 x V1 = .00790 x 0.520
V1 = .012448484 mL?? <-- this is how I would've done it, though I don't understand how Alfred did his one...anyone care to explain that?


7. Select the spectator ions for the following reaction.

AgNO3(aq) + NaCl(aq) --> AgCl(s) + NaNO3(aq)

a. Ag+(aq), Cl-(aq)
b. Na+(aq), NO3-(aq)
c. Ag+(aq), NO3-(aq)
d. Na+(aq), Cl-(aq)

ionic equation: Ag+ + NO3- + Na+ Cl- --> AgCl(s) + Na+ NO3-

Ag+ and Cl- can't be canceled out because they are not in solution, they form an insoluble ppt. But NO3- and Na+ can cancel out, therefore they gonskies.

B

8. When balanced, the coefficient of O2 in the following equation is:

__ C2H4 + __ O2 --> __ CO2 + __ H2O

C2H4 + 3 O2 --> 2 CO2 + 2 H2O

therefore, 3

9. What is the theoretical yield of vanadium that can be produced by the reaction of 40.0 g of V2O5 with 40.0 g of calcium, based on the following chemical reaction?

V2O5(s) + 5Ca(l) --> 2V(l) + 5CaO(s)

m(V2O5) = 40.00g
MM(V2O5) = 181.8
n(V2O5) = m/MM = 40/181.8 = .22
n(V) = 0.22
n(V) = m/MM
0.22 = m/50.9
therefore, m(V) = 11.198
According to the equation/stoichiometry, there are 2 atoms of V;
therefore m(V) = 11.198 x 2 = 22.396g of V yield!

 

[Soul Searcher]

10. If Hg and 2.30g O2 are obtained from heating 65.0g HgO, what is the mass percent yield of O2 ? Hint work out the stoichiometry of the reaction first.

Wouldn't you agree that the question is terribly worded? Or possibly that I have terribly misinterpreted it... shouldn't the equation be:
HgO + O2 --> Hg + O2

It says "heating HgO" to obtain "Hg and O2"...but logically it makes no sense...

 

[Soul Searcher]

6. What volume of 0.330 M HCl solution would be required to prepare 520 mL of 0.00790 M HCl solution ?

0.0079mol/1000ml:x mol/520ml
x mol = 0.004108 mol

1000ml/0.33mol:x ml/0.004108mol
x ml= 12.45ml

Could you just explain your working out here? Can I use the C1V1=C2V2 formula in this situation?

 

[Bank$]

Can I use the C1V1=C2V2 formula in this situation?

No because the number of moles in each solution is differant.

His working is a hard to interprit but it is correct, u c i think u guys are over looking the fact that it is 520 mL of 0.00790 M HCl as in we have 520ml of a 0.0079mol/L solution.

so in his 1st step he is calculating how many moles in the 520ml:

0.0079mol/1000ml:x mol/520ml
x mol = 0.004108 mol

and then finds out the volume of 0.330 M HCl solution that contains that x mol:

1000ml/0.33mol:x ml/0.004108mol
x ml= 12.45ml

 

[xiao1985]

Wouldn't you agree that the question is terribly worded? Or possibly that I have terribly misinterpreted it... shouldn't the equation be:
HgO + O2 --> Hg + O2

It says "heating HgO" to obtain "Hg and O2"...but logically it makes no sense...

I would suppose it means 2 HgO ---> 2Hg + O2

though i pretty much doubt you can obtain mercury metal this way =/