November 30, 2021, 10:45:27 AM
Forum Rules: Read This Before Posting

### Topic: Concentration  (Read 448 times)

0 Members and 1 Guest are viewing this topic.

#### Apple1977

• New Member
• Posts: 7
• Mole Snacks: +0/-0
##### Concentration
« on: April 27, 2021, 05:10:43 PM »

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

#### Borek

• Mr. pH
• Deity Member
• Posts: 26863
• Mole Snacks: +1742/-403
• Gender:
• I am known to be occasionally wrong.
##### Re: Concentration
« Reply #1 on: April 27, 2021, 06:13:59 PM »
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### Apple1977

• New Member
• Posts: 7
• Mole Snacks: +0/-0
##### Re: Concentration
« Reply #2 on: April 29, 2021, 12:27:27 PM »
Sorry I didn’t know … thank you

#### sjb

• Global Moderator
• Sr. Member
• Posts: 3603
• Mole Snacks: +219/-42
• Gender:
##### Re: Concentration
« Reply #3 on: April 29, 2021, 01:36:49 PM »
What. for instance, does 163 ppm mean?

#### Apple1977

• New Member
• Posts: 7
• Mole Snacks: +0/-0
##### Re: Concentration
« Reply #4 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

#### sjb

• Global Moderator
• Sr. Member
• Posts: 3603
• Mole Snacks: +219/-42
• Gender:
##### Re: Concentration
« Reply #5 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?

#### Babcock_Hall

• Chemist
• Sr. Member
• Posts: 4982
• Mole Snacks: +292/-22
##### Re: Concentration
« Reply #6 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.