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    So I'm currently doing an undergrad Biology module which involves lots of Chemistry calculations. I thought doing a-level Chemistry would help but the basic conc=moles/volume and mass = Mr/moles is no longer sufficient.

    I was wondering if anyone had any resources they recommended to help with the calculation side of things. Some examples of questions we need to be able to are things like:

    - What volume of this solution of 1g NaCl in 100ml water would you use to make 500mL of a 10microgram/mL solution.
    - You dilute the entire 500mL in 5L of water, what is the final conc of NaCl?
    - What is the molarity of this NaCl conc?

    We were given these questions to practice ready for an assignment and weren't told how to complete them and I have no idea. I've looked on Chemguide (my saviour for a-level chemistry lol) but to no avail.

    Any advice or suggestions please?
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    (Original post by LeaX)
    So I'm currently doing an undergrad Biology module which involves lots of Chemistry calculations. I thought doing a-level Chemistry would help but the basic conc=moles/volume and mass = Mr/moles is no longer sufficient.

    I was wondering if anyone had any resources they recommended to help with the calculation side of things. Some examples of questions we need to be able to are things like:

    - What volume of this solution of 1g NaCl in 100ml water would you use to make 500mL of a 10microgram/mL solution.
    - You dilute the entire 500mL in 5L of water, what is the final conc of NaCl?
    - What is the molarity of this NaCl conc?

    We were given these questions to practice ready for an assignment and weren't told how to complete them and I have no idea. I've looked on Chemguide (my saviour for a-level chemistry lol) but to no avail.

    Any advice or suggestions please?
    It's just simple sums.

    There are 1000 mg in a gram
    There are 1000 micrograms in a mg

    There are 1000 mL in litre.

    Go for the target solution first and work out the total micrograms per volume required. Then work backwards..
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    (Original post by charco)
    It's just simple sums.

    There are 1000 mg in a gram
    There are 1000 micrograms in a mg

    There are 1000 mL in litre.

    Go for the target solution first and work out the total micrograms per volume required. Then work backwards..
    Thank you, I've had a go at the questions and was wondering if you would possibly be able to look through them please? I understand if you don't have time to, though. Also what is the difference between concentration and molarity? I always thought that they were interchangeable?

    How much NaCl do you need to weigh out to prepare 1 L of a 1M solution of NaCl?
    - Moles = conc x vol
    - Moles = 1
    - Mass = Mr x Mole
    - Mass = 58.44 x 1
    - Mass = 58.44g

    How many millimoles of NaCl are there in 1 gram?
    - Moles = Mass/Mr
    - Moles = 1/58.44
    - Moles = 0.017mol
    - Milimoles = 17.11mol

    You dissolve 1 gram of NaCl in 100mL of water, convert this conc to mg/mL
    - 1000/100 = 10mg/mL

    What volume of this solution is required in order to make 500mL of a 10microgram/mL solution?
    - 10microgram/mL solution equals 0.01mg/mL
    - mg/mL x mL = mg
    - 0.01 x 500 = 5mg required
    - mg / mg/mL = mL
    - 5 / 10 = 0.5mL

    Dilute the entire 500mL of solution in 5L of water, what is the final conc of NaCl?
    - 500ml contains 5mg of NaCl
    - Moles of NaCl: 5x10^-3 / 58.44 = 8.56x10^-5mol
    - Conc = moles / total volume
    - Conc = 8.56x10^-5mol / 5.5 = 1.55x10^-5moldm-3

    What is the molarity of NaCl in this solution?
    1.55x10^-5moldm-3.
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    (Original post by LeaX)
    Thank you, I've had a go at the questions and was wondering if you would possibly be able to look through them please? I understand if you don't have time to, though. Also what is the difference between concentration and molarity? I always thought that they were interchangeable?

    How much NaCl do you need to weigh out to prepare 1 L of a 1M solution of NaCl?
    - Moles = conc x vol
    - Moles = 1
    - Mass = Mr x Mole
    - Mass = 58.44 x 1
    - Mass = 58.44g


    How many millimoles of NaCl are there in 1 gram?
    - Moles = Mass/Mr
    - Moles = 1/58.44
    - Moles = 0.017mol
    - Milimoles = 17.11mol
    You mean 17.11 millimoles


    You dissolve 1 gram of NaCl in 100mL of water, convert this conc to mg/mL
    - 1000/100 = 10mg/mL



    What volume of this solution is required in order to make 500mL of a 10microgram/mL solution?
    - 10microgram/mL solution equals 0.01mg/mL
    - mg/mL x mL = mg
    - 0.01 x 500 = 5mg required
    - mg / mg/mL = mL
    - 5 / 10 = 0.5mL
    bit long winded ..

    you want 500 x 0.01 mg = 5 mg

    solution concentration = 10mg/mL

    so you need 0.5 mL


    Dilute the entire 500mL of solution in 5L of water, what is the final conc of NaCl?
    - 500ml contains 5mg of NaCl
    - Moles of NaCl: 5x10^-3 / 58.44 = 8.56x10^-5mol
    - Conc = moles / total volume
    - Conc = 8.56x10^-5mol / 5.5 = 1.55x10^-5moldm-3

    What is the molarity of NaCl in this solution?
    1.55x10^-5moldm-3.
    It looks like they are asking for concentration in micrograms per mL (or equivalent) and then moles per litre (mmol per litre)
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    (Original post by charco)
    :x
    Thank you.
 
 
 
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