moles and mg

Can someone say how to do d and e please?

2. An experiment requires a solution which is 160 mM glycine and 10 mM MgSO4.What you have available in the lab is distilled water, a 2.2 M stock solution of glycine, and a 0.5 M MgSO4 stock solution. The experiment requires 5 ml of the solution in a test tube.

(a) What volume of the stock glycine solution do you need to transfer to the test tube?

C1V1 = C2V2
= 2.2M x V1 = 5ml x 0.16M / 2.2M
= V1 = 5ml x 0.16M / 2.2M
= 0.36ml of glycine

(b) What volume of stock MgSO4 solution do you need to transfer to the test tube?

10mM / 1000 = 0.01M MgSO4

C1V1 = C2V2
= 0.5M x V1 = 5ml x 0.01M / 0.5M
= V1 = 5ml x 0.01M / 0.5M
= 0.1ml of MgSO4

(c) What volume of distilled water do you need to transfer to the test tube?

0.36ml + 0.1ml = 0.46ml
V1 - V2
= 5ml - 0.46ml
= 4.54ml water needed

(d) How many moles of glycine are in the test tube?

(e) How many mg of glycine does this represent? (The mass of 1 mole of Glycine is 75g.)

Reply 1

random88

13

Original post by John158

Can someone say how to do d and e please?

2. An experiment requires a solution which is 160 mM glycine and 10 mM MgSO4.What you have available in the lab is distilled water, a 2.2 M stock solution of glycine, and a 0.5 M MgSO4 stock solution. The experiment requires 5 ml of the solution in a test tube.

(a) What volume of the stock glycine solution do you need to transfer to the test tube?

C1V1 = C2V2
= 2.2M x V1 = 5ml x 0.16M / 2.2M
= V1 = 5ml x 0.16M / 2.2M
= 0.36ml of glycine

(b) What volume of stock MgSO4 solution do you need to transfer to the test tube?

10mM / 1000 = 0.01M MgSO4

C1V1 = C2V2
= 0.5M x V1 = 5ml x 0.01M / 0.5M
= V1 = 5ml x 0.01M / 0.5M
= 0.1ml of MgSO4

(c) What volume of distilled water do you need to transfer to the test tube?

0.36ml + 0.1ml = 0.46ml
V1 - V2
= 5ml - 0.46ml
= 4.54ml water needed

(d) How many moles of glycine are in the test tube?

(e) How many mg of glycine does this represent? (The mass of 1 mole of Glycine is 75g.)

D) moles of glycine in test tube = conc x vol. Read question carefully and you will realise that you know the conc of glycine added to the test tube and in a) you calculated the volume of glycine. You’ve done the bulk of the hard work, simply plug these values into your formula to get the moles

Reply 2

random88

13

Original post by random88

D) moles of glycine in test tube = conc x vol. Read question carefully and you will realise that you know the conc of glycine added to the test tube and in a) you calculated the volume of glycine. You’ve done the bulk of the hard work, simply plug these values into your formula to get the moles

Original post by John158

Can someone say how to do d and e please?

2. An experiment requires a solution which is 160 mM glycine and 10 mM MgSO4.What you have available in the lab is distilled water, a 2.2 M stock solution of glycine, and a 0.5 M MgSO4 stock solution. The experiment requires 5 ml of the solution in a test tube.

(a) What volume of the stock glycine solution do you need to transfer to the test tube?

C1V1 = C2V2
= 2.2M x V1 = 5ml x 0.16M / 2.2M
= V1 = 5ml x 0.16M / 2.2M
= 0.36ml of glycine

(b) What volume of stock MgSO4 solution do you need to transfer to the test tube?

10mM / 1000 = 0.01M MgSO4

C1V1 = C2V2
= 0.5M x V1 = 5ml x 0.01M / 0.5M
= V1 = 5ml x 0.01M / 0.5M
= 0.1ml of MgSO4

(c) What volume of distilled water do you need to transfer to the test tube?

0.36ml + 0.1ml = 0.46ml
V1 - V2
= 5ml - 0.46ml
= 4.54ml water needed

(d) How many moles of glycine are in the test tube?

(e) How many mg of glycine does this represent? (The mass of 1 mole of Glycine is 75g.)

E) we can say Mr of glycine = mass/moles. Then mass= Mr x moles(you worked out in D)
Alternatively you could simply say 1 mole = 75g D moles = how many grams?(use ratio)

Reply 3

John158

OP

6

Original post by random88

D) moles of glycine in test tube = conc x vol. Read question carefully and you will realise that you know the conc of glycine added to the test tube and in a) you calculated the volume of glycine. You’ve done the bulk of the hard work, simply plug these values into your formula to get the moles

Thanks for that.
so N = C x V
C = 0.36 ml? I thought this would be the volume but I'm not very good at this
and V = 5 ml?

Reply 4

random88

13

Not quite. 0.36 and 5 are both volumes as they are measured in ml(the unit for volume). Now which one of these do we use as V? Well we want moles of glycine so we use volume of glycine which if you read question a) and your working you will see is 0.36ml

Reply 5

random88

13

But be careful as the concentrations are measured in M which is mol per dm^3. We know that 1dm^3 =1 litre = 1000ml. So since they give you concentration in moldm^-3 before plugging in your numbers you must convert you volume to dm^3