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### Topic: Studying for exams, need help with some questions  (Read 2218 times)

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#### Zero2Hero

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##### Studying for exams, need help with some questions
« on: June 06, 2012, 01:26:51 AM »
If you can answer any of these i would appreciate it! Just posting the ones which i am unsure about, the practice examination papers don't have answer sheets to go with em so decided to nag you guys for some! I have some assumptions on some of the answers. Thanks

For the reaction 3FeS(s) +  2H3PO4(aq)   → Fe3(PO4)2(s) + 3H2S(g), how many moles of
H3PO4 are required to produce 1 mole of H2S?

a.0.67        b. 1.5          c.  2           d. 3

Atoms of Uranium 234U decay by α particle emission. What is the Mass Number of the atom formed as a result? 92

a.   230   b.   231   c.   232   d.   234

I think the answer is a, but i'm unsure

Atoms of Lead 212Pb decay by β particle emission forming atoms of Bismuth.

What is the Atomic Number of Bi?

a.   83     b.  82          c.  81          d.  80

Think the answer is 83 as it is the atomic number of Bismuth

If 20 g of a compound is dissolved in water to make 250 mL of a 0.5 mol L-1 solution,
the Molar Mass of the compound in g mol-1 is:

a.  10            b. 40          c. 80          d. 160

Don't know how to work this out, if you do could you please post the formula!

A particular reaction carried out at 60C takes 5 minutes. Approximately how long will it take at 30C ?

a.  10 minutes       b.  20 minutes       c. 40 minutes        d. 21/2 minutes

Is the answer 40mins as the every 10 degrees of an decreases doubles the time?

In which one of the following reactions does an element show the greatest increase in
oxidation number?

a.  MnO4-  +  8H+  +  5Fe2+  →  Mn2+  + 5Fe3+  + 4H2O
b.  2Al  +  6H+   →  2Al3+  +  3H2
c.  SO2  +  2H2S  →    3S  +  2H2O
d   Cl2  +  Sn2+  →  2Cl-   +  Sn4+

Don't know how to work this out, if you do could you please post how!

Which one of the following will occur if the temperature of a gas is increased from 30oC
to 60C?

a.   The volume will double
b.   The volume will increase by a small amount
c.   The volume will decrease by a small amount
d.   The volume will be halved

Think the answer is A but unsure..

Which property of water is due to it being a polar molecule?

a.  Its boiling point.
b.  Its ability as a solvent
c.  Its high specific heat
d.  All of the above.

I think it's D although i'm unsure

In which class of compounds has the carbon been most highly oxidized?
a.  Carboxylic acids.
b.  Aldehydes.
c.  Ketones.
d.  Alcohols

Think the answer is B, but posted it up just incase it's wrong

Sorry if it's a bit long

#### Borek

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##### Re: Studying for exams, need help with some questions
« Reply #1 on: June 06, 2012, 03:55:18 AM »
For the reaction 3FeS(s) +  2H3PO4(aq)   → Fe3(PO4)2(s) + 3H2S(g), how many moles of
H3PO4 are required to produce 1 mole of H2S?

a.0.67        b. 1.5          c.  2           d. 3

You got it reversed.

Quote
If 20 g of a compound is dissolved in water to make 250 mL of a 0.5 mol L-1 solution,
the Molar Mass of the compound in g mol-1 is:

a.  10            b. 40          c. 80          d. 160

Don't know how to work this out, if you do could you please post the formula!

You can calculate number of moles, you know mass - that's all you need to calculate molar mass.

Quote
In which one of the following reactions does an element show the greatest increase in
oxidation number?

a.  MnO4-  +  8H+  +  5Fe2+  →  Mn2+  + 5Fe3+  + 4H2O
b.  2Al  +  6H+   →  2Al3+  +  3H2
c.  SO2  +  2H2S  →    3S  +  2H2O
d   Cl2  +  Sn2+  →  2Cl-   +  Sn4+

Don't know how to work this out, if you do could you please post how!

Assign oxidation numbers to all elements.

Quote
Which one of the following will occur if the temperature of a gas is increased from 30oC
to 60C?

a.   The volume will double
b.   The volume will increase by a small amount
c.   The volume will decrease by a small amount
d.   The volume will be halved

Think the answer is A but unsure..

Do you know what absolute temperature is?

Quote
In which class of compounds has the carbon been most highly oxidized?
a.  Carboxylic acids.
b.  Aldehydes.
c.  Ketones.
d.  Alcohols

Think the answer is B, but posted it up just incase it's wrong

Aldehydes can be oxidized further.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### Zero2Hero

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##### Re: Studying for exams, need help with some questions
« Reply #2 on: June 06, 2012, 04:08:13 AM »
Cheers for the reply, ill check all the stuff you posted!

#### Rutherford

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##### Re: Studying for exams, need help with some questions
« Reply #3 on: June 06, 2012, 09:56:21 AM »
The U and Pb problems are correct.