Why is it ok to get liquid on the neck over the meniscus when filling the volumetric flask? I'm talking about 2:54 and 3:44, you can see that there are drops which are over the meniscus; won't this falsify the concentration when the volumetric flask is filled up to the meniscus, as there is residuos liquid above it?
hi I need help diluting 6% weight of hydrogen peroxide and i’m unsure of the calculations. (stock solution is 6% weight in 100g so it’s 6g in 100g of water) i want to obtain a molar concentration of 0.100moldm^-3 but how much distilled water do i need to dilute
To find the concentration in mg/L, you will want to convert 0.004 mol to g using the n = m/M formula (solve for m which is mass in grams), then convert grams to mg by multiplying by 1000. 🙂
@@lyannapadillo991 Hi Lyanna - there are two general steps to finding the mass of solute needed to make the stock solution: 1) calculate the number of moles required to make 0.100 L of a 0.250 mol/L solution: V = 0.100L C = 0.250 mol/L n = ? Rearrange C=n/V to n = C×V, then substitute in the values above: n = (0.100L)(0.250mol/L) n = 0.0250 mol Therefore 0.0250 mol are required to make the stock solution. 2) Find the mass of copper(II) sulphate pentahydrate (CuSO4•5H2O) needed to make the solution: n = 0.0250 mol (from Step 1) M = 249.72 g/mol (from periodic table) m = mass? Rearrange n = m/M to isolate m: m = n × M m = (0.0250 mol)(249.72 g/mol) m = 6.243 g m = 6.24 g (to 3 significant digits) Hope this makes sense!
@@lyannapadillo991 you can use the process I've outlined above, except your concentration is 1.25 mol/L and you need to prepare 1L. 1) find the number of moles required using n = C×V 2) find the mass required using the moles found in Step 1 and the molar mass (M) of sugar (C12H22O11) n = M = m =? m = n × M
@@Samuitsuki so are you clear on how to use the C1V1=C2V2 formula to find the amount of stock required? C1 is the original stock concentration, C2 is the desired concentration (0.1M), and V2 is the final volume you need (1L). Then you will solve for V1. Not sure what your stock concentration is, but your rearranged formula will look like this: V1 = (C2 x V2)/C1 Once you know how much stock you need, then you can determine how much water needs to be added to top it up to 1L. Hope this helps!
Thank you. This is a great video for my virtual students this year.
Hope it helps! I must say I'm relieved we had some if these videos prepared before covid. Wishing you and your students the best of luck this year!
Penny Marcotte 7 years ago and your still responding 😭
Why is it ok to get liquid on the neck over the meniscus when filling the volumetric flask? I'm talking about 2:54 and 3:44, you can see that there are drops which are over the meniscus; won't this falsify the concentration when the volumetric flask is filled up to the meniscus, as there is residuos liquid above it?
Great observation! But the volume of the drops is insignificant when compared to the volume of water in the flask below.
@@pennymarcotte thanks for the quick reply, I always wondered about that!
hi I need help diluting 6% weight of hydrogen peroxide and i’m unsure of the calculations. (stock solution is 6% weight in 100g so it’s 6g in 100g of water) i want to obtain a molar concentration of 0.100moldm^-3 but how much distilled water do i need to dilute
in this solution 0,004 mol equal to how much mg/l ?
To find the concentration in mg/L, you will want to convert 0.004 mol to g using the n = m/M formula (solve for m which is mass in grams), then convert grams to mg by multiplying by 1000. 🙂
can you show the calculation?
how to did you get the mass of solute?
@@lyannapadillo991 Hi Lyanna - there are two general steps to finding the mass of solute needed to make the stock solution:
1) calculate the number of moles required to make 0.100 L of a 0.250 mol/L solution:
V = 0.100L
C = 0.250 mol/L
n = ?
Rearrange C=n/V to n = C×V, then substitute in the values above:
n = (0.100L)(0.250mol/L)
n = 0.0250 mol
Therefore 0.0250 mol are required to make the stock solution.
2) Find the mass of copper(II) sulphate pentahydrate (CuSO4•5H2O) needed to make the solution:
n = 0.0250 mol (from Step 1)
M = 249.72 g/mol (from periodic table)
m = mass?
Rearrange n = m/M to isolate m:
m = n × M
m = (0.0250 mol)(249.72 g/mol)
m = 6.243 g
m = 6.24 g (to 3 significant digits)
Hope this makes sense!
@@pennymarcotte How can I prepare 1.25 M sugar solution diluted to 1 L?
@@lyannapadillo991 you can use the process I've outlined above, except your concentration is 1.25 mol/L and you need to prepare 1L.
1) find the number of moles required using n = C×V
2) find the mass required using the moles found in Step 1 and the molar mass (M) of sugar (C12H22O11)
n =
M =
m =?
m = n × M
Just totally skips the calculation.
Which calculation did you need some extra assistance with?
@@pennymarcotte I'm need to make a liter of a 0.1 M HCl from a stock. So I need to know what volume of water and HCl I need to add for that.
@@Samuitsuki so are you clear on how to use the C1V1=C2V2 formula to find the amount of stock required? C1 is the original stock concentration, C2 is the desired concentration (0.1M), and V2 is the final volume you need (1L). Then you will solve for V1. Not sure what your stock concentration is, but your rearranged formula will look like this:
V1 = (C2 x V2)/C1
Once you know how much stock you need, then you can determine how much water needs to be added to top it up to 1L. Hope this helps!
@@pennymarcotte Thanks for the quick reply.
@@Samuitsuki good luck with your calculations