muffin_selight
Badges: 9
Rep:
?
#1
Report Thread starter 7 years ago
#1
Hello, can you help me with how to work out the following questions please? I'll show the method I used to work them out but I am not sure whether it is right or not:

25cm3 of 1.0 mol dm-3 HCl = 0.025*1=0.025
50cm3 of 0.5 mol dm-3 HCl = 0.05*0.5=0.025
250cm3 of 0.25 mol dm-3 HCl = 0.25*0.25=0.0625
500cm3 of 0.01 mol dm-3 HCl = 0.5*0.01=0.005
25cm3 of 1.0 mol dm-3 NaOH = 0.025*1=0.025

Am I working them out correctly?

Thanks
0
reply
muffin_selight
Badges: 9
Rep:
?
#2
Report Thread starter 7 years ago
#2
How would you calculate the mass of material in given volume of solution? e.g. 25cm3 of 1 mol dm-3 HCl and 50cm3 of 0.5 mol dm-3 NaCl?

Also, how would you work out the concentration in m,oles of dm-3? e.g. 3.65g of HCl in 1000cm3 of solution; 3.65g of HCl in 100cm3 of solution; 6.62g of Pb(NO3)2 in 250cm3 of solution; 1.00g of NaOH in 250cm3 of solution?
1
reply
username890104
Badges: 2
Rep:
?
#3
Report 7 years ago
#3
(Original post by muffin_selight)
Hello, can you help me with how to work out the following questions please? I'll show the method I used to work them out but I am not sure whether it is right or not:

25cm3 of 1.0 mol dm-3 HCl = 0.025*1=0.025
50cm3 of 0.5 mol dm-3 HCl = 0.05*0.5=0.025
250cm3 of 0.25 mol dm-3 HCl = 0.25*0.25=0.0625
500cm3 of 0.01 mol dm-3 HCl = 0.5*0.01=0.005
25cm3 of 1.0 mol dm-3 NaOH = 0.025*1=0.025

Am I working them out correctly?

Thanks
Yeah, all of those are correct.

3.65 g of HCl in 1000 cm^3 of solution. What is the concentration in mol dm^3?
Concentration = Moles / Volume

Moles = 3.65/36.5 = 0.1

Volume = 1000 cm^3 = 1 dm^3

Concentration = 0.1 / 1 = 0.1 mol dm^3
0
reply
muffin_selight
Badges: 9
Rep:
?
#4
Report Thread starter 7 years ago
#4
(Original post by Tullia)
Yeah, all of those are correct.



Concentration = Moles / Volume

Moles = 3.65/36.5 = 0.1

Volume = 1000 cm^3 = 1 dm^3

Concentration = 0.1 / 1 = 0.1 mol dm^3
Why did you divide by 36.5?
0
reply
Secret.
Badges: 12
Rep:
?
#5
Report 7 years ago
#5
(Original post by muffin_selight)
Why did you divide by 36.5?


As moles = mass/mr, he divided the mass by the Mr of HCl which is 35.5 (Cl) + 1(H)
0
reply
muffin_selight
Badges: 9
Rep:
?
#6
Report Thread starter 7 years ago
#6
Thanks, I understand now.

How would I do 3.65g of HCl in 100cm3 of solution then? I'm stuck on converting the units..
0
reply
muffin_selight
Badges: 9
Rep:
?
#7
Report Thread starter 7 years ago
#7
Also, how do I calculate the mass of material in the given volume of solution? I found the following equations:

molarity = concentration in grams per 1000cm3/Mr of the material dissolved
number of moles of material in a given volume = (molarity x volume(cm3))/1000
mass of material in a given volume of solution = (molarity x volume(cm3) x Mr)/1000

But they are just confusing me further

I tried working out a question, I'll show you my working and can you tell where I am going wrong please.

25cm3 of 1mole dm-3 HCL

So I worked out the molarity first...

25cm3 x 4 = 1000cm3
1000cm3 / 36.5 = 27.4

Then I put this in the formula: (molarity x volume x Mr)/1000

(27.4 x 25 x 36.5)/1000 = 25

Can you PLEASE tell me how to do it, I am getting so frustrated because I can't do it, I feel like giving up *sigh*
0
reply
username890104
Badges: 2
Rep:
?
#8
Report 7 years ago
#8
(Original post by muffin_selight)
Thanks, I understand now.

How would I do 3.65g of HCl in 100cm3 of solution then? I'm stuck on converting the units..
Concentration = Moles / Volume

Moles = 3.65/36.5 = 0.1 (36.5 being the Mr of HCl)

Volume = 100 cm^3 = 0.1 dm^3 (as you divide by 1000 to get from cm^3 to dm^3)

Concentration = 0.1 / 0.1 = 1 mol dm^3

Also, how do I calculate the mass of material in the given volume of solution? I found the following equations:

molarity = concentration in grams per 1000cm3/Mr of the material dissolved
number of moles of material in a given volume = (molarity x volume(cm3))/1000
mass of material in a given volume of solution = (molarity x volume(cm3) x Mr)/1000

But they are just confusing me further

I tried working out a question, I'll show you my working and can you tell where I am going wrong please.

25cm3 of 1mole dm-3 HCL

So I worked out the molarity first...

25cm3 x 4 = 1000cm3
1000cm3 / 36.5 = 27.4

Then I put this in the formula: (molarity x volume x Mr)/1000

(27.4 x 25 x 36.5)/1000 = 25

Can you PLEASE tell me how to do it, I am getting so frustrated because I can't do it, I feel like giving up *sigh*
OK, so the mass of a solute within a given volume is its density. In terms of equation this is Density = Mass / Volume.

You have the mass of HCl as 36.5 (molar mass). You have the volume in dm^3 of your solution as 25/1000 = 0.025 dm^3.

You merely divide the two sums to get the density. In this case 36.5/0.025 = 1460 g/dm^3 (1.46 g/cm^3).
0
reply
muffin_selight
Badges: 9
Rep:
?
#9
Report Thread starter 7 years ago
#9
(Original post by Tullia)
Concentration = Moles / Volume

Moles = 3.65/36.5 = 0.1 (36.5 being the Mr of HCl)

Volume = 100 cm^3 = 0.1 dm^3 (as you divide by 1000 to get from cm^3 to dm^3)

Concentration = 0.1 / 0.1 = 1 mol dm^3



OK, so the mass of a solute within a given volume is its density. In terms of equation this is Density = Mass / Volume.

You have the mass of HCl as 36.5 (molar mass). You have the volume in dm^3 of your solution as 25/1000 = 0.025 dm^3.

You merely divide the two sums to get the density. In this case 36.5/0.025 = 1460 g/dm^3 (1.46 g/cm^3).
Thanks, how comes you don't do anything with the moles? e.g. 25cm3 of 1 MOLE dm-3 HCl
0
reply
muffin_selight
Badges: 9
Rep:
?
#10
Report Thread starter 7 years ago
#10
Hang on, wouldn't you use the mass equation: mass=concentration/volume?

So for 25cm3 of 1 mol dm-3 HCl, wouldn't you do 25x1?
0
reply
muffin_selight
Badges: 9
Rep:
?
#11
Report Thread starter 7 years ago
#11
Can you check whether these are correct please?

Calculating the mass ofmaterial in the given volume of solution:

50cm3 of 0.5mol dm-3 NaCl
58.5/(50/1000)=1170g/dm3

100cm3 of 0.25mol dm-3 of NH4NO3
80/(100/1000)=800g/dm3

25cm3 of 1 mol dm-3 BaCl2
208.3/(25/1000)=8332g/dm3

Calculating the concentration in moles dm-3 of the following:

6.62g of Pb(NO3)2 in 250cm3 solution
6.62/331.2=0.02
0.02/0.25=0.08mol/dm3

1.00g of NaOH in 250cm3 of solution
1/4-=0.025
0.025/0.25=0.1mol/dm3

1.58g of KMnO4 in 250cm3 of solution
1.58/158=0.01
0.01/0.25=0.04mol/dm3

Is my working correct?
0
reply
username890104
Badges: 2
Rep:
?
#12
Report 7 years ago
#12
(Original post by muffin_selight)
Calculating the mass ofmaterial in the given volume of solution:

50cm3 of 0.5mol dm-3 NaCl
58.5/(50/1000)=1170g/dm3

Incorrect. It is Moles = (Concentration)(Volume)/1000. So (0.5)(50)/1000 = 0.025. Then Moles x Molar Mass = Mass. So (0.025)(58.5) = 1.4625 g

100cm3 of 0.25mol dm-3 of NH4NO3
80/(100/1000)=800g/dm3

Incorrect. See above.

25cm3 of 1 mol dm-3 BaCl2
208.3/(25/1000)=8332g/dm3

Incorrect. See above.

Calculating the concentration in moles dm-3 of the following:

6.62g of Pb(NO3)2 in 250cm3 solution
6.62/331.2=0.02
0.02/0.25=0.08mol/dm3

Correct.

1.00g of NaOH in 250cm3 of solution
1/4-=0.025
0.025/0.25=0.1mol/dm3

Correct.

1.58g of KMnO4 in 250cm3 of solution
1.58/158=0.01
0.01/0.25=0.04mol/dm3

Correct.
Hope that helps.
0
reply
Abdullaalqamzi
Badges: 1
Rep:
?
#13
Report 2 years ago
#13
Why don't you divude by 1000 insted of 1.
0
reply
Pigster
Badges: 19
Rep:
?
#14
Report 2 years ago
#14
(Original post by Abdullaalqamzi)
Why don't you divude by 1000 insted of 1.
Who in this five year old thread were you asking and expecting an answer from?

The only person I see dividing anything by 1 was Tullia, who was working out the concentration of something in 1000 cm3 = 1 dm3, and since conc = n / v (in dm3) it made sense to divide by 1, rather than dividing by 1000/1000.
0
reply
sarah junne
Badges: 1
Rep:
?
#15
Report 1 year ago
#15
How many moles of hydrochloric acid are in 100cm of 2M hydrochloric acid ?
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • University of Surrey
    All subjects except Veterinary Medicine and Guildford School of Acting Undergraduate
    Wed, 20 Nov '19
  • The University of Law
    Solicitor Series: Discover Your Type of Law - LPC and GDL - Birmingham campus Postgraduate
    Wed, 20 Nov '19
  • Buckinghamshire New University
    Postgraduate and professional courses Postgraduate
    Wed, 20 Nov '19

what's your favourite season?

Summer (62)
32.29%
Spring (36)
18.75%
Autumn/Fall (48)
25%
Winter (36)
18.75%
I love them all equally (10)
5.21%

Watched Threads

View All
Latest
My Feed