[mookxi]

1. Which of the following substances would give a pH of 7.0 in aqueous solution at 25 degrees celcius:

A. KNO3
B: CH3COONa
C. KOH
D: NH4NO3

the answer is A, why? I'm not sure how to do the calculations here or if it's a theory based question.

2. In the reaction of 20g of sulfuric acid with 20g of sodium hydroxide approximately

A. 20g of sodium sulfate are formed
B. 9.1g of sulfuric acid remains
C. 9.0g of water is formed
D. 3.7 of sodium hydroxide reminds

The answer is D.

3. When 100ml of 1.0M HCl are added to 1.0g of granulated zinc at 20 degrees celcius, hydrogen gas is evovled. all of the following will increase the initial rate at which hydrogen gas is released except:

A. increasing the temperature of the 1.0M HCl to 40 degrees celcius
B. using 150ml of 1.0 M HCl instead of 100ml
C. using finely powered zinc instead of granular zinc
D. using 2.0M Hcl instead of 1.0M HCl

the answer is D but i thought it would be B because isn't it increasing the volume therefore the reaction will be slower? Please explain this.

4. Which of the following compounds would be least soluble in water?

A. ethanoic acid
B. ethanol
C. methyl methanoate
D. ethene

the answer is D - ethene, why?

Sorry if that's a lot of questions! Your help would be appreciated!

[mike]

3. When 100ml of 1.0M HCl are added to 1.0g of granulated zinc at 20 degrees celcius, hydrogen gas is evovled. all of the following will increase the initial rate at which hydrogen gas is released except:

A. increasing the temperature of the 1.0M HCl to 40 degrees celcius
B. using 150ml of 1.0 M HCl instead of 100ml
C. using finely powered zinc instead of granular zinc
D. using 2.0M Hcl instead of 1.0M HCl

the answer is D but i thought it would be B because isn't it increasing the volume therefore the reaction will be slower? Please explain this.

I would have said B too.

4. Which of the following compounds would be least soluble in water?

A. ethanoic acid
B. ethanol
C. methyl methanoate
D. ethene

the answer is D - ethene, why?

Think about their polarities..

[mookxi]

Thanks Mike. Yup, it's actually B. I checked with other people and they said the answer was wrong. ^_^ yuppie, that's one less I can't do. & thanks. It's ethene right? Cause' it's non-polar, the rest are polar cause' they're hydroxides.

Thanks, & I figured out the rest. ;-D

3. When 100ml of 1.0M HCl are added to 1.0g of granulated zinc at 20 degrees celcius, hydrogen gas is evovled. all of the following will increase the initial rate at which hydrogen gas is released except:

A. increasing the temperature of the 1.0M HCl to 40 degrees celcius
B. using 150ml of 1.0 M HCl instead of 100ml
C. using finely powered zinc instead of granular zinc
D. using 2.0M Hcl instead of 1.0M HCl

the answer is D but i thought it would be B because isn't it increasing the volume therefore the reaction will be slower? Please explain this.

I would have said B too.

4. Which of the following compounds would be least soluble in water?

A. ethanoic acid
B. ethanol
C. methyl methanoate
D. ethene

the answer is D - ethene, why?

Think about their polarities..

[Borek]

1. Which of the following substances would give a pH of 7.0 in aqueous solution at 25 degrees celcius:

A. KNO3
B: CH3COONa
C. KOH
D: NH4NO3

the answer is A, why? I'm not sure how to do the calculations here or if it's a theory based question.

B is the only solution of strog acid and strong base.

All other solutions are either of the base (KOH) or salt of the weak acid (acetate) or the weak base (ammonia). Such solutions are never neutral due to hydrolyzis.

(In reality the only answer to this question is: NONE. But that's completely other story.)

[anarchron]

The reason why KNO3 would give you a solution closest to 7 is because it's a neutral salt as KOH is a strong base and HNO3 is a strong acid.

By the way, are you doing VCE mid years? One of the question looks familar, probably from a STAV.

[mookxi]

The reason why KNO3 would give you a solution closest to 7 is because it's a neutral salt as KOH is a strong base and HNO3 is a strong acid.

By the way, are you doing VCE mid years? One of the question looks familar, probably from a STAV.

Yes, actually, I am! How did you know? :-D Yes, that was from the STAV 2003 Unit 3 Trial exam paper.

[swati]

2. In the reaction of 20g of sulfuric acid with 20g of sodium hydroxide approximately

A. 20g of sodium sulfate are formed
B. 9.1g of sulfuric acid remains
C. 9.0g of water is formed
D. 3.7 of sodium hydroxide reminds

The answer is D.

The equation would be           
H₂SO₄   +  2NaOH  --------->   Na₂SO4   +   2H₂O

20g H₂SO₄   = 0.204 moles
20g NaOH = 0.5 moles

Now 0.204 moles of H₂SO₄ will react with (2 * 0.204) = 0.408 moles of NaOH
Therefore ( 0.5 - 0.408 ) = 0.092 moles of NaOH are left
That is ( 0.092 * 40 ) g = 3.68 g of NaOH are left

So the answer is D.