Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta
    • Thread Starter
    Offline

    3
    ReputationRep:
    Hi! I just have a quick question for chemistry.
    I am lost on whhy when you dilute a solution the concentration becomes less but moles stay the same, but when you take lets say half of a solution moles become half yet concentration stays the same....
    Please help mee to understand it and when I can recognise this!


    Thankk you!!
    Offline

    3
    ReputationRep:
    when you dilute a solution you are increasing the volume but the moles stay the same

    And how do you work out concentration?

    concentration = moles / volume

    so if you dilute a solution the new conc. is same number of moles/ larger volume , i.e the same number divided by a larger number- which of course will give you a smaller number (hence the concentration decreases)

    Hope this attempt at an explanation helps lol
    Offline

    19
    ReputationRep:
    (Original post by ranz)
    Hi! I just have a quick question for chemistry.
    I am lost on whhy when you dilute a solution the concentration becomes less but moles stay the same, but when you take lets say half of a solution moles become half yet concentration stays the same....
    Please help mee to understand it and when I can recognise this!

    Thankk you!!
    because concentration = moles of the substance/ total volume
    so if you increase the volume that it's in (by diluting it) but keep the moles the same (so don't change the amount of the substance itself you have in there), your concentration will decrease

    lets say you had a bag with 6 red marbles in it. This is very concentrated because it just has red marbles in it but if you add 10 blue marbles to the bag you'll STILL have 6 red marbles (same moles) but there's blue ones in there as well so it is less concentrated now

    also same equation, moles = volume x concentration
    so if you decrease the volume, but keep concentration the same, your moles will also decrease
    say you had the red bag again with the 6 red marbles and 10 blue marbles - the ratio is 3:5
    conc = moles/volume = 6/16 = 0.375

    if you took 8 marbles out of that bag
    you'll have 3 red marbles and 5 blue marbles
    so HALF the number of moles but the ratio is still 3:5
    conc = moles/volume = 3/8 = 0.375

    same concentration! different moles

    i hope that made sense (and was correct!)
    Offline

    1
    ReputationRep:
    Moles are to do with the number of particles/molecules in a solution. Pretend you have 1 litre of solution in a jug. In it you have one mole of OH- ions. (One mole of any element is equal to 6.022x10 ^22 according to Avogadro so you have 6x10 ^22 ions in that solution).

    If you add 0.5 litres of another solution to the jug, you've diluted it as you've made the volume of the overall solution bigger, but the number of OH- ions still remain the same. The number of moles can be found be using the equation: number of moles = concentration x volume.

    If the number of moles is staying the same but the volume is increasing, the concentration of the solution must decrease for the formula to still work. This make sense?

    Remember to think of moles as number of 'things' and it should help distinguish between concentration and moles. If you have five pens, 3 blue and 2 red. If we added 5 more blue pens, we'd still have the same number of red pens (moles stays the same) but now it takes up a smaller percentage of the group of pens (concentration has decreased).

    Hope that helps.
 
 
 
Poll
Do you agree with the proposed ban on plastic straws and cotton buds?
Help with your A-levels

All the essentials

The adventure begins mug

Student life: what to expect

What it's really like going to uni

Rosette

Essay expert

Learn to write like a pro with our ultimate essay guide.

Uni match

Uni match

Our tool will help you find the perfect course for you

Study planner

Create a study plan

Get your head around what you need to do and when with the study planner tool.

Study planner

Resources by subject

Everything from mind maps to class notes.

Hands typing

Degrees without fees

Discover more about degree-level apprenticeships.

A student doing homework

Study tips from A* students

Students who got top grades in their A-levels share their secrets

Study help links and info

Can you help? Study help unanswered threadsRules and posting guidelines

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.