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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Apple1977 on April 27, 2021, 05:10:43 PM

Title: Concentration
Post by: Apple1977 on April 27, 2021, 05:10:43 PM

Hello could somebody please work this out for me please

250mL of water.....1mL of sample was taken and diluted to 25mL.....and was analysed and shown to contain 163.3ppm of arsenic ....calculate the concentration of the arsenic in the original sample in mol dm-3.    Please can you show all the working for me so I can understand it

Title: Re: Concentration
Post by: Borek on April 27, 2021, 06:13:59 PM

Please read the forum rules (https://www.chemicalforums.com/index.php?topic=65859.0). You have to show your attempts at answering the question/solving the problem to receive help, it is a forum policy.

Title: Re: Concentration
Post by: Apple1977 on April 29, 2021, 12:27:27 PM

Sorry I didn’t know … thank you

Title: Re: Concentration
Post by: sjb on April 29, 2021, 01:36:49 PM

What. for instance, does 163 ppm mean?

Title: Re: Concentration
Post by: Apple1977 on April 29, 2021, 01:56:56 PM

parts per million ... you didn't know that ?  and its not Gcse level its advanced A level

Title: Re: Concentration
Post by: sjb on April 29, 2021, 02:39:44 PM

So what is the concentration in your 25 ml sample, in the 1 ml sample and in the 250 ml sample?

Title: Re: Concentration
Post by: Babcock_Hall on April 29, 2021, 09:20:57 PM

There is a simple formula for dilution calculations.  In my experience students make two kinds of mistakes when using it.  One is to ignore units.  The other is to plug numbers into it without regards to what a given number means.