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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: /0 on July 21, 2008, 07:36:00 pm

Title: Aspirin in reaction
Post by: /0 on July 21, 2008, 07:36:00 pm: Acetyl salicyclic acid ( $C_9H_8O_4$ , relative atomic mass 180) is an acid called aspirin with one replaceable hydrogen (monoprotic). A tablet of aspirin contains aspirin and fillers. A tablet is crushed and dissolved in water. The acid in it was neutralised by 12.25mL of 0.1466 M NaOH. 1 grain of aspirin = 0.0648g.

$C_9H_8O_4+NaOH \rightarrow C_9H_7O_4Na+H_2O$

How many grains of aspiring are in the tablet?

A. 232
B. 20.9
C. 15.0
D. 4.99

Thanks. The main problem I have with this question is I don't know what the M stands for in 0.1466 M NaOH.
Title: Re: Aspirin in reaction
Post by: orangez on July 21, 2008, 07:38:44 pm: The M stands for "molar" or "mol / L" -- unit for molarity/concentration.
Title: Re: Aspirin in reaction
Post by: Matt The Rat on July 21, 2008, 07:39:31 pm: Molarity.

$c=n/v$
Title: Re: Aspirin in reaction
Post by: /0 on July 21, 2008, 07:41:05 pm: @ orangez

But shouldn't the molar mass of NaOH be (23+16+1) = 40 M?

So... M used interchangeably for Molar Mass and Concentration?
Title: Re: Aspirin in reaction
Post by: orangez on July 21, 2008, 07:41:38 pm: Molar mass is measure in g/mol
Title: Re: Aspirin in reaction
Post by: orangez on July 21, 2008, 07:42:57 pm: $0.1466 M$ is the concentration of NaOH :)
Title: Re: Aspirin in reaction
Post by: /0 on July 21, 2008, 07:46:15 pm: ok thanks
Title: Re: Aspirin in reaction
Post by: Mao on July 21, 2008, 07:49:30 pm: Quote from: DivideBy0 on July 21, 2008, 07:41:05 pm
@ orangez

But shouldn't the molar mass of NaOH be (23+16+1) = 40 M?

So... M used interchangeably for Molar Mass and Concentration?

you've confused M [a unit for concentration measured in $mol\; L^{-1}$ ] with $M_r$ [the relative molecular mass measured in $g\; mol^{-1}$ , also applies to $A_r$ to a lesser extent]
Title: Re: Aspirin in reaction
Post by: /0 on July 21, 2008, 08:05:28 pm: Lol... in my class we just use $M$ for relative molecular mass. I'll take note of this :P, thanks
Title: Re: Aspirin in reaction
Post by: Collin Li on July 21, 2008, 10:11:38 pm: M is a unit, standing for "Molarity"

M(NaOH), on the other hand, is often how you'd refer to the molar mass of NaOH.

They are different.

Examples:

[NaOH] = 0.1366 M
M(NaOH) = 40.0 g/mol

(Note that a species in square brackets often means its concentration)