H.W. Buffer Preparation Problems
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Buffer Preparation Problems Work out the problem below for homework. Do your work on a separate page before writing your answers here. Show, in a logical order, the calculations to make 1 liter of 0.01M phosphate buffer pH 5.8. Be sure to include all units. V 1 X C 1 = V 2 X C 2 1. Calculate how to make 1 liter of 0.01M phosphate buffer @ pH 5.8 from the 0.2M stock solutions. V 1 X 0.2M = 1liter X 0.01M V 1 = 1000ml x 0.01M = 50 ml 0.2 50ml of the two 0.2M stock solutions to make 1liter of 0.01M phosphate buffer. 2. Calculate the amount needed from each stock solution at pH 5.8: x= 50ml x 92%= 46ml ; y= 50ml x 8%= 4ml When and why do you use a beaker? A beaker is a cylindrical thick walled container used for mixing chemicals with a magnetic stir bar and for pouring chemicals. When and why do you use an Erlenmeyer flask? An Erlenmeyer flask is commonly used for simple measuring, storing and mixing of liquids. The narrow conical neck means there is little risk of spillage and slows evaporation, the flat bottom also lowers the risk of spills. When and why do you use a volumetric flask? Volumetric flasks are used to make solutions of known a concentration by the dilution of a more concentrated solution. They are calibrated to yield very precise amounts of liquid. Describe briefly, in their proper sequence, the main steps required to make up 0.5 liters of 0.01M phosphate buffer pH 6.6 (include your actual calculations and the glassware required etc.)? 1 | Page Phosphate Buffer Table x y pH 92.0 8.0 5.8 x=monobasic ; y=dibasic
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Transcript of H.W. Buffer Preparation Problems
Buffer Preparation Problems
Work out the problem below for homework. Do your work on a separate page before writing your answers here.Show, in a logical order, the calculations to make 1 liter of 0.01M phosphate buffer pH 5.8. Be sure to include all units.
V1 X C1 = V2 X C2
1. Calculate how to make 1 liter of 0.01M phosphate buffer @ pH 5.8 from the 0.2M stock solutions.
V1 X 0.2M = 1liter X 0.01M V1= 1000ml x 0.01M= 50 ml 0.2 50ml of the two 0.2M stock solutions to make 1liter of 0.01M phosphate buffer.
2. Calculate the amount needed from each stock solution at pH 5.8:
x= 50ml x 92%= 46ml ; y= 50ml x 8%= 4ml
When and why do you use a beaker?A beaker is a cylindrical thick walled container used for mixing chemicals with a magnetic stir bar and for pouring chemicals.
When and why do you use an Erlenmeyer flask? An Erlenmeyer flask is commonly used for simple measuring, storing and mixing of liquids. The narrow conical neck means there is little risk of spillage and slows evaporation, the flat bottom also lowers the risk of spills.
When and why do you use a volumetric flask?Volumetric flasks are used to make solutions of known a concentration by the dilution of a more concentrated solution. They are calibrated to yield very precise amounts of liquid.
Describe briefly, in their proper sequence, the main steps required to make up 0.5 liters of 0.01M phosphate buffer pH 6.6 (include your actual calculations and the glassware required etc.)?
1. Calculate how to make 500ml of 0.01M phosphate buffer from the 0.2M stock solutions.
V1 X 0.2M = 500mL X 0.01M V1= 500ml x 0.01M= 25ml 0.2 25ml of the two 0.2M stock solutions to make 500ml of 0.01M phosphate buffer.
2. Calculate the amount needed from each stock solution at pH 6.6:
1 | P a g e
Phosphate Buffer Tablex y pH
92.0 8.0 5.8x=monobasic ; y=dibasic
Phosphate Buffer Tablex y pH
62.5 37.5 6.6x=monobasic ; y=dibasic
x= 62.5% 25ml = 15.6 ml ; y= 37.5% x 25ml = 9.4ml
3. Using a 50ml graduated cylinder measure out the amount of each stock solution into a 1000ml beaker with stirring bar. Add 350 ml of distilled water (dH2O) to solution. Check pH with pH meter and adjust to target pH 6.6.
4. Use a funnel to add the solution in the beaker to a 500 ml volumetric flask and bring to volume using dH2O and measure the last few ml using a clean Pasteur pipette.
5. Once at the correct volume pour into a labeled (initials, date, contents and pH) 500 ml glass bottle with cap.
2 | P a g e
Do the following for homework.1. How much dibasic sodium phosphate 12 H2O would one have to weigh out to produce 1 liter of a 1M solution?
____________.
FW=358g to make 1 L of a 1M solution.
2. How much dibasic sodium phosphate 7 H2O would one have to weigh out to produce 1 liter of a 1M solution? FW=268g to make 1L of a 1M soltuon.
3. Do both of the solutions above have the same number of phosphate molecules?
Monobasic sodium phosphate =NaH2PO4 & dibasic sodium phosphate Na2HPO4 both have the same number of phosphate molecules it is the number of Na and H molecules that differentiate between the them.
4. What is the final concentration that results when you dilute 100 mL of 0.2M sodium phosphate to a final volume of 1000 mL ?_________.
0.2M x 100 = 0.02M 1000
5. How would you make up 250 mL of a 0.05M sodium phosphate buffer pH 6.8? V1 X C1 = V2 X C2
1. Calculate how to make 250ml of 0.05M phosphate buffer from the 0.2M stock solutions.
V1 X 0.2M = 250mL X 0.05M V1= 250ml x 0.05M= 62.5ml 0.2 62.5ml of the two 0.2M stock solutions to make 250ml of 0.05M phosphate buffer.
2. Calculate the amount needed from each stock solution at pH 6.8:
x= 51% x 62.5ml = 31.9ml; y= 49% x 62.5ml = 30.6
3. Using a 100ml graduated cylinder measure out the amount of each stock solution into a 400ml beaker with stirring bar. Add 150ml of distilled water (dH2O) to solution. Check pH with pH meter and adjust to target pH 6.8.4. Use a funnel to add the solution in the beaker to a 250 ml volumetric flask and
bring to volume using dH2O.5. Once at the correct volume pour into a labeled (initials, date, contents and pH)
250 ml bottle with cap.
3 | P a g e
Phosphate Buffer Tablex y pH
51.0 49.0 6.8x=monobasic ; y=dibasic
