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November 01, 2025, 11:10:59 am
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Author Topic: ATAR's y11 Chemistry Qs!  (Read 9450 times)  Share 

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iNerd

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Re: ATAR's y11 Chemistry Qs!
« Reply #30 on: March 28, 2011, 08:44:50 pm »
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Milk of magnesia, Mg(OH)2, is used to neutralise excess stomach acid, HCl, when a person has an upset stomach. What mass of magnesium hydroxide will neutralise 0.242g of hydrochloric acid?

Molar mass of Mg(OH)2 = 24.3 + (17x2) = 24.3 + 34 = 56.3 g/mol

n(HCl) = 0.242 divided by M(HCl) which is 36.5 so 0.242/36.5 = 6.63 x 10^-3

m[Mg(OH)2] = 6.63 x 10^-3 x 56.3 = 0.3732g

Answer is 0.193g.
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luken93

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Re: ATAR's y11 Chemistry Qs!
« Reply #31 on: March 28, 2011, 08:57:49 pm »
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Mg(OH)2 + 2HCl -> Mg(Cl)2 + 2H2O

n(HCl) = .242/36.5 = 0.00663 mol
n(Mg(OH)2) = 1/2 x n(HCl) = 0.003315 mol
m(Mg(OH)2) = .003315 x 58.3 = 0.193g

Molar Mass of Mg(OH)2 is incorrect...
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iNerd

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Re: ATAR's y11 Chemistry Qs!
« Reply #32 on: March 28, 2011, 08:59:15 pm »
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Quote from: luken93 on March 28, 2011, 08:57:49 pm
Mg(OH)2 + 2HCl -> Mg(Cl)2 + 2H2O

n(HCl) = .242/36.5 = 0.00663 mol
n(Mg(OH)2) = 1/2 x n(HCl) = 0.003315 mol
m(Mg(OH)2) = .003315 x 58.3 = 0.193g

Molar Mass of Mg(OH)2 is incorrect...
Ah. How on earth am I meant to know that equation -.-

Thanks!
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luken93

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Re: ATAR's y11 Chemistry Qs!
« Reply #33 on: March 28, 2011, 09:09:26 pm »
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Quote from: ATAR on March 28, 2011, 08:59:15 pm
Quote from: luken93 on March 28, 2011, 08:57:49 pm
Mg(OH)2 + 2HCl -> Mg(Cl)2 + 2H2O

n(HCl) = .242/36.5 = 0.00663 mol
n(Mg(OH)2) = 1/2 x n(HCl) = 0.003315 mol
m(Mg(OH)2) = .003315 x 58.3 = 0.193g

Molar Mass of Mg(OH)2 is incorrect...
Ah. How on earth am I meant to know that equation -.-

Thanks!
All I'm doing is equating the coefficients, but I wouldn't worry too much about that, it will come with time..
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2010: Business Management [47]
2011: English [44]   |   Chemistry [45]  |   Methods [44]   |   Specialist [42]   |   MUEP Chemistry [5.0]   |   ATAR: 99.60
UMAT: 69 | 56 | 82 | = [69 / 98th Percentile]
2012: MBBS I @ Monash

iNerd

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Re: ATAR's y11 Chemistry Qs!
« Reply #34 on: March 29, 2011, 07:15:41 am »
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Quote from: luken93 on March 28, 2011, 09:09:26 pm
Quote from: ATAR on March 28, 2011, 08:59:15 pm
Quote from: luken93 on March 28, 2011, 08:57:49 pm
Mg(OH)2 + 2HCl -> Mg(Cl)2 + 2H2O

n(HCl) = .242/36.5 = 0.00663 mol
n(Mg(OH)2) = 1/2 x n(HCl) = 0.003315 mol
m(Mg(OH)2) = .003315 x 58.3 = 0.193g

Molar Mass of Mg(OH)2 is incorrect...
Ah. How on earth am I meant to know that equation -.-

Thanks!
All I'm doing is equating the coefficients, but I wouldn't worry too much about that, it will come with time..
I don't understand? By equating coefficients do you mean balancing 'cause I can balance...I meant how am I meant to know that acid + base ---> salt + water. That is Unit 2 knowledge I don't know :/
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Greatness

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Re: ATAR's y11 Chemistry Qs!
« Reply #35 on: March 29, 2011, 07:22:14 am »
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You have to balance the equation first i.e. get all elements equal. Then you use mole ratios to figure out how much you need to multiply the mol of something by to find the mol of what you want.
n(unknown) = (coefficient of unknown)/(coefficient of known) * no. of mol reacting
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iNerd

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Re: ATAR's y11 Chemistry Qs!
« Reply #36 on: March 29, 2011, 07:27:40 am »
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Quote from: swarley on March 29, 2011, 07:22:14 am
You have to balance the equation first i.e. get all elements equal. Then you use mole ratios to figure out how much you need to multiply the mol of something by to find the mol of what you want.
n(unknown) = (coefficient of unknown)/(coefficient of known) * no. of mol reacting
I know stoich -.-

I obviously couldn't do that because I had no idea what the equation would like :/

All we accelerate is Mass-mass stoich from U2 to U1.

I had to self-learn that acid equation thing.
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Greatness

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Re: ATAR's y11 Chemistry Qs!
« Reply #37 on: March 29, 2011, 07:34:14 am »
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Ohhh right. hahah
Yeah you learn the acid base reactions in unit 2.
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pi

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Re: ATAR's y11 Chemistry Qs!
« Reply #38 on: March 29, 2011, 08:33:10 pm »
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Quote from: swarley on March 29, 2011, 07:34:14 am
Ohhh right. hahah
Yeah you learn the acid base reactions in unit 2.

The equation could have been found using yr10 Science knowledge though... I believe that acid + metal hydroxide equations are in the chem chapter.
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pi

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Re: ATAR's y11 Chemistry Qs!
« Reply #39 on: March 29, 2011, 08:47:23 pm »
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Quote from: Bazza16 on March 29, 2011, 08:38:57 pm
lol mole and stoich have got to be the easiest chem chapters -

2 formulas and your done :)

Easy for now... You obviously haven't met PV=nRT, or the 5 gas conversions between units (mmHg, Pa, ppm, etc.), or even back titrations...
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Water

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Re: ATAR's y11 Chemistry Qs!
« Reply #40 on: March 29, 2011, 08:48:36 pm »
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Not as scary as pi makes it to be, since they are formulas.


Year 12 Chemistry looks hard with the theory ):

Moderator action: removed real name, sorry for the inconvenience
« Last Edit: January 15, 2017, 05:16:56 pm by pi »
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Souljette_93

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Re: ATAR's y11 Chemistry Qs!
« Reply #41 on: March 29, 2011, 08:59:29 pm »
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If you are good with numbers, then yes it is
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iNerd

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Re: ATAR's y11 Chemistry Qs!
« Reply #42 on: March 29, 2011, 09:02:05 pm »
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Can you please stop spamming my thread...go discuss easiness of chem somewhere else :/
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luken93

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Re: ATAR's y11 Chemistry Qs!
« Reply #43 on: March 29, 2011, 09:26:21 pm »
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Quote from: Bazza16 on March 29, 2011, 09:03:31 pm
you don't have ownership over your threads...
well he kinda does, I don't see Bazza16's thread written anywhere here? Afterall, it is ATAR's chemistry questions. He is asking for help, and from the above posts, you aren't really giving any...
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2010: Business Management [47]
2011: English [44]   |   Chemistry [45]  |   Methods [44]   |   Specialist [42]   |   MUEP Chemistry [5.0]   |   ATAR: 99.60
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iNerd

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Re: ATAR's y11 Chemistry Qs!
« Reply #44 on: March 29, 2011, 09:27:13 pm »
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Quote from: luken93 on March 29, 2011, 09:26:21 pm
Quote from: Bazza16 on March 29, 2011, 09:03:31 pm
you don't have ownership over your threads...
well he kinda does, I don't see Bazza16's thread written anywhere here? Afterall, it is ATAR's chemistry questions. He is asking for help, and from the above posts, you aren't really giving any...
I request a moderator to delete page 3 and 4...you're blowing out my threads :/

(not luken..luken has actually helped me in more ways than one).. :smitten:
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