You wish to prepare 1.000 l of a 0.0600 m phosphate buffer at ph 7.640 . to do this, you choose to mix the two salt forms involved in the second ionization, nah2po4 and na2hpo4 , in a 1.000 l volumetric flask and add water to the mark. what mass of each salt will you add to the mixture?

We need 1.908 grams of NaH2PO4 and 6.1299 grams of Na2HPO4

Explanation:

Step 1: Given data

We want to prepare a buffer with pH = 7.64, a volume of 1L and a concentration of 0.06M

pKa1 = 2.148

pKa2 = 7.198

pKa3 = 12.375

Step 2: Calculate [H2PO4-]

For the equation H3PO4 ⇔ H+ + H2PO4-  we consider [H+] and [H2PO4-] as X and [H3PO4] = 0.06 - X

pKa1 = 2.148 = [H+][H2PO4 -] / [H3PO4]

2.148 = x² / 0.06 - x

x² + 2.148x - 0.12888 = 0

x = [H2PO4-] = 0.05841

Step 3: Plug into the pH formula

pH = pKa + log[Na2HPO4]/[NaH2PO4]

7.64 = 7.198 + log[Na2HPO4]/[NaH2PO4]

0.442 = log[Na2HPO4]/[NaH2PO4]

2.77 = [Na2HPO4]/[NaH2PO4]

This means we will need 2.77x the amount of Na2HPO4compared to NaH2PO4

x / y = 2.77

x + y = 0.06

2.77y + y = 0.06

3.77y = 0.06

y = 0.0159M = [NaH2PO4]

x = 0.0441M = [Na2HPO4]

Step 4: Calculate mass

0.0159 moles NaH2PO4 * 120g/mole = 1.908 g

0.0441 moles Na2HPO4 x 139g/mole = 6.1299 g

We need 1.908 grams of NaH2PO4 and 6.1299 grams of Na2HPO4

a mercury barometer is a device that uses the physical properties of mercury in a tube to measure barometric pressure. mercury barometers are used for : -

1. measurement of atmospheric pressure  

2. determining the altitude of a place

3. weather forecasting

4. calibration and checking of aneroid barometers

5. application in fluid mechanics

6. measurement of pressure in aircrafts

7. surface weather analysis

8. preparation of barographs

9. usage in physical sciences like physics, astronomy & chemistry

10. preparation of aircraft altimeters

characteristics of mercury barometer : -

1.used to define and measure atmospheric pressure.

2.on the average at sea level the column of mercury rises to a height of about 760 mm.

3.this quantity is equal to 1 atmosphere.

4.it is also known as standard atmospheric pressure.

5.a barometer in which the weight of a column of mercury in a glass tube with a sealed top is balanced against that of the atmosphere pressing on an exposed cistern of mercury at the base of the mercury column, the height of the column varying with atmospheric pressure.