You are instructed to create 900. mL of a 0.29 M phosphate buffer with a pH of 7.8. You have phosphoric acid and the sodium salts NaH2PO4, Na2HPO4, and Na3PO4 available. (Enter all numerical answers to three significant figures.)

H3PO4(s) + H2O(l) <> H3O+(aq) + H2PO4−(aq) Ka1 = 6.9 ✕ 10−3
H2PO4−(aq) + H2O(l) <> H3O+(aq) + HPO42−(aq) Ka2 = 6.2 ✕ 10−8
HPO42−(aq) + H2O(l) <> H3O+(aq) + PO43−(aq) Ka3 = 4.8 ✕ 10−13

Which of the available chemicals will you use for the acid component of your buffer?

A. H3PO4
B. NaH2PO4
C. Na2HPO4
D. Na3PO4

Which of the available chemicals will you use for the base component of your buffer?

A. H3PO4B. NaH2PO4C. Na2HPO4D. Na3PO4

B and C

Explanation:

When we have to do a buffer solution we always have to choose the reaction that has the pKa closer to the desired pH value. When we find the pKa values we will obtain:

The closer value is pKa2 with a value of 7.2. Therefore we have to use the second reaction. In which   is the acid and is the base. Therefore the answer for the first question is B and the answer for the second question is C.

a pan containing water is placed in a positio n where it is exposed to a 10 mile per hour wind. the pan contains a uniform depth of 1.27 cm of water, is quite wide, and has a length of 2.44 m in the wind direction. the water in the pan is at a constant temperature of 15.5 °c.

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2