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Topic: A couple of multiple choice questions:  (Read 8051 times)

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petze

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A couple of multiple choice questions:
« on: June 06, 2005, 07:52:00 AM »
I only resorted to this because for some reason the teacher cant explain why the answers are, (not all of them but some) what they are and guess its just a missprint but i thought it would be cool if you guys if you got the time to confirm this:
If you are doing yr 12 chemistry in victoria u might find these familiar...

1. A student takes 10ml of a solution that has a PH of 5 and dilutes it by adding 90 ml of water. The hydroxide ion concentration, in mol L-1, of the new solution would be:

A 10^-5
B 10^-6
C 10^-8
D 10^-9

I believed that the Answer is C due to : Ph of 5 is [H30] = 10^-5  therefore [OH] is 10^-9 so i picked D.
Answer however is C... any input ??

2 Consider the following equillibrium that exists in water containing bromine:
 Br2(aq)+ H2O(l) ---> Br^-(aq)+2H^+(aq)+BrO^-(aq)
                        <---
The equilibrium position could be moved towards the products by adding one drop of concentrated:

A Potassium Nitrate Solution
B Sodium Carbonate Solution
C Sulfuric Acid
D Sodium bromide Solution

I picked D but the answer was B... any reasons why?

3 Which of the following substances would give a ph of 7.0 in aqueous solution at 25 degrees?

A KNO3
B CH3COONa
C KOH
D NH4NO3

I picked d but answer is A... im not sure whats happening here... im guessing you will have to draw out equations for each one....


4 At 20 degrees and 101 kPa pressure 3.9g of methane occupies 5.88L The same volume of another unknown gaseous hydrocarbon at the same temprature and pressure has a mass of 10.7G. The unknown gas could be:

A C2H4
B C2H6
C C3H8
D C4H10

This has something to do with empirical formulas i believe. Answer is C....

5 In the reaction of 20g of Sulfuric acid with 20g of sodium hydroxide approximately:

A 20 g of Sodium sulfate are formed
B 9.1g of Sulfurik acid remains
C 9.0g of water is formed
D. 3.7g of Sodium Hydroxide remains

After balancing out the equations (which was not supplied to us and we have do make out own) it turned out to H2SO4+2NaOH -----> Na2SO4 + 2H20. It involves basic stochiometry but i am not quite sure how the correct answer is D and not C. I made out to believe that A is incorrect as actually 28g of Sulfuric Acid remained. Any idea?

6 Assuming complete conversion of sulfu dioxide into sulfuric acid, the maximum mass, in tonne, of sulfuric acid produced from 1.00 tonne (10^6g) of iron pyrites is:

A 0.817
B 1.00
C 1.07
D 1.63

Im not quite sutr which formula to apply my stochiometry on... The answer is D

7 Iron(III) Sulfide, Fe2S3, reacts with hydrochloric acid according to the equation: Fe2S3(s)+6HCl(aq) ----> 2FeCl3(aq)+ 3H2S(g)
If 20.8g of Fe2S3, is combined with 1.50L of 0.500 M HCL the expected maximum volume of H2S gas evolved, at SLC is approximately:

A 2.45L
B 7.35L
C 9.19L
D 18.45L

Correct answer is B

8The label on a bottle of cleaning agent claims that the product contains 1.25%m/v sodium hydroxide. From this information, the mass, in g, of hydroxide ions in a 750 mL bottle would be

A 0.531
B 3.98
C 5.39
D 9.38

The answer for that is B.

9 The substance with the lowest Ph when dissolved in water is

A C2H5COONa
B C3H7OH
C CH3COOCH3
D C2H5COOH

The answer for that is D. would you look at the molar mass of these to figure it out, would you just know one is more acidic than the other? A gets crossed of straightaway as its a base correct?

10 Water that had discharged from a drain into a local creek was found to be contaminated with NAOH at a concentration of 0.0010 M. The volume of HCL solution having a pH of 1.0 that would be needed to neutralise 10L of conatminated water is:

A 0.10L
B 1.0L
C 10L
D 1.0*10^2

The correct answe is A

11 A chemist needs to adjust the ph of a 25mL of barium hydroxide solution from 10 to 8 by adding distilled water. The initial concentration of the undiluted barium hydroxide would be.

A 1.0*10^-10 M
B 5*10^-11 M
C 1*10^-4 M
D 5*10^-5 M

The correct answer is D. This one is especially tricky.. well if you got no idea whats happening like me lol.

12 A chemist analyses a 10.9 g ore sample of chalcopyrite CuFeS2. A gravimetri analysis is carried out so that all the sulfur in CuFeS2, is precipitated at BaSO4. The amount of BaSO4 is determined to be 0.10 mol. What is the percentage mass of sulfur in the ore?

A 1.6%
B 6.4%
C 16%
D 32%

Correct answer is D


And last but not least:

13 Which of the following contains the greatest number of copper ions?
A 64mg of copper nitrate
B 0.5cm^3 of metallic copper that has a density of 8.94g/cm^3
C 20ml of a 0.20 M copper(II) sulfate solution.
D 20mL of a 10% (w/v) copper(I) nitrate solution.

This involves conversions i guess. The answer is B

Well thats all of them from about a zillion questions before that :P i guess cramming it down to 13 aint so bad. If anyone has any free time and would be willing to answer some of those it would be greately appreciated.

I will now be off byyyy byyyy :) :D
thanks again in advance!!
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Offline Borek

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Re:A couple of multiple choice questions:
« Reply #1 on: June 06, 2005, 08:50:34 AM »
I doubt if you have really tried to do these questions and that these are only left from the longer list. But let's see...

Quote from: petze on June 06, 2005, 07:52:00 AM
I believed that the Answer is C due to : Ph of 5 is [H30] = 10^-5  therefore [OH] is 10^-9 so i picked D.
Answer however is C... any input ??

What about dilution?

Quote
Consider the following equillibrium that exists in water containing bromine:
 Br2(aq)+ H2O(l) <--> Br^-(aq)+2H^+(aq)+BrO^-(aq)

I picked D but the answer was B... any reasons why?

What states LeChateliers Principle? What will happen if you add base to the solution?

Quote
Which of the following substances would give a ph of 7.0 in aqueous solution at 25 degrees?

I picked d but answer is A... im not sure whats happening here... im guessing you will have to draw out equations for each one....

What is hydrolysis? What kind of substance hydrolize?

Quote
At 20 degrees and 101 kPa pressure 3.9g of methane occupies 5.88L The same volume of another unknown gaseous hydrocarbon at the same temprature and pressure has a mass of 10.7G. The unknown gas could be:

This has something to do with empirical formulas i believe. Answer is C....

pV = nRT. You are asked to calculate molar mass of the second substance.

Quote
In the reaction of 20g of Sulfuric acid with 20g of sodium hydroxide approximately:

After balancing out the equations (which was not supplied to us and we have do make out own) it turned out to H2SO4+2NaOH -----> Na2SO4 + 2H20. It involves basic stochiometry but i am not quite sure how the correct answer is D and not C. I made out to believe that A is incorrect as actually 28g of Sulfuric Acid remained. Any idea?

28g left out of 20g added?

Quote
Assuming complete conversion of sulfu dioxide into sulfuric acid, the maximum mass, in tonne, of sulfuric acid produced from 1.00 tonne (10^6g) of iron pyrites is:

What are pyrites? What reactions are taking place?

Quote
Iron(III) Sulfide, Fe2S3, reacts with hydrochloric acid according to the equation: Fe2S3(s)+6HCl(aq) ----> 2FeCl3(aq)+ 3H2S(g)
If 20.8g of Fe2S3, is combined with 1.50L of 0.500 M HCL the expected maximum volume of H2S gas evolved, at SLC is approximately:

Correct answer is B

And?

[auote]The label on a bottle of cleaning agent claims that the product contains 1.25%m/v sodium hydroxide. From this information, the mass, in g, of hydroxide ions in a 750 mL bottle would be

The answer for that is B.
Quote

Great.

Quote
The substance with the lowest Ph when dissolved in water is

The answer for that is D. would you look at the molar mass of these to figure it out, would you just know one is more acidic than the other? A gets crossed of straightaway as its a base correct?

There is only one acid in this question. Have you looked at the formulas?

Quote
Water that had discharged from a drain into a local creek was found to be contaminated with NAOH at a concentration of 0.0010 M. The volume of HCL solution having a pH of 1.0 that would be needed to neutralise 10L of conatminated water is:

The correct answe is A

Super.

Quote
A chemist needs to adjust the ph of a 25mL of barium hydroxide solution from 10 to 8 by adding distilled water. The initial concentration of the undiluted barium hydroxide would be.

The correct answer is D. This one is especially tricky.. well if you got no idea whats happening like me lol.

C1V1 = C2V2 to quote Garneck ;)

Quote
A chemist analyses a 10.9 g ore sample of chalcopyrite CuFeS2. A gravimetri analysis is carried out so that all the sulfur in CuFeS2, is precipitated at BaSO4. The amount of BaSO4 is determined to be 0.10 mol. What is the percentage mass of sulfur in the ore?

Correct answer is D

If you say so...

Quote
Which of the following contains the greatest number of copper ions?

This involves conversions i guess.

So convert them.

Quote
Well thats all of them from about a zillion questions before that :P i guess cramming it down to 13 aint so bad. If anyone has any free time and would be willing to answer some of those it would be greately appreciated.

First of all, you have to prove that you really tried to do them by yourself. Posting a question with information "right answer is C" doesn't prove anything. As long as I don't see your work, I won't help further. Others will hopefully follow.
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petze

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Re:A couple of multiple choice questions:
« Reply #2 on: June 06, 2005, 09:51:54 AM »
it saddens me that you dont believe me :( but i understand, plenty of s#*$ talkers r on the net so i see where your coming from.. sorry bout not writing the working out for some of them, i got lazy typing all the things out.... some though i admit i didnt do a lot of working out and wasnt exactly sure how to begin them.

just so you know though "if they were questions that had to be done for homework and if i was to be just cheating i guess i would have just circled the right question and done with that in my textbooks there are even answers at the back of the book where it shows you the answer....so i wouldnt go through the trouble of going on the net to ask for help.. . but yeah lets see what i can further explain:::
----------------------------


What about dilution?
^^^^^^
so how would i dilute to make it work. 10/90 ml or 90ml/10? Is there a dilution factor of 2 missing somewhere. i believe what my teacher said once.

What states LeChateliers Principle? What will happen if you add base to the solution?
^^^^^
So sodium carbonate is a "base" solution and by adding it to this particular equation will make the equilibrium shift right? The reason i got confused here is because i believed there had to be a particular chemical added in relevance to the equation to make the equilibrium move either left or right. For eg: You would add more Br2 solution to push the reactant forward to make more producs. Or you would remove particular products such as  Bro to make more BrO.

What is hydrolysis? What kind of substance hydrolize?
^^^^^^^^^^^^
How can you tell which of those hydrolyze just by looking at them,  is it expected to know that KNO3 will hydrolize and CH3COONa will aswell or wont? So if you were to work through it You would wright each one as follows as an eg: KNO3+H20<====> H30^+ + KNO3^- ??


pV = nRT. You are asked to calculate molar mass of the second substance.
^^^^^^^^^^^^^^^^^
but the information doesnt tell you what type of substance it is so there is no way of working out the moles of the original substance to then be able to work out the new equation from the given infomation. I believed you had to do something with emperical formulas anyway and was hoping to get some start to it? if that is the right way at all?


28g left out of 20g added?
^^^^^^
LOLL obviously im an idiot if you cant tell by now. i must have gone wrong with the equation. Did my equation look right to you the one i added.


What are pyrites? What reactions are taking place?
^^^^^^^^^^
Are you asking me what are pyrites as you dont know or you want me to think about them. Arent pyrites Fe2 or such. The reaction taking place is basically a AB+CD ----> AD+CB isint it?


And?
^^^
is this question a basic PV=nRt one because i must be doing something wrong with the calculations and i get the wrong answer....


Great.
^^^^^^
Im just confused because im not familiar with conversing the %m/v... how do i start it of..


There is only one acid in this question. Have you looked at the formulas?
^^^^^^^^^^
ohhhhhhhhh They are to omg *blinks* i didnt even look at the fact that the OH and Na were present for A and B making them obviously Bases.. hey i even said i originally thought A is a base loll... see im not so dumb... But what about C..?

Super.
^^^^^
Im really not good with dilution factors.. i always mix them up the other way around and make the answer seem so rong.... any advice u can give me.... (its up to u of course :D )


C1V1 = C2V2 to quote Garneck
^^^^^^^^^
c1v1=c2v2

OMG ofcourse... no wait you just do 0.025ml*sodiumHydroxide concentration = OH* . wait are you give all the information though OOOOh is the concentration of C1 10^-10 AND The concentration of C2 10^-8!!!! AM I on the right track??!?!


If you say so...
^^^^^^
i keep getting the answer C for that.. im guessing i got the equation wrong.... is it possible if you can point me the right equation.. i would write out all the working out but im lazzyyyy loll^^^^^but considering im doing all this u should be grateful :P heheh jk
 
So convert them.
^^^^^
i got no probelm convertin A and B (i convert them into moles)
But C and D get me really confused.... and help starting them of



There is that proof enough for yah :P Jk ... it probably aint but any more help would be appreciated...

later for now!~


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Offline Borek

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Re:A couple of multiple choice questions:
« Reply #3 on: June 06, 2005, 12:32:25 PM »
Quote from: petze on June 06, 2005, 09:51:54 AM
What about dilution?
^^^^^^
so how would i dilute to make it work. 10/90 ml or 90ml/10? Is there a dilution factor of 2 missing somewhere. i believe what my teacher said once.

Original solution has pH = 5, that gives you [H+ ]. What is the final volume? c1v1 = c2v2. Then convert to pOH.

Quote
What states LeChateliers Principle? What will happen if you add base to the solution?
^^^^^
So sodium carbonate is a "base" solution and by adding it to this particular equation will make the equilibrium shift right?

The magic word is "hydrolysis". See also answer to the next question.

Quote
The reason i got confused here is because i believed there had to be a particular chemical added in relevance to the equation to make the equilibrium move either left or right. For eg: You would add more Br2 solution to push the reactant forward to make more producs. Or you would remove particular products such as  Bro to make more BrO.

H+ is the particular product removed by Na2CO3.

Quote
What is hydrolysis? What kind of substance hydrolize?
^^^^^^^^^^^^
How can you tell which of those hydrolyze just by looking at them,  is it expected to know that KNO3 will hydrolize and CH3COONa will aswell or wont? So if you were to work through it You would wright each one as follows as an eg: KNO3+H20<====> H30^+ + KNO3^- ??

Some things you have to memorize. Carbonic acid and acetic acid are weak. Ammonia is a weak base. Rule of thumb says that salts of weak acids and/or weak bases hydrolize changing pH of solution. Salts of strong acids and bases don't hydrolize.

Quote
pV = nRT. You are asked to calculate molar mass of the second substance.
^^^^^^^^^^^^^^^^^
but the information doesnt tell you what type of substance it is so there is no way of working out the moles of the original substance to then be able to work out the new equation from the given infomation. I believed you had to do something with emperical formulas anyway and was hoping to get some start to it? if that is the right way at all?

No need for empirical formula. Calculate number of moles of methane (you can do it either using mass of methane, or using pV = nRT). You are told the other substance mass in the same circumstances - which means there will be the same number of moles. This gives molar mass of the substance in question. Just compare it with molar masses of A, B, C and D.

Quote
28g left out of 20g added?
^^^^^^
LOLL obviously im an idiot if you cant tell by now. i must have gone wrong with the equation. Did my equation look right to you the one i added.

Equation seems OK.

Quote
What are pyrites? What reactions are taking place?
^^^^^^^^^^
Are you asking me what are pyrites as you dont know or you want me to think about them. Arent pyrites Fe2 or such. The reaction taking place is basically a AB+CD ----> AD+CB isint it?

I want you to think. You have to find out what pyrites are and write down what reactions take place when converting pyrites to sulfuric acid. Rest will be simple stoichiometry.

Quote
And?
^^^
is this question a basic PV=nRt one because i must be doing something wrong with the calculations and i get the wrong answer....

It is basic limiting reagent and pV = nRT question.

Quote
Great.
^^^^^^
Im just confused because im not familiar with conversing the %m/v... how do i start it of..

The best point to start is with definition... If in doubt, check help to my CASC, you will find all definitions there.

Quote
There is only one acid in this question. Have you looked at the formulas?
^^^^^^^^^^
ohhhhhhhhh They are to omg *blinks* i didnt even look at the fact that the OH and Na were present for A and B making them obviously Bases.. hey i even said i originally thought A is a base loll... see im not so dumb... But what about C..?

You are making mistakes faster then I can correct. A is a sodium poropionate - salt of a weak organic acid. B is propanol - alcohol. C is methyl acetate - ester. And finally D is propanoic acid.

Quote
Super.
^^^^^
Im really not good with dilution factors.. i always mix them up the other way around and make the answer seem so rong.... any advice u can give me.... (its up to u of course :D )

It is C1V1 = C2V2 type question.

Quote
C1V1 = C2V2 to quote Garneck
^^^^^^^^^
c1v1=c2v2

OMG ofcourse... no wait you just do 0.025ml*sodiumHydroxide concentration = OH* . wait are you give all the information though OOOOh is the concentration of C1 10^-10 AND The concentration of C2 10^-8!!!! AM I on the right track??!?!

Sorry, I just realized I did a mistake. Forget about C1V1 here. What is pOH of the original solution? What is OH- concentration? How does [OH- ] conevrts to Ba(OH)2 concentration?


Quote
If you say so...
^^^^^^
i keep getting the answer C for that.. im guessing i got the equation wrong....

Write down step by step how you get to 16%.
 
Quote
So convert them.
^^^^^
i got no probelm convertin A and B (i convert them into moles)
But C and D get me really confused.... and help starting them of

Are you sure you have copied questions properly? If it asks about number of copper ions B is not an option. As for conversions - start with definitions of concentrations, see what you have and what you need.
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petze

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Re:A couple of multiple choice questions:
« Reply #4 on: June 06, 2005, 06:53:46 PM »
thanks for all the extra help. i will use what you have given me to help me (i am at school now revising.... im surprised a lot of those questions required c1v1=c2v2 knowledge... i thought they were harder than that.

k ill get going by by now!
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